Residual colour vision in a human hemianope: spectral responses and colour discrimination.

We present data for a patient, GY, with a right hemianopia caused by traumatic damage to the left occipital cortex. Previous studies have established that this patient has residual vision which enables him to detect and localize transient stimuli presented to his 'blind' hemifield. We have now examined spectral responses associated with this residual vision by using two-colour incremental threshold methods to measure II-spectral functions, and a white light background to examine spectral data for 'colour-opponent' characteristics. We report that both methods yield normal spectral response characteristics for GY's 'blind' hemifield. We have also investigated the patient's ability to identify, verbally, coloured stimuli presented to his 'blind' hemifield, and found that, in 'forced choice' experiments, he achieves a high proportion of correct responses to large stimuli. The patient reported that in threshold detection measurements his responses were based on the presence or absence of a percept associated with transient light stimulation of the 'blind' hemifield (residual vision), whereas colour naming was achieved without conscious perception of colour ('blindsight').