TY - JOUR
T1 - The McCollough effect reveals orientation discrimination in a case of cortical blindness
AU - Humphrey, G. Keith
AU - Goodale, Melvyn A.
AU - Corbetta, Maurizio
AU - Aglioti, Salvatore
N1 - Funding Information:
The authors would like to thank P.B. for the cooperation he showed throughout testing. This research was supported by funds from the Consiglio Nazionable delle Ricerche, Italy to S.A., from the Natural Sciences and Engineering Research Council of Canada to G.K.H., and from the Medical Research Council of Canada to M.A.G.
PY - 1995/5
Y1 - 1995/5
N2 - Background: The McCollough effect is a colour aftereffect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns - such as a red-and-black vertical grating and a green-and-black horizontal grating - are viewed alternately for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. Results Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90° differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. Conclusion These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.
AB - Background: The McCollough effect is a colour aftereffect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns - such as a red-and-black vertical grating and a green-and-black horizontal grating - are viewed alternately for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. Results Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90° differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. Conclusion These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.
UR - http://www.scopus.com/inward/record.url?scp=0029294681&partnerID=8YFLogxK
U2 - 10.1016/S0960-9822(95)00107-2
DO - 10.1016/S0960-9822(95)00107-2
M3 - Article
C2 - 7583104
AN - SCOPUS:0029294681
SN - 0960-9822
VL - 5
SP - 545
EP - 551
JO - Current Biology
JF - Current Biology
IS - 5
ER -