Cortical neurons: isolation of contrast gain control.
The selectivity of cortical neurons remains invariant with contrast, even though the contrast-response function saturates. Both the invariance and the saturation might be due to a contrast-gain control mechanism. To test this hypothesis, a drifting grafting was used to measure the contrast-response function, while a counterphase grating was simultaneously presented at the null position of the receptive field (where it evokes no response at any contrast). When the contrast of the counterphase grating increased, the contrast-response function shifted primarily to the right. This result is consistent with the hypothesis that there is a fast-acting gain-control mechanism which effectively scales the input contrast by the average local contrast.
Geisler
W S
WS
Department of Psychology, University of Texas, Austin 78712.
Albrecht
D G
DG
D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D009039:Motion Perception / Q000502:physiology; D010364:Pattern Recognition, Visual / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000502:physiology*