Loss of visual information in neglect: the effect of chromatic- versus luminance-contrast stimuli in a "what" task.

One to four vertical bars were tachistoscopically presented at various eccentricities along the horizontal meridian to patients with right brain damage and neglect (n=7) and to a control group of right brain damaged patients without neglect (n=4). Luminance contrast stimuli and isoluminant chromatic contrast stimuli were used. The patients' task was to report the number of bars. With luminance stimuli the neglect patients' discrimination in the left visual field was reduced, particularly at the most leftward position tested (ca 20 degrees ) where about 20% of the bars were omitted. The loss of information was limited to luminance contrast stimuli. When chromatic contrast stimuli were used, accuracy was comparable in the two hemifields and between groups of patients. The differential pattern of results for chromatic and luminance contrast stimuli is consistent with the hypothesis of a selective deficit of the magno-cellular pathway in neglect.