DIFFERENT USES OF CHROMATIC SIGNALS IN PATIENTS WITH CONGENITAL AND ACQUIRED COLOR-VISION DEFICIENCIES

Chromatic signals can be used to generate perceived colour and also to detect spatially structured objects defined only by chromatic differe nces. These two attributes have previously been investigated in dichro mats and cerebral achromatopsic patients using a new colour vision tes t developed at City University that makes possible the isolation of pu re chromatic signals (Barbur et al. Proc. R. Sec. London B 258, 327-33 4, 1994(1)). We have investigated acquired colour vision changes in a 69-year-old patient, after conventional colour vision tests gave ambig uous results. His ability to detect an object using chromatic signals was impaired more than his ability to detect a colour change, and this impairment was greater in the right eye than in the left eye. This di ssociation suggests parallel pathways may be involved in the two proce sses of coding chromatic signals. Recent neurological testing on the s ame patient has indicated the onset of multiple sclerosis. Our much ea rlier finding based on colour vision testing may therefore have useful diagnostic implications.