Abstract

Cases of cerebral achromatopsia have increased our understanding of the anatomy of extrastriate cortex. Some features of the reported cases have not so far been explained: for example, 1) Why can some but not all patients read pseudoisochromatic plates? 2) Why do some patients have a relatively greater impairment of short wavelength mechanisms? Results obtained in four cases of cerebral achromatopsia will be presented in an attempt to address these and other issues. One patient showed a marked deterioration in both chromatic processing and achromatic contrast sensitivity at low light levels, suggesting that the testing conditions may be important. In some cases dynamic random luminance masking (which disables achromatic mechanisms) results in a total failure of chromatic discrimination, while in others this has no effect on residual color discrimination. Thus the extent to which discrimination depends upon residual chromatic or achromatic mechanisms may vary. In one case it has been shown by using incremental threshold techniques that S-cone sensitivity may be reduced by 1.5 log units in the presence of near normal L-cone sensitivity, suggesting that the relatively greater impairment of short wavelength mechansisms is reflected in detection thresholds as well as chromatic discrimination. These differences in residual vision are discussed in the context of the underlying anatomy.

© 1992 Optical Society of America