Mechanisms of visual motion detection

Visual motion is processed by neurons in primary visual cortex that are sen sitive to spatial orientation and speed. Many models of local velocity comp utation are based on a second stage that pools the outputs of first-stage n eurons selective for different orientations, but the nature of this pooling remains controversial. in a human psychophysical detection experiment, we found near-perfect summation of image energy when it was distributed unifor mly across all orientations, but poor summation when it was concentrated in specific orientation bands. The data are consistent with a model that inte grates uniformly over all orientations, even when this strategy is sub-opti mal.