VEP IN NEGLECT PATIENTS HAVE LONGER LATENCIES FOR LUMINANCE BUT NOT FOR CHROMATIC PATTERNS

IN patients with unilateral neglect, visual evoked potentials (VEP) to stimuli displayed in the left visual field are delayed compared with responses to right visual field stimuli. In the present study, 10 pati ents with right brain damage and neglect were tested with contrast-rev ersed sinusoidal gratings, modulated either in luminance or in chromat icity. For gratings of luminance contrast modulated over relatively hi gh temporal frequencies (4-10.5 Hz), latencies of VEP were about 30 ms longer for stimuli presented to the contralesional (left) visual fiel d than to the field ipsilateral to the lesion. For equiluminant stimul i modulated at relatively low temporal frequencies (1-4 Hz), however, VEP latency was the same for both hemifields. As this condition activa tes predominately the parvocellular pathway the results are consistent with our previous suggestion that the delay observed with luminance s timuli in neglect patients results from selective disruption of the fa ster response of the magnocellular pathway.