Perceptual and Motor Shills, 1979,48, 143-146. @ Perceptual and Motor Skills 1979
DURATION OF THE MOTION AFTEREFFECT AS A FUNCTION O F RETINAL LOCUS A N D VISUAL FIELD1 ALAN A. BEATON
University College, Cardiff' Srrmmary.-The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.
If a rotating disc is viewed for some length of time then, after the rotation ceases, the disc appears to revolve in the opposite direction. ?'his motion aftereffect has received a great deal of study (Holland, 1965) and is believed to have both peripheral and central components (Anstis & Moulden, 1970). However, although it is known that the strength of the aftereffect varies with the area of retina stimulated (Freud, 1964; Holland, 1965), no one appears ro have investigated whether there is any consistent difference between stimulation of the nasal and temporal hemiretinae of the two eyes. A second question of interest, given the evidence for a central contribution to the motion aftereffect, is whether there is any difference in the magnitude of the effect between left and right cerebral hemispheres. Lateralicy differences have been reported for such relatively simple tasks as the perception of colour (Davidoff, 1975, 1976; Pirot, Pulton, & Sucker, 1977) and the detection of dots (Davidoff, 1977) as well as for more complex perceptual tasks (Kimura & D~unford,1974). The aim of the present experiment, therefore, was to explore possible differences betwen nasal and temporal hemiretinae and between left and right cerebral hemispheres in the duration omf the motion aftereffect. .
MKTHOD Subjects The subjecn were seven male and five female srudent volunteers all of whom were naive as to the purposes of the experiment. All subjects were right handed in view of the uncertain relationship between left handedness and cerebral asymmetry of function; see Hardyck and Petrinovich (1977) for a review of this topic. Apparatus and Procedure The stimulus slide (luminance 30.14 cd/m2) displayed a disc of computergenerated random dots which subtended 8' 04' of visual angle when projected 'Reprints may be obtained from Dr. A. A. Beaton, Psychology Department, North Arts Buildinrr. Universiw Colleae of Swansea. Singleton Park. Swansea SA2 8PP. Wales. United also in ~ o c u m e n tNAPS-031.89 from ~ i c r i f i c h ePublica~ i n ~ d o m~ables.availa6le . tions, 440 Park Avenue South, New York, N. Y. 10016. Remit $3.00 for fiche or $8.50 for photocopy.
144
A. A. BEATON
on a screen 3 m. in front of the subject. The slide was blacked out except for the circle of docs and could be made to rotate by means of an electric motor attached to the front of a modified Rank Aldis Tutor 1000 projector. Two fixation points of light were set horizontally on either side of the disc 15 cm from its circumference and two further points of light were set 40 cm vertically above these fixation p i n t s . The four points of light were produced by means of pin holes made in black cardboard placed in the slide holder of a second projector. The procedure required the subject to monocularly fixate one of the fixation points for a period of 45 sec. during which the stimulus revolved at a speed of 15 rpm. By directing the subject's gaze to the appropriate fixation point on the left or right of the circle it was possible to stimulate the desired nasal or temporal hemiretina of the viewing eye. At 1.5 sec. from the end of the 45-sec. adaptation period, by which time the scimulus had ceased to rotate, an electronic with an auditory metronome which sounded at intimer started simultaneo~~sly tervals of 1.5 sec. The subject's task was to listen for the first metronome beat, to note the occurrence of any aftereffect and then, on hearing the second beat, to switch his gaze to the spot of light vertically above the fixation point. This meant that the now stationary stimulus fell on an unadapted region of retina and no aftereffect was observed. On the third beat of the metronome he was to switch his gaze back to the fixation point when the aftereffect again became visible. By switching gaze back and forth between the two points of light in time with the metronome the subject was able to compare the presence of any aftereffect when viewing the fixation point with its absence when looking at the upper point. As soon as he no longer detected any difference between these two positions he was required to depress a key which stopped both the timer and che metronome. After sufficient practice trials for the subject to dark-adapt and to become familiar with the procedure, four trials were given for each of the four hemiretinae. Presentation order of the four conditions was counterbalanced across subjects, each subject receiving the four trials for a given retinal locus before passing to the next condition. There was an interval of at least 30 sec. between the subject's response and the start of the following trial. The direction of motion, clockwise or anti-clockwise, was alternated on each trial. The experiment took place in a photographic dark room, the level of ambient light being approximately 107 lum/m2. At the end of the experiment the subject's sighting dominance was assessed by requiring him to look with one eye at one of the points of light through a small hole in a piece of card held with both hands. This was repeated mice more and the eye used to look on at least two of the three occasions was noted. RESULTS Aftereffect duration as shown on the electronic timer constituted the raw data. As this included the time taken to make a motor response, the time for
145
DURATION OF AFTEREFFECT
each trial was arbitrarily rounded down to the nearest completed metronome interval. The mean duration of the aftereffect thus calculated is shown for each retinal locus in Table 1. The data were submitted to rwo analyses of variance for a fully repeated measures design. In the first analysis the two factors were eye (left vs right) and retinal locus (nasal vs temporal). The only significant effect was the interaction between these two factors (F = 7.17, df = 1/11, p < 0.025). Subsequent testing showed that the nasal-temporal difference was significant for the right eye (for correlated data, t = 3.06, df = 11, p 0.02) but not for the lefc eye. In the second analysis of variance, hemisphere was entered as a factor in place of eye, the second factor being retinal locus as before. This analysis now showed the difference between left and right hemispheres co be the only significant source of variation (F = 7.17, df = 1/11, p 0.25).
DURATION OF THE MOTION AFTEREFFECT AS A FUNCTION O F RETINAL LOCUS A N D VISUAL FIELD1 ALAN A. BEATON
University College, Cardiff' Srrmmary.-The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.
If a rotating disc is viewed for some length of time then, after the rotation ceases, the disc appears to revolve in the opposite direction. ?'his motion aftereffect has received a great deal of study (Holland, 1965) and is believed to have both peripheral and central components (Anstis & Moulden, 1970). However, although it is known that the strength of the aftereffect varies with the area of retina stimulated (Freud, 1964; Holland, 1965), no one appears ro have investigated whether there is any consistent difference between stimulation of the nasal and temporal hemiretinae of the two eyes. A second question of interest, given the evidence for a central contribution to the motion aftereffect, is whether there is any difference in the magnitude of the effect between left and right cerebral hemispheres. Lateralicy differences have been reported for such relatively simple tasks as the perception of colour (Davidoff, 1975, 1976; Pirot, Pulton, & Sucker, 1977) and the detection of dots (Davidoff, 1977) as well as for more complex perceptual tasks (Kimura & D~unford,1974). The aim of the present experiment, therefore, was to explore possible differences betwen nasal and temporal hemiretinae and between left and right cerebral hemispheres in the duration omf the motion aftereffect. .
MKTHOD Subjects The subjecn were seven male and five female srudent volunteers all of whom were naive as to the purposes of the experiment. All subjects were right handed in view of the uncertain relationship between left handedness and cerebral asymmetry of function; see Hardyck and Petrinovich (1977) for a review of this topic. Apparatus and Procedure The stimulus slide (luminance 30.14 cd/m2) displayed a disc of computergenerated random dots which subtended 8' 04' of visual angle when projected 'Reprints may be obtained from Dr. A. A. Beaton, Psychology Department, North Arts Buildinrr. Universiw Colleae of Swansea. Singleton Park. Swansea SA2 8PP. Wales. United also in ~ o c u m e n tNAPS-031.89 from ~ i c r i f i c h ePublica~ i n ~ d o m~ables.availa6le . tions, 440 Park Avenue South, New York, N. Y. 10016. Remit $3.00 for fiche or $8.50 for photocopy.
144
A. A. BEATON
on a screen 3 m. in front of the subject. The slide was blacked out except for the circle of docs and could be made to rotate by means of an electric motor attached to the front of a modified Rank Aldis Tutor 1000 projector. Two fixation points of light were set horizontally on either side of the disc 15 cm from its circumference and two further points of light were set 40 cm vertically above these fixation p i n t s . The four points of light were produced by means of pin holes made in black cardboard placed in the slide holder of a second projector. The procedure required the subject to monocularly fixate one of the fixation points for a period of 45 sec. during which the stimulus revolved at a speed of 15 rpm. By directing the subject's gaze to the appropriate fixation point on the left or right of the circle it was possible to stimulate the desired nasal or temporal hemiretina of the viewing eye. At 1.5 sec. from the end of the 45-sec. adaptation period, by which time the scimulus had ceased to rotate, an electronic with an auditory metronome which sounded at intimer started simultaneo~~sly tervals of 1.5 sec. The subject's task was to listen for the first metronome beat, to note the occurrence of any aftereffect and then, on hearing the second beat, to switch his gaze to the spot of light vertically above the fixation point. This meant that the now stationary stimulus fell on an unadapted region of retina and no aftereffect was observed. On the third beat of the metronome he was to switch his gaze back to the fixation point when the aftereffect again became visible. By switching gaze back and forth between the two points of light in time with the metronome the subject was able to compare the presence of any aftereffect when viewing the fixation point with its absence when looking at the upper point. As soon as he no longer detected any difference between these two positions he was required to depress a key which stopped both the timer and che metronome. After sufficient practice trials for the subject to dark-adapt and to become familiar with the procedure, four trials were given for each of the four hemiretinae. Presentation order of the four conditions was counterbalanced across subjects, each subject receiving the four trials for a given retinal locus before passing to the next condition. There was an interval of at least 30 sec. between the subject's response and the start of the following trial. The direction of motion, clockwise or anti-clockwise, was alternated on each trial. The experiment took place in a photographic dark room, the level of ambient light being approximately 107 lum/m2. At the end of the experiment the subject's sighting dominance was assessed by requiring him to look with one eye at one of the points of light through a small hole in a piece of card held with both hands. This was repeated mice more and the eye used to look on at least two of the three occasions was noted. RESULTS Aftereffect duration as shown on the electronic timer constituted the raw data. As this included the time taken to make a motor response, the time for
145
DURATION OF AFTEREFFECT
each trial was arbitrarily rounded down to the nearest completed metronome interval. The mean duration of the aftereffect thus calculated is shown for each retinal locus in Table 1. The data were submitted to rwo analyses of variance for a fully repeated measures design. In the first analysis the two factors were eye (left vs right) and retinal locus (nasal vs temporal). The only significant effect was the interaction between these two factors (F = 7.17, df = 1/11, p < 0.025). Subsequent testing showed that the nasal-temporal difference was significant for the right eye (for correlated data, t = 3.06, df = 11, p 0.02) but not for the lefc eye. In the second analysis of variance, hemisphere was entered as a factor in place of eye, the second factor being retinal locus as before. This analysis now showed the difference between left and right hemispheres co be the only significant source of variation (F = 7.17, df = 1/11, p 0.25).
