RESEARCH NOTE
INTEROCULAR TRANSFER OF COLOR-CONTINGENT AFTEREFFECTS: POSITIVE AFTEREFFECTS’
MOTION
OLGA EUNER FAVRMG
Department of Psychology, UniversitC de Montrial. 90 Vincent d’indy.
Montr6al. Qu&ec. H3C 357. Canada (Received
27 May
1977: in reuisedjbrm
The first report of a contingent aftereffect was made by McCollough in 1965. The effect, which is commonly known by her name, can be induced after one has viewed alternate presentations of orthogonally oriented square wave gratings in complementry colors One may, for example. look at vertical gratings in green light alternating with horizontal gratings in red light. Subsequently, achromatic vertical gratings look pinkish and horizontal gratings appear to have a greenish hue. This is an orientation contingent color aftereffect. Other contingencies can also be established. Hepler (1958) and Stromeyer and Mansfield (1970) found that complementary color aftereffects can be made contingent on direction of motion. Held and Shattuck (1971) showed that it is possible to reverse the contingency of the McCollough effect so that the apparent orientation of a grating is contingent on color. After one has viewed square wave gratings in green light tihed clockwise away from vertical and red gratings tilted counterclockwise, vertical gratings in green light appear to lean counterclockwise, while vertical gratings in red light lean in the clockwise direction. Similarly, Favreau, Emerson and Corballis (1972) and Mayhew and Anstis (1972) reported color-contingent motion aftereffects, in which the apparent direction of rotation of a stationary spirat is contingent on the complementary colors which had previously been paired with opposite directions of rotation. The common feature of all of these aftereffects is that they are negative. That is, the color, orientation, or direction of motion which is seen in the test stimulus after an adaptation period is the opposite of what had been paired with the test stimulus during adap tation. This is also true of simple aftereffects, such as the motion aftereffect, tilt aftereffect, and complementary afterimages. A widely used method for estimating neural locus is to test for interocular transfer. When one eye only is exposed to the adapting stimulus and the aftereffect can subsequently be obtained in the unadapted eye. it is inferred that the site of the effect is located central ‘The work reported in this paper was made possible by grants from the following sources. National Research Council of Canada grant No. APA-IO&Ito D. C. Donderi, and National Research Council of Canada grant No. A 9785 to the author.
23 Augusr
1977)
to the point at which information from the two eyes is combined, Generally, simple noncontingent spatial aftereffects, such as motion. orientation. and spatial frequency can be transferred interocularly. albeit with reduced strength. By contrast, many attempts to induce interocular transfer of effects involving color, including contingent aftereffects, have generally met with failure (see Coltheart. 1973, for review). Failure to induce interocular transfer of color-related contingent aftereffects has been interpreted as an indication that color and spatial properties are coded together at a level peripheral to binocular combination (CoItheart. 1973). It is not entirely accurate to say that all attempts to obtain interocular transfer of contingent aftereffects have failed. The few “successes” appear to have an unusual feature. A hint of this was seen as early as McCollough’s original report (1965). AU but one of her twenty-two observers who were tested for interocular transfer reported seeing no color aftereffects. One observer who did report a color aftereffect with the unadapted eye, claimed that the colors seen on the vertical and horizontal test gratings were the sutne as the colors which had earher been paired with the respective orientations, i.e. a positive aftereffect. Mikaelian (1975). found more consistent reports of positive aftereffects with interocular transfer of the McCollough effect-14 of 27 observers claimed they saw positive aftereffects. MacKay and MacKay (1973) used a si&htly different procedure and also found same-color interocular transfer. Their observers saw alternating red and green homogeneous color fields with one eye and simultaneous aftemating presentations of orthogonally oriented achromatic gratings with the other eye. When the eye which had seen the color fields was tested with achromatic gratings, observers reported seeing the usual complementary orientation contingent color aftereffect. However, when the same test was administered to the other eye which had viewed the gratings observers reported seeing positive color aftereffects Murcb (1974) used a similar paradigm, but exposed one eye to red and green and the other eye to a spiral rotating in alternate directions. The observers were tested for color-contingent motion aftereffects with. stationary spirals in red or green light only 4 of 8 observers reported seeing aftereffects in the spiral-
841
841
Research Note
eye. but 3 of these reported that the effects about 7 min after adaptation (Favreau. 1976). During the were positive. 7 min interval between the two pairs of tests the spiral In summary. it seems that interocular transfer of was hidden from view by a blank screen. and light from the projector was transmitted through a neutral density contingent aftereffects may result in positive rather filter stbcted so that the degree of light adaptation would than negative aftereffects. The ex~riments reported remain constant. below investigate interocular transfer of color-contingent motion aftereffects. In these experiments the motion and color are presented to the same eye. un- Results like the experiments by Murch (1974) and by Mackay On each test an observer could make 2 responses and Mackay (1973). The findings provide additional by indicating (I) the direction in which the stationary evidence that interocular transfer leads to positive spiral appeared to rotate and (2) the duration. if any. contingent aftereffects. of the apparent motion. Details of the scoring procedure are described in Favreau (1976). Essentially, each observer receives a numerical score signed negaEXPERIMENT 1 tively or positively. The sign indicates whether the reported direction of rotation was appropriate for negative aftereffect (positive sign).’ The numeric value A single throw 33 turn arithmetic spiral cut out of black indicates the duration. Zeroes. which indicate that no matte paper was pasted on an 8 cm dia white cardboard disk which had previously been covered with an irregular duration was recorded were also signed negatively or stippled black and white pattern (Letratone No. tT 134). positivefy according to the forced-choice guess. For The spiral and background each covered about 50% of each observer, the scores of tests 1 and 2 were the area of the disk. The spiral was mounted vertically summed as were the scores of tests 3 and 4, 5 and on the shaft of a variable speed motor which was hidden 6, and 7 and 8. In order to determine whether signififrom the observers’ view by a screen, so that the observers cant aftere~ects had occurred. the summed scores saw the spiral against a uniform background. The spiral were ranked ordinally. regardless of sign, and tested subtended approximately 3’ of visual angle. During adap with the Wilcoxon Signed Ranks test to determine tation it was rotated at 5 rpm. so that the tangential velwhether the difference between the positive and negaocity of the rim was 0.78S”/sec. Tungsten light from a Kodak Carousel projector was projected onto the spiral tive values is greater than chance. Greater positive through Kodak Wratten filter 92 (red) and 74 (green). The values indicate a negative aftereffect; greater negative color of the light and the direction of rotation of the spiral values indicate a positive aftereffect. were alternated every IS sec. for a total adaptation time The results of Experiment 1 showed that no signifiof 15 min. First seen color and first seen direction of cant aftereffects occurred when observers were tested rotation were counterbaianced among observers. for interocular transfer, nor when they were tested The 20 observers who participated in this experiment for monocular color contingent motion aftereffects were seated at a distance of 1.5 m from the spiral and were instructed to keep their gaze fixated at the spiral’s (see Table 1 for Summary of results of Experiments center. During adaptation observers watched the spiral 1 and 2). The mean duration of the immediate interrotate with one eye only. The other eye was occluded with ocular test was - 1.10 set (W- = 110, iV = 19. NS) a piece of cardboard held by the observer. Half of the and of the delayed test it was - 1.22 set (W- = 120. observers were adapted using the dominant eye and the pli’z: 19, NS). for the monocular test the correspondother half with the non-dominant eye. They were in- ing values were 7.67 set (W- = 124, N = 20. NS) structed to keep their gaze tixated at the spiral’s center. and-3.0sec (W- = 112. N = 20, NS). They were further instructed that at the end of the adap A closer analysis of the data reveals a trend tation period they would be asked to judge whether the towards positive aftereffect in interocular transfer. stationary spiral appeared to be turning clockwise or counThus in the immediate test 14 observers had negative terclockwise. This was a forced choice-observers were asked to guess the direction even if they felt they had seen scores compared to only 5 who had positive scores no apparent motion. A lever-operated hand-held micro- (one observer had an unsigned score) On the 7 min switch connected to a timer permitted the observers to delayed test, while the overall results indicated that there was no interocular transfer, when the scores on indicate the duration of the aftereffect. After adaptation observers occluded the adapted eye and the nondominant eye were considered alone, there wert tested with the unadapttd eye. They were then tested was a highly significant positive aftereffect (W-t = with the adapted eye to check on tht strength of the mono2.5, p < 0.00s). cular color contingent afttrtffect Thus there were four It is difficult to evaluate the results of this experitests immediately following adaptation and four further ment as regards interocular transfer since the failure tests 7 min later: on test 1 the observer saw the stationary to obtain monocular color-contingent motion afterspira1 ifluminattd in the color which had not appeared on the last seen adaptation alternation. This test was fol- effects may imply that there was nothing to transfer. In a previous experiment (Favreau. 1976) under lowed by test 2 in which the spiral was seen illuminated almost identical conditions. binocular color continin the other color. Tests 3 and 4 were identical except that they were performed with adapted eye. Afttr a 7 min gent MAES had been obtained, so the failure to delay the four tests were repeated in the same order (tests obtain them with monocular adaptation was puzzling. 5, 6. 7 and 8). The 7 min delay tests were given because One possible cause of this failure may have been the of evidence that. under these conditions, the color-contorder of testing, In Experiment 1 the test for inttrocuingent ___.__.motion ._ _ -aftereffect __-___does -- not reach fuil streng_th until tar transfer was always given first. If the mon~ular aftereffect was of very brief duration, then it may have * While it may be confusing to use a positive sign to dissipated by the time the adapted eye had been indicate a negative aftereffect, this is done in order to maintested. Experiment 2 was performed as a test of this tain consistency with previously reported research (Favpossibility. reau, 1976). adapted
Research Note
843
Tabie I. Mean duration of c~~or~ont~n~nt
motion aftereffects (set)
Experiment I
Monocular
Immediate test - 1.10 (tests 1 + 2) 7.67 (tests 3 + 4)
Monocular Interocular transfer
7.45* (tests I -r- 2) -2.69’ (tests 3 + 4)
Interocular transfer
Delayed test
- 1.22(tats 5 + 6) -3.0 (tests 7 -+ 8) Experiment 2 10.46** (tests S + 6) -0.65 (tests 7 + 8)
* p < 0.025 ** p < O.#S
EXPERIMENT
2
Method The procedure in Experiment 2 was identical to that of Experiment 1 except that the adapted eye was always
tested first, and the unadapted
eye was tested second.
Twenty observers who had not participated in Experiment t served in Experiment 2. Results Monocular aftereffects. As can be seen from inspection of Table 1 negative monocular aftereffects were obtained on both the immediate test (X = 7.45. N_= 19, W- = 34, p < 0.02) and on the delayed test (X = 10.46, w- = 3, N = 19, p < 0.005). There was a significant increase on the delayed test, (W= 44. N = 19, p < 0.05) which is consistent with previous results obtained with binocular color-contingent motion aftereffect (Favreau, 1976). The fact that the aftereffect is even greater on the 7 min delayed test than immediately after adaptation shows that failure to obtain it in Experiment 1 was not due simply to the passage of time. It seems, rather, that the test for interocular transfer had exerted an active interference. fnterocular transfer. There was a signific*t positive color contingent motion aftereffect (X = -2.69, W-t- = 36, N = 18, p < 0.025) with interocular transfer on the immediate test but the effect was not test (X = -0.65, significant on the delayed W+ = 67, N = 16, NS). When compared with the results of Experiment 1, the results of the present experiment imply that the order in which the adapted and unadapted eyes are tested exerts an effect on whether aftereffects are obtained. To properly verify this it is appropriate to make direct comparisons between the results of the two experiments. This was done using the Wilcoxon rank sum test for independent samples (Ferguson, 1971). When the effects of the monocufar test administered second (Experiment 1) were compared with those of the monocular test when it was administered first on the immediate test, the difference was not significant (N, = 20, N2 = 18. R, = 337, p > 0.10). However the corresponding comparison on the delayed test confirmed that the difference between Experiments 1 and 2 in this condition was significant (N, = 18, Nr = 16, R, = 179, p < 0.001). That is the test for interocular transfer seems to inhibit the monocular color-contingent motion aftereffect. AS far as interocular transfer is concerned, the difference between the two conditions is significant on
both the immediate and the delayed test, but in opposite directions. On the immediate test there is interocular transfer of a positiw aftereffect only when the test for fnterocular transfer follows the test for monocular aftereffect. By the time the delayed test, are given the positive aftereffect has dissipated and the observers in Experiment 2 are in fact “closer” to negative aftereffects then those in Experiment 1, although neither group within itself differs signiticantly from chance. DISCUSSION
Two main findings emerge from these experiments. One is that, contrary to previous reports that contingent aftereffects do not transfer interocularly, interocular transfer of color-contingent motion aftereffects is possible, but gives rise to positive rather than negative aftereffects. Secondly, it was seen that whether transfer occurs depends on the order in which the eyes are tested: the adapted eye must be tested first. In fact even the occurrence of monocular color-contingent motion aftereffects requires that the adapted eye be tested before the unadapted eye, as testing the latter first appears to exert an inhibitory action on the monocular negative aftereffect. The finding of positive aftereffects in the contralateral eye confirms a trend which becomes evident upon examination of some reports on orientation contingent color aftereffects (MacKay and MacKay, 1973; Mikaelian, 1975) and on color-contingent motion aftereffects (Murch, 1974). MacKay and MacKay (1973) suggested that the occurrence of positive coior aftereffects in interocular transfer may be due to inhibitory interactions between color-coded inputs from both eyes. The present work shows that inhibitory action can also involve pattern motion perception when it is paired with color. As MacKay and MacKay (1973) pointed out, there is considerable neurophysiologi~i evidence that inhibition between the inputs of the two eyes occurs at the lateral geniculate nucleus (Sanderson et a/., 1969; Singer, 1970; Suzuki and Kato, 1966; Suzuki and Takahashi, 1970). This kind of inhibition could possibly be responsible for the occurrence of positive aftereffects in the unadapted eye. That the order in which the eyes are tested should affect the results so strongly is problematical. It would seem that exposing the unadapted eye to the test stimulus inhibits the subsequent occurrence of the negative aftereffect in the adapted eye. whiie also pre-
84-t
Research Note
eluding the appearance of the positive aftereffect in the unadapted eye. Conversely. exposing the adapted eye to the test stimuIus first appears to potentiate both the negative aftereffect in the adapted eye and the subsequent positive aftereffect in the unadapted eye. However before postulating a relativefy simple inhibitory interaction. one must take into account two further complexities in the data. First. although the occurrence of positive and negative aftereffects may be interdependent as described above, they do not attain their highest values concurrently, In Experiment 2 it was seen that positive aftereffects occurred only on the immediate test and had dissipated 7 min later. The negative aftereffects. on the other hand. were much stronger on the 7 min test than they had been on the immediate test. Thus, although the occurrence of the negative and positive aftereffects may depend on reIated mechanisms their maintenance apparently does not. Second, it does not seem to be exposure of the unadapted eye as such that inhibits the occurrence of aftereffects. This can be seen in Experiment 2. where negative aftereffects were obtained on the delayed tests some 7 min after observers had had a test with the unadapted eye. Thus there would seem to be a complicated interaction of inhibition and potentiation between the adapted and unadapted eyes. REFERENCES
Coltheart M. (1973) Color specificity and monocularity in
the visual cortex.
Vision
Rcs.
13. 2595-2598.
Favreau 0. E.. Emerson V. F. and Corballis M. C. (1972) Motion perception: a color-contingent after-effect. Science. N.Y. 176. 78-79.
Favreau 0. E. (1976) Interference in colour-contingent motion after-effects Q. JI. exp. Psycho/. 28. jj3-560. Frrguson G. A. (1971) Sra:isricai .~nui~~is in ps~ci~uioy~ and Educarian. McGraw-Hill, New York. Held R. and Shattuck S. R. (1971) Color- and edqe-scnsitive channels in the human visual system: tuning for orientation. Sciencr. .V.Y. 174. 314316. Hepler N. 11968) Color: a motion-contingent color aftereffect. Science, N. Y. 162. 376-377. MacKay 13. and IMacKay V. (1973) Orientation sensitive aftereffect of dichoptically presented colour and form. Rrature.
Lond.
242.
477-479.
Mayhew J. E. W. and Anstis S. M. (1972). Movement aftereffects contingent on color, intensity, and pattern. Percept. Psychophys. 12, 77-85. McCollough C. (1965) Color adaptation of edge-detectors in the human visual system. Science. X.Y 149, 1115-1116. IMikaelian H. H. (1974) Interocular generalization of orientation specific color aftereffects. Vision Res. 15. 66 l-664. Murch G. M. (1974) Color contingent motion aftereffects: single or multiple levels of processing? Vision Res. 14. l181-1184. Sanderson K. .I.. Darian-Smith I. and Bishop P. 0. (1969) Binocular corresponding receptive fields of single units in the cat dorsal lateral geniculate nucleus. Vision Res. 9. 1297-1303. Singer W. (1970) Inhibitory binocular interaction in the lateral geniculate body of the cat. Brain Rex 18, 165-170. Stromeyer C. and Mansfield R. (1970) Colored after-effects produced with moving edges. Percept. Psychophys. 7. 108-I Suzuki
14.
H. and Kate E. (1966) Binocular interaction at cat*s
lateral geniculate body. J. Neurophysiol. 29, 909-920. Suzuki H. and Takahashi M. (1970) Organization of lateral geniculate neurons in binocular interaction. Bruin Res. 23, 261-264.
INTEROCULAR TRANSFER OF COLOR-CONTINGENT AFTEREFFECTS: POSITIVE AFTEREFFECTS’
MOTION
OLGA EUNER FAVRMG
Department of Psychology, UniversitC de Montrial. 90 Vincent d’indy.
Montr6al. Qu&ec. H3C 357. Canada (Received
27 May
1977: in reuisedjbrm
The first report of a contingent aftereffect was made by McCollough in 1965. The effect, which is commonly known by her name, can be induced after one has viewed alternate presentations of orthogonally oriented square wave gratings in complementry colors One may, for example. look at vertical gratings in green light alternating with horizontal gratings in red light. Subsequently, achromatic vertical gratings look pinkish and horizontal gratings appear to have a greenish hue. This is an orientation contingent color aftereffect. Other contingencies can also be established. Hepler (1958) and Stromeyer and Mansfield (1970) found that complementary color aftereffects can be made contingent on direction of motion. Held and Shattuck (1971) showed that it is possible to reverse the contingency of the McCollough effect so that the apparent orientation of a grating is contingent on color. After one has viewed square wave gratings in green light tihed clockwise away from vertical and red gratings tilted counterclockwise, vertical gratings in green light appear to lean counterclockwise, while vertical gratings in red light lean in the clockwise direction. Similarly, Favreau, Emerson and Corballis (1972) and Mayhew and Anstis (1972) reported color-contingent motion aftereffects, in which the apparent direction of rotation of a stationary spirat is contingent on the complementary colors which had previously been paired with opposite directions of rotation. The common feature of all of these aftereffects is that they are negative. That is, the color, orientation, or direction of motion which is seen in the test stimulus after an adaptation period is the opposite of what had been paired with the test stimulus during adap tation. This is also true of simple aftereffects, such as the motion aftereffect, tilt aftereffect, and complementary afterimages. A widely used method for estimating neural locus is to test for interocular transfer. When one eye only is exposed to the adapting stimulus and the aftereffect can subsequently be obtained in the unadapted eye. it is inferred that the site of the effect is located central ‘The work reported in this paper was made possible by grants from the following sources. National Research Council of Canada grant No. APA-IO&Ito D. C. Donderi, and National Research Council of Canada grant No. A 9785 to the author.
23 Augusr
1977)
to the point at which information from the two eyes is combined, Generally, simple noncontingent spatial aftereffects, such as motion. orientation. and spatial frequency can be transferred interocularly. albeit with reduced strength. By contrast, many attempts to induce interocular transfer of effects involving color, including contingent aftereffects, have generally met with failure (see Coltheart. 1973, for review). Failure to induce interocular transfer of color-related contingent aftereffects has been interpreted as an indication that color and spatial properties are coded together at a level peripheral to binocular combination (CoItheart. 1973). It is not entirely accurate to say that all attempts to obtain interocular transfer of contingent aftereffects have failed. The few “successes” appear to have an unusual feature. A hint of this was seen as early as McCollough’s original report (1965). AU but one of her twenty-two observers who were tested for interocular transfer reported seeing no color aftereffects. One observer who did report a color aftereffect with the unadapted eye, claimed that the colors seen on the vertical and horizontal test gratings were the sutne as the colors which had earher been paired with the respective orientations, i.e. a positive aftereffect. Mikaelian (1975). found more consistent reports of positive aftereffects with interocular transfer of the McCollough effect-14 of 27 observers claimed they saw positive aftereffects. MacKay and MacKay (1973) used a si&htly different procedure and also found same-color interocular transfer. Their observers saw alternating red and green homogeneous color fields with one eye and simultaneous aftemating presentations of orthogonally oriented achromatic gratings with the other eye. When the eye which had seen the color fields was tested with achromatic gratings, observers reported seeing the usual complementary orientation contingent color aftereffect. However, when the same test was administered to the other eye which had viewed the gratings observers reported seeing positive color aftereffects Murcb (1974) used a similar paradigm, but exposed one eye to red and green and the other eye to a spiral rotating in alternate directions. The observers were tested for color-contingent motion aftereffects with. stationary spirals in red or green light only 4 of 8 observers reported seeing aftereffects in the spiral-
841
841
Research Note
eye. but 3 of these reported that the effects about 7 min after adaptation (Favreau. 1976). During the were positive. 7 min interval between the two pairs of tests the spiral In summary. it seems that interocular transfer of was hidden from view by a blank screen. and light from the projector was transmitted through a neutral density contingent aftereffects may result in positive rather filter stbcted so that the degree of light adaptation would than negative aftereffects. The ex~riments reported remain constant. below investigate interocular transfer of color-contingent motion aftereffects. In these experiments the motion and color are presented to the same eye. un- Results like the experiments by Murch (1974) and by Mackay On each test an observer could make 2 responses and Mackay (1973). The findings provide additional by indicating (I) the direction in which the stationary evidence that interocular transfer leads to positive spiral appeared to rotate and (2) the duration. if any. contingent aftereffects. of the apparent motion. Details of the scoring procedure are described in Favreau (1976). Essentially, each observer receives a numerical score signed negaEXPERIMENT 1 tively or positively. The sign indicates whether the reported direction of rotation was appropriate for negative aftereffect (positive sign).’ The numeric value A single throw 33 turn arithmetic spiral cut out of black indicates the duration. Zeroes. which indicate that no matte paper was pasted on an 8 cm dia white cardboard disk which had previously been covered with an irregular duration was recorded were also signed negatively or stippled black and white pattern (Letratone No. tT 134). positivefy according to the forced-choice guess. For The spiral and background each covered about 50% of each observer, the scores of tests 1 and 2 were the area of the disk. The spiral was mounted vertically summed as were the scores of tests 3 and 4, 5 and on the shaft of a variable speed motor which was hidden 6, and 7 and 8. In order to determine whether signififrom the observers’ view by a screen, so that the observers cant aftere~ects had occurred. the summed scores saw the spiral against a uniform background. The spiral were ranked ordinally. regardless of sign, and tested subtended approximately 3’ of visual angle. During adap with the Wilcoxon Signed Ranks test to determine tation it was rotated at 5 rpm. so that the tangential velwhether the difference between the positive and negaocity of the rim was 0.78S”/sec. Tungsten light from a Kodak Carousel projector was projected onto the spiral tive values is greater than chance. Greater positive through Kodak Wratten filter 92 (red) and 74 (green). The values indicate a negative aftereffect; greater negative color of the light and the direction of rotation of the spiral values indicate a positive aftereffect. were alternated every IS sec. for a total adaptation time The results of Experiment 1 showed that no signifiof 15 min. First seen color and first seen direction of cant aftereffects occurred when observers were tested rotation were counterbaianced among observers. for interocular transfer, nor when they were tested The 20 observers who participated in this experiment for monocular color contingent motion aftereffects were seated at a distance of 1.5 m from the spiral and were instructed to keep their gaze fixated at the spiral’s (see Table 1 for Summary of results of Experiments center. During adaptation observers watched the spiral 1 and 2). The mean duration of the immediate interrotate with one eye only. The other eye was occluded with ocular test was - 1.10 set (W- = 110, iV = 19. NS) a piece of cardboard held by the observer. Half of the and of the delayed test it was - 1.22 set (W- = 120. observers were adapted using the dominant eye and the pli’z: 19, NS). for the monocular test the correspondother half with the non-dominant eye. They were in- ing values were 7.67 set (W- = 124, N = 20. NS) structed to keep their gaze tixated at the spiral’s center. and-3.0sec (W- = 112. N = 20, NS). They were further instructed that at the end of the adap A closer analysis of the data reveals a trend tation period they would be asked to judge whether the towards positive aftereffect in interocular transfer. stationary spiral appeared to be turning clockwise or counThus in the immediate test 14 observers had negative terclockwise. This was a forced choice-observers were asked to guess the direction even if they felt they had seen scores compared to only 5 who had positive scores no apparent motion. A lever-operated hand-held micro- (one observer had an unsigned score) On the 7 min switch connected to a timer permitted the observers to delayed test, while the overall results indicated that there was no interocular transfer, when the scores on indicate the duration of the aftereffect. After adaptation observers occluded the adapted eye and the nondominant eye were considered alone, there wert tested with the unadapttd eye. They were then tested was a highly significant positive aftereffect (W-t = with the adapted eye to check on tht strength of the mono2.5, p < 0.00s). cular color contingent afttrtffect Thus there were four It is difficult to evaluate the results of this experitests immediately following adaptation and four further ment as regards interocular transfer since the failure tests 7 min later: on test 1 the observer saw the stationary to obtain monocular color-contingent motion afterspira1 ifluminattd in the color which had not appeared on the last seen adaptation alternation. This test was fol- effects may imply that there was nothing to transfer. In a previous experiment (Favreau. 1976) under lowed by test 2 in which the spiral was seen illuminated almost identical conditions. binocular color continin the other color. Tests 3 and 4 were identical except that they were performed with adapted eye. Afttr a 7 min gent MAES had been obtained, so the failure to delay the four tests were repeated in the same order (tests obtain them with monocular adaptation was puzzling. 5, 6. 7 and 8). The 7 min delay tests were given because One possible cause of this failure may have been the of evidence that. under these conditions, the color-contorder of testing, In Experiment 1 the test for inttrocuingent ___.__.motion ._ _ -aftereffect __-___does -- not reach fuil streng_th until tar transfer was always given first. If the mon~ular aftereffect was of very brief duration, then it may have * While it may be confusing to use a positive sign to dissipated by the time the adapted eye had been indicate a negative aftereffect, this is done in order to maintested. Experiment 2 was performed as a test of this tain consistency with previously reported research (Favpossibility. reau, 1976). adapted
Research Note
843
Tabie I. Mean duration of c~~or~ont~n~nt
motion aftereffects (set)
Experiment I
Monocular
Immediate test - 1.10 (tests 1 + 2) 7.67 (tests 3 + 4)
Monocular Interocular transfer
7.45* (tests I -r- 2) -2.69’ (tests 3 + 4)
Interocular transfer
Delayed test
- 1.22(tats 5 + 6) -3.0 (tests 7 -+ 8) Experiment 2 10.46** (tests S + 6) -0.65 (tests 7 + 8)
* p < 0.025 ** p < O.#S
EXPERIMENT
2
Method The procedure in Experiment 2 was identical to that of Experiment 1 except that the adapted eye was always
tested first, and the unadapted
eye was tested second.
Twenty observers who had not participated in Experiment t served in Experiment 2. Results Monocular aftereffects. As can be seen from inspection of Table 1 negative monocular aftereffects were obtained on both the immediate test (X = 7.45. N_= 19, W- = 34, p < 0.02) and on the delayed test (X = 10.46, w- = 3, N = 19, p < 0.005). There was a significant increase on the delayed test, (W= 44. N = 19, p < 0.05) which is consistent with previous results obtained with binocular color-contingent motion aftereffect (Favreau, 1976). The fact that the aftereffect is even greater on the 7 min delayed test than immediately after adaptation shows that failure to obtain it in Experiment 1 was not due simply to the passage of time. It seems, rather, that the test for interocular transfer had exerted an active interference. fnterocular transfer. There was a signific*t positive color contingent motion aftereffect (X = -2.69, W-t- = 36, N = 18, p < 0.025) with interocular transfer on the immediate test but the effect was not test (X = -0.65, significant on the delayed W+ = 67, N = 16, NS). When compared with the results of Experiment 1, the results of the present experiment imply that the order in which the adapted and unadapted eyes are tested exerts an effect on whether aftereffects are obtained. To properly verify this it is appropriate to make direct comparisons between the results of the two experiments. This was done using the Wilcoxon rank sum test for independent samples (Ferguson, 1971). When the effects of the monocufar test administered second (Experiment 1) were compared with those of the monocular test when it was administered first on the immediate test, the difference was not significant (N, = 20, N2 = 18. R, = 337, p > 0.10). However the corresponding comparison on the delayed test confirmed that the difference between Experiments 1 and 2 in this condition was significant (N, = 18, Nr = 16, R, = 179, p < 0.001). That is the test for interocular transfer seems to inhibit the monocular color-contingent motion aftereffect. AS far as interocular transfer is concerned, the difference between the two conditions is significant on
both the immediate and the delayed test, but in opposite directions. On the immediate test there is interocular transfer of a positiw aftereffect only when the test for fnterocular transfer follows the test for monocular aftereffect. By the time the delayed test, are given the positive aftereffect has dissipated and the observers in Experiment 2 are in fact “closer” to negative aftereffects then those in Experiment 1, although neither group within itself differs signiticantly from chance. DISCUSSION
Two main findings emerge from these experiments. One is that, contrary to previous reports that contingent aftereffects do not transfer interocularly, interocular transfer of color-contingent motion aftereffects is possible, but gives rise to positive rather than negative aftereffects. Secondly, it was seen that whether transfer occurs depends on the order in which the eyes are tested: the adapted eye must be tested first. In fact even the occurrence of monocular color-contingent motion aftereffects requires that the adapted eye be tested before the unadapted eye, as testing the latter first appears to exert an inhibitory action on the monocular negative aftereffect. The finding of positive aftereffects in the contralateral eye confirms a trend which becomes evident upon examination of some reports on orientation contingent color aftereffects (MacKay and MacKay, 1973; Mikaelian, 1975) and on color-contingent motion aftereffects (Murch, 1974). MacKay and MacKay (1973) suggested that the occurrence of positive coior aftereffects in interocular transfer may be due to inhibitory interactions between color-coded inputs from both eyes. The present work shows that inhibitory action can also involve pattern motion perception when it is paired with color. As MacKay and MacKay (1973) pointed out, there is considerable neurophysiologi~i evidence that inhibition between the inputs of the two eyes occurs at the lateral geniculate nucleus (Sanderson et a/., 1969; Singer, 1970; Suzuki and Kato, 1966; Suzuki and Takahashi, 1970). This kind of inhibition could possibly be responsible for the occurrence of positive aftereffects in the unadapted eye. That the order in which the eyes are tested should affect the results so strongly is problematical. It would seem that exposing the unadapted eye to the test stimulus inhibits the subsequent occurrence of the negative aftereffect in the adapted eye. whiie also pre-
84-t
Research Note
eluding the appearance of the positive aftereffect in the unadapted eye. Conversely. exposing the adapted eye to the test stimuIus first appears to potentiate both the negative aftereffect in the adapted eye and the subsequent positive aftereffect in the unadapted eye. However before postulating a relativefy simple inhibitory interaction. one must take into account two further complexities in the data. First. although the occurrence of positive and negative aftereffects may be interdependent as described above, they do not attain their highest values concurrently, In Experiment 2 it was seen that positive aftereffects occurred only on the immediate test and had dissipated 7 min later. The negative aftereffects. on the other hand. were much stronger on the 7 min test than they had been on the immediate test. Thus, although the occurrence of the negative and positive aftereffects may depend on reIated mechanisms their maintenance apparently does not. Second, it does not seem to be exposure of the unadapted eye as such that inhibits the occurrence of aftereffects. This can be seen in Experiment 2. where negative aftereffects were obtained on the delayed tests some 7 min after observers had had a test with the unadapted eye. Thus there would seem to be a complicated interaction of inhibition and potentiation between the adapted and unadapted eyes. REFERENCES
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