Spatiotemporal contrast detection threshold surface is bimodal

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Abstract
We find that the spatiotemporal contrast-detection threshold surface is bimodal. The two sensitivity maxima correspond to the regions described by the subject as governed by pattern or flicker detection. The pattern sensitivity maximum is located at the boundary of the spatiotemporal parameter plane, well within the region where eye movements must be expected to dominate the temporal component of the retinal stimulation. The pattern extremum is located at 4 cycles per degree (cpd), 0 Hz; the flicker extremum at 0.5 cpd, 7.6 Hz. The sensitivity is somewhat higher at the pattern maximum than at the flicker maximum.