Mug handle affordance and automatic response inhibition: behavioural and electrophysiological evidence.

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Mug handle affordance and automatic response inhibition: Behavioural and electrophysiological evidence a

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L. Vainio , H. Ala-Salomäki , T. Huovilainen , H. Nikkinen , M. Salo , J. a

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Väliaho & P. Paavilainen a

Division of Cognitive Psychology and Neuropsychology, Institute of Behavioural Sciences, University of Helsinki, Siltavuorenpenger, Finland b

Cognitive Brain Research Unit, Institute of Behavioural Sciences, University of Helsinki, Siltavuorenpenger, Finland Accepted author version posted online: 22 Nov 2013.Published online: 13 Jan 2014.

To cite this article: L. Vainio, H. Ala-Salomäki, T. Huovilainen, H. Nikkinen, M. Salo, J. Väliaho & P. Paavilainen , The Quarterly Journal of Experimental Psychology (2014): Mug handle affordance and automatic response inhibition: Behavioural and electrophysiological evidence, The Quarterly Journal of Experimental Psychology, DOI: 10.1080/17470218.2013.868007 To link to this article: http://dx.doi.org/10.1080/17470218.2013.868007

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THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2014 http://dx.doi.org/10.1080/17470218.2013.868007

Mug handle affordance and automatic response inhibition: Behavioural and electrophysiological evidence L. Vainio1, H. Ala-Salomäki1, T. Huovilainen1, H. Nikkinen1, M. Salo1, J. Väliaho1, and P. Paavilainen1,2 1


Division of Cognitive Psychology and Neuropsychology, Institute of Behavioural Sciences, University of Helsinki, Siltavuorenpenger, Finland 2 Cognitive Brain Research Unit, Institute of Behavioural Sciences, University of Helsinki, Siltavuorenpenger, Finland

Behavioural evidence has shown that the perception of an object’s handle automatically activates the corresponding action representation. The activation appears to be inhibited if the object is a task-irrelevant prime mug that is presented very briefly prior to responding to the target arrow. The present study uses an electrophysiological indicator of automatic response priming, the lateralized readiness potential (LRP), to investigate the mechanisms of this inhibition effect. We presumed that this effect would reflect motor self-inhibition processes. The self-inhibition explanation of the effect would assume that the effect reflects activation-followed-by-inhibition observed rapidly after the offset of the prime at the primary motor cortex. However, the results showed that the effect is not associated with modulation of the early LRP deflections. In contrast, the inhibition manifested itself in the later LRP deflections that we assume to be linked to interference in the processing of response-related aspects of the target. We propose that the LRP pattern is similar to what would be predicted from the negative priming explanation of the effect. The study sheds light on understanding inhibition mechanisms associated with automatically activated affordance representations. Keywords: Negative priming; Response activation; Motor inhibition; Handle affordance; Lateralized readiness potential.

It has been demonstrated numerous times that certain action-relevant properties of viewed objects automatically activate the corresponding motor representations (for example, Chao & Martin, 2000; Tucker & Ellis, 2001). However, it is still largely unknown what kind of mechanisms prevent people impulsively acting upon these activated motor representations and how these taskirrelevant motor activations can be blocked from interfering with the ongoing task-relevant motor processes. The present study aims at exploring

motor inhibition processes previously observed with handle information of task-irrelevant objects by Vainio, Hammarén, Hausen, Rekolainen, and Riskilä (2011). Their study showed that the orientation of viewed mugs produces a negative S–R (stimulus–response) compatibility effect in relation to the hand of response when the mugs are task irrelevant and presented very briefly—that is, the reaction times were longer when the orientation of a viewed mug was compatible with the hand of response. It is important to notice that typically

Correspondence should be addressed to L. Vainio, Division of Cognitive Psychology and Neuropsychology, Institute of Behavioural Sciences, University of Helsinki, Siltavuorenpenger 5 A, PL 9, 00014, Finland. E-mail: lari.vainio@helsinki.fi We would like to thank Kalevi Reinikainen and Miika Leminen for their technical help in carrying out the experiment. © 2014 The Experimental Psychology Society

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this kind of stimuli has been associated with positive S–R compatibility effects (e.g., Tucker & Ellis, 1998; Vainio, Ellis, & Tucker, 2007). In theory, this kind of behavioural output can be predicted at least from two well-known models of response inhibition: the motor self-inhibition (Eimer & Schlaghecken, 1998) and the negative priming (Tipper, 1985). Similar experimental conditions that produced the negative compatibility effect with the mugs have been observed to produce self-inhibition effects as well as negative priming effects—both of these phenomena have been observed with briefly displayed task-irrelevant primes (Eimer & Schlaghecken, 2003; Milliken, Joordens, Merikle, & Seiffert, 1998). Hence, our main prediction was that the negative compatibility effect associated with the orientation of a mug is likely to be based on either one of these two inhibition mechanisms. Importantly, these inhibition models predict differential electrophysiological patterns—the self-inhibition model predicts activation-followed-by-inhibition in the primary motor cortex, which rises rapidly after onset of the prime. In contrast, the negative priming explanation for the inhibition effect observed by Vainio et al. (2011) would predict that the negative compatibility effect would be associated with the modulations in response-related activation after the onset of the target object that is presented after the offset of the prime. Hence, the present study uses an electrophysiological indicator of automatic response priming, the lateralized readiness potential (LRP), to investigate the mechanisms of this inhibition effect.

Handle affordance The notion of affordance, originally introduced by Gibson (1979), assumes that visual properties of objects guide behaviour directly. This theory has influenced several models concerning the interactions between actions and visual objects. The central thesis of these models is that merely viewing an object activates associated action representations (routines for interaction with the object; Arbib, 1981; Ellis, 2009; Fagg & Arbib, 1998; Hommel, Müsseler, Aschersleben, &

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Prinz, 2001). This thesis has been supported by behavioural (e.g., Criaghero, Fadiga, Umilta, & Rizzolatti, 1996; Tucker & Ellis, 2001), neuropsychological (e.g., Riddoch, Edwards, Humphreys, West, & Heafielkd, 1998), electrophysiological (e. g., Goslin, Dixon, Fischer, Cangelosi, & Ellis, 2012), single-cell (e.g., Murata, Fadiga, Fogassi, Gallese, Raos, & Rizzolatti, 1997), and brainimaging (e.g., Chao & Martin, 2000) studies. Reaching-to-grasp movement is one of the most often used action routines that are largely guided by visual information. In addition to spatial location and size information of an object, orientation of an object has a great relevance on planning these movements. In turn, the orientation of many common graspable objects such as kitchen utensils or tools is determined by the direction of the handle. Considering the above-mentioned thesis concerning the involvement of motor schemas in an object representation, it could be assumed that observing a handle would automatically activate the reaching-to-grasp representation of the hand that is compatible with this handle affordance. There is evidence supporting this hypothesis. A number of studies using a S–R compatibility as a paradigm have shown that the handle affordance of a viewed object automatically influences responseselection processes (e.g., McBride, Sumner, & Husain, 2012; Phillips & Ward, 2002; Tipper, Paul, & Hayes, 2006). Originally, this effect was reported by Tucker and Ellis (1998) whose participants were asked to decide whether a common graspable object, presented in a computer monitor, was upright or inverted and to respond as fast as possible with their left or right hand according to these categories. Responses were made faster and more accurately with the hand that was compatible with the orientation of the object. This handle-affordance effect has been assumed to reflect the automatic activation of an action representation associated with the hand that would be optimal for grasping the object (Ellis, 2009). Similar behavioural effect has been observed even when the entire object, not only its orientation, is irrelevant to the task. For example, Vainio, Ellis, and Tucker (2007) found the effect when their participants were presented with an

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HANDLE AFFORDANCE AND RESPONSE INHIBITION

image of a mug whose handle was pointing toward the left or right hand. The participants had to select the hand of response according to the colour of a target dot that was superimposed over the mug 300 ms after the onset of the mug. Hence, the handle-affordance effect occurs in relation to the prime object even though the responses are performed according to colour of the target that is separate from the prime, suggesting that the effect operates in a relatively involuntary and automatic fashion. The action representations related to the affordances of perceived objects are often associated with processes of parieto-premotor circuits. Single-cell studies in monkeys have shown that certain parietal (e.g., Sakata, Taira, Murata, & Mine, 1995) and premotor (e.g., Murata et al., 1997) areas are representing action possibilities of perceived objects. In humans, brain-imaging studies (e.g., Martin & Chao, 2001; Martin, Wiggs, Ungerleider, & Haxby, 1996) have similarly associated object affordances with processes of specific parietal and premotor areas, in particular in the posterior parietal and ventral premotor areas. Importantly, representing objects that contain handle affordance information has been observed to employ this parieto-premotor circuit (Grezes & Decety, 2002). Hence, the evidence supports the view that perceiving handle affordances prepares an individual to perform the action with the suitable hand. According to the model of Fagg and Arbib (1998), parietal processes extract the action opportunities provided by affordances of viewed objects, and premotor processes are more responsible for selecting motor programmes that correspond to the perceived affordances. Furthermore, recent electrophysiological evidence suggests that the motor processing related to the handle information of a perceived object can be also observed in an increased activation of the primary motor area contralateral to the handle orientation only 100–200 ms after the object onset (Goslin et al., 2012). This suggests that in addition to the parietal and premotor processes, the primary motor processes might be also involved in automatic motor preparation associated with the affordances of perceived objects.

Object affordances and motor inhibition People are continuously exposed to potential affordances in their everyday environment, provided by encountered commonplace objects, such as door handles, mugs, or tools. However, normally the automatic activation of action representations triggered by these affordances does not lead to involuntary execution of the corresponding action. Neuropsychological research has shown that patients whose motor inhibition mechanisms have been damaged have an increased tendency to execute action programmes that are triggered by affordances. Frontal lobe lesions have been observed to be linked to automatically activated reach-to-grasp actions triggered by viewed objects even though these individuals are told not to act on the object (e.g., Lhermitte, 1983). More specifically, Riddoch et al. (1998) found that when a patient with an anarchic hand syndrome was asked to reach for a target mug using the hand that was on the same side of space as the mug, the patient frequently reached incorrectly with the hand that was compatible with the handle of the mug. This suggests that mechanisms that enable representation of motor schemas of perceived objects necessarily involve inhibition mechanisms that assure that this automatically triggered motor activation does not interfere with the ongoing behaviour by, for example, triggering unwanted actions. Although the inhibition associated with handle affordances is a fundamental mechanism, related to motor preparation processes, only three studies, to our knowledge, have investigated this issue. First, Pavese and Buxbaum (2002) showed that when the participant is presented simultaneously with two mugs with handles and then she or he is instructed to reach towards the target mug cued by colour, the distractor mug causes the most interference on the reaching performance when its handle is pointing toward the responding hand. This finding fits nicely with the model according to which the action planning system is capable of simultaneously activating action plans for multiple objects (Cisek & Kalaska, 2005), and the action plans triggered by distractors are automatically


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inhibited (e.g., Ellis, Tucker, Symes, & Vainio, 2007; Houghton & Tipper, 1994). More recently Vainio (2009) found that when participants are required to reach for an object whose handle is pointing toward the left or right hand, and this object is removed at the onset of the reach response, the reach is performed slower with the hand that is compatible with the orientation of the object. The result was interpreted to show that if a sensory support that updates the initial response activation is removed during the response execution, the initial motor programme is immediately inhibited. The study most relevant to the present study was reported by Vainio et al. (2011). They observed that if the handle information is viewed very briefly before the responding hand is selected, the handle information is associated with a negative S–R compatibility effect (negative mug handle priming— NMHP). The participants were presented for 30, 70, 170, or 370 ms with an image of a mug (i.e., the prime) whose handle was pointing toward the left or right hand. Participants had to select the hand of response according to the pointing direction of the arrow that was presented 50 ms after the prime offset at the central location of the removed prime object. The standard positive handle affordance effect was observed only when the mug was displayed for 370 ms. Interestingly, the presentation times of 30 and 70 ms were associated with the NMHP. Vainio et al. (2011) found that the NMHP effect was replaced by a positive compatibility effect when the mug prime was replaced by an arrow or a modified version of the prime mug (abstract shape) in which the familiarity of the mug was removed without removing the spatial (left–right) properties associated with the handle. The positive compatibility effect that was observed with the arrow cues and abstract shapes produced a similar effect to that previously observed with peripherally displayed spatial cues (e.g., Posner, 1980) as well as with centrally presented direction cues such as arrows (e.g., Eimer, 1995; Pratt & Hommel, 2003). In other words, a standard spatial cueing effect was observed when affordance information specific to a mug handle was removed

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from the prime but the prime still contained the same left–right saliency biases as the mug stimulus. The fact that the negative compatibility effect was only produced by handle information of real (recognizable) mugs, and was not observed when the mug stimulus was replaced by these spatially corresponding abstract mugs, suggests that some specific inhibition mechanisms are employed for visuomotor processing of handle affordances. Furthermore, Vainio et al. (2011) argued that the NMHP might be caused by similar motor selfinhibition processes to those that have been previously associated with a backward-masked priming (BMP) paradigm. Typically, in a BMP paradigm (see Eimer & Schlaghecken, 2003, for a review), participants are presented with a left- or right-pointing prime arrow for 30 ms, which is replaced by a mask. Finally, participants are required to select the hand of response according to the pointing direction of a target arrow that is presented after the offset of the mask. When the interval between the prime and the target is longer than 60 ms, a negative compatibility effect is observed with a behavioural benefit in incompatible trials. Eimer and Schlaghecken (1998) proposed that this BMP effect reflects selfinhibitory mechanisms of the motor system. Selfinhibitory mechanisms in motor control have been suggested to ensure that turning motor activation into inhibitory state is an immediate, automatic, and unavoidable consequence of any primed unwanted response activation (e.g., Arbuthnott, 1995; Houghton & Tipper, 1996). Typically BMP studies have used arrows as primes and targets. It appears that the effect can be only observed if the action-relevant attribute of the prime, which triggers the initial response activation, is identical to that action attribute to which responses are executed (e.g., the prime and the target are both right-pointing arrows; Eimer & Schlaghecken, 1998). In addition, it has been proposed that the BMP can only be observed when the prime arrow is presented subliminally, and it is backward masked (Eimer & Schlaghecken, 2003). According to this view, the inhibition occurs because the motor activation that is triggered by the prime is treated by the




motor system as an unwanted activation since the masking stimulus effectively removes a sensory support that updates the initial response activation (Boy, Clarke, & Sumner, 2008). The BMP can be observed if the response selection takes place during this inhibitory phase. Electrophysiological data obtained by measuring the lateralized readiness potential (LRP) have provided perhaps the most convincing support for the motor self-inhibition argument of the BMP. The LRP is an event-related potential (ERP) component reflecting movement-related electrical activity at the left and right motor cortices (Eimer, 1998; Smulders & Miller, 2011). The LRP starts even before the response is executed, and its onset time can be taken as a measure of the time at which the brain begins preparing to make the response. Therefore, the LRP can provide information about the preliminary activation of a response that is never actually produced, such as activation followed by inhibition of a response hand, which is primed by the prime object but not used to respond to the target. Eimer and Schlaghecken (1998) found, using backward-masked primes, an LRP pattern that would be predicted by the motor self-inhibition account. They observed an initial activation of the prime-related response (correct response in compatible trials and incorrect response in incompatible trials) 200–270 ms after the prime onset. Approximately 100 ms later, this response activation was reversed, reflecting an inhibition of the initial response tendency: For compatible conditions, the LRPs indicated a momentary activation of the incorrect response, whereas on incompatible conditions, the correct response was at the same time already partially activated. This electrophysiological pattern of events explains well the simultaneously observed BMP—that is, a delayed activation of the correct response for compatible conditions and a fast activation of the correct response for incompatible conditions. Thus, according to the inhibition account, the BMP is observed because the response selection occurs during the inhibitory phase, giving a benefit for correct responses on incompatible conditions compared to compatible conditions.

If the NMHP is indeed based on similar neural inhibition mechanisms to those for the BMP, it importantly demonstrates that the motor self-inhibition is a general motor phenomenon that can be observed in naturalistic contexts, in the absence of rather artificial experimental conditions such as subliminal presentation or backward masking of the prime. However, there seems to be obvious differences between stimulus conditions associated with the NMHP and BMP. The NMHP was observed even though the prime was presented supraliminally without a backward mask and when the prime did not contain elements that could have been in any way relevant to the task. Nevertheless, the motor self-inhibition explanation of NMHP is in line with the evidence that the handle affordance can produce a very rapid motor activation (100 ms after the onset of the object) of the corresponding hand (Goslin et al., 2012). It could be expected that it is exactly this initial motor activation that is inhibited in the NMHP. Also the recent results of Vainio et al. (2013) support the hypothesis that the NMHP is produced by the motor self-inhibition mechanisms. They demonstrated, using exactly the same priming procedure as the one that also produced the NMHP, that motor self-inhibition processes can explain the negative compatibility effect produced by briefly presented hand images. Originally, Vainio and Mustonen (2011; see also Vainio, 2011) showed that when the participant is first presented with an image of a left or a right hand for 200–900 ms, and thereafter required to respond to the target arrow superimposed on the prime hand, responses are faster and more accurate if the responding hand is compatible with the left– right identity of the prime hand. However, this positive compatibility effect was replaced by a negative compatibility effect when the prime onset duration was reduced to 30–80 ms. Exactly the same pattern of behavioural results was observed with the mug primes by Vainio et al. (2011)—brief onset durations produced negative priming, and longer durations produced positive priming. Vainio et al. (2013) used LRP to show that this effect is produced by similar motor self-inhibition processes to those for the BMP. That is, the LRP


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data revealed a pattern of motor activation that was in line with the motor self-inhibition hypothesis. The waveforms between 280 and 330 ms after the prime onset revealed an activation of the incorrect response on compatible conditions and an activation of the correct response on incompatible conditions. An alternative likely explanation for the NMHP is that it is a version of a negative priming phenomenon (Tipper, 1985). In a typical experimental procedure of negative priming, the prime stimuli consist of two different objects from which only one has to be attended to. Shortly after the prime offset, the participant is presented with the probe object to which the response is executed. If the unattended prime shares some semantic features with the probe (e.g., they are both utensils), responses are impaired in terms of reaction times (RTs) and accuracy. Negative priming effects are observed for delays of 20 ms to 8000 ms between the prime and the probe (Dempster, 1995). Typically, negative priming effects are explained either by the episodic retrieval account or inhibition account even though several authors have concluded that both of these mechanisms are likely to contribute to the effect (Kane, May, Hasher, Rahhal, & Stoltzfus, 1997; Tipper, 2001). Within the retrieval account, the negative priming is observed because the semantic representation that is activated by the unattended prime is tagged with task-related information such as “do-notrespond”. When the processing of the probe object requires that this same representation is retrieved, the additional task-related information (e.g., “do-not-respond”) is also retrieved as a byproduct of previously occurred processing, which in turn interferes with the response. Within the inhibition account, semantic representation that is activated by the unattended object is actively suppressed by selective attention mechanisms during the processing of the prime stimuli. If the processing of the target requires activation of the same previously inhibited representation, the responding is impaired. Moreover, Tipper and Cranston (1985) suggested that what might be inhibited in the negative priming is the response-related

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representation associated with the unattended prime rather than perceptual information. Importantly, previous negative priming studies have revealed that the effects can be produced even by a single prime in the absence of any distractor in the prime stimuli when the prime is actively ignored. Milliken et al.’s (1998) subjects were presented with a single word for 200 ms, which they were asked to ignore. This prime was followed 500 ms later by a target word that they had to name. The negative priming effect was observed when the prime matched semantically with the probe. Tipper (2001) proposed that this is exactly what would be predicted to occur according to the inhibition model of Houghton and Tipper (1994). What appears to be central in these negative priming effects is that they appear when the selective attention processes in relation to the prime are interfered by ignoring the prime, for example, so that the prime is a distractor or participants are explicitly asked to ignore it. According to this inhibition model, an inhibitory process is a normal component of selective attention, particularly essential in planning actions in relation to visual objects. The model assumes that it is unavoidable that visual information of viewed objects automatically activates higher representations such as semantic and motor-related representations associated with the object. If this activation is linked to unattended (ignored) object, the representation is automatically inhibited. According to this logic, what might happen in the NMHP is that the sensorimotor system implicitly “interprets” the prime as a to-be-ignored distractor because the prime is irrelevant to the ongoing task, and it is continuously presented only very briefly (e.g., 30 ms)—therefore the action representation that is activated by the handle affordance of the object is automatically inhibited. The NMHP might turn into a positive handle priming effect when the prime is displayed for sufficiently long duration (e.g., 370 ms), as it was observed in the original study by Vainio et al. (2011), because attentional processes cannot avoid selecting a single object that is presented at the central visual field for that long duration.




The primary focus of the current study is to investigate what kind of inhibitory processes might be responsible for the NMHP phenomenon using behavioural and LRP recordings. As reviewed above, the NMHP paradigm has similarities with both the negative priming and BMP paradigms in that they all produce similar inhibition effects. In all of these paradigms, the prime that produces the inhibitory effect receives decreased processing because it either was an unattended distractor or was displayed very briefly. The most obvious difference between the assumed processes behind the motor self-inhibition and the negative priming is that the behavioural effects suggested to be caused by the motor self-inhibition mechanisms are associated with activation-followed-by-inhibition processes operating in the primary motor cortex in relation to the prime stimuli (e.g., Eimer & Schlaghecken, 1998). In contrast, interpretations of the negative priming generally assume that the behavioural priming effect would be linked to increased neural effort associated with the processing of semantic or response-related aspects of the target when the unattended prime and the target are semantically associated. In general, increased cognitive effort can be assumed to be associated with larger amplitudes of corresponding electrophysiological measures (see, e.g., Otten & Rugg, 2005). For instance, increased P300 amplitudes have been linked to requirements for the enhanced processing of invalidly cued target stimuli in spatial priming paradigms (e.g., Eimer, 1994). In addition, larger LRP amplitudes have been previously observed when preparedness to perform the response with the specific hand cannot be exploited but the response has to be executed with the unprepared hand (Gibbons, Rammsayer, & Stahl, 2006; see also Smulders & Miller, 2011). As a consequence, it could be assumed that negative priming would be associated with increased amplitudes of electrophysiological measures linked to the processing of the target object when the unattended prime and the target are semantically associated.

EXPERIMENT 1 Experiment 1 is mostly a replication of the study reported by Vainio et al. (2011). The participants are presented with the same prime stimuli as those that were used by Vainio et al. (2011) for 25 ms. They are asked to respond to the target arrow that is displayed 50 ms after the offset of the prime. The prime is either an image of a mug whose handle is pointing to the left or right or an abstract shape that is built from the mug stimuli so that the resemblance of the mug is removed but it still has the same critical left–right spatial features as those of the mug stimuli. In contrast to the previous study, we additionally use LRP recordings to investigate what kind of inhibition mechanisms might be responsible for the NMHP effect. Moreover, in addition to the original study, we were interested in exploring whether the NMHP reflects more inhibition of compatible responses or facilitation of incompatible responses or whether both of these components are involved in this negative compatibility effect. Thus, the participants were also presented with the neutral version of the stimuli. These response-neutral stimuli were simply created by removing the spatially biasing information (e.g., handle) from the stimuli. As discussed above, Vainio et al.’s (2011) NMHP effect was eliminated when the mug prime was replaced by a modified version of the prime mug in which the resemblance of the mug was removed without removing the spatial (left– right) properties associated with the handle. These spatially biased abstract shapes produced a standard positive cueing effect (e.g., Posner, 1980). Hence, we know that when the prime is displayed for 30 ms, it produces positive priming effect if it shares abstract spatial properties with the target arrow. In contrast, if the prime presented for 30 ms provides handle affordance information, it produces negative priming effect even though its critical spatial properties are identical to the abstract shape. We propose that this small stimulus manipulation in the abstract mug stimulus, which keeps the left–right saliency biases untouched but


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removes familiarity of a mug, offers a nice possibility to explore what kind of inhibition processes might operate behind the negative compatibility effect associated with handle affordances. To sum up the hypotheses of Experiment 1, the motor self-inhibition explanation of the NMHP would assume that the NMHP is caused by an immediate processing of the handle affordance information of the prime at the motor level, leading in the LRPs to an activation-followed-byinhibition sequence rapidly after the offset of the prime. This account does not predict that there should occur any significant interference during the later processing of the stimuli (e.g., Eimer & Schlaghecken, 1998). Alternatively, it is possible that the NMHP is caused by similar processes to those for the negative priming, more reflecting the selection of the correct response according to the target, which in turn should modify the later LRP waveforms.

Method Participants Fifteen participants volunteered in a single session that lasted approximately 60 min. However, the data of three participants had to be rejected due to too noisy electroencephalogram (EEG) recordings. The remaining subjects (8 female) were between 19 and 33 years of age (M = 23.5 years). Nine participants were naïve as to the purpose of the experiment. One participant was left-handed. All had normal or corrected-to-normal vision. All persons gave their informed consent prior to their inclusion in the study. The study was approved by

the Ethical Committee of the Institute of Behavioural Sciences at the University of Helsinki. Apparatus and stimuli Each participant sat in a dimly lit room with his or her head 70 cm in front of a 19′′ CRT monitor (screen refresh rate: 100 Hz; screen resolution: 1152 × 864 pixels) and with the index finger of each hand resting on two response buttons 30 cm apart and 40 cm in front of the screen. The prime stimuli consisted of images of mug whose handle was pointing toward the left or right hand (subtended a visual angle of 6.3° vertically and 6.5° horizontally). In the orientation-neutral stimulus condition, the handle was removed (6.3° × 5.2°). The mug stimulus was created from a greyscale photograph of a mug. In order to remove any visual biases that might have been associated with differential shadings of the left and right parts of the mug’s main body, the body of the mug was cut in half, and the handleless side of the body was copied and pasted as a mirror image and attached to the original handleless side of the body. Then the handle was attached to this new main body of a mug. The left-orientation stimuli were created by flipping the right-orientation images horizontally, and the neutral stimuli were created by removing the handle from the mug. The abstract shape prime was constructed from the prime mug by removing the top and bottom elements of the mug (see Figure 1). In addition, the recognizability of the mug was decreased by removing the elements that attach the main body of the mug to the handle and partially removing the shading of the handle from the lower part of

Figure 1. The prime stimuli used in Experiment 1. The first two images show the left-oriented real and abstract primes, and the last two images show the response-neutral real and abstract primes.

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the handle. These manipulations can be seen in Figure 1. A left/right pointing arrow (0.6° × 1°) was used as a target stimulus. The black arrow was superimposed over a grey disc (1° × 1.3°). All stimuli were displayed on a white background at the centre of the screen (e.g., the centre of the main body of the mug/shape was in the centre of the screen). Design and procedure Each stimulus was displayed 50 times in each of the 12 conditions. In total, the experiment consisted of 600 trials [50 × 3 (orientation) × 2 (hand of response) × 2 (prime type)]. Each trial started with the presentation of a fixation point that was a grey disc—the same disc as that used as the background of the target arrow. The disc was displayed for 500 ms. Then the disc was replaced by an empty white screen, displayed for 1000 ms. Next the prime stimulus appeared on the screen for 25 ms. The prime stimuli were presented in random order with equal probability. Then the prime was displaced by an empty white screen for 50 ms. Finally, the target arrow appeared on the screen for 70 ms. A blank white screen was displayed until the participant responded or the trial timed out 1500 ms after arrow offset. The mug primes and abstract shape primes were presented in different experimental blocks, and the block order was counterbalanced between the participants. There

was a short break between the blocks. In addition, the participant was allowed to have a break twice within each block. The participants were asked to respond with their right hand if the arrow was pointing to the right and with their left hand if it was pointing to the left. The participants were instructed to respond as quickly as possible whilst maintaining accuracy. They were told that an image of a mug or an abstract shape would appear briefly on the screen an instant before the onset of the arrow. They were also told that they were not required to pay any attention to this prime stimulus. Instead, their performance would be better if they tried not to pay attention to the prime. The experiment began with approximately 20 practice trials. Figure 2 provides a figurative representation of the trial structure of the experiment. Electrophysiological recordings An EEG was recorded with silver/silver chloride (Ag/AgCl) electrodes from Fpz, Fz, Cz, Pz, C3′ , and C4′ (1 cm anterior to C3 and C4, respectively). Only the data from C3′ and C4′ that were used to compute the LRPs are reported in this article. A vertical and a horizontal electro-oculogram (EOG) were recorded at electrodes placed above the left eye and at the canthus of the left eye, respectively. Left mastoid served as a reference to all electrodes. The amplifier bandpass was 0.1–40

Figure 2. A figurative representation of the trial structure of the study. See text for details. THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2014

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Hz. The EEG and EOG data were sampled with a digization rate of 200 Hz and stored on disc for offline analysis. ERPs were averaged separately to all 12 different stimulus conditions. The analysis period started 100 ms before the onset of the prime and continued 600 ms after its appearance. The 100-ms period preceding the onset of the prime served as a baseline for amplitude measurements. Trials including eye blinks or other EOG or EEG changes exceeding +100 µV were excluded from the averaging, as well as trials with false or missing responses. The LRPs were calculated separately for the compatible, incompatible, and neutral trials using the double subtraction method introduced by De Jong, Wierda, Mulder, and Mulder (1988; see also Eimer, 1998; Smulders & Miller, 2011): the C3′ –C4′ difference potentials for trials with righthand responses were subtracted from the C3′ –C4′ difference potentials for trials with left-hand responses. As a result of this double subtraction, positive deflections in the LRP waveforms indicate the activation of a correct response, whereas negative deflections indicate incorrect-response activation. In order to statistically analyse the LRP amplitude differences between the three trial types, mean LRP amplitudes during certain time windows were calculated, as recommended by Smulders and Miller (2011). The time windows were centred over the most notable differences seen in the grand-average LRPs.

Results Behavioural performance Errors and RTs more than two standard deviations from each participant’s condition means were excluded from the analysis. Of the trials, 4.1% were removed as errors, and 3.9% were removed as outliers. The combined removal of errors and outliers left 92% of the raw data as correct responses. The condition means of these remaining data were computed for each participant and subjected to a repeated measures analysis of variance (ANOVA) with the within-subjects variables of prime type (mug or abstract) and compatibility between the stimulus identity and the hand of response (compatible, neutral, or incompatible). The RTs and error rates for the different prime types and conditions are presented in Figure 3. The ANOVA revealed a main effect of prime type, F(1, 11) = 7.84, MSE = 2374.48, p = .017, η2p = .416, and compatibility, F(2, 22) = 8.77, MSE = 707.18, p = .002, η2p = .444. Importantly, the analysis also revealed an interaction between prime type and compatibility, F(2, 22) = 50.87, MSE = 3895.87, p , .001, η2p = .822. This suggests that the compatibility effects were different between the two types of primes. Below we provide results for analysis that were carried out separately for mug primes and abstract primes. Mug primes: A main effect of compatibility, F(2, 22) = 18.65, MSE = 952.92, p , .001, η2p = .629,

Figure 3. The mean reaction times (RTs; left panel) and error rates (right panel) in Experiment 1 as a function of compatibility (prime orientation–hand of response) and the prime type (mug prime, abstract prime). Bars refer to the standard error of the mean.

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revealed faster RTs in incompatible (M = 380 ms) than in compatible (M = 397 ms) or neutral (M = 383 ms) conditions. A separate analysis of the simple main effects for each condition pair revealed that the effect was significant between compatible and incompatible conditions (p , .001) as well as between compatible and neutral conditions (p , .001). However, the effect was not significant between neutral and incompatible conditions (p = .460). Similar analysis of percentage error rates revealed a pattern of results parallel to the RT analysis. The error rates revealed a significant main effect of compatibility, F(2, 22) = 11.57, MSE = 75.36, p , .001, η2p = .513. The participants made more errors in compatible (M = 7.0%) than in incompatible (M = 2.3%) or neutral (M = 3.1%) conditions. The effect was significant between compatible and incompatible conditions (p = .002) as well as between compatible and neutral conditions (p = .008). Similarly to that observed in the RTs, the effect was not significant between neutral and incompatible conditions (p = .267). Abstract primes: A main effect of compatibility, F(2, 22) = 34.39, MSE = 3650.13, p , .001, η2p = .758, revealed faster RTs in compatible (M = 382 ms) than in incompatible (M = 417 ms) or neutral (M = 395 ms) conditions. The effect was significant between compatible and incompatible conditions (p , .001), compatible and neutral conditions (p , .001), and neutral and incompatible conditions (p , .001). Again, an analysis of percentage error rates revealed a pattern of results parallel to the RT analysis. The error rates revealed a significant main effect of compatibility, F(2, 22) = 23.08, MSE = 169.75, p , .001, η2p = .677. The participants made more errors in incompatible (M = 9.2%) than in compatible (M = 2.4%) or neutral (M = 2.9%) conditions. The effect was significant between compatible and incompatible conditions (p , .001) as well as between incompatible and neutral conditions (p , .001). However, the effect was not significant between neutral and compatible conditions (p = .40).

LRP data Figure 4 shows the grand-average LRPs in compatible, incompatible, and neutral conditions, separately for both prime types. The first marked difference between compatible, neutral, and incompatible conditions is observed with mug primes about 120–270 ms and with abstract primes 150– 300 ms after the prime onset. These early LRP deflections indicate activation of the incorrect response in incompatible conditions and activation of the correct response in compatible conditions. The neutral-condition LRPs do not show any prominent deviations from the baseline during these time windows. Following these early deflections, a late largeamplitude positivity indicating the activation of the correct response develops in all conditions, peaking at about 400 ms after the prime onset. Importantly, a marked difference between the conditions is seen in the amplitude of this positive deflection at about 350–500 ms after the prime onset (275–425 ms after target onset). In the mug prime condition, the amplitude is largest in the compatible condition, whereas in the abstract prime condition, it is largest in the incompatible condition. Early LRP: To assess statistically the significance of the early LRP effects, the mean amplitudes of the compatible-, neutral-, and incompatiblecondition LRPs for the two prime types were calculated (Figure 5). The time windows for the mean amplitudes were for the mug prime condition 120–270 ms and for the abstract prime condition 150–300 ms after the prime onset. These latency windows were chosen as they captured in both conditions the essential differences between the LRPs. The mean amplitudes were subjected to a repeated measures ANOVA, the within-participants factors being prime type (mug or abstract) and compatibility between the stimulus identity and the hand of response (compatible, neutral, or incompatible). The ANOVA revealed a main effect of compatibility, F(2, 22) = 14.48, MSE = 28.93, p , .001, η2p = .568. The LRP amplitudes were negative in incompatible and positive in compatible conditions, the neutral-condition amplitudes falling between them (Figure 5, left panel). The


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Figure 4. Grand-average lateralized readiness potential (LRP) waveforms for the mug primes (left panel) and abstract primes (right panel) data in Experiment 1. The LRPs are presented in the interval between prime onset (occurring at the crossing of x and y axis) and 600 ms after prime onset, separately for the compatible, incompatible, and neutral trials. Positive (downward-going) deflections in the LRP waveforms indicate correct-response activation, and negative (upward-going) deflections incorrect-response activation. The letters A, B, and C in the figure provide information about timings of onsets and offsets of the prime and the target. A: the time when the prime was removed and replaced by a blank screen; B: the time when the target appeared; C: the time when the target was removed and replaced by a blank screen.

interaction between prime type and compatibility was not significant, F(2, 22) = 0.10, MSE = 0.19, p = .902, η2p = .009, suggesting that the compatibility effects on LRP amplitudes were similar for both prime types. The analyses that were carried out separately for mug primes and abstract primes showed that the

compatibility effect was significant for both prime types [mug: F(2, 22) = 14.59, MSE = 16.93, p , .001, η2p = .570; abstract: F(2, 22) = 4.44, MSE = 12.19, p = .024, η2p = .288]. For the mug primes, the effect was significant between compatible and incompatible conditions (p , .001) as well as between incompatible and neutral conditions

Figure 5. The mean amplitudes of the early (left panel) and late (right panel) part of the lateralized readiness potential (LRP) in compatible, neutral, and incompatible trials for the two prime types in Experiment 1. The latency intervals used for calculating the mean amplitudes were for the early part 120–270 ms (mug primes)/150–300 ms (abstract primes) and for the late part 350–500 ms. Note that negativity (incorrectresponse activation) is plotted upward. Bars refer to the standard error of the mean.

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(p , .001). The effect was only marginally significant between compatible and neutral conditions (p = .061). For the abstract primes, the effect was significant between compatible and incompatible conditions (p = .03) as well as between incompatible and neutral conditions (p = .039). However, the effect was not significant between compatible and neutral conditions (p = .286). Late LRP: To assess statistically the significance of the late LRP effects, the mean amplitudes of the compatible-, neutral-, and incompatible-condition LRPs during 350–500 ms after prime onset for the two prime types were calculated (Figure 5, right panel). The mean amplitudes were subjected to a repeated measures ANOVA, the within-participants factors being prime type (mugs or abstract shapes) and compatibility between the stimulus identity and the hand of response (compatible, neutral, or incompatible). The ANOVA revealed a significant interaction between prime type and compatibility, F(2, 22) = 15.55, MSE = 25.68, p , .001, η2p = .586. This suggests that the compatibility effects on LRP amplitudes were different for the two prime types. The analyses carried out separately for mug primes and abstract primes showed that the compatibility effect was significant for both prime types [mug: F(2, 22) = 7.27, MSE = 8.95, p = .004, η2p = .398; abstract: F(2, 22) = 13.28, MSE = 20.13, p , .001, η2p = .547]. For the mug primes, the effect was significant between compatible and incompatible conditions (p = .008) as well as between compatible and neutral conditions (p = .007). However, the effect was not significant between neutral and incompatible conditions (p = .737). For the abstract primes, the effect was significant between compatible and incompatible conditions (p , .001), between compatible and neutral conditions (p = .032), and between neutral and incompatible conditions (p = .032).

Discussion The results of Experiment 1 replicated the negative and positive priming effects previously observed by Vainio et al. (2011) with the same prime stimuli. The orientation of the abstract mug stimulus

produced a positive priming effect. In contrast, the orientation of the real mug produced a negative priming effect even though it had lateral visual biases that were the same as those with the abstract mug, and there were not any differences in temporal properties of the two types of prime stimuli. The only difference between the two stimuli that can be assumed to cause this shift from positive priming to negative in the case of the real mug is the familiarity of the object, and as a consequence the recognizable handle affordance of the object. In addition, the results of the LRP data suggest that this negative priming effect, in the case of real mug, manifests itself in the later phase of the LRP pattern rather than the early phase of the LRP pattern. However, details of this finding are discussed in the General Discussion.

EXPERIMENT 2 It is important to underline that Experiment 1 used the same prime stimuli as those in the study reported by Vainio et al. (2011). Hence, in order to demonstrate the robustness of these effects, first it is important to show that the negative priming effect can be produced by several different kinds of oriented mugs. Secondly, as far as we know, the Simon effect has not been explored with prime stimuli that are task irrelevant and presented only for 25 ms. In fact, in theory it is possible that a briefly presented laterally biased stimulus always produces a negative Simon effect. As a consequence, in contrast to what was suggested by Vainio et al. (2011), it is the priming associated with the real mug rather than with the abstract mug that can be explained by the same visuomotor processes as those for the Simon effect—that is, the visuomotor processes that are driven by low-level (abstract) visual features of the stimulus. In other words, it is possible that there is something peculiar in the abstract mug stimulus, and, in fact, the positive priming observed with the abstract mug is the only effect in Experiment 1 that cannot be explained by standard Simon-effect types of mechanisms. Thus, it is important to show that similar positive priming as observed with the abstract


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Figure 6. The prime stimuli used in Experiment 2. The mugs from the left to right are Mug 1, Mug 2, and Mug 3.

mug can be observed with more traditional Simoneffect types of stimuli in which the prime is more clearly lateralized to the left or right of the fixation but which have the same temporal properties as those of the prime in Experiment 1. Furthermore, Experiment 2 also investigated whether the abstract mug that was used in Experiment 1 is generally identified as some kind of mug and whether it is seen to have any kinds of handle-like properties if this is explicitly asked from participants.

Method Participants Twelve new participants volunteered in a single session that lasted approximately 30 min. All of them were naïve as to the purpose of the experiment. The data of one participant had to be rejected because her error percentage exceeded 10%. The remaining subjects (9 female) were between 22 and 31 years of age (M = 26.8 years). All participants were right-handed, had normal or corrected-to-normal vision, and were naïve as to the purpose of the experiment. In addition, all participants gave their informed consent prior to their inclusion in the study. The study was approved by the Ethical Committee of the Institute of Behavioural Sciences at the University of Helsinki. Apparatus, stimuli, and procedure The stimuli, apparatus, and procedure were similar to those of Experiment 1 except that different prime stimuli were employed, and EEG recordings were not included to this experiment. Also different to the first experiment, neutral stimuli (neutral in relation to left- and right-hand responses) were not used in this experiment. The stimuli consisted

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of five different prime stimuli: the three different black-and-white images of mugs (Mug 1: 6.4° vertically × 6.5° horizontally; Mug 2: 6.9° × 6.8°; Mug 3: 5.7° × 6.5°), a grey circle (1.6° × 1.6°), and a mug handle (3.7° × 1.8°). All potential visual salience biases associated with the main body of these three mugs were removed in the same way as in Experiment 1. The left-orientation stimuli were again created by flipping the rightorientation images horizontally. As can be seen in Figure 6, shapes, brightnesses, contrasts, and sizes were somewhat different between the three mugs. The handle stimuli were built by removing the main body of Mug 1. As a consequence, the handle stimuli were located in the screen exactly at the same left–right locations as the handles of the stimuli of Mug 1. The mug stimuli were presented centrally (e.g., the centre of the main body of the mug was in the centre of the screen). The circle and handle stimuli were presented laterally to the left or right of the central point. The distance of the centre of the circle was 3.5° from the screen centre whereas the furthest point of the handle was 4.2° from the screen centre. The experiment consisted of five blocks. A different prime stimulus was used in each block. The stimuli of the first and second blocks consisted of the circle and the handle. The order of these blocks was counterbalanced between the participants. The circle and the handle blocks were administered before the blocks in which the stimuli consisted of real mugs because we were concerned that the mug bocks could produce some kind of unwanted carryover effects in the circle and/or the handle-alone blocks. That is, if, for example, the participants would do the handle-alone block after three different mug blocks, the visuomotor operations that are actively employed in these




mug blocks could be carried over in the handlealone block, which in turn might boost the processing of handle affordance information even though the stimuli are fundamentally degraded. However, we wanted to eliminate any of that kind of potential carryover effect because we were interested in whether the handle alone can produce negative compatibility effect in the absence of any potential carryover effects. The stimuli of the third, fourth, and fifth blocks consisted of the three different mug images. A different mug was presented in each block. The order of these blocks was also counterbalanced between the participants. There was a short break between each block. During the second break (the break between the second and third blocks), the participants were asked whether they found the stimuli used in the first or second block familiar. In addition, a clear shortcoming in the methods of Experiment 1 was that participants were not asked whether they recognized the abstract prime resembling a mug. It would have been important to know how well we managed to make the abstract prime unrecognizable as a mug. Hence, we presented the same abstract mug stimulus as that used in Experiment 1 to all participants of Experiment 2 for 10 times in the computer monitor. The duration of the stimulus onset was 25 ms, and there was a 2-s delay between the stimulus onsets. After that, participants were asked “is the stimulus familiar to you or does it remind you of something familiar?”. In addition, there was a short practice session (approximately one minute) at the beginning of the first and third blocks. In total, the experiment consisted of 480 trials [24 × 5 (object type) × 2 (stimulus orientation/location) × 2 (hand of response)].

subjected to a repeated measures ANOVA with the within-subjects variables of prime type (circle, handle, Mug 1, Mug 2, or Mug 3) and compatibility between the stimulus orientation/location and the hand of response (compatible or incompatible). The analysis revealed a interaction between prime type and compatibility, F(4, 40) = 16.57, MSE = 3893.75, p , .001, η2p = .624. This suggests that the compatibility effects were different between the primes. As can be seen in Figure 7, the circle and the handle primes produced positive compatibility effects whereas all of the three mug stimuli produced negative compatibility effects. The analyses that were carried out separately for all prime types showed that the main effects of compatibility were significant in relation to all of the prime types (circle: p , .001; handle: p , .05; Mug 1: p , .001; Mug 2: p , .005; Mug 3: p , .001). Similar analyses of percentage error rates did not reveal any significant main effects of interactions, which is not very surprising given that the mean error rate was only 2.2%—that is, the participants made on average two errors in the each block. Finally, none of the participants recognized the handle when they were asked after the second block whether they found either of the first two prime stimuli familiar, and none of the participants identified the abstract shape as a mug when they were presented with the abstract shape used in Experiment 1.

Results Errors and RTs more than two standard deviations from each participant’s condition means were excluded from the analysis. Of the trials, 2.2% were removed as errors, and 3.8% were removed as outliers. The combined removal of errors and outliers left 94% of the raw data as correct responses. The condition means of these remaining data were computed for each participant and were

Figure 7. The mean reaction times (RTs) in Experiment 2 as a function of compatibility (prime orientation–hand of response) and the prime type (a circle, a handle, Mug 1, Mug 2, and Mug 3). Bars refer to the standard error of the mean.


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Discussion


There are two important findings in the results of Experiment 2, which are discussed in more detail in the General Discussion. First, the experiment replicated the NMHP with three new mug images, suggesting that the effect is very robust. Secondly, the negative priming effect was not observed when the mug stimuli were replaced by traditional Simon-effect types of stimuli. This supports the view that the NMHP reflects inhibitory processes that operate in motor planning associated with handle affordances rather than in visuomotor processes that are associated with the Simon effect.

GENERAL DISCUSSION The behavioural results of Experiment 1 replicated the negative and positive priming effects originally reported by Vainio et al. (2011). In the mug prime condition, the participants responded faster and more accurately when the orientation of the mug was incompatible rather than compatible with the responding hand. In contrast, in the abstract prime condition, the participants responded faster and more accurately when the spatial bias of the prime was compatible rather than incompatible with the responding hand. Hence, the former effect replicates the NMHP whereas the latter effect replicates the positive priming effect observed with abstract primes in the original study—an effect that can be assumed to be identical to the positive spatial priming effects (e.g., Eimer, 1995; Posner, 1980). Moreover, it was found in Experiment 1 that the effect associated with the abstract primes includes both the excitatory and the inhibitory components as the neutral conditions provided mean RTs that were between those of the compatible and incompatible conditions. This pattern of results replicates the standard spatial cueing effect, which typically consists of excitatory as well as inhibitory components (e.g., Posner, Nissen, & Ogden, 1978). In contrast, the NMHP produced by the mug primes only consisted of an inhibitory component associated with compatible responses. The mean

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RTs were significantly slower in the compatible condition than in the neutral or incompatible condition. However, the data did not provide significant difference between mean RTs of incompatible and neutral responses. The lack of an excitatory component in the negative compatibility effect associated with handle affordances was also observed in percentage of errors. Hence, it appears that the NMHP reflects inhibition of an action representation associated with the handle affordance in the absence of any excitation of the action representation opposite to that which is inhibited by the handle. Importantly, the NMHP was observed in Experiment 2 with three new mug stimuli. This suggests that the effect is very robust and can be easily produced by different kinds of mug stimuli. In addition, the results of Experiment 2 showed that the same positive priming as that observed in Experiment 1 with the abstract mug can be observed when the mug is replaced by a more traditional Simon-effect type of stimulus, which, however, has the same temporal properties as the abstract mug had in Experiment 1. The positive priming was observed with the circle and the mug handle that were presented to the left or right side of the central fixation. This supports the argument according to which the positive priming observed with the abstract mug in Experiment 1 is produced by the same underlying mechanisms as those for the standard Simon effect. Quite surprisingly, even though the behavioural data demonstrated opposite priming effects for mug primes and abstract primes, the electrophysiological results of Experiment 1 showed that the early LRP pattern was identical for these prime types, as can be seen in Figures 4 and 5 (left panel). In both prime conditions, the waveforms between 120 and 300 ms after the prime onset revealed an activation of the correct response on compatible conditions and an activation of the incorrect response on incompatible conditions. In addition, response-neutral stimuli were not associated with motor activation. This LRP pattern conforms with the behavioural results associated with the abstract primes—that is, the delayed RTs and more erroneous reactions in incompatible




conditions than in neutral and compatible conditions and speeded RTs and more accurate reactions in compatible conditions than in neutral and incompatible conditions. Importantly, however, this LRP pattern does not conform with the behavioural results associated with the mug primes. The LRP pattern should have been opposite for mug primes in comparison to abstract primes if the NMHP would reflect such motor self-inhibition processes that are typically observed in the LRP waveforms rapidly after the offset of the prime (see, e.g., Eimer & Schlaghecken, 1998; Vainio et al., 2013). Therefore, this finding suggests that the inhibition observed in the behavioural data with mug primes does not reflect motor self-inhibition processes related to handle-affordance triggered motor preparation. In addition, the early LRP pattern is not completely in line with the previous findings, according to which the handle affordance should produce a rapid motor preparation in the primary motor cortex of the compatible hand 100 ms after the stimulus onset (Goslin et al., 2012). Even though we observed such a motor preparation effect in the LRPs approximately 130 ms after the prime onset, it was identical for the abstract and mug primes, suggesting that what we actually observed was a manifestation of a standard Simon effect (Simon, 1969) in the LRP. Typical behavioural pattern of the Simon effect shows that responses are performed faster and more accurately with the hand ipsilateral to the stimulus location. Importantly, it has been shown that when the stimulus is presented unilaterally to the left or right of fixation, or when the visual stimulation is presented bilaterally so that the target is presented to the left or right of fixation, and the similar distractor is presented to the opposite side of fixation, the LRP pattern is similar to that observed in the present study. Valle-Inclan (1996) observed that the Simon effect produced by visual stimuli located to the left or right of fixation is associated with an increased activation of the incorrect response on incompatible conditions and an increased activation of the correct response on compatible conditions between 100 and 300 ms after stimulus onset. Similarly, typical spatial cueing

has been associated with LRP patterns in which responses compatible to the direction of the cue arrow are activated about 200 ms after cue onset (Eimer, 1995). Hence, it appears that in the present study, both prime types triggered a rapid motor activation of the hand congruent with the spatial attribute of the prime, exactly in the same way as spatially (horizontally) biased stimuli do in the Simon and spatial cueing tasks. That is, it is likely that the early LRP pattern observed with both prime types reflected abstract spatial motor priming, triggered by spatially biased visual information of the primes. This spatial bias was identical in both prime types. The early LRP pattern observed in the present study was very similar to that observed by Goslin et al. (2012) as stated above. Consequently, it is possible that, similarly to the present study, the early motor activation contralateral to the handle affordance observed by Goslin et al. in fact also reflects processing of abstract spatial biases rather than processing of handle affordances of the observed objects. To our knowledge, Goslin et al. did not control abstract spatial biases that could be associated with the objects they used as stimuli. However, this argument cannot be solidly verified by the present results. It is also possible that the early LRP pattern observed by Goslin et al. indeed reflects rapid processing of handle affordance information at the motor level, whereas in our study this early LRP pattern reflects more abstract spatial response priming. This is because task-relevant objects (used in Goslin et al.’s, 2012, study) and irrelevant objects (used in the present study) receive a different kind of neural processing (e.g., Haxby et al., 1994; O’Craven, Downing, & Kanwisher, 1999). In addition, one has to be careful when interpreting early LRP patterns associated with horizontally lateralized visual stimuli because it has been shown that these kinds of stimuli produce lateralized sensory processing in occipital and parietal cortices. This activation, in turn, can be propagated by volume conduction to electrodes C3′ and C4′ (used for calculating the LRP), contaminating the genuine motor-related LRPs (see Eimer, 1998; Smulders & Miller, 2011). It has been proposed


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that this is likely to be the case particularly until 200 ms after stimulus onset (Eimer, 1998). In the present study, both prime types were associated with a clear saliency bias to the left or right visual field, and, consequently, the LRP patterns observed 120–300 ms after the prime onset might be partially contaminated by lateralized sensory processes. However, if the difference observed in the behavioural data between the mug primes and abstract primes reflected true motor self-inhibition processes associated with the processing of the prime, we should have observed at least to some extent differential modulation also in the early LRP patterns between the two prime types. In the absence of any sensory contamination, the LRP patterns should have been opposite for the two conditions. Hence, even in the presence of contamination, the trend that the incorrect response was activated in incompatible conditions and the correct response in compatible conditions should have been at least smaller for the mug primes than for the abstract primes. However, in the present data the early responses to mug primes and abstract primes in compatible, neutral, and incompatible conditions are practically overlapping (Figure 5, left panel). Consequently, our results suggest that (a) briefly displayed mugs do not produce rapid increased activation in the motor areas contralateral to the handle affordance, and (b) the NMHP is not caused by motor self-inhibition processes related to motor activation, triggered by the handle affordance. Importantly, the present results suggest that the NMHP can be associated with modulation of the late LRP waveform. Both with mug primes and with abstract primes, the condition that was the most demanding to perform on the basis of the behavioural data (RTs were longest and error percentages highest) was associated with the largest late LRP amplitude. However, the conditions were opposite for the two prime types—that is, incompatible condition with the abstract primes and compatible condition with the mug primes. In other words, the responses inhibited on the basis of the behavioural data were associated with increased LRP amplitudes 350–500 ms after the prime onset (that is, 275–425 ms after the target

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onset). This observation is in line with the previous findings, according to which increased amplitudes of electrophysiological measures are observed if responding requires increased allocation of processing resources to the target object—for example, if the semantic, spatial, or action representation activated by the prime object is at an inhibitory state prior to the onset of the target (e.g., Eimer, 1994; Gibbons et al., 2006). As discussed in the introduction, this kind of modulation of late LRP waveforms could be expected to occur in relation to negative priming effects. The central question here is why the handle affordance was associated with an inhibition effect while the abstract prime whose temporal and critical spatial (left–right) elements were identical to the mug prime produced a standard spatial (positive) cueing effect. That is, if the NMHP is based on negative priming processes as proposed above, why was the negative priming only observed with handle affordances and not with the abstract shapes? One potential explanation is that it might be relatively resource and time consuming to extract handle affordance information from the abstract shapes used in the present study. That is, although the visuomotor system would be eventually capable of extracting this affordance information from handle-like features of the abstract shape, this process takes so long that it does not influence response processes when the response has to be performed rapidly after the offset of the prime. However, this explanation of the results does not contradict with the main arguments of this paper concerning the motor inhibition processes associated with handle affordances. It only assumes that the processes that lead to the handle affordance effects (i.e., extracting handle affordance information from viewed objects and activating the corresponding motor representations) are so overwhelming that they operate with any shapes that have any kind of handle-like features. However, the explanation that we prefer for this distinction between the effects associated with the real mugs and the abstract stimuli is linked to the differential nature of the action representation that is triggered by the abstract spatial shape and the ecologically meaningful mug handle. The




action representation triggered by the visual attribute of the abstract shape is likely to be based on spatial attentional processes in the same way as, for example, the Simon effect (Nicoletti & Umilta, 1994) or spatial cueing effects (Posner & Cohen, 1984). In these effects, the visual stimuli exogenously modulate attentional processes—for example, by producing a reflexive shift of attention toward the visually salient part of the object, the pointing direction of the prime arrow, and/or the location of the prime. The action representation that is triggered by these kinds of processes can be assumed to be relatively abstract, modulating eye, head, body, and limb movements toward the object. In the light of the previous research, it is possible that the priming effects triggered by spatial attentional processes are associated with inhibitory processes only when the prime is presented subliminally (as is the case in BMP; Eimer & Schalghecken, 1998) or when the delay between the offset of the prime and the onset of the target is sufficiently long (as is the case in the inhibition of return; Posner & Cohen, 1984). In contrast, the action representation triggered by the mug handle affordance might be related to preparing reaching-to-grasp movements of the specific hand. That is, the handle affordance activates a specific action-related semantic representation and hence can be assumed to be treated in the same way as other similar semantic representations activated by ignored objects—that is, inhibited by negative priming processes. Taken together, we propose that the handle affordance of a briefly displayed task-irrelevant mug leads to the inhibition of the action representation that is compatible with the handle affordance. This action representation and related processes may operate mostly outside of the primary motor cortex, and, consequently, the inhibitory effects are not seen in the early LRP. However, when the target arrow requires selection of the same action representation for responses as the one that is in an inhibitory state after the offset of the prime, the performance is impaired. This can be observed on the behavioural level as relatively slow and inaccurate responses as well as in the late LRPs in which the compatible conditions were associated with increased motor

activation, presumably because it requires additional effort to overcome this inhibition for processing response to the target. We propose, in the light of the current LRP results, that the NMHP is an action-related version of negative priming phenomenon in which the representation activated by affordance information of a viewed object is automatically inhibited. However, in contrast to the standard negative priming, in the NMHP the initial activation is not associated with an unattended secondary (distractor) object. Rather, we suggest that similar negative priming can also be observed when the prime is displayed very briefly. In these conditions, the negative priming can be observed because the prime cannot be fully attended due to its brief onset and/or because the system that prepares actions interprets the briefly displayed prime as a distractor (clearly these two explanations do not need to be mutually exclusive). This interpretation of the results is in line with the view of negative priming proposed by Tipper, Weaver, and Houghton (1994), according to which only those representations of the ignored prime are inhibited that are relevant to the behavioural goal of the task. That is, when the task requires processing of the direction of the arrow in relation to the left and right hand, it is more likely that the representation related to the pointing direction of the handle affordance is inhibited than the representation related to the abstract spatial properties of the prime shape. It should be noticed that the existence of handle affordance phenomena has been previously challenged. For example, Anderson, Yamagishi, and Karavia (2002) suggested that the behavioural handle affordance effect might be based on directing visual attention to the most salient or behaviourally relevant part (e.g., handle) in the object. In other words, this view assumes that motor signals in the handle affordance effect are based on the same neural processes as those for the Simon effect—that is, on an attention shift toward the salient horizontally biased spatial information in the object rather than representing handle affordance. The validity of this argument would have required that the behavioural as well


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as LRP patterns associated with the mug and abstract primes would have been identical in the current study. However, both the behavioural and (late) LRP patterns between mug primes and abstract primes were opposite. Hence, the current study supports the continuously growing evidence according to which the handle affordance effect is based on neural processes separate from other spatial priming effects (e.g., Di Pellegrino, Rafal, & Tipper, 2005; Grezes & Decety, 2002; Symes, Ellis, & Tucker, 2005). Finally, as already mentioned, it has recently been shown that the negative compatibility effect can be produced by briefly presented hand images using exactly the same priming procedure as one that also produces NMHP (Vainio, 2011). This phenomenon was recently shown to be based on similar motor self-inhibition processes to those for the BMP (Vainio et al., 2013). The present results demonstrate that this negative hand-identity priming is not operating under the same excitation– inhibition mechanisms as the NMHP. The former phenomenon appears to be associated with motor self-inhibition whereas the latter appears to be linked to similar inhibition mechanisms to those for negative priming. It is likely that the hand-identity priming effect is caused by a more direct flow of visual information to the primary motor system than the NMHP effect because visual monitoring of the moving hand is continuously used to control one’s hand movements. As a consequence, it is likely that viewing an image of a hand directly activates the motor representation of the corresponding hand, and rapid self-inhibition is needed to suppress this initial unwanted motor activation. In contrast to the inhibition mechanisms behind the NMHP, the negative compatibility effect linked to the hand identity is observed when the response is selected during the self-inhibition phase. To conclude, our study showed that the handle affordance of a task-irrelevant mug does not produce a similar attention orienting effect in the motor system to that for spatial cues. Handle affordance information did not produce any motor activation or inhibition rapidly after the onset of the prime that could be separated from spatial cueing

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effect associated with the abstract visual properties of the object. As a consequence, it can be stated that the NMHP is not caused by motor self-inhibition processes. In contrast, the electrophysiological results revealed that the NMHP produced an LRP pattern that can be predicted from the effects that operate under similar inhibition mechanisms to those for negative priming effects. Hence, we suggest that the NMHP phenomenon presents a novel action-based negative priming phenomenon in which attention-selection processes in relation to the prime are impaired by making the prime entirely task irrelevant and presenting it very briefly. Finally, we propose that even though these negative priming processes in the present study were exclusively linked to mug handles, it seems very unlikely that there would exist inhibition mechanisms that are exclusively operating for controlling affordance effect associated only with mug handles. Thus, it is very likely that the same control mechanisms are operating when one has to rapidly select the hand of response according to the handle affordance of any object. Original manuscript received 15 February 2013 Accepted revision received 22 October 2013 First published online 15 January 2014

REFERENCES Anderson, S. J., Yamagishi, N., & Karavia, V. (2002). Attentional processes link perception and action. Proceedings of the Royal Society of London, Series B, 1225–1232. Arbib, M. A. (1981). Perception and distributed motor control. In V. B. Brooks (ed.), Handbook of physiology, section 1: The Nervous System, Motor Control (Vol. 2, pp. 1449–14480). Baltimore: Williams and Wilkins. Arbuthnott, K. D. (1995). Inhibitory mechanisms in cognition: Phenomena and models. Current Psychology of Cognition, 14, 3–28. Boy, F., Clarke, K., & Sumner, P. (2008). Mask stimulus triggers inhibition in subliminal visuomotor priming. Experimental Brain Research, 190, 111–116. Chao, L. L., & Martin, A. (2000). Representation of manipulable manmade objects in the dorsal stream. Neuroimage, 12, 478–484.




Cisek, P., & Kalaska, J. F. (2005). Neural correlates of reaching decisions in dorsal premotor cortex: Specification of multiple direction choices and final selection of action. Neuron, 45(5), 801–814. Criaghero, L., Fadiga, L., Umilta, D., & Rizzolatti, G. (1996). Evidence of visuomotor priming effect. Neuroreport, 7, 347–349. De Jong, R., Wierda, M., Mulder, G., & Mulder, L. J. M. (1988). Use of partial stimulus information in response processing. Journal of Experimental Psychology: Human Perception and Performance, 14, 682–692. Dempster, F. N. (1995). Interference and inhibition in cognition. An historical perspective. In F. N. Dempster & C. J. Brainerd (Eds.), Interference and inhibition in cognition (pp. 3–26). New York: Academic Press. Di Pellegrino, G., Rafal, R., & Tipper, S. P. (2005). Implicitly evoked actions modulate visual selection: Evidence from parietal extinction. Current Biology, 15, 1469–1472. Eimer, M. (1994). An ERP study on visual spatial priming with peripheral onset. Psychophysiology, 31, 154–163. Eimer, M. (1995). Stimulus-response compatibility and automatic response activation: Evidence from psychophysiological studies. Journal of Experimental psychology: Human Perception and Performance, 21, 837–854. Eimer, M. (1998). The lateralized readiness potential as an on-line measure of central response activation processes. Behavior Research Methods, Instruments, and Computers, 30, 146–156. Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence. Journal of Experimental Psychology: Human Perception and Performance, 24, 1737–1747. Eimer, M., & Schlaghecken, F. (2003). Response facilitation and inhibition in subliminal priming. Biological Psychology, 64, 7–26. Ellis, R. (2009). Interactions between action and visual objects. In E. Morsella, J. Bagh, & P. Gollwitzer (Eds.), The Oxford handbook of human action (pp. 213–224). New York, NY: Oxford University Press. Ellis, R., Tucker, M., Symes, E., & Vainio, L. (2007). Does selecting one visual object from several require inhibition of the actions associated with nonselected objects? Journal of Experimental Psychology: Human Perception and Performance, 33, 670–691. Fagg, A. H., & Arbib, M. A. (1998). Modeling parietalpremotor interactions in primate control of grasping. Neural Network, 11, 1277–1303.

Gibbons, H., Rammsayer, T. H., & Stahl, J. (2006). Multiple source of positive- and negative-priming effects: An event-related potential study. Memory & Cognition, 34, 172–186. Gibson, J. J. (1979). The ecological approach to visual perception. Boston, MA: Houghton Mifflin Company. Goslin, J., Dixon, T., Fischer, M. H., Cangelosi, A., & Ellis, R. (2012). Electrophysiological examination of embodiment in vision and action. Psychological Science, 23, 152–157. Grezes, J., & Decety, J. (2002). Does visual perception of object afford action? Evidence from a neuroimaging study. Neuropsychologia, 40, 212–222. Haxby, J. V., Horwitz, B., Ungerleider, L. G., Maisog, J. M., Pietrini, P., & Grady, C. L. (1994). The functional organization of human extrastriate cortex: A PET–rCBF study of selective attention to faces and locations. Journal of Neuroscience, 14, 6336–6353. Hommel, B., Müsseler, J., Aschersleben, G., & Prinz, W. (2001). The theory of event coding (TEC): A framework for perception and action planning. Behavioral and Brain Sciences, 24, 849–878. Houghton, G., & Tipper, S. P. (1994). A model of inhibitory mechanisms in selective attention. In D. Dagenbach & T. H. Carr (Eds.), Inhibitory processes in attention, memory, and language (pp. 53–112). San Diego: Academic Press. Houghton, G., & Tipper, S. P. (1996). Inhibitory mechanisms of neural and cognitive control: Applications to selective attention and sequential action. Brain & Cognition, 30, 20–43. Kane, M. J., May, C. P., Hasher, L., Rahhal, T., & Stoltzfus, E. R. (1997). Dual mechanisms of negative priming. Journal of Experimental Psychology: Human Performance and Perception, 23, 632–650. Lhermitte, F. (1983). Utilization behavior and its relation to lesions of the frontal lobes. Brain, 106, 237–255. Martin, A., & Chao, L. L. (2001). Semantic memory and the brain: Structure and processes. Current Opinion in Neurobiology, 11, 194–201. Martin, A., Wiggs, C. L., Ungerleider, L. G., & Haxby, J. V. (1996). Neural correlates of category-specific knowledge. Nature, 379, 649–652. McBride, J., Sumner, P., & Husain, M. (2012). Conflict in object affordance revealed by grip force. Quarterly Journal of Experimental Psychology, 65, 13–24. Milliken, B., Joordens, S., Merikle, P. A., & Seiffert, A. E. (1998). Selective attention: A reevaluation of the


21


VAINIO ET AL.

implications of negative priming. Psychological Review, 105, 203–229. Murata, A., Fadiga, L., Fogassi, L., Gallese, V., Raos, V., & Rizzolatti, G. (1997). Object representation in the ventral premotor cortex (area F5) of the monkey. Journal of Neurophysiology, 78, 2226–2230. Nicoletti, R., & Umiltà, C. (1994). Attention shifts produce stimulus spatial codes. Psychological Research, 56, 144–150. O’Craven, K. M., Downing, P. E., & Kanwisher, N. (1999). fMRI evidence for objects as the units of attentional selection. Nature, 401, 584–587. Otten, L. J., & Rugg, M. D. (2005). Interpreting eventrelated brain potentials. In T. C. Handy (Ed.), EventRelated Potentials: A Methods Handbook (pp. 3–16). Cambridge, MA: The MIT Press. Pavese, A., & Buxbaum, L. J. (2002). Action matters: The role of action plans and object affordances in selection for action. Visual Cognition, 9, 559–590. Phillips, J., & Ward, R. (2002). S–R correspondence effects of irrelevant visual affordance: Time-course and specificity of response activation. Visual Cognition, 9, 540–558. Posner, M. I. (1980). Orienting of attention. Quartely Journal of Experimental Psychology, 32, 2–25. Posner, M. I., & Cohen, Y. (1984). Components of visual orienting. In H. Bouma & D. G. Bouwhuis (Eds.), Attention and performance X: Control of language processes (pp. 531–556). Hillsdale, NJ: Erlbaum. Posner, M. I., Nissen, M. J., & Ogden, W. C. (1978). Attended and unattended processing modes: The role of set for spatial location. In J. H. I. Pick & E. Saltzman (Eds.), Modes of perceiving and processing information (pp. 137–157). Hillsdale, NJ: Erlbaum. Pratt, J., & Hommel, B. (2003). Symbolic control of visual attention: The role of working memory and attentional control settings. Journal of Experimental Psychology: Human Perception & Performance, 29, 835–845. Riddoch, M., Edwards, M., Humphreys, G., West, R., & Heafield, T. (1998). Visual affordances direct action: Neuropsychological evidence from manual interference. Cognitive Neuropsychology, 15, 645–683. Sakata, H., Taira, M., Murata, A., & Mine, S. (1995). Neural mechanisms of visual guidance of hand action in the parietal cortex of the monkey. Cerebral Cortex, 5, 429–438. Simon, J. R. (1969). Reactions towards the source of stimulation. Journal of Experimental Psychology, 81, 174–176.

22

Smulders, F. T. Y., & Miller, J. O. (2011). The lateralized readiness potential. In S. J. Luck & E. Kappenman (Eds.), Oxford handbook of event-related potential components (pp. 209–229). New York: Oxford University Press. Symes, E., Ellis, R., & Tucker, M. (2005). Dissociating object-based and space-based affordances. Visual Cognition, 12, 1337–1361. Tipper, S. P. (1985). The negative priming effect: Inhibitory effects of ignored primes. The Quarterly Journal of Experimental Psychology, 37A, 571–590. Tipper, S. P. (2001). Does negative priming reflect inhibitory mechanisms? A review and integration of conflicting views. Quarterly Journal of Experimental Psychology, 54A, 321–343. Tipper, S. P., & Cranston, M. (1985). Selective attention and priming: Inhibitory and facilitatory effects of ignored primes. Quarterly Journal of Experimental Psychology, 37A, 591–611. Tipper, S. P., Paul, M., & Hayes, A. (2006). Vision-foraction: The effects of object property discrimination and action state on affordance compatability effects. Psychonomic Bulletin & Review, 13, 493–498. Tipper, S. P., Weaver, B., & Houghton, G. (1994). Behavioral goals determine inhibitory mechanisms of selective attention. Quarterly Journal of Experimental Psychology, 47A, 809–840. Tucker, M., & Ellis, R. (1998). On the relations of seen objects and components of potential actions. Journal of Experimental Psychology: Human Perception and Performance, 24, 830–846. Tucker, M., & Ellis, R. (2001). The potentiation of grasp types during visual object categorization. Visual Cognition, 8, 769–800. Vainio, L. (2009). Interrupted object-based updating of reach program leads to a negative compatibility effect. Journal of Motor Behavior, 41, 305–315. Vainio, L. (2011). Negative stimulus–response compatibility observed with a briefly displayed image of a hand. Brain and Cognition, 77(3), 382–390. Vainio, L., Alén, H., Hiltunen, S., Lehikoinen, K., Lindbäck, H., Patrikainen, A., & Paavilainen, P. (2013). Response inhibition triggered by the briefly viewed image of a hand: Behavioural and electrophysiological evidence. Neuropsychologia, 51, 493–499. Vainio, L., Ellis, R., & Tucker, M. (2007). The role of visual attention in action priming. Quarterly Journal of Experimental Psychology, 60, 241–261. Vainio, L., & Mustonen, T. (2011). Mapping the identity of a viewed hand in the motor system: Evidence from stimulus–response compatibility. Journal of



Quarterly Journal of Experimental Psychology, 64, 1094–1110. Valle-Inclán, F. (1996). The locus of interference in the Simon effect: An ERP study. Biological Psychology, 43, 147–162.


Experimental Psychology: Human Perception and Performance, 37, 207–221. Vainio, L., Hammarén, L., Hausen, M., Rekolainen, E. & Riskilä, S. (2011). Motor inhibition associated with the affordance of briefly displayed objects. The


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Behavioural, modeling, and electrophysiological evidence for supramodality in human metacognition.

Electrophysiological evidence for automatic processing of erroneous stimuli.

Electrophysiological evidence that inhibition supports lexical selection in picture naming.

Handedness consistency influences bimanual coordination: a behavioural and electrophysiological investigation.

Pregnenolone sulphate enhances spatial orientation and object discrimination in adult male rats: evidence from a behavioural and electrophysiological study.

Contributions of stimulus encoding and memory search to right hemisphere superiority in face recognition: behavioural and electrophysiological evidence.

Striatal GABA-MRS predicts response inhibition performance and its cortical electrophysiological correlates.

Limb apraxia and the "affordance competition hypothesis".

Electrophysiological evidence for phenomenal consciousness.

Response: No need to match: a comment on Bach, Nicholson, and Hudson's "Affordance-Matching Hypothesis".

Dissociation between the behavioural and electrophysiological effects of the face and body composite illusions.

NoGo study.

When bilinguals choose a single word to speak: Electrophysiological evidence for inhibition of the native language.

Nogo tasks: evidence from an electrophysiological study.

Dissociating Simon and affordance compatibility effects: silhouettes and photographs.

Behavioural modification of bulbospinal serotonergic inhibition and morphine analgesia.

Electrophysiological and behavioural responses of turbot (Scophthalmus maximus) cooled in ice water.

Neurofeedback training produces normalization in behavioural and electrophysiological measures of high-functioning autism.

Handle with care--"bucket handle" imperforate anus.

Intrathecal galanin potentiates the spinal analgesic effect of morphine: electrophysiological and behavioural studies.

Attractiveness and affordance shape tools neural coding: insight from ERPs.

Aging and response conflict solution: behavioural and functional connectivity changes.

Reversing the testing effect by feedback: Behavioral and electrophysiological evidence.

Inhibition of misleading heuristics as a core mechanism for typical cognitive development: evidence from behavioural and brain-imaging studies.