Two mechanisms, one for the detection of fast, and the other for slow movement of a sinusoidal grating are identified, and investigated under central, parafoveal, and peripheral viewing conditions. The fast movement data is considered in terms of the Reichardt model, in which signals from two adjacent inputs are cross-correlated leading to halving of the spatial resolving power for movement detection, compared with that for pattern detection. The mechanism underlying slow movement detection is regarded as being closely related to pattern detection, probably at the single unit level. The characteristics of this mechanism are discussed in the light of recent electrophysiological experiments describing clusters of simple cells in the visual cortex with "directional preference" properties.