Tactile warning signals for in-vehicle systems.

Accident Analysis and Prevention 75 (2015) 333–346

Contents lists available at ScienceDirect

Accident Analysis and Prevention journal homepage: www.elsevier.com/locate/aap

Tactile warning signals for in-vehicle systems Fanxing Meng a,b , Charles Spence a, * a b

State Key Laboratory of Automotive Safety and Energy, Department of Industrial Engineering, Tsinghua University, China Crossmodal Research Laboratory, Department of Experimental Psychology, University of Oxford, UK

A R T I C L E I N F O

A B S T R A C T

Article history: Received 28 March 2014 Received in revised form 6 November 2014 Accepted 16 December 2014 Available online 7 January 2015

The last few years have seen growing interest in the design of tactile warning signals to direct driver attention to potentially dangerous road situations (e.g. an impending crash) so that they can initiate an avoidance maneuver in a timely manner. In this review, we highlight the potential uses of such warning signals for future collision warning systems and compare them with more traditional visual and auditory warnings. Basic tactile warning signals are capable of promoting driver alertness, which has been demonstrated to be beneficial for forward collision avoidance (when compared to a no warning baseline condition). However, beyond their basic alerting function, directional tactile warning signals are now increasingly being utilized to shift the attention of the driver toward locations of interest, and thus to further facilitate their speeded responses to potential collision events. Currently, many researchers are focusing their efforts on the development of meaningful (iconic) tactile warning signals. For instance, dynamic tactile warnings (varying in their intensity and/or location) can potentially be used to convey meaningful information to drivers. Finally, we highlight the future research that will be needed in order to explore how to present multiple directional warnings using dynamic tactile cues, thus forming an integrated collision avoidance system for future in-vehicle use. ã 2014 Elsevier Ltd. All rights reserved.

Keywords: Driving Collision avoidance Tactile warning Dynamic warning Spatial attention Interface design

1. Introduction Over the last decade or two, there has been a rapid growth of interest in the development of collision avoidance systems (CASs) designed to direct a driver’s attention to an impending crash so that they can initiate an avoidance maneuver in a manner that is both timely and appropriate (Dingus et al., 1997; Fitch et al., 2011 see Campbell et al., 2007, for a review). The hope is that the various components of CASs, such as forward collision warning systems (FCWSs), lane departure warning systems (LDWSs), blind spot detection systems (BSDSs), and lane changing warning systems (LCWSs), will help to prevent a substantial number of rear-end collisions, roadway departures, and crashes attributable to drivers changing lanes inappropriately (see Kim et al., 2010; Fitch et al., 2011). Such systems may, in the future, present a viable solution to help significantly reduce the number and severity of collisions on our roads (e.g. see Yonas et al., 1977; Kiefer et al., 1999; Tijerina et al., 2000). One important question that has arisen in the design of CASs concerns the optimal means of presenting a collision warning

* Correspondence to: Department of Experimental Psychology, University of Oxford, 9 South Parks Road, Oxford OX1 3UD, UK. Tel.: +44 1865 271364. E-mail addresses: [email protected] (F. Meng), [email protected] (C. Spence). http://dx.doi.org/10.1016/j.aap.2014.12.013 0001-4575/ ã 2014 Elsevier Ltd. All rights reserved.

signal to the driver (Kaufmann et al., 2008; Mohebbi et al., 2009; Fitch et al., 2011). While related research has demonstrated the potential benefits associated with the presentation of visual, auditory, tactile, and even multisensory warning signals in terms of alerting the driver and rapidly orienting their spatial attention in the direction of potential danger (for a review, see Spence and Ho, 2008a; Ho and Spence, 2013; Haas and Van Erp, 2014; see also Lee et al., 2002, 2004; Ho et al., 2005a,c; Spence and Ho, 2008b,c; Gray, 2011,b; Baldwin et al., 2012a,b; Liu and Jhuang, 2012), research interest in the utilization of tactile warning signals in vehicles has only really emerged more recently (e.g. see Gallace and Spence, 2014; Spence and Ho, 2008a). The sense of touch (on our body surface) compromises those sensations elicited by the stimulation of the skin, such as pressure, temperature, pain, and vibration (Deatherage, 1972; Gemperle et al., 2003; McGlone and Spence, 2010). Embedded within our skin are many different classes of sensory receptors, each capable of receiving (or transducing) different kinds of sensory inputs (Geldard, 1957). The majority of the tactile warning signals covered in this review involve only a small number of tactile receptors for vibration presented by stimulators capable of stimulating various body surfaces (also including the force feedback from foot pedals) or else torque delivered by the jerking of the steering wheel. Knowledge concerning how to communicate information via the

334

F. Meng, C. Spence / Accident Analysis and Prevention 75 (2015) 333–346

skin is still, relatively-speaking, fairly limited, at least when compared to what is known about visual or auditory communication (e.g. Geldard, 1957; Lerner, 1996). However, several commercial tactile warning systems are already available in the marketplace, for example, the LDWS in certain models of Citroen and BMW cars (Spence and Ho, 2008a) and a pre-collision advanced vehicle safety management (AVSM) in Kia cars (see López, 2012). We are therefore now starting to see a transition from tactile stimulation as an optional extra to it becoming a standard feature on at least certain models of car. Therefore, a critical review of what is currently known in terms of the design of tactile warning signals for safe driving may help to highlight a number of potentially important implications for the future design of in-vehicle tactile warnings. This review starts by discussing visual, auditory, tactile, and even olfactory warning signals, before highlighting the potential promise as well as the limitations inherent in the implementation of various types of invehicle tactile warning displays. In the sections that follow, we attempt to classify the literature on tactile warning signals. Specifically, a distinction is made between non-directional tactile warnings (basic tactile alerts), directional tactile warnings, and meaningful tactile warnings. Finally, we conclude by highlighting what we see as the most pressing questions that will need to be addressed by future research in this area, specifically related to resolving the challenges associated with the implementation of multi-tactile alert systems. 2. Do tactile cues provide a good solution (modality) for invehicle warnings? Previously, visual and auditory warnings have been trialed extensively in the design of CASs (e.g. Ben-Yaacov et al., 2002; Shinar and Schechtman, 2002; Lee et al., 2004 Scott and Gray, 2008; Bueno et al., 2013). A few researchers have even considered the possibility of using olfactory warnings (Baron and Kalsher, 1998; Ho and Spence, 2005; Raudenbush et al., 2005; Schuler and Raudenbush, 2005 see Spence and Ho, 2008c, for a review). For instance, Grayhem et al. reported that the presentation of both cinnamon and peppermint odour led to improved alertness while driving (Grayhem et al., 2005). Meanwhile, others have reported that ‘unpleasant’ smells, such as (synthetic) body odour, might be even more effective in terms of alerting people than pleasant

odours (Chen et al., 2006). Such results would appear to hint at the promise of olfactory cues as a novel and potentially subtle means of keeping the drowsy driver alert (Baron and Kalsher, 1998; Schuler and Raudenbush, 2005; Spence and Ho, 2008c; Susami et al., 2011). Ambient odours (no matter whether they are pleasant or unpleasant) can also be used to reduce people’s reaction times (RTs) to visual or auditory stimuli (e.g. Millot et al., 2002), and give rise to an increased accuracy of responding to tactile stimuli (Ho and Spence, 2005). However, given the fact that olfactory stimuli are difficult to perceive in a timely manner, at least when compared to visual, auditory, or even tactile cues (Spence and Squire, 2003), they do not really represent a plausible alternative for time-critical collision avoidance situations. Hence, olfactory warning signals will not be elaborated on further within the scope of the present review. As shown in Table 1, visual warning signals are typically relatively straightforward and can be used to convey various signals by including symbolic information and colour (or colour change; Laughery et al., 1993; Braun and Silver, 1995; Baldwin et al., 2012a,b). However, as a complicated sensorimotor task, driving undoubtedly involves a relatively high visual workload (Senders et al., 1967; Chun et al., 2013). Indeed, it has been estimated that as much as 95% of the information received while driving is identified visually (Shinar and Schieber, 1991 though also see Sivak, 1996 and Spence and Ho 2008b, for a critical assessment of the empirical evidence in support of this particular statistic). Visual warnings may therefore be expected to have to compete for access to the visual resources required for effective vehicular control (Horberry et al., 2006; Scott and Gray, 2008). More worrying still is the fact that the drivers are likely to miss visual warnings when driving (Hirst and Graham, 1997; Fitch et al., 2007) or when distracted by a secondary visual task in vehicle, such as operating the entertainment system, checking email, or dealing with navigation messages (Ashley, 2001; Harms and Patten, 2003; Horberry et al., 2006; Clark, 2013). These practical limitations mean that visual warnings run the risk of becoming ineffective in terms of increasing the margin of safety for the driver. As audition is considered to be intimately connected with the brain’s arousal and activation systems, auditory warnings usually produce faster responses than do visual warnings (see Jones and Furner, 1989). Additionally, verbal warnings, as one class of auditory warning signal, can undoubtedly also convey spatial

Table 1 The comparison among olfactory, visual, auditory and tactile warnings for in-vehicle warning systems. Modality

Advantages

Disadvantages

Olfactory

Improving alertness while driving Reducing reaction times to visual or auditory stimuli

Not suitable for time-critical collision avoidance situations

Visual

Straightforward means of conveying information

Competing with the visual resources for vehicle control Can easily be missed while driving

Auditory

Easy to convey spatial information by verbal signals Perception of auditory stimuli is “gaze-free”

To be easily masked by background noise or be interfered with by secondary tasks

Can be difficult to localize the spatial direction from which auditory warning signals presented

Some drivers suffer from a hearing impairment The phenomenon of “inattentional deafness” Tactile

Less central to driving Its utilization not expected to increase visual or auditory workload Less interfered with by secondary tasks while driving

Can only be delivered from seat, pedal and seat belt Some drivers use only one hand while driving, thick clothing/gloves, not to mention in-vehicle vibration might impair effectiveness

The phenomenon of “change numbness”


information regarding potential collisions, thus reducing the perception and response time to the danger (Chang et al., 2008). More importantly, the perception of auditory stimuli is “Gazefree”; that is, people will hear an auditory stimulus no matter where they happen to be looking (Graham, 1999). This makes audition suitable as a modality for the delivery of warning signals. It is, however, important to note that the application of auditory warnings to realistic driving situations may be somewhat limited because sounds may potentially be masked by any ambient background noise/music (see Deatherage, 1972; Ramsey and Simmons, 1993; Lerner, 1996; McKeown and Isherwood, 2007; Beruscha et al., 2011) and/or be interfered with by secondary tasks that the driver might be engaged in, such as talking to a passenger or using a mobile phone (see Mohebbi et al., 2009). Furthermore, drivers can find it difficult to localize the spatial direction from which auditory cues (or warning signals) come in the interior environment of a car when precise spatial information is being conveyed (Fitch et al., 2007). Furthermore, it should also be remembered that some proportion of drivers suffer from a hearing impairment, and this may be expected to adversely affect their ability to process the auditory signal (see McKeown and Isherwood, 2007; Hickson et al., 2010). Laboratory research from Macdonald and Lavie (2011) demonstrates the existence of a potentially relevant deleterious crossmodal effect of visual attentional load on people’s awareness of auditory information (a phenomenon known as “inattentional deafness”; see also Mack and Rock, 1998). In their study, 79% of participants failed to notice the presence of auditory stimuli that were presented at the same time as the visual targets when under conditions of high visual load (see also Spence et al., 2011, for a review of the related literature of the Colavita visual dominance effect). Given the high visual workload that is usually encountered while driving, one may therefore expect to find that such crossmodal perceptual impairments might well impact negatively on the effectiveness of auditory warnings in time-critical situations (Spence, 2010; Chun et al., 2013). On the other hand, the sense of touch is commonly considered as being far less central to driving than either vision or audition; it is also relatively underutilized in driving tasks (Van Erp and Van Veen, 2004; Spence and Ho, 2008b; Hogema et al., 2009; Baldwin et al., 2012a,b). Since the skin represents the largest of our senses, having a surface area of approximately 1.8 m2 and accounting for roughly 18% of our body mass (Montagu, 1971; Spence and Ho, 2008a; White, 2010), the sense of touch can be seen as providing a readily available channel for the presentation of warning (and other informational) signals to the driver without necessarily increasing their visual or auditory workload (Drew and Hayes, 2012; Prewett et al., 2012; Gallace and Spence, 2014). Previously, some researchers have attempted to evaluate the capacity of painful warning signals (e.g. presented by means of a pinprick on the skin surface) to grab people’s attention (McGlone et al., 1999); however, this review will focus on another more popular type of warning signal delivered by the sense of touch—namely, vibrotactile. Although tactile warnings are, of necessity, going to be presented in the driver’s peripersonal space (that is, in the space directly around their body, see Previc, 1998; Spence and Driver, 2004), they have been shown to be effective in orienting a driver’s visual attention to distal locations in extrapersonal space (that is, to locations that may fall outside of their peripersonal space) and where a potential collision event is likely to occur (Ho and Spence 2008b; Rosli et al., 2011 Rosli et al., 2011). Tactile warning signals can elicit faster reactions from drivers in response to potential collisions than comparable visual or auditory warning signals (for a review, see Prewett et al., 2012; see also Ho et al., 2005a; Terrence et al., 2005; Fitch et al., 2007; Scott and Gray,

335

2008). For example, one study by Mohebbi et al. (2009) revealed that when drivers were engaged in a simple, casual cell phone conversation, their braking reaction times (BRTs) to forward collisions following the presentation of auditory warnings were no faster than in the absence of a warning signal. By contrast, conversation did not produce a significant slowing of BRTs when tactile warnings were used. Additionally, due to the fact that the tactile warnings were delivered directly to the driver’s body (that is, without having to alert the vehicle’s other occupants), they can be seen as less intrusive and were therefore rated as being less annoying than those warnings presented visually or auditorily (see Lee et al., 2004 Stanley 2006; Fitch et al., 2007). This transition property of tactile cues also means that they are unlikely to be affected by the level of background noise (e.g. the sound of the radio) in the driving experiment to anything like the same extent as auditory cues (Ho et al., 2005a; Spence and Ho, 2008c). While considering the advantages of tactile in-vehicle warnings over other types of warning signals, it is also important to note that there are undoubtedly still some practical constraints to be resolved in terms of the effective utilization of tactile warning signals. First, the assumption by those working in the field is that drivers will not be willing to put on (or wear) any additional device before getting into their vehicles (Ho et al., 2006a; Spence and Ho, 2008a). Thus, the tactile cues have to be presented from those surfaces in the vehicle that the driver is already in contact with, such as the seat belt (Ho et al., 2006b, 2007; Chun et al., 2013), the driver’s seat (Fitch et al., 2011; Drew and Hayes, 2012; Lee et al., 2004), the steering wheel (Tijerina et al., 2000; Chun et al., 2012, 2013) or the gas/brake pedals (Lloyd et al., 1999; Lee et al., 2007; Mulder et al., 2008; De Rosario et al., 2010). Of course, given such a constraint, the fact that some drivers operate their vehicles one-handed (Walton and Thomas, 2005), and the fact that drivers may sometimes wear thick clothing/gloves (McGehee and Raby, 2002; Spence and Ho, 2008a), might be expected to degrade the effectiveness of tactile warnings in terms of alerting the driver to any potential collisions. Second, any ambient in-vehicle vibration (see Ryu et al., 2010) might also be expected to interfere with the ability of drivers to perceive vibrotactile cues in a timely and appropriate manner (e.g. when confronting an imminent collision). Third, the perception of tactile stimuli might be suppressed by a simultaneous bodily movement (such as the turning of the steering wheel, see Gallace et al., 2010). The phenomenon of change blindness, which has been demonstrated to affect tactile perception (see Gallace et al., 2005, 2006; see also Spence and Gallace, 2007; Gallace and Spence, 2008 for a review of the topic) would certainly be expected to degrade the effectiveness of tactile warnings under realistic driving conditions. Finally, although some studies have demonstrated that drivers can differentiate navigational signals (such as left turn, right turn, go straight ahead, etc.) delivered via the tactile modality effectively and efficiently (Van Erp and Van Veen, 2004), the ability of people to discriminate the physical parameters of vibrotactile stimulation, such as their rhythm, spatial patterning, and/or distinctive intensity is nevertheless still limited (e.g. see Brown et al., 2006; Jones, Kunkel, and Piateski, 2009 Gallace and Spence, 2014). A great deal of effort has been directed at the design of effective tactile warnings for drivers. To date, several different kinds of tactile warning signals, including non-directional tactile, spatially directional tactile, and meaningful tactile warnings, have been trialed in laboratory and/or field tests. However, further research is undoubtedly still required in order to deal with the practical constraints associated with the implementation of tactile warnings. In the following section, we will take a look at what has been learned thus far concerning the design and evaluation of tactile warning signals to enhance safe driving.

336


3. Basic (non-directional) tactile warning signals At their simplest, non-directional (as opposed to directional) vibrotactile warnings consist of one or more tactors delivering one or more pulses of vibration to the driver or interface operator (Haas and Van Erp, 2014). Of course, all tactile stimuli presented to the surface of the human body will have some directional information attached to them (i.e. the direction of the source of stimulation); however, “non-directional” here is used to refer to the fact that the direction (or origin) of the tactile stimuli is not meant to provide any useful/relevant information to the driver. The vast majority of previous studies that have presented such basic tactile warning signals have demonstrated that they can be used to effectively shift the driver’s attention from non-driving tasks to the critical events (such as a potential imminent collision), and significantly enhance the driver’s behavioral performance as a result (see Scott and Gray, 2008; Fitch et al., 2011; Chun et al., 2012; Gray et al., 2013; Haas and Van Erp, 2014). Or at least this is what has been demonstrated in the majority of those studies that have been published to date in this area. For instance, Scott and Gray (2008) directly compared visual, auditory, and tactile warnings in terms of their effectiveness in delivering a forward collision avoidance signal. These researchers presented a static tactile cue by means of three tactors positioned on the front-center of the driver’s abdomen. The participants were instructed to maintain a 2.0-s time headway with respect to the lead vehicle, which would sometimes unpredictably brake suddenly in order to create a number of potential rear-end collision scenarios. Different types of warning signals were presented in order to alert the participants when the time to collision (TTC) reached the warning activation threshold. The results revealed that the static tactile warning signals effectively attracted the driver’s attention to the time-critical event and resulted in faster BRTs than either the equivalent visual or auditory warning signals. The tactile warnings themselves contained neither information concerning the direction in which the drivers should direct their attention, nor any information about the potential external collision itself. However, the non-directional tactile warnings are considered capable of increasing the overall alertness of the drivers, thus promoting their performance in terms of effective collision avoidance1 (Posner and Petersen, 1990; Cummings et al., 2007; Lees et al., 2012; Haas and Van Erp, 2014). An important issue when it comes to the presentation of tactile warning signals is how best to convey urgent information to the driver. Previously, it has been demonstrated that warnings with a higher perceived level of urgency result in faster RTs and more accurate responding (see Deatherage, 1972; Suied et al., 2008; Arrabito, 2009; Baldwin, 2011; Politis et al., 2013). As shown in Table 2, parameters of the signal such as its intensity, pulse rate, and the locus of stimulation have been used to manipulate the perceived urgency of tactile warnings (see Brown et al., 2006; White, 2011,b; Baldwin et al., 2012a,b; Pratt et al., 2012; Baldwin and Lewis, 2014). Previously, it has been revealed that tactile cues delivering a higher intensity vibration give rise to a higher level of

1 It should be noted that the warning signals were presented 11 times within an 8–10 min trial in Scott and Gray (2008)'s study. Thus, the occurrence of the warning signal was much, much more frequent than is likely to be seen in real driving (which is, fortunately, very rare, see Parasuraman et al.. 1997; Spence and Ho, 2008a). The frequent occurrence of such warnings is obviously an issue that should be addressed when it comes to thinking about the implications of such results for the design of realistic in-vehicle warning system (see Ho et al., 2014b, for a recent critical review). Another issue that should be noted is that although tactile warnings elicited faster response than either auditory or visual warnings, one cannot be sure that these signals were equated for saliency, given the fundamental difficulty of matching stimulus intensity across the modalities.

perceived urgency as well (Brown et al., 2006; White, 2011), and are usually associated with faster RTs (Diederich and Colonius, 2008; Lee and Spence, 2008). Baldwin and Lewis (2014) investigated the variation of perceived urgency of tactile warnings as a function of the interpulse interval (IPI) between successive tactile stimuli comprising a signal in a driving context. The IPI was divided into seven levels from 9 to 475 ms. The decrease in the IPI of the tactile warnings was shown to result in an increased subjective level of perceived urgency (see also Baldwin et al., 2012a,b; Pratt et al., 2012), and the IPI of the tactile warnings had a greater impact on perceived urgency than on their ratings of annoyance (see Lewis and Baldwin, 2012). Therefore, reducing the IPI may well help to increase the urgency of tactile warnings without necessarily increasing the annoyance of the warnings (cf. McKeown and Isherwood, 2007). Moreover, a higher level of perceived urgency has been shown to result when tactile stimuli are presented from close to an individual’s shoulders as opposed to when the same stimuli are presented in the middle of the back or from close to their waist instead (Li and Burns, 2013). Although few studies have directly investigated the relationship between the duration of vibration and perceived urgency when it comes to tactile warnings, the recommendation has been made that the duration of any vibration should not exceed 200 ms, if tactile warnings are not to become annoying for the user2 (Kaaresoja and Linjama, 2005). In previous studies where non-directional tactile warnings have been used, only one type of CAS was normally involved (such as a FCWS in the potential forward collision scenario). The participants in these studies were presumably clear enough about where they should direct their attention whenever they perceived a tactile warning signal (for example, paying attention to the roadway in front in the read-end collision scenario). However, it is important to note that the potential collisions that may occur under realistic driving situations are likely to come from a variety of directions, and hence different types of CAS components may need to be installed together in order to form an integrated multipurpose warning system (e.g. using FCWS to warn the frontal collisions and using the LDWS to warn the driver about possible collisions from the left or right, see Sayer et al., 2005). Of course, under such conditions, it may become more difficult for the drivers to determine where exactly their attention should be directed when the non-directional warnings are presented (given the variety of signals/meanings). Therefore, a number of studies have tried to embed directional information into the tactile warning signals in order to orient the driver’s spatial attention in different locations. 4. Directional tactile warning signals In the driving situation, the driver’s visual resources are directed to the front most of the time (Senders et al., 1967; Shinar and Schieber, 1991). This is obviously going to limit the range of directions from which the visual warning signals can be presented to indicate (for example, the potential danger in the blind spot or from the rear). For auditory warning signals, due to the limited ability of people to localize auditory cues in the car’s interior, spatial direction (as indicated by directional auditory cues) may result in a relatively poor ability to correctly localize the source of any danger. It should be noted that a verbal directional warning could be used to effectively direct a driver’s spatial attention (see Chang et al., 2008); however, the verbal warning may not be so

2 It has been suggested that pressure adaption might likely occur if tactile cues are presented for more than 200 ms on a single location of human body (see Van Erp and Self, 2008), thus reducing the sensitivity of the skin to the tactile stimuli (Nafe and Wagoner, 1941).


337

Table 2 Relationship between the parameters of tactile warning signals and perceived urgency. Tactile warning signals parameters

Results

Related studies

Vibration intensity

Higher vibration intensity tactile cues gives rise to a higher level of perceived urgency, and (Brown et al., 2006; Diederich and Colonius, 2008; Lee are usually associated with faster RTs. and Spence, 2008; White, 2011)

Inter-pulse interval Decreasing the IPI of the tactile warnings results in an increased level of perceived urgency. (McKeown and Isherwood, 2007 Lewis and Baldwin, (IPI) 2012; Pratt et al., 2012; Baldwin and Lewis, 2014) Location of stimulation

(Li and Burns, 2013) Higher perceived urgency results when tactile stimuli are presented from close to the shoulders as opposed to when the same stimuli are presented from the middle of the back or close to the waist.

effective as to elicit a time-critical response from a driver who is not familiar to the language of verbal warnings. Additionally, these auditory warnings still run the risk of being masked by other background noise, or else being interfered with by some other secondary task (e.g. Ramsey and Simmons, 1993; Lerner, 1996; McKeown and Isherwood, 2007; Mohebbi et al., 2009; Beruscha et al., 2011). On the other hand, touch is, in some sense, omnidirectional. That is, unlike vision, it is not necessary for tactile receptors to be oriented in a certain direction in space in order to be able to perceive signals that are applied to the body surface (Ferris and Sarter, 2010). We would like to argue that this property makes the tactile modality an especially promising candidate for the presentation of spatial warning signals (although, unlike visual or auditory cues, the driver’s body has to be in contact with the vibrating surface when perceiving the tactile cues). 4.1. Crossmodal links between touch and version There has been a rapid growth of empirical research investigating the nature of crossmodal links in attention between touch and vision in recent years. The presentation of directional tactile cues has been shown to lead to a shift of visual attention to the cued side, which may facilitate people’s speeded responses when the direction of the tactile cues and the visual target coincide spatially (see Butter et al., 1989; Spence and Driver, 2004; Ho et al., 2005b; Ferris et al., 2006; Ngo and Spence, 2010; Gallace and Spence, 2014 though see Ferris and Sarter, 2008). In particular, researchers have typically studied the nature of the crossmodal links in spatial attention between vision and touch separately for the case of exogenous (see Spence et al., 1998; Kennett et al., 2001, 2002) and endogenous (see Spence et al., 2000) spatial orienting (see Spence and Driver, 2004; Spence and Driver, 2004, for a review). The exogenous orienting of spatial attention in response to the sudden presentation of a tactile cue is thought to take place automatically, as attention is “pulled” to the side that has been cued by the tactile stimuli (Spence and Driver, 1994 though see also Spence, 2010). In fact, the presentation of a spatially non-predictive tactile cue to the left or right hand leads to a short-lasting exogenous shift of spatial attention to the side of the cue (at least under conditions of low perceptual load; see Lavie, 2005), that facilitated the speeded detection/discrimination of visual targets that happen to be presented on that side over the ensuing half second or so, as opposed to those presented on the other side (Kennett et al., 2002). Endogenous orienting, by contrast, is under strategic control, as attention is “pushed” to the location where a target is expected to occur (Spence and Driver, 1994). When participants are informed that a target is more likely to be presented on one side rather than the other, speeded target discrimination responses tend to be significantly faster (and more accurate) on the expected

side thus showing that attention can be endogenously directed to a particular location, direction, or side of space (Spence et al., 2000). 4.2. Directing attention to the front and back The existence of crossmodal links in spatial attention between vision and touch (see Gallace and Spence, 2014 for a review) certainly has a number of implications for the design of in-vehicle directional tactile warning signals. Researchers have, for example, documented facilitatory effects of tactile warning signals on directing the driver’s spatial attention to the front or to the rearview mirror (see Ho et al., 2005b, 2006a), thus speeding their responses and increasing the accuracy of their responses. In one such study, the participants had to “drive” in a simulated driving context with a car on the roadway ahead and another car visible in the rearview mirror (Ho et al., 2005b). At the same time, the participants were distracted by having to perform an attentiondemanding rapid serial visual presentation (RSVP) monitoring task. They were required to accelerate whenever they realized that the car was approaching rapidly from behind and to brake if they approached the car in front rapidly. The directional vibrotactile cues were presented on either their front or back (potentially from the seat belt or seat back) in order to indicate the location of the potential “critical event”. The tactile warning signals correctly predicted the direction of the visual driving events on 80% of trials, while the visual driving events occurred in the direction opposite to the cue on the remaining 20% of trials. The results revealed that participants responded more rapidly (and somewhat more accurately) to critical visual driving events following the presentation of valid tactile warnings (i.e. where the direction of the tactile cue and the critical visual event was spatially compatible) than following the presentation of tactile warning signals that turned out to be invalid. It was hypothesized that such results reflected some unknown combination of exogenous and endogenous spatial attentional orienting effects. In a further experiment, when the tactile warning signals were made spatially non-predictive with regard to the likely location of any visual driving events (i.e. the tactile warnings were now just as likely to be presented from the opposite direction to any critical visual driving events as from the same direction), the participants still responded more rapidly and accurately to critical visual driving events preceded by tactile warnings from the same rather than from the opposite direction. Taking the findings from these two experiments together, the authors concluded that the facilitatory effects that were observed following the presentation of a directionally appropriate tactile warning signal might result from an exogenous shift of the driver’s visual attention in the direction of the cue. That is, there was a stimulus-driven capture of spatial attention by the directional tactile cues, no matter whether that cue happened to be predictive or not.

338


However, one potential limitation with the above research is that the experimental design cannot discriminate the facilitatory influence of tactile cues attributable to some sort of priming of the driver’s responses and the exogenous orienting effect of the tactile cues (see Gray et al., 2014). That is, it is possible that the spatial tactile cues on the front and back, respectively, primed braking and accelerating responses, rather than necessarily leading to perceptual enhancement attributable to the spatial aspect of the cues coinciding with that of the targets. In order to address this issue, Ho et al. (2006b) therefore conducted another experiment to try and isolate the response priming effects by requiring their participants to make speeded discrimination responses regarding the colour change of the license plates, instead of responding to the approach of the front or rear vehicles. Given that the participants’ responses were orthogonal to the spatial direction of the tactile cues (i.e. the front and the rear cuing of spatial attention), any performance facilitation documented following the presentation of directionally appropriate tactile cues can only have been attributable to the exogenous spatial orienting of the tactile cues. Interestingly, however, the results revealed no significant spatial cuing effect following the presentation of the tactile cues. Contrast this with the robust spatial cuing effects that have been reported in previous studies where the drivers’ responses consisted of braking or accelerating (see Ho et al., 2005b, 2006a). The authors therefore concluded that the spatially directional tactile cues on the participant’s body surface may have elicited an automatic response bias (Prinzmetal et al., 2005; Gray et al., 2013), rather than necessarily leading to a shift of the driver’s spatial attention in the direction that happened to have been cued by the tactile stimuli (or warning signals). 4.3. Directing attention to the left or right Another popular application of directional tactile warnings is the lane departure warning system (LDWS). Such systems are designed to improve drivers’ situation awareness by indicating that the drivers are getting too close to the edge of the lane on either side (Tijerina et al., 1996; Navarro et al., 2007; Kullack et al., 2008; Beruscha et al., 2011; Deroo et al., 2013). The Federal Motor Carrier Safety Administration recommends that the LDWS should apply a tactile or auditory warning in an imminent lane departure situation (Houser et al., 2005). By now, many studies of LDWSs have reported that tactile warnings are more effective than auditory warnings (more effective even than the multisensory warning signals that combined both auditory and tactile cues) in terms of facilitating corrective steering RTs, drivers’ acceptability of the warning signal, or the magnitude of any lane departure (see Suzuki and Jansson, 2003; Sayer et al., 2005; Kozak et al., 2006; Stanley, 2006). The tactile warnings for lane departure might be presented from either the seat (Sayer et al., 2005; Stanley 2006) or from the steering wheel (Navarro et al., 2010 see Beruscha et al., 2011; Navarro et al., 2011, for reviews). It has been suggested that the warnings would be more effective if presented from the effector associated with the desired responses (Gray et al., 2013). Therefore, it has commonly been suggested that LDWS warnings would be more effective if presented from the steering wheel, where some response is likely expected to be taken in order to correct for the lane deviation (see Suzuki and Jansson, 2003; Campbell et al., 2007). An important factor in the design of directional tactile warnings in the LDWS is how to present the tactile cues in order to warn drivers of the impending lane drift, thus eliciting a speeded corrective steering response that is consistent with the action(s) that will be needed in order to return the vehicle to the lane. Is it better to present the tactile warnings on the same side as the

potential lane departure or to present the tactile warning on the side of the expected correction, should one need to be made? According to the well-known “stimulus-response compatibility” rule, responses are normally both faster and more accurate when the location of the stimulus is spatially compatible with the expected responses (see Proctor and Reeve, 1989, for a review). For example, in simple choice reaction tasks involving either a left or right key-press response to target stimuli presented on either the left or right, spatially compatible responses (i.e. left response to left stimuli and right response to right stimuli) yield significantly better performance in terms of both the RTs and accuracy of responding (e.g. see Proctor et al., 2005; Vu and Proctor, 2004). However, when one comes to look at the available guidelines concerning how to make warning signals that are compatible with drivers’ responses in the case of lane departure warnings, the recommendation is that the warning signals should induce an orienting response, causing the drivers to look in the direction of the potential hazard (see Campbell et al., 2007). In a driving scenario where there may be a need to initiate a steering avoidance response, it has been found that most drivers seem to have learned to turn away from the side indicated by the warnings (Straughn et al., 2009). This learning effect is perhaps the reason why “S-R incompatible” warnings seem more intuitive to the majority of drivers (Campbell et al., 1996). Such an approach has been adopted in the majority of lane departure warnings studies that have been published to date (e.g. Suzuki and Jansson, 2003; Sayer et al., 2005; Jenkins et al., 2007). It is, however, critical to note that the context of the lane departure in the driving situation is significantly different from the “keypress task” typically utilized in laboratory studies. The former situation obviously requires high-level situation awareness (i.e. judging which side the vehicle is drifting toward) prior to the initiation and execution of the corresponding steering maneuver, whereas the response in the latter case is extremely straightforward and simple. In their daily experience on roads that are equipped with rumble strips, drivers will hear a noise or feel a vibration on the side where the vehicle is going to cross the edge of the lane (Navarro et al., 2011). This combined (i.e. multisensory) noise and vibration signal then serves to warn the driver about the side of the imminent lane departure. S-R incompatible tactile warning signals are also presented from the side of the near lane departure, as in the situation with rumble strips. This natural mapping between SR incompatible warnings and the realistic driving situation might well be expected to enhance the driver’s performance in diagnosing the direction of drift of the vehicle and accordingly have facilitated their corrective steering movements. Other than the tactile warnings delivered by means of the vibration of the seat or steering wheel, another type of tactile warning signal is known as motor priming (MP). This has recently been tested in the context of LDWS. MP involves the presentation of directional stimulation to the driver’s hands by means of the application of a fast, small, and asymmetric oscillation, with one direction of the oscillation being stronger than the other. This gives the impression that the steering wheel is being pushed in the direction where the corrective steering maneuver should be performed (i.e. toward the center of the lane; see Navarro et al., 2007, 2010; Deroo et al., 2013). A comparison between MP and more traditional warning systems (e.g. auditory or tactile) revealed that although a similar reduction in steering RTs was observed in the MP and other warning conditions, the MP gave rise to a significant advantage over the other warnings in terms of the reduction in the duration of any deviation from the centre of the lane (Navarro et al., 2007). Traditional warning systems are designed to improve drivers’ situation awareness of the near lane departure. MP not only improved situation diagnosis, but also delivered direct


intervention concerning the likely action required, by providing some directional information to the driver’s hands via the oscillation of the steering wheel. It is worth noting that the tactile warnings in the comparison condition were presented by the vibration of the entire steering wheel, rather than by means of directional tactile cues. It is, however, worth pointing out that directional pulses (as in the oscillation involved in MP warning signals) may also result in the driver making reflexive counteractions by turning the steering wheel in the direction opposite to the pulse without the appropriate diagnosis of the situation, especially in time critical situations (see Ziegler, 1995; Kullack et al., 2008; Deroo et al., 2012). For example, in the study of a LDWS that also used a similar directional pulse as the MP on the steering wheel, Suzuki and Jansson (2003) found that many of their participants (approximately 50%) actually turned the steering wheel in the opposite direction in order to compensate for the steering pulses toward the center of the lane. Therefore, such characteristic of the drivers’ response to the directional pulses on the steering wheel should be taken into account when designing the warning systems for LDWSs. 4.4. Directing attention to multiple spatial directions Thus far, we have discussed directional tactile warnings that are capable of presenting two directions (front/back or left/right). However, given the complexity of any realistic driving situation, a tactile warning signal that is capable of presenting more directions may be used in vehicle, and each direction of warning signal may be associated with a somewhat different response by the driver (Cummings et al., 2007; Gray et al., 2013). Another important question to arise at this point concerns whether drivers can effectively and efficiently differentiate the spatial information conveyed by these directional tactile warnings. Of particular interest here, Terrence et al. (2005) examined the ability of participants to localize eight directions around the participant’s abdomen via tactile stimulation. The results suggested that tactile cues robustly enhanced participants’ performance in terms of the accuracy of their localization responses and in terms of their RTs, as opposed to those conditions in which directional auditory alerts were presented. Based on this finding, it would therefore be interesting to investigate how to communicate multiple and meaningfully different warnings by means of directional tactile cues such that drivers could execute the corresponding maneuver rapidly (see Sayer et al., 2005; Fitch et al., 2007). Fitch et al. (2011) designed a haptic seat that could deliver three longitudinal warnings and four lateral warnings. Although the accuracy of drivers’ responses declined as the number of possible warnings exceeded one, this impairment was, at worst, still a pretty impressive 94% correct, thus suggesting that drivers can execute the correct driving maneuver in response to multiple tactile warnings. However, drivers’ RTs were also lengthened by about 300 ms when the situation went from a single warning up to seven warnings. The authors concluded that a haptic seat conveying three or less tactile warnings might not significantly increase driver workload and RTs; however, whenever more than three warnings are being considered, further investigation prior to implementation is probably advisable. Similarly, Sayer et al. (2005) combined FCWS and LDWS warnings together by means of four tactors situated in the base of the seat in an instrumented vehicle. They evaluated the experience of drivers in localizing different tactile warnings during a 4-week operational field test. The FCWS warnings were generated by the simultaneous vibration of the front-left and front-right tactors, and the left and right warnings for LDWS were presented by means of

339

the simultaneous vibration of the front-left and back-left, or the front-right and back-right tactors, respectively. The results of this evaluation indicated that a number of the drivers were unable to differentiate the lateral (left and right) warnings in the LDWS from the frontal warnings in the FCWS, as they felt that “the whole seat buzzed” and “couldn’t tell which leg was being vibrated” (Sayer et al., 2005). Such confusion in terms of the localization of tactile warning signals as documented in this study might indicate one of the limitations of static cues in terms of conveying multiple directional warnings. The involvement of dynamic tactile cues might be used to improve drivers’ localization and differentiation to the tactile warnings. For example, using the dynamic toward-torso tactile cues warns drivers of the frontal collision and utilizing the dynamic moving to left and right indicates the lane departure direction. Recently, Murata et al. (2013) utilized an 8-directional warning system to orient the driver’s attention to the eight potential directions (including front, rear, left, right, front left, front right, rear left, and rear right). Dynamic tactile cues were used to present directional information via a 4 (longitude) 2 (lateral) matrix of tactors embedded in the driver’s seat. For example, the sequential operation of the two columns of four longitudinally arrayed tactors from the front to the back was used to signal that a potential hazard was situated out in front of the driven vehicle. The dynamic tactile warning systems were shown to lead to a 10% increase in the rate of hazard recognition (and somewhat faster RTs), as opposed to the static warnings. However, while dynamic tactile warnings showed a high degree of promise in terms of conveying multiple sources of directional information to the driver, it should be noted that the recognition rate of the hazard direction under dynamic tactile cues in Murata et al.’s study was only 74%, which is obviously still rather low when it comes to practical applications. 5. Meaningful tactile warning signals Fortunately, dangerous collisions constitute a very rare occurrence for most drivers under realistic driving conditions (Parasuraman et al., 1997; Spence and Ho, 2008a). This means that tactile warning signals will likely be presented very infrequently, especially if one wants to keep a low rate of “cry wolf” type false alarms (Breznitz, 1983Breznitz, 1983 Bliss and Acton, 2003; Dixon et al., 2007; Spence and Ho, 2008a; Ho et al., 2014a). Given the fact that the average driver is undoubtedly going to be very reluctant to undergo (extensive) training before using a tactile warning signal in their car (Spence and Ho, 2008a,b; Ho et al., 2014a,b), future tactile warning signals need to be designed so that their meanings are immediately apparent (that is, drivers ideally need to be able to recognize the meaning conveyed by the tactile warnings easily) even they have not experienced this warning signal for a long time. Recent studies have designed a particular class of tactile signals, called tactile icons or tactons, that constitute a form of structured abstract messaging that can potentially convey meaningful information by simultaneously manipulating one or several of the parameters of tactile cues (such as vibration frequency, duration, intensity, waveform and location; see, Brewster and Brown, 2004; Jones and Sarter, 2008; Jones et al., 2009; Ferris and Sarter, 2011). In fact, some of the earliest attempts to communicate meaningful information via the skin surface can be traced back to Geldard (1957)'s seminal early work, where the first tactile language called “Vibratese” was designed (for conditions of passive stimulation). Vibratese was capable of conveying the entire English alphabet, all of the digits, and the most frequently encountered short words (e.g. “of”, “and”, “the”) by means of variations in vibration intensity,

340


duration, and the bodily locations that were stimulated. However, it can easily be imagined that conveying meaningful information via tactons will be much harder than it is to generate meaningful visual icons or auditory icons, because of our limited ability to process tactile information across the body surface (Gallace et al., 2007; Gallace and Spence, 2014). Nevertheless, some exciting developments have been seen in this area in recent years, especially in the interface design of mobile phone and navigation devices (e.g. Brewster and Brown, 2004; Brown et al., 2005; Brown and Kaaresoja, 2006; Qian et al., 2009). For instance, Brown and Kaaresoja created nine tactons with a standard mobile phone motor in order to communicate the type of alert (voice call, text message, or multimedia message) and the priority of that alert (low, medium, or high). The overall recognition rates by participants for the different tactile alerts were approximately 75%. Meanwhile, in another study, Brown et al. (2005) evaluated the sensitivity of people to different patterns (that is, to different tactons). Their participants’ recognition rate to the rhythm of the tactile cues reached as high as 93%. More recently, Jones et al. (2009) evaluated the effectiveness of a tactile display that was mounted on the back of the user and could be used to communicate simple military instructions and commands. Seven hand-and-arm signals that are used to communicate in military contexts were converted into tactile patterns that were displayed on the back of the participant. The participants in this study were able to accurately recognize approximately 98% of the tactile patterns, and, importantly, the average rate of recognition was also high (92%) when the participants were engaged in a congruent physical or cognitive task. However, the utilization of meaningful tactile icons with complex information is still limited in the case of in-vehicle warning signals designed for drivers. On the one hand, it would be difficult for a driver to decode the information that is embedded in the tactile icons when engaged in a demanding driving task (see Ferris and Sarter, 2010). On the other, it would presumably require extensive training for the driver to discriminate the complex information conveyed by means of the tactons, which is, as mentioned above, a problem for any new in-vehicle display system. Over the last decade or so, researchers have started to assess the effectiveness of a number of dynamic tactile warning signals capable of conveying some meaningful information concerning critical external driving events to the drivers with only a minimal period of familiarization prior to testing. It is commonly believed that the urgency of a warning signal can be enhanced simply by adding more dynamic qualities (Edworthy and Hellier, 2006; Haas and Edworthy, 2006; Laughery, 2006), and people usually show a

tendency to respond to dynamic stimuli over static stimuli, especially when the stimuli are approaching the person in their peripersonal space (see Canzoneri et al., 2012). Neuropsychological research using functional MRI has documented increased neural activity in people’s brains while presenting dynamic approaching visual, auditory, or tactile stimuli (see Bremmer et al., 2001). Those stimuli that approach a person appear to be treated as a fundamentally important potential threat signal, thus triggering people’s defensive reactions and speeding their response times (Graziano and Cooke, 2006). For example, Canzoneri et al. (2012) measured people’s RTs to tactile stimuli presented on their hands at different delays from the onset of task-irrelevant dynamic sounds which gave the impression of a sound source either approaching or receding from the participant’s hand. The participants responded more rapidly to the tactile targets delivered to the hand when the dynamic auditory stimulus was perceived from close to the hand. This facilitatory effect was stronger when the sounds approached the participants as compared to when they were heard to recede. Such properties of our responses to dynamic stimuli can potentially be utilized in the design of in-vehicle warnings. Previous research has demonstrated the advantage of dynamic auditory warnings in terms of speeding drivers’ braking response to potential collisions. In Gray (2011)'s study, for example, a dynamic auditory warning (whose intensity increased as the distance between the driven vehicle and the lead vehicle decreased) was compared with a static one (whose intensity was kept constant) in a simulated forward collision avoidance scenario. The results revealed that the dynamic auditory warnings produced significantly faster BRTs relative to the static auditory warnings. It would seem that the dynamic property of the auditory intensity provides a natural impression that the sound-emitting object is approaching the driver (Shaw et al., 1991), which has been shown to be more biologically and attentionally salient (e.g. see Hall and Moore, 2003; Leo et al., 2011), thus facilitating drivers’ speeded BRTs. Inspired by the facilitatory effect of dynamic qualities in auditory warnings, some studies (though, it has to be said, very few) have tried to design dynamic tactile warnings by manipulating the intensity of the vibrotactile signal or by presenting patterns of tactile stimulation that gave rise to some form of movement (either apparent or real; see Table 3). Ho et al. (2013) designed a dynamic tactile warning signal by increasing the intensity of the vibration while the stimulus was actually being presented. Increasing the intensity of tactile cues can potentially be used to convey information about the proximity of a vehicle to an obstacle in a driving environment (Jones and Sarter, 2008). It might therefore be expected that dynamic tactile warning signals that

Table 3 Summary of the studies concerning dynamic vibrotactile warning signals. Type of dynamic vibrotactile Results warning signal

Related studies

Increasing intensity

(Ho et al., 2013; Gray et al., Ramped (i.e. increasing intensity) tactile warning signals (no matter whether the intensity increase happens to be dependent on the closing velocity between the driven vehicle and the lead vehicle or not) 2014) do not necessarily stand out from the other constant intensity warning signals.

Toward-head warning signals

When the motion toward the head is independent of the external critical event, the toward-head tactile (Ho et al., 2014; Gray et al., 2014 warnings are significantly more effective than static tactile warnings. However, no significant difference Gray et al., 2014) between the toward-head and away-from-head tactile warnings has been found to date. However, when the motion toward the head is linked to the closing velocity (CV) between the driven vehicle and the lead vehicle, CV-linked toward-head tactile cues are significantly more effective than CV-constant towardhead, CV-linked away-from-head, and CV-constant away-from-head tactile cues.

Toward-torso warning signals

(Meng et al., 2014a,b,b) Dynamic toward-torso cues are significantly more effective than static tactile cues presented to the driver’s hands, static tactile cues presented to the waist, static tactile cues presented simultaneously on (in press) hands and waist, and dynamic away-from-torso tactile cues.


incorporate increasing intensity can be used to produce an impression that something is approaching the driver, thus inducing speeded responses as seen in the auditory modality. However, the results that have been published to date instead reveal that dynamic tactile intensity warning signals do not necessarily stand out from other static tactile warnings (with constant intensity) in terms of their ability to speed a driver’s BRTs in forward collision avoidance conditions. Given that the increase in intensity of the vibrotactile stimuli in Ho et al.'s (2013) study was independent to the relative emergency/danger of the external event, Gray et al. (2014) went on to investigate whether the dynamic tactile warnings whose vibration intensity varied as a function of the closing velocity (CV) between the driven vehicle and the lead vehicle would facilitate the driver’s braking performance in a potential rear-end collision scenario. Given that more information concerning the external events can be conveyed by means of the contingent tactile stimulation (Díaz et al., 2012), it was hypothesized that the CVlinked dynamic tactile warnings would be more effective than the CV-constant dynamic tactile warnings (i.e. the vibration intensity increased at a constant rate no matter the value of CV). Disappointingly, however, the results of this study failed to reveal any significant difference between the CV-linked and CV-constant dynamic tactile warnings. The results of the two studies reported above (Ho et al., 2013; Gray et al., 2014) demonstrated that increasing the vibration intensity of a tactile cue at a single body site doesn’t necessarily produce an impression of approach (or looming) that matches that seen in auditory modality. Given the tactile stimulus is perceived as a proximal cue (i.e. it has to be presented on the drivers’ body surface), it would appear that increasing intensity alone cannot provide a natural mapping to an approaching external event (which usually occurs in distal space), thus failing to facilitate drivers’ braking responses to potential forward collision events. Therefore, other studies have examined whether a dynamic pattern of vibrotactile stimulation can be used to more effectively convey information concerning external driving events to the drivers.

341

Ho et al. (2014a,b); Ho et al. (2014a,b) designed a tactile warning signal for forward collision avoidance that was designed to give the impression of a stimulus travelling toward/away from the driver’s head via the sequential activation of three tactors aligned along the driver’s midline (without any inter-tactor interval (ITI), see Fig. 1). Comparing the results revealed that the toward-head triple tactile warnings were significantly more effective in facilitating a participant’s braking responses to the potential rear-end collision than the conditions in which a single or pair of tactors was activated. However, Ho et al.’s results failed to reveal any significant difference between the toward-head and away-fromhead tactile warnings. These results would therefore appear to indicate that the advantage of the dynamic triple tactile towardhead warnings over the static tactile cues might be attributable to the intrinsic property of the tactile movement per se, without regard to the directional information embedded in the dynamic tactile warnings. That is, the toward-head tactile cues do not necessarily convey approach information concerning the external event, and it is the multiple stimulations in the dynamic tactile warnings that benefit drivers’ BRTs as compared to the single stimulation in the case of static cues. Similarly, the toward-head and away-from-head dynamic tactile cues via three sequentially operated tactors presented on the abdomen were also compared in Gray et al. (2014) study in terms of their effectiveness in speeding drivers’ responses to forward collision events. However, in contrast to the dynamic tactile cues utilized in Ho et al. (2014a,b); Ho et al. (2014a,b) latest study, the toward- and away-from head tactile cues used by Gray et al. involved varying the inter-tactor interval, which was dependent on the CV between the driven vehicle and the lead vehicle (CV-linked tactile cues). The ITI was manipulated in such a manner that the ITI was shorter at higher closing velocities, giving rise to a perception of faster apparent motion toward/away from the head. The results suggested that drivers’ BRTs were faster following the presentation of CV-linked toward-head tactile cues than following the presentation of CV-constant toward-head, CVlinked away-from-head and CV-constant away-from-head tactile

[(Fig._1)TD$IG]

Fig. 1. The dynamic toward-head tactile warning signals (left) presented by the sequential activation of three tactors aligned along the driver’s midline and the dynamic toward-torso tactile warning signals (right) presented by the sequential activation of two pairs of tactors on hands and waist.

342


cues. Taking the findings of the two studies together, it would appear that by themselves the multiple stimuli embedded in the dynamic toward-head cues do not generate an impression of approaching motion; however, when the presentation of dynamic patterns of stimulation are combined with a CV-linked ITI to form an apparent motion stimulus, the toward-head cues are more easily associated with an object approaching the body. Given the tactile cues in Ho et al.'s (2014a,b) study were moving along the driver’s coronal plane (an imaginary plane dividing the body into dorsal and ventral parts, cf. Fiel et al., 1991), it would be difficult to produce an approaching impression along the coronal plane because the forward collision in the driving context is always approaching the driver from the front. Therefore, Meng et al.'s (2014a,b) (in press) studies evaluated dynamic tactile warnings that travelled toward, or away from, the driver along the sagittal plane (an imaginary plane dividing the body into right and left sides, cf. Fiel et al., 1991), whose motion direction was congruent with the direction of the potential rear-end collision. Meng et al. (2014a) (in press) compared the effectiveness of static tactile cues presented to the hands, static tactile cues presented to the waist, static tactile cues presented simultaneously on the hands and waist, a dynamic toward-torso tactile cue, and a dynamic awayfrom-torso tactile cue in the forward collision avoidance (see Fig. 2). The dynamic toward-and away-from-torso warnings were presented by means of the sequential activation of two tactors on the participants’ hands and another two tactors on their waist. The results of Meng et al. (2014a,b)'s study revealed that the dynamic toward-torso cues were significantly more effective than the other types of tactile cues in terms of facilitating driver’s braking responses. It was suggested that the directional congruency between the dynamic toward-torso warnings and the forward collision (also approaching the driver from the front) may have been informative in terms of conveying the impression that there was something approaching the driver. Given the dynamic towardtorso tactile warnings were presented in the driver’s peripersonal space, they would likely have been more effective in terms of conveying the impression of an approaching threat to the driver, thus triggering drivers’ defensive reactions and speeding their responses (Graziano and Cooke, 2006). Although the effectiveness of tactile warnings in directing a driver’s spatial attention has been extensively demonstrated, the subjective feelings of drivers towards these kinds of tactile warnings should also be taken into consideration when it comes to their possible implementation. For instance, in a study by Chang et al. (2011), tactile signals delivered from a haptically-enabled seat caused similar subjective satisfaction as the auditory warnings when they were used as the ringing signals of vehicle Bluetooth hands-free systems; however, when the tactile signals were used in a vehicle navigation system, they produced lower subjective satisfaction than the auditory warnings. The authors explained these results in terms of the drivers being unfamiliar with the tactile signals delivered from the navigation system (which always used auditory and visual signals), thus eliciting the relatively low satisfaction in response to the tactile signals.

[(Fig._2)TD$IG]

6. Conclusions

Fig. 2. Mean latency of BRTs (in ms) as a function of the warning signal type. Error bars indicate the standard errors of the means. Results show that the dynamic toward-torso tactile cues were more effective than the away-from-torso tactile cues (a and c), static tactile cues presented to the hands, static tactile cues presented to the waist (b), static tactile cues presented simultaneously on hands and waist (c) in the forward collision avoidance.

In this review of the literature on tactile warnings for safe driving, the different findings from studies that have presented non-directional, directionally-informative, and meaningful tactile warnings for collision avoidance have been summarized. As the above analysis shows, the dynamic vibrotactile warning signals are definitely promising when it comes to the future design of more effective warnings than the static vibrotactile warnings that have typically been considered to date, or are currently in use. Given that dynamic tactile stimuli presented by the activation of different


spatial patterns are more feasible when it comes to conveying directional information by means of manipulating the pattern of vibration, dynamic tactile warnings merit further exploration as a means of combining multiple directional information together for orienting drivers’ spatial attention efficiently. Further research will therefore be needed in order to investigate how to enhance drivers’ performance in the differentiation of directional information conveyed by tactile warnings. It is also worth noting that caution should be taken before combining spatially directional and nondirectional tactile cues in any in-vehicle warning system, otherwise the driver might be confused by the inconsistent type of warning signals. Another important issue that should be stressed before a decision is made to implement tactile warning signals is the crossmodal effects of visual and/or auditory perceptual load on the effectiveness of tactile warning signal (see Spence, 2010). The phenomenon of “inattentional blindness” has been extensively reported in the visual and auditory modalities (e.g. Mack and Rock, 1998; Mack, 2003; Fougnie and Marois, 2007; Lee et al., 2009; Macdonald and Lavie, 2011), whose results revealed that people may lack an awareness of visual/auditory stimuli when their attention is focused on a different stimulus. Although, to date, few attempts have been made to study the phenomenon of “inattentional blindness” in the tactile modality (Gallace and Spence, 2008, 2014 though see also Mack and Rock, 1998), one may expect that high visual perceptual load would impact deleteriously on tactile information processing (for this topic, see the perceptual load theory: Lavie, 1995, 2005). Given the fact that driving usually involves high visual (sometimes also auditory) perceptual load, the drivers’ ability to perceive the tactile warning signal may be adversely affected, especially when the tactile warnings are presented rarely. However, the majority of the current studies have tended to assess the effectiveness of various tactile warning signals under relatively low perceptual load and high presentation rate. It should be noted, therefore that results may likely differ from those seen under more ecological conditions. Therefore, the tactile warning signals should be tested under conditions of high perceptual load, with infrequent presentation rate, before their implementation in realistic driving situations. Acknowledgements This research was supported in part by the EPSRC under grant EP/J008001/1, and the National Natural Science Foundation of China under grant number 71371103 and 31271100. References Arrabito, G.R., 2009. Effects of talker sex and voice style of verbal cockpit warnings on performance. Hum. Factors 51 (1), 3–20. Ashley, S., 2001. Driving the info highway. Sci. Am. 285 (4), 44–50. Baldwin, C.L., 2011. Verbal collision avoidance messages during simulated driving: perceived urgency, alerting effectiveness and annoyance. Ergonomics 54 (4), 328–337. Baldwin, C.L., Eisert, J.L., Garcia, A., Lewis, B., Pratt, S.M., Gonzalez, C., 2012a. Multimodal urgency coding: auditory, visual, and tactile parameters and their impact on perceived urgency. Work 41 (Suppl. 1), 3586–3591. Baldwin, C.L., Spence, C., Bliss, J.P., Brill, J.C., Wogalter, M.S., Mayhorn, C.B., Ferris, T. K., 2012b. Multimodal cueing: the relative benefits of the auditory, visual, and tactile channels in complex environments. Proceedings of the 56th Human Factors and Ergonomics Society Meeting 56, 1431–1435. Baldwin, C.L., Lewis, B.A., 2014. Perceived urgency mapping across modalities within a driving context, Appl. Ergono. 45 (5), 1270–1277. Baron, R.A., Kalsher, M.J., 1998. Effects of a pleasant ambient fragrance on simulated driving performance the sweet smell of...safety? Environ. Behav. 30 (4), 535–552. Ben-Yaacov, A., Maltz, M., Shinar, D., 2002. Effects of an in-vehicle collision avoidance warning system on short-and long-term driving performance. Hum. Factors 44 (2), 335–342.

343

Beruscha, F., Augsburg, K., Manstetten, D., 2011. Haptic warning signals at the steering wheel: a literature survey regarding lane departure warning systems Haptics-e. Electron. J. Haptic Res. 4 (5), 1–6. Bliss, J.P., Acton, S.A., 2003. Alarm mistrust in automobiles: how collision alarm reliability affects driving. Appl. Ergon. 34 (6), 499–509. Braun, C.C., Silver, N.C., 1995. Interaction of signal word and colour on warning labels: differences in perceived hazard and behavioural compliance. Ergonomics 38 (11), 2207–2220. Bremmer, F., Schlack, A., Shah, N.J., Zafiris, O., Kubischik, M., Hoffmann, K.-P., Zilles, K., Fink, G.R., 2001. Polymodal motion processing in posterior parietal and premotor cortex: a human fMRI study strongly implies equivalencies between humans and monkeys. Neuron 29 (1), 287–296. Brewster, S., Brown, L.M., 2004. Tactons: structured tactile messages for non-visual information display. Proceedings of the Fifth Conference on Australasian User Interface 28, 15–23. Brown, L.M., Brewster, S.A., Purchase, H.C., 2005. A first investigation into the effectiveness of tactons. Proceedings of the First Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems 167–176. Brown, L.M., Brewster, S.A., Purchase, H.C., 2006. Multidimensional tactons for nonvisual information presentation in mobile devices. Proceedings of the 8th Conference on Human-Computer Interaction with Mobile Devices and Services 231–238. Brown, L.M., Kaaresoja, T., 2006. Feel who’s talking: using tactons for mobile phone alerts. Proceedings of the CHI’06 Extended Abstracts on Human Factors in Computing Systems 604–609. Bueno, M., Fort, A., Francois, M., Ndiaye, D., Deleurence, P., Fabrigoule, C., 2013. Effectiveness of a forward collision warning system in simple and in dual task from an electrophysiological perspective. Neurosci. Lett. 541 (1), 219–223. Butter, C.M., Buchtel, H.A., Santucci, R., 1989. Spatial attentional shifts: Further evidence for the role of polysensory mechanisms using visual and tactile stimuli. Neuropsychologia 27 (10), 1231–1240. Campbell, J.L., Campbell, J.L., Gore, F., Kantowitz, B.H., Mitchell, E., 1996. Investigation of Alternative Displays for Side Collision Avoidance Systems. Report No. DOT HS 808 579. Battelle Human Factors Transportation Center, Seattle, WA. Campbell, J.L., Richard, C.M., Brown, J.L., Mccallum, M., 2007. Crash warning system interfaces: Human factors insights and lessons learned. US Department of Transportation, National Highway Traffic Safety Administration, Washington, DC (HS 810 697). Canzoneri, E., Magosso, E., Serino, A., 2012. Dynamic sounds capture the boundaries of peripersonal space representation in humans. PloS One 7 (9), e44306. Chang, S.-H., Lin, C.-Y., Fung, C.-P., Hwang, J.-R., Doong, J.-L., 2008. Driving performance assessment: effects of traffic accident location and alarm content. Accid. Anal. Prev. 40 (5), 1637–1643. Chang, W., Hwang, W., Ji, Y.G., 2011. Haptic seat interfaces for driver information and warning systems. Int. J. Hum. Comput. Interact. 27 (12), 1119–1132. Chen, D., Katdare, A., Lucas, N., 2006. Chemosignals of fear enhance cognitive performance in humans. Chem. Senses 31, 415–423. Chun, J., Han, S.H., Park, G., Seo, J., Choi, S., 2012. Evaluation of vibrotactile feedback for forward collision warning on the steering wheel and seatbelt. Int. J. Ind. Ergon. 42 (5), 443–448. Chun, J., Lee, I., Park, G., Seo, J., Choi, S., Han, S.H., 2013. Efficacy of haptic blind spot warnings applied through a steering wheel or a seatbelt. Transp. Res. Part F Traffic Psychol. Behav. 21, 231–241. Clark, J. 2013. March 26. 2014 Mercedes-Benz S-Class interior is the essence of luxury. Retrieved March 26, 2014. from http://www.emercedesbenz.com/autos/ mercedes-benz/s-class/2014-mercedes-benz-s-class-interior-is-the-essenceof-luxury/ Cummings, M.L., Kilgore, R.M., Wang, E., Tijerina, L., Kochhar, D.S., 2007. Effects of single versus multiple warnings on driver performance. Hum. Factors 49 (6), 1097–1106. Deatherage, B.H., 1972. Auditory and other sensory forms of information processing. In: Van Cott, H.P., Kinkade, R.G. (Eds.), Human Engineering Guide to Equipment Design. John Wiley and Sons, New York, pp. 124–160. Díaz, A., Barrientos, A., Jacobs, D.M., Travieso, D., 2012. Action-contingent vibrotactile flow facilitates the detection of ground level obstacles with a partly virtual sensory substitution device. Hum. Mov. Sci. 31 (6), 1571–1584. De Rosario, H., Louredo, M., Díaz, I., Soler, A., Gil, J.J., Solaz, J.S., Jornet, J., 2010. Efficacy and feeling of a vibrotactile frontal collision warning implemented in a haptic pedal. Transp. Res. Part F Traffic Psychol. Behav. 13 (2), 80–91. Deroo, M., Hoc, J.-M., Mars, F., 2012. Influence of risk expectation on haptically cued corrective manoeuvres during near lane departure. Ergonomics 55 (4), 465–475. Deroo, M., Hoc, J.-M., Mars, F., 2013. Effect of strength and direction of haptic cueing on steering control during near lane departure. Transp. Res. Part F Traffic Psychol. Behav. 16 (1), 92–103. Diederich, A., Colonius, H., 2008. When a high-intensity distractor is better then a low-intensity one: modeling the effect of an auditory or tactile nontarget stimulus on visual saccadic reaction time. Brain Res. 1242 (1), 219–230. Dingus, T.A., Mcgehee, D.V., Manakkal, N., Jahns, S.K., Carney, C., Hankey, J.M., 1997. Human factors field evaluation of automotive headway maintenance/collision warning devices. Hum. Factors 39 (2), 216–229.

344


Dixon, S.R., Wickens, C.D., McCarley, J.S., 2007. On the independence of compliance and reliance: are automation false alarms worse than misses? Hum. Factors 49 (4), 564–572. Drew, D.A., Hayes, C.C., 2012. An exploration of decision support for drivers, inside and outside the vehicle. Hum. Factor Ergon. Man. Serv. Ind. 22 (5), 420–436. Edworthy, J., Hellier, E., 2006. Complex nonverbal auditory signals and speech warnings. In: Wogalter, M.S. (Ed.), Handbook of Warnings. Lawrence Erlbaum Associates, Mahwah, NJ, pp. 199–220. Ferris, T., Penfold, R., Hameed, S., Sarter, N., 2006. The implications of crossmodal links in attention for the design of multimodal interfaces: a driving simulation study. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 406–409. Ferris, T.K., Sarter, N.B., 2008. Cross-modal links among vision, audition, and touch in complex environments. Hum. Factors 50 (1), 17–26. Ferris, T.K., Sarter, N., 2010. When content matters: the role of processing code in tactile display design. IEEE Trans. Haptic 3 (3), 199–210. Ferris, T.K., Sarter, N., 2011. Continuously informing vibrotactile displays in support of attention management and multitasking in anesthesiology. Hum. Factors 53 (6), 600–611. Fiel, R.J., Alletto, J.J., Severin, C.M., Nickerson, P.A., Acara, M.A., Pentney, R.J., 1991. MR imaging of normal rat brain at 0.35 T and correlated histology. J. Magn. Reson. Imaging 1 (6), 651–656. Fitch, G.M., Hankey, J.M., Kleiner, B.M., Dingus, T.A., 2011. Driver comprehension of multiple haptic seat alerts intended for use in an integrated collision avoidance system. Transp. Res. Part F Traffic Psychol. Behav. 14 (4), 278–290. Fitch, G.M., Kiefer, R.J., Hankey, J.M., Kleiner, B.M., 2007. Toward developing an approach for alerting drivers to the direction of a crash threat. Hum. Factors 49 (4), 710–720. Fougnie, D., Marois, R., 2007. Executive working memory load induces inattentional blindness. Psychon. Bull. Rev. 14 (1), 142–147. Gallace, A., Spence, C., 2008. The cognitive and neural correlates of tactile consciousness: a multisensory perspective. Conscious. Cogn. 17 (1), 370–407. Gallace, A., Spence, C., 2014. In Touch with the Future: The Sense of Touch from Cognitive Neuroscience to Virtual Reality. Oxford University Press, Oxford. Gallace, A., Tan, H.Z., Spence, C., 2005. Tactile change detection. In Proceedings of the First World Haptic Conference WHC 2005. IEEE Computer Society, Washington, DC, pp. 12–16. Gallace, A., Tan, H.Z., Spence, C., 2006. The failure to detect tactile change: a tactile analogue of visual change blindness. Psychon. Bull. Rev. 13, 300–303. Gallace, A., Tan, H.Z., Spence, C., 2007. Do mudsplashes induce tactile change blindness? Percept. Psychophys. 69 (4), 477–486. Gallace, A., Zeeden, S., Röder, B., Spence, C., 2010. Lost in the move? Secondary task performance impairs the detection of tactile change on the body surface. Conscious. Cogn. 19 (1), 215–229. Geldard, F.A., 1957. Adventures in tactile literacy. Am. Psychol. 12 (3), 115–124. Gemperle, F., Hirsch, T., Goode, A., Pearce, J., Siewiorek, D., Smailigic, A., 2003. Wearable vibro-tactile display Technical Report. Carnegie Mellon Wearable Group, Carnegie Mellon University. Graham, R., 1999. Use of auditory icons as emergency warnings: evaluation within a vehicle collision avoidance application. Ergonomics 42 (9), 1233–1248. Gray, R., 2011. Looming auditory collision warnings for driving. Hum. Factors 53 (1), 63–74. Gray, R., Ho, C., Spence, C., 2014. A comparison of different informative vibrotactile forward collision warnings: does the warning need to be linked to the collision event? PLos One 9 (1), e87070. Gray, R., Spence, C., Ho, C., Tan, H.Z., 2013. Efficient multimodal cuing of spatial attention. Proc. IEEE 101 (9), 2113–2122. Graziano, M.S., Cooke, D.F., 2006. Parieto–frontal interactions, personal space, and defensive behavior. Neuropsychologia 44 (6), 845–859. Haas, E., Edworthy, J., 2006. An introduction to auditory warnings and alarms. In: Wogalter, M.S. (Ed.), Handbook of Warnings. Lawrence Erlbaum Associates, Mahwah, NJ, pp. 189–198. Haas, E.C., Van Erp, J.B., 2014. Multimodal warnings to enhance risk communication and safety. Saf. Sci. 61 (1), 29–35. Hall, D.A., Moore, D.R., 2003. Auditory neuroscience: the salience of looming sounds. Curr. Biol. 13 (3), R91–R93. Harms, L., Patten, C., 2003. Peripheral detection as a measure of driver distraction. A study of memory-based versus system-based navigation in a built-up area. Transp. Res. Part F Traffic Psychol. Behav. 6 (1), 23–36. Hickson, L., Wood, J., Chaparro, A., Lacherez, P., Marszalek, R., 2010. Hearing impairment affects older people’s ability to drive in the presence of distracters. J. Am. Geriatr. Soc. 58 (6), 1097–1103. Hirst, S., Graham, R., 1997. The format and presentation of collision warnings. In: Noy, Y.I. (Ed.), Ergonomics and Safety of Intelligent Driver Interfaces. Erlbaum, Mahwah, NJ, pp. 203–219. Ho, C., Gray, R., Spence, C., 2014a. Reorienting driver attention with dynamic tactile cues. IEEE Trans. Haptic 7 (1), 86–94. Ho, C., Gray, R., Spence, C., 2014b. To what extent do the findings of laboratory-based spatial attention research apply to the real-world setting of driving? IEEE Trans. Hum. Mach. Syst. 44 (4), 524–530. Ho, C., Reed, N., Spence, C., 2006a. Assessing the effectiveness of intuitive vibrotactile warning signals in preventing front-to-rear-end collisions in a driving simulator. Accid. Anal. Prev. 38 (5), 988–996.

Ho, C., Reed, N., Spence, C., 2007. Multisensory in-car warning signals for collision avoidance. Hum. Factors 49 (6), 1107–1114. Ho, C., Spence, C., 2005. Olfactory facilitation of dual-task performance. Neurosci. Lett. 389 (1), 35–40. Ho, C., Spence, C., 2013. Affective multisensory driver interface design. Int. J. Veh. Noise Vib. 9, 61–74 (Special Issue on Human Emotional Responses to Sound and Vibration in Automobiles). Ho, C., Spence, C., Gray, R., 2013. Looming auditory and vibrotactile collision warnings for safe driving. Proceedings of the 7th International Driving Symposium on Human Factors in Driver Assessment, Training, and Vehicle Design. Bolton Landing, New York, pp. 551–557. Ho, C., Spence, C., Tan, H.Z., 2005a. Warning signals go multisensory. Proceedings of the 11th Annual Conference on Human-Computer Interaction, Las Vegas, Nevada, pp. 1–10. Ho, C., Tan, H.Z., Spence, C., 2005b. Using spatial vibrotactile cues to direct visual attention in driving scenes. Transp. Res. Part F Traffic Psychol. Behav. 8 (6), 397–412. Ho, C., Tan, H.Z., Spence, C., 2006b. The differential effect of vibrotactile and auditory cues on visual spatial attention. Ergonomics 49 (7), 724–738. Hogema, J.H., De Vries, S.C., Van Erp, J., Kiefer, R.J., 2009. A tactile seat for direction coding in car driving: field evaluation. IEEE Trans. Haptic 2 (4), 181–188. Horberry, T., Anderson, J., Regan, M.A., Triggs, T.J., Brown, J., 2006. Driver distraction: the effects of concurrent in-vehicle tasks, road environment complexity and age on driving performance. Accid. Anal. Prev. 38 (1), 185–191. Houser, A., Pierowicz, J., Fuglewicz, D., 2005. Concept of Operations and Voluntary Operational Requirements for Lane Departure Warning System (LDWS) onBoard Commercial Motor Vehicles. Federal Motor Carrier Safety Administration, Washington, DC. Jenkins, D.P., Stanton, N.A., Walker, G.H., Young, M.S., 2007. A new approach to designing lateral collision warning systems. Int. J. Veh. Des. 45 (3), 379–396. Jones, S.D., Furner, S.M., 1989. The construction of audio icons and information cues for human-computer dialogues. In: Megaw, E.D. (Ed.), Contemporary Ergonomics 1989. Taylor & Francis, London, pp. 436–441. Jones, L.A., Kunkel, J., Piateski, E., 2009. Vibrotactile pattern recognition on the arm and back. Perception 38 (1), 52. Jones, L.A., Sarter, N.B., 2008. Tactile displays: guidance for their design and application. Hum. Factors 50 (1), 90–111. Kaaresoja, T., Linjama, J., 2005. Perception of short tactile pulses generated by a vibration motor in a mobile phone. Proceedings of the First Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems. IEEE Computer Society, Los Alamitos, CA, pp. 471–472. Kaufmann, C., Risser, R., Geven, A., Sefelin, R., 2008. Effects of simultaneous multimodal warnings and traffic information on driver behaviour. Proceedings of European Conference on Human Centred Design for Intelligent Transport Systems, Lyon, France, pp. 33–42. Kennett, S., Eimer, M., Spence, C., Driver, J., 2001. Tactile-visual links in exogenous spatial attention under different postures: convergent evidence from psychophysics and ERPs. J. Cognit. Neurosci. 13 (4), 462–478. Kennett, S., Spence, C., Driver, J., 2002. Visuo-tactile links in covert exogenous spatial attention remap across changes in unseen hand posture. Percept. Psychophys. 64 (7), 1083–1094. Kiefer, R., Leblanc, D., Palmer, M., Salinger, J., Deering, R., Shulman, M., 1999. Development and Validation of Functional Definitions and Evaluation Procedures for Collision Warning/Avoidance Systems. Project No. DOT HS 808 964. National Highway Traffic Safety Administration, U.S. Department of Transportation. Kim, M.H., Lee, Y.T., Son, J., 2010. Age-related physical and emotional characteristics to safety warning sounds: design guidelines for intelligent vehicles. IEEE Trans. Syst. Man Cybern. Part C Appl. Rev. 40 (5), 592–598. Kozak, K., Pohl, J., Birk, W., Greenberg, J., Artz, B., Blommer, M., Cathey, L., Curry, R., 2006. Evaluation of lane departure warnings for drowsy drivers. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 2400–2404. Kullack, A., Ehrenpfordt, I., Lemmer, K., Eggert, F., 2008. Reflektas: lane departure prevention system based on behavioural control. IET Intel. Transport Syst. 2 (4), 285–293. Laughery, K.R., 2006. Safety communications: warnings. Appl. Ergon. 37 (4), 467–478. Laughery, K.R., Young, S.L., Vaubel, K.P., Brelsford Jr., N., 1993. The noticeability of warnings on alcoholic beverage containers. J. Public Policy Mark. 12 (1), 38–56. Lavie, 1995. Perceptual load as a necessary condition for selective attention. J. Exp. Psychol. Hum. Percept. Perform. 21 (3), 451–468. Lavie, N., 2005. Distracted and confused? Selective attention under load. Trends Cogn. Sci. 9 (2), 75–82. Lee, J.D., McGehee, D.V., Brown, T.L., Reyes, M.L., 2002. Collision warning timing, driver distraction, and driver response to imminent rear-end collisions in a high-fidelity driving simulator. Hum. Factors 44 (2), 314–334. Lee, J.D., Hoffman, J.D., Hayes, E., 2004. Collision warning design to mitigate driver distraction Proceedings of the SIGCHI. Conference on Human Factors in Computing Systems, Vienna, Austria, pp. 65–72. Lee, Y.-C., Lee, J.D., Boyle, L.N., 2009. The interaction of cognitive load and attentiondirecting cues in driving. Hum. Factors 51 (3), 271–280. Lee, J., Mcgehee, D., Brown, T., Nakamoto, J., 2007. Driver sensitivity to brake pulse duration and magnitude. Ergonomics 50 (6), 828–836. Lee, J.-H., Spence, C., 2008. Assessing the benefits of multimodal feedback on dualtask performance under demanding conditions. Proceedings of the 22nd British

F. Meng, C. Spence / Accident Analysis and Prevention 75 (2015) 333–346 HCI Group Annual Conference on People and Computers: Culture, Creativity, Interaction 1, 185–192. Lees, M.N., Cosman, J., Lee, J.D., Vecera, S.P., Dawson, J.D., Rizzo, M., 2012. Crossmodal warnings for orienting attention in older drivers with and without attention impairments. Appl. Ergon. 43 (4), 768–776. Leo, F., Romei, V., Freeman, E., Ladavas, E., Driver, J., 2011. Looming sounds enhance orientation sensitivity for visual stimuli on the same side as such sounds. Exp. Brain Res. 213 (2–3), 193–201. Lerner, N., 1996. Preliminary Human Factors Guidelines for Crash Avoidance Warning Devices. NHTSA Project No. DTNH 22-91-07004. Silver Spring, MD. Lewis, B.A., Baldwin, C.L., 2012. Equating perceived urgency across auditory, visual, and tactile signals. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 1307–1311. Li, Y., Burns, C., 2013. Perceived urgency of tactile warnings. Proceedings of 2013 IEEE International Conference on the Systems, Man and Cybernetics (SMC) 530–535. Liu, Y.-C., Jhuang, J.-W., 2012. Effects of in-vehicle warning information displays with or without spatial compatibility on driving behaviors and response performance. Appl. Ergon. 43 (4), 679–686. Lloyd, M.M., Wilson, G.D., Nowak, C.J., Bittner, J., Alvah, C., 1999. Brake pulsing as haptic warning for an intersection collision avoidance countermeasure. Transp. Res. Rec. J. Transp. Res. Board 1694 (1), 34–41. López, J.A. 2012. July 18. Kia named Quoris his K9 flagship sedan for export markets. Retrieved March 25, 2013. http://thekoreancarblog.com/2012/07/kia-namedquoris-k9-flagship-sedan-export-markets-wvideos/ Macdonald, J.S., Lavie, N., 2011. Visual perceptual load induces inattentional deafness. Atten. Percept. Psychophys. 73 (6), 1780–1789. Mack, A., 2003. Inattentional blindness looking without seeing. Curr. Dir. Psychol. Sci. 12 (5), 180–184. Mack, A., Rock, I., 1998. Inattentional Blindness. MIT Press, Cambridge, MA. McGehee, D.V., Raby, M., 2002. Snowplow lane awareness system. Final report prepared for the 3M company and the Minnesota Department of Transportation. McGlone, F.P., Lloyd, D.M., Tipper, S., 1999. Manipulation of attention within the somatosensory systems. In: Harris, D. (Ed.), Engineering Psychology and Cognitive Ergonomics: Job Design, Product Design and Human-Computer Interaction, vol. 4. Ashgate Publishing, Hampshire, pp. 309–315. McGlone, F.P., Spence, C., 2010. Editorial: the cutaneous senses: touch, temperature, pain/itch, and pleasure. Neurosci. Biobehav. Rev. 34 (2), 145–147. McKeown, D., Isherwood, S., 2007. Mapping candidate within-vehicle auditory displays to their referents. Hum. Factors 49 (3), 417–428. Meng, F., Gray, R., Ho, C., Mujthaba, A., Spence, C., 2014a. Dynamic vibrotactile signals for forward collision warning systems. Hum. Factors (in press). Meng, F., Ho, C., Gray, R., Spence, C., 2014b. Dynamic vibrotactile warning signals for rear-end collision avoidance: toward the torso vs. toward the head. Ergonomics (in press). Millot, J.-L., Brand, G., Morand, N., 2002. Effects of ambient odors on reaction time in humans. Neurosci. Lett. 322 (2), 79–82. Mohebbi, R., Gray, R., Tan, H.Z., 2009. Driver reaction time to tactile and auditory rear-end collision warnings while talking on a cell phone. Hum. Factors 51 (1), 102–110. Montagu, A., 1971. Touching: The Human Significance of the Skin. Columbia University Press, Montagu, Ashley. Mulder, M., Mulder, M., Van Paassen, M., Abbink, D., 2008. Haptic gas pedal feedback. Ergonomics 51 (11), 1710–1720. Murata, A., Kemori, S., Moriwaka, M., Hayami, T., 2013. Proposal of automotive 8directional warning system that makes use of tactile apparent movement. In: Duffy, V.G. (Ed.), Digital Human Modeling and Applications in Health, Safety, Ergonomics, and Risk Management. Springer, Berlin, pp. 98–107. Nafe, J.P., Wagoner, K.S., 1941. The nature of pressure adaptation. J. Gen. Psychol. 25 (2), 323–351. Navarro, J., Mars, F., Forzy, J.-F., El-Jaafari, M., Hoc, J.-M., 2010. Objective and subjective evaluation of motor priming and warning systems applied to lateral control assistance. Accid. Anal. Prev. 42 (3), 904–912. Navarro, J., Mars, F., Hoc, J.-M., 2007. Lateral control assistance for car drivers: a comparison of motor priming and warning systems. Hum. Factors 49 (5), 950–960. Navarro, J., Mars, F., Young, M.S., 2011. Lateral control assistance in car driving: classification, review and future prospects. IET Intel. Transport Syst. 5 (3), 207–220. Ngo, M.K., Spence, C., 2010. Auditory, tactile, and multisensory cues facilitate search for dynamic visual stimuli. Atten. Percept. Psychophys. 72 (6), 1654–1665. Parasuraman, R., Hancock, P., Olofinboba, O., 1997. Alarm effectiveness in drivercentred collision-warning systems. Ergonomics 40 (3), 390–399. Politis, I., Brewster, S., Pollick, F., 2013. Evaluating multimodal driver displays of varying urgency. Proceedings of the 5th International Conference on Automotive User Interfaces and Interactive Vehicular Applications 92–99. Posner, M.I., Petersen, S.E., 1990. The attention system of the human brain. Ann. Rev. Neurosci. 13 (1), 25–42. Pratt, S.M., Lewis, B.A., Peñaranda, B., Roberts, D.M., Gonzalez, C., Baldwin, C.L., 2012. Perceived urgency scaling in tactile alerts. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 1303–1306. Previc, F.H., 1998. The neuropsychology of 3-D space. Psychol. Bull. 124 (2), 123–164. Prewett, M.S., Elliott, L.R., Walvoord, A.G., Coovert, M.D., 2012. A meta-analysis of vibrotactile and visual information displays for improving task performance. IEEE Trans. Syst. Man Cybern. Part C Appl. Rev. 42 (1), 123–132.

345

Prinzmetal, W., Mccool, C., Park, S., 2005. Attention: reaction time and accuracy reveal different mechanisms. J. Exp. Psychol. Gen. 134 (1), 73. Proctor, R.W., Reeve, T.G., 1989. Stimulus-Response Compatibility: An Integrated Perspective. North-Holland, Amsterdam. Proctor, R.W., Tan, H.Z., Vu, K.-P.L., Gray, R., Spence, C., 2005. Implications of compatibility and cuing effects for multimodal interfaces. Proceedings of International Conference on Human-Computer Interaction 11, 1–10. Qian, H., Kuber, R., Sears, A., 2009. Towards identifying distinguishable tactons for use with mobile devices. Proceedings of the 11th International ACM SIGACCESS Conference on Computers and Accessibility 257–258. Ramsey, K., Simmons, F., 1993. High-powered automobile stereos. Otolaryngol. Head Neck Surg. 109 (1), 108–110. Grayhem, R., Esgro, W., Sears, T., Raudenbush, B., 2005. Effects of odor administration on driving performance, safety, alertness, and fatigue. Poster Presented at the 27th Annual Meeting of the Association for Chemoreception Sciences, Sarasota, FL. Rosli, R.M., Tan, H.Z., Proctor, R.W., Gray, R., 2011. Attentional gradient for crossmodal proximal–distal tactile cueing of visual spatial attention. ACM Trans. Appl. Percept. 8 (4), 23:1–23:12. Ryu, J., Chun, J., Park, G., Choi, S., Han, S.H., 2010. Vibrotactile feedback for information delivery in the vehicle. IEEE Trans. Haptic 3 (2), 138–149. Sayer, T.B., Sayer, J.R., Devonshire, J.M., 2005. Assessment of a driver interface for lateral drift and curve speed warning systems: mixed results for auditory and haptic warnings. Proceedings of Driving Assessment 218–224. Schuler, A., Raudenbush, B., 2005. Effects of intermittent peppermint odor administration on alertness, mood, mobility, and sleep patterns. Poster Presented at the 27th Annual Meeting of the Association for Chemoreception Sciences, Sarasota, FL. Scott, J., Gray, R., 2008. A comparison of tactile, visual, and auditory warnings for rear-end collision prevention in simulated driving. Hum. Factors 50 (2), 264–275. Senders, J.W., Kristofferson, A., Levison, W., Dietrich, C., Ward, J., 1967. The attentional demand of automobile driving. Highway Res. Rec. 195, 15–33. Shaw, B.K., Mcgowan, R.S., Turvey, M., 1991. An acoustic variable specifying time-tocontact. Ecol. Psychol. 3 (3), 253–261. Shinar, D., Schechtman, E., 2002. Headway feedback improves intervehicular distance: a field study. Hum. Factors 44 (3), 474–481. Shinar, D., Schieber, F., 1991. Visual requirements for safety and mobility of older drivers. Hum. Factors 33 (5), 507–519. Sivak, M., 1996. The information that drivers use: is it indeed 90% visual? Perception 25 (9), 1081–1089. Crossmodal Space and Crossmodal Attention. In: Spence, C., Driver, J. (Eds.), Oxford University Press. Spence, C., Gallace, A., 2007. Recent developments in the study of tactile attention. Can. J. Exp. Psychol. 3, 196–207 61. Spence, C., Ho, C., 2008a. Tactile and multisensory spatial warning signals for drivers. IEEE Trans. Haptic 1 (2), 121–129. Spence, C., Ho, C., 2008b. Crossmodal information processing in driving. In: Castro, C. (Ed.), Human Factors of Visual Performance in Driving. CRC Press, Boca Raton, FL, pp. 187–200. Spence, C., Ho, C., 2008c. Multisensory warning signals for event perception and safe driving. Theor. Issues Ergon. Sci. 9 (6), 523–554. Spence, C., Nicholls, M.E., Gillespie, N., Driver, J., 1998. Cross-modal links in exogenous covert spatial orienting between touch, audition, and vision. Percept. Psychophys. 60 (4), 544–557. Spence, C., Parise, C., Chen, Y.-C., 2011. The Colavita visual dominance effect. In: Murray, M.M., Wallace, M. (Eds.), Frontiers in the Neural Bases of Multisensory Processes. CRC Press, Boca Raton, FL, pp. 523–550. Spence, C., Pavani, F., Driver, J., 2000. Crossmodal links between vision and touch in covert endogenous spatial attention. J. Exp. Psychol. Hum. Percep. Perform. 26 (4), 1298–1319. Spence, C., Squire, S.B., 2003. Multisensory integration: maintaining the perception of synchrony. Curr. Biol. 13 (13), R519–R521. Spence, C.J., Driver, J., 1994. Covert spatial orienting in audition: exogenous and endogenous mechanisms. J. Exp. Psychol. Hum. Percept. Perform. 20 (3), 555–574. Stanley, L.M., 2006. Haptic and auditory cues for lane departure warnings. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 2405–2408. Straughn, S.M., Gray, R., Tan, H.Z., 2009. To go or not to go: stimulus-response compatibility for tactile and auditory pedestrian collision warnings. IEEE Trans. Haptic 2 (2), 111–117. Suied, C., Susini, P., McAdams, S., 2008. Evaluating warning sound urgency with reaction times. J. Exp. Psychol. Appl. 14 (3), 201–212. Susami, K., Oshima, C., Muto, K., Ando, H., Matsuo, N., 2011. Stimulation with an intermittent fragrance relieves the sleepiness of a driver. Poster Presented at the 12th International Multisensory Research Forum, Fukuoka, Japan. Suzuki, K., Jansson, H., 2003. An analysis of driver’s steering behaviour during auditory or haptic warnings for the designing of lane departure warning system. JSAE Rev. 24 (1), 65–70. Terrence, P.I., Brill, J.C., Gilson, R.D., 2005. Body orientation and the perception of spatial auditory and tactile cues. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 1663–1667. Tijerina, L., Jackson, J.L., Pomerleau, D.A., Romano, R.A., Petersen, A.D., 1996. Driving simulator tests of lane departure collision avoidance systems. Proceedings of ITS America Sixth Annual Meeting, Houston, TX, pp. 636–648.

346


Tijerina, L., Johnston, S., Parmer, E., Pham, H., Winterbottom, M., 2000. Preliminary Studies in Haptic Displays for Rear-End Collision Avoidance System and Adaptive Cruise Control System Applications. Techical Report. US Department of Transportation, National Highway Traffic Safety Administration, Washington, DC. Van Erp, J., Self, B., 2008. Tactile displays for orientation, navigation and communication in air, sea and land environments. Technical Report. NATO Science and Technology Organization (RTO-TR-HFM-122). Van Erp, J.B., Van Veen, H.A., 2004. Vibrotactile in-vehicle navigation system. Transp. Res. Part F Traffic Psychol. Behav. 7 (4), 247–256. Vu, K.P.L., Proctor, R.W., 2004. Mixing compatible and incompatible mappings: elimination, reduction, and enhancement of spatial compatibility effects. Q. J. Exp. Psychol. Sect. A 57 (3), 539–556.

Walton, D., Thomas, J.A., 2005. Naturalistic observations of driver hand positions. Transp. Res. Part F Traffic Psychol. Behav. 8 (3), 229–238. White, T.L., 2010. Suitable body locations and vibrotactile cueing types for dismounted soldiers. Army Research Laboratory (ARL-TR-5186). White, T.L., 2011. The Perceived Urgency of Tactile Patterns. Army Research Laboratory (ARL-TR-5557). Yonas, A., Bechtold, A.G., Frankel, D., Gordon, F.R., Mcroberts, G., Norcia, A., Sternfels, S., 1977. Development of sensitivity to information for impending collision. Percept. Psychophys. 21 (2), 97–104. Ziegler, W., 1995. Computer vision on the road: a lane departure and drowsy driver warning system. Society of Automotive Engineers, Technical paper 952256.

Dynamic vibrotactile signals for forward collision avoidance warning systems.

Warning signals from Oregon.

Maternal early warning systems.

A Tactile Sensor for Ultrasound Imaging Systems.

Computational intelligence techniques for tactile sensing systems.

Early warning signals of ecological transitions: methods for spatial patterns.

Early warning signals of regime shifts in coupled human-environment systems.

Prototype early warning systems for vector-borne diseases in Europe.

Evolution of tsunami warning systems and products.

European Neolithic societies showed early warning signals of population collapse.

Early warning signals detect critical impacts of experimental warming.

Simulating tactile signals from the whole hand with millisecond precision.

Warning signals are under positive frequency-dependent selection in nature.

Order restricted inference for oscillatory systems for detecting rhythmic signals.

Using thin-film piezoelectret to detect tactile and slip signals for restoring sensation of prosthetic hands.

Merkel disc is a serotonergic synapse in the epidermis for transmitting tactile signals in mammals.

Dynamic vibrotactile warning signals for frontal collision avoidance: towards the torso versus towards the head.

Detecting early-warning signals for influenza A pandemic based on protein dynamical network biomarkers.

Neural systems for choice and valuation with counterfactual learning signals.

Hybrid soft computing systems for electromyographic signals analysis: a review.

Geological hazards: from early warning systems to public health toolkits.

Integrated biological-behavioural surveillance in pandemic-threat warning systems.

Lights and siren: a review of emergency vehicle warning systems.

Software to Facilitate Remote Sensing Data Access for Disease Early Warning Systems.