0028-3932;91$3W.l+000 c 1991 Pergamon Pressplc
NOTE DIRECTION
OF GAZE DURING
VIBROTACTILE TASKS
CHOICE
REACTION
TIME
JANE M. PIEKSON. JOHN L. BKAUSHAW,* TAMAKA F. MEYEK, MICHELLE J. HOWARD and JUOY A. BKADSHAW Department
of Psychology,
Monash
University,
Clayton,
(Received 24 August 1990: accepted
Victoria
24 February
3168, Australia
1991)
Abstract-A vibrotactile choice reaction time (RT) task was used. with the hands in their own hemispace (arms uncrossed), and in their opposite hemispace (arms crossed). Gaze was directed at the stimulated and responding hand, away from it at the other (inactive) hand, or at a central fixation point (a neutral control). Responses were slower in the crossed than the uncrossed condition. Further, in the crossed condition, responses were faster when subjects looked at the stimulated and responding hand, rather than at the inactive hand or at the central fixation point. As RT in the latter two conditions did not differ, there is a benefit when subjects look at the stimulated and responding hand, rather than a cost when they look at the inactive hand. In the look at condition, visual or attentional factors may reduce the response coding conflict which occurs when arms are crossed.
INTRODUCTION IN i\ vibrotactile simple reaction time (SRT) task, response speed ofthe two hands did not differ, but either hand was faster when in the right rather than the left side of space 131. This effect may reflect differences in ihe ability to focus attention to the left and right for an extended time [4. 5,9]. It appeared when side of presentation was blocked and attention could be focused to one location, but was absent with vibrotactile choice reaction time (CRT) where trials were presented randomly to the two sides and subjects continually switched attention [S]. While there were no side differences in our CRT task, two effects appeared which were absent with SRT. The right hand was faster than the left, an effect which is also absent in visual SRT tasks [I, 71, but may appear when responses to visual stimuli require a choice between hands [IO]. There was also a hand/hemispace compatibility eflectresponses were faster when each hand was in its own side of space (arms uncrossed), than when each was in its opposite space (arms crossed). A similar effect has also been reported for visual CRT. but not SRT [I, 71. In CRT tasks. response location needs to be encoded. When the arms are crossed there may be a conflict between the (anatomical) code for the responding hand and the code for its location [7], or the code for location of the response goal [I I]. In the experiments discussed above subjects fixated ahead. While mechanisms controlling direction of attention are likely to be closely linked to overt orienting systems, such as the eyes and hands [6], studies using visual stimuli have shown that, under certain circumstances, attention may be directed to locations in space independently ofgaze 1121. In tactual tasks, with blocks of trials at one location, the stimulated and responding hand may induce covert orientation of attention to its locus irrespective of gaze direction. We examined the influence of gaze by systematically manipulating its direction in two previous vibrotactile experiments [Z]. The first experiment used a SRT paradigm, with the stimulated and responding hand in left or right hemispace for blocks of trials. Subjects cithcr looked at the hand. or away from it towards the opposite (empty) hemispatial location. Predictably, responses were faster in right hemispace, there were no hand differences, no hand/hemispace compatibility effects and no effects ofgaze direction. As had been the case for SRT and straight ahead fixation, subjects still seemed able to direct attention to the region where events were occurring, without the need for gaze to be directed there as well. In the second experiment, using CRT, the hands were in either their own or opposite hemispaces and gaze was directed to one or other hand for blocks of trials. As trials were randomized between hands, subjects were looking at the
*To whom
requests
for reprints
should
be addressed. 925
926
NOTE
stimulated and responding hand for some trials in a block, and away from it (at the inactive hand) on others. Subjects were faster when looking at the stimulated and responding hand, rather than away from it, but this effect appeared only when the arms were crossed and each hand was in its opposite space. In the experiment reported hem we now ask whether looking at the hand required to respond in fact provides benefits, compared with a neutral control condition of fixating straight ahead, and/or whether looking away from the responding hand, towards the currently inactive hand, is costly. A subsidiary aim was to determine if the right hand was faster than the left as it had been in our previous CRT experiment where subjects fixated straight ahead 157. This effect was not significant in the CRT experiment where subjects looked at or away from the stimulated and responding hand [2]. If deviation of gaze is responsible for the loss of hand differences we would expect that, in the present experiment, a right hand superiority would appear when subjects look straight ahead, but be absent in both the look at, and look away conditions. If this is the case then it may shed light on both the mechanisms underlying the gaze effect and the hand effect.
METHOD Suhjecrs Eighteen strongly to the same criteria
dextrdl students at Monash University (nine males and nine females) were recruited, used in our previous vibrotactile studies 12, 3. 5, 91,
according
Apparatus
As in our previous vibrotactile studies, Oticon A bone-conduction vibrators (47 Q impedance) with vibrating surfaces of 1.7 cm in diameter were used as vibrotactile transducers. They were driven by oscillators under computer control. Frequency (250 Hz), intensity (2.75 V, peak-to-peak), duration (80 msec) and rise and fall times (each 20 msec) were set so as to produce a clearly perceptible signal. The computer also recorded RT.
Subjects sat at a table, positioned within a wooden guide extending arounding the sides of the body. The hand positions, one in either hemispace, were identified by two response buttons placed 30 cm left and right of the subject’s midline, and 14 cm to the front of the chesthne (i.e. 65 to the left or right of the midline). The transducers were taped to the underside of the index lingers leaving the pads free. Subjects rested the pads of the index fingers on the response buttons and pressed the button upon which the stimulated finger rested, as soon as a stimulus was felt. Between experimental sessions, the transducers and buttons were interchanged between hands. The experimenter and all control apparatus were positioned directly behind the subject, in a symmetrical room with overhead lighting. To mask any auditory cues, white noise was played to the subject over earphones. Trials (stimulation and response) were pseudorandomly alternated between the two hands, with an intertrial interval of 1.5 sec. There were 960 trials altogether, halfin each of two separate sessions of about 20 min each. There were 12 experimental conditions (each with 80 trials), corresponding to the stimulation and response of left and right hand, in left and right hemispace, and with gaze directed to the left, to the right, and at a central fixation point at eye level. The pseudorandom alternation of trials between hands meant that when subjects turned their heads and looked left or right for a block of trials, they were in fact looking UI the stimulated and responding hand on some trials in a block and awarfrom it (at the inactive hand) on others. In a single session, three of the subjects commenced with each hand in its own space (arms uncrossed) and looked left for IO trials. ccntre for 10. and right for IO, then repeated this with each hand in its opposite space (arms crossed). They then returned to arms uncrossed commencing for 10 trials with a rtghtward gaze. then IOcentrc and IOleftward trials.This was then followed by arms crossed, again commencing with 10 trials whcrc gaze was to the right. Three subjects commcnccd with each of the remaining five combinations of gaze direction and arm position (uncrossed, crossed). In the second session. configurations at commencement were reversed for each subject. To overcome practic effects and to stabilize RT, a minimum of40 practice trials preceded the experimental series in each session. The criterion for rejection ofsubjects on the basis of overall error rate was set at IO%, but no subject was rejected on this basis.
RESULTS The RT data were analyzed using a four-way ANOVA with the non-repeated factor Sex, and the rcpcatcd factors Hand. left, right; Hemispace, left right; and Gaze. at (the stimulated and responding hand), centre, and away (from the stimulated and responding hard). Four clfccts wcrc signilicant, including the three-way interaction, [F(2, 32)= 11.75, P
NOTE DIRECTION
OF GAZE DURING
VIBROTACTILE TASKS
CHOICE
REACTION
TIME
JANE M. PIEKSON. JOHN L. BKAUSHAW,* TAMAKA F. MEYEK, MICHELLE J. HOWARD and JUOY A. BKADSHAW Department
of Psychology,
Monash
University,
Clayton,
(Received 24 August 1990: accepted
Victoria
24 February
3168, Australia
1991)
Abstract-A vibrotactile choice reaction time (RT) task was used. with the hands in their own hemispace (arms uncrossed), and in their opposite hemispace (arms crossed). Gaze was directed at the stimulated and responding hand, away from it at the other (inactive) hand, or at a central fixation point (a neutral control). Responses were slower in the crossed than the uncrossed condition. Further, in the crossed condition, responses were faster when subjects looked at the stimulated and responding hand, rather than at the inactive hand or at the central fixation point. As RT in the latter two conditions did not differ, there is a benefit when subjects look at the stimulated and responding hand, rather than a cost when they look at the inactive hand. In the look at condition, visual or attentional factors may reduce the response coding conflict which occurs when arms are crossed.
INTRODUCTION IN i\ vibrotactile simple reaction time (SRT) task, response speed ofthe two hands did not differ, but either hand was faster when in the right rather than the left side of space 131. This effect may reflect differences in ihe ability to focus attention to the left and right for an extended time [4. 5,9]. It appeared when side of presentation was blocked and attention could be focused to one location, but was absent with vibrotactile choice reaction time (CRT) where trials were presented randomly to the two sides and subjects continually switched attention [S]. While there were no side differences in our CRT task, two effects appeared which were absent with SRT. The right hand was faster than the left, an effect which is also absent in visual SRT tasks [I, 71, but may appear when responses to visual stimuli require a choice between hands [IO]. There was also a hand/hemispace compatibility eflectresponses were faster when each hand was in its own side of space (arms uncrossed), than when each was in its opposite space (arms crossed). A similar effect has also been reported for visual CRT. but not SRT [I, 71. In CRT tasks. response location needs to be encoded. When the arms are crossed there may be a conflict between the (anatomical) code for the responding hand and the code for its location [7], or the code for location of the response goal [I I]. In the experiments discussed above subjects fixated ahead. While mechanisms controlling direction of attention are likely to be closely linked to overt orienting systems, such as the eyes and hands [6], studies using visual stimuli have shown that, under certain circumstances, attention may be directed to locations in space independently ofgaze 1121. In tactual tasks, with blocks of trials at one location, the stimulated and responding hand may induce covert orientation of attention to its locus irrespective of gaze direction. We examined the influence of gaze by systematically manipulating its direction in two previous vibrotactile experiments [Z]. The first experiment used a SRT paradigm, with the stimulated and responding hand in left or right hemispace for blocks of trials. Subjects cithcr looked at the hand. or away from it towards the opposite (empty) hemispatial location. Predictably, responses were faster in right hemispace, there were no hand differences, no hand/hemispace compatibility effects and no effects ofgaze direction. As had been the case for SRT and straight ahead fixation, subjects still seemed able to direct attention to the region where events were occurring, without the need for gaze to be directed there as well. In the second experiment, using CRT, the hands were in either their own or opposite hemispaces and gaze was directed to one or other hand for blocks of trials. As trials were randomized between hands, subjects were looking at the
*To whom
requests
for reprints
should
be addressed. 925
926
NOTE
stimulated and responding hand for some trials in a block, and away from it (at the inactive hand) on others. Subjects were faster when looking at the stimulated and responding hand, rather than away from it, but this effect appeared only when the arms were crossed and each hand was in its opposite space. In the experiment reported hem we now ask whether looking at the hand required to respond in fact provides benefits, compared with a neutral control condition of fixating straight ahead, and/or whether looking away from the responding hand, towards the currently inactive hand, is costly. A subsidiary aim was to determine if the right hand was faster than the left as it had been in our previous CRT experiment where subjects fixated straight ahead 157. This effect was not significant in the CRT experiment where subjects looked at or away from the stimulated and responding hand [2]. If deviation of gaze is responsible for the loss of hand differences we would expect that, in the present experiment, a right hand superiority would appear when subjects look straight ahead, but be absent in both the look at, and look away conditions. If this is the case then it may shed light on both the mechanisms underlying the gaze effect and the hand effect.
METHOD Suhjecrs Eighteen strongly to the same criteria
dextrdl students at Monash University (nine males and nine females) were recruited, used in our previous vibrotactile studies 12, 3. 5, 91,
according
Apparatus
As in our previous vibrotactile studies, Oticon A bone-conduction vibrators (47 Q impedance) with vibrating surfaces of 1.7 cm in diameter were used as vibrotactile transducers. They were driven by oscillators under computer control. Frequency (250 Hz), intensity (2.75 V, peak-to-peak), duration (80 msec) and rise and fall times (each 20 msec) were set so as to produce a clearly perceptible signal. The computer also recorded RT.
Subjects sat at a table, positioned within a wooden guide extending arounding the sides of the body. The hand positions, one in either hemispace, were identified by two response buttons placed 30 cm left and right of the subject’s midline, and 14 cm to the front of the chesthne (i.e. 65 to the left or right of the midline). The transducers were taped to the underside of the index lingers leaving the pads free. Subjects rested the pads of the index fingers on the response buttons and pressed the button upon which the stimulated finger rested, as soon as a stimulus was felt. Between experimental sessions, the transducers and buttons were interchanged between hands. The experimenter and all control apparatus were positioned directly behind the subject, in a symmetrical room with overhead lighting. To mask any auditory cues, white noise was played to the subject over earphones. Trials (stimulation and response) were pseudorandomly alternated between the two hands, with an intertrial interval of 1.5 sec. There were 960 trials altogether, halfin each of two separate sessions of about 20 min each. There were 12 experimental conditions (each with 80 trials), corresponding to the stimulation and response of left and right hand, in left and right hemispace, and with gaze directed to the left, to the right, and at a central fixation point at eye level. The pseudorandom alternation of trials between hands meant that when subjects turned their heads and looked left or right for a block of trials, they were in fact looking UI the stimulated and responding hand on some trials in a block and awarfrom it (at the inactive hand) on others. In a single session, three of the subjects commenced with each hand in its own space (arms uncrossed) and looked left for IO trials. ccntre for 10. and right for IO, then repeated this with each hand in its opposite space (arms crossed). They then returned to arms uncrossed commencing for 10 trials with a rtghtward gaze. then IOcentrc and IOleftward trials.This was then followed by arms crossed, again commencing with 10 trials whcrc gaze was to the right. Three subjects commcnccd with each of the remaining five combinations of gaze direction and arm position (uncrossed, crossed). In the second session. configurations at commencement were reversed for each subject. To overcome practic effects and to stabilize RT, a minimum of40 practice trials preceded the experimental series in each session. The criterion for rejection ofsubjects on the basis of overall error rate was set at IO%, but no subject was rejected on this basis.
RESULTS The RT data were analyzed using a four-way ANOVA with the non-repeated factor Sex, and the rcpcatcd factors Hand. left, right; Hemispace, left right; and Gaze. at (the stimulated and responding hand), centre, and away (from the stimulated and responding hard). Four clfccts wcrc signilicant, including the three-way interaction, [F(2, 32)= 11.75, P
