Cortical evoked potentials due to motion contrast in the blind hemifield.
Subcortical visual inputs to motion-selective cortex in primates survive after damage to the primary visual cortex (area 17/V1). Activation of human motion cortex was examined using scalp electrodes in a V1-damaged hemianope. Blind field motion-onset visual evoked potentials (VEPs) shared many of the characteristics associated with sighted vision but were smaller in amplitude and had longer latencies. The representative negative wave (C(II) peak) showed typical dependency on stimulus contrast, its peak latency increased and amplitude decreased as contrast decreased, reflecting the difficulty with which directional information could be detected. VEPs were present at contrasts below 25% when blind field motion was imperceptible even though direction guessing was paradoxically accurate. Subcortical inputs to motion cortex contribute to visual experience but not to conscious perception.
Benson
P J
PJ
University Laboratory of Physiology, Oxford, UK.
Guo
K
K
Hardiman
M J
MJ
D000328:Adult; D003243:Consciousness / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology*; D004566:Electrodes; D004594:Electrophysiology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006423:Hemianopsia / Q000503:physiopathology*; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D014787:Vision Tests; D014793:Visual Cortex / Q000503:physiopathology*; D014794:Visual Fields / Q000502:physiology*