Pii: S0042-6989(96)00248-9

The characteristics of directionally selective cells in area 17 of the cat are studied using moving random pixel arrays (RPAs) with 50Y0white and 50Y0black pixels. The apparent motion stimulus is similar to that used in human psychophysics [Fredericksen et al. (1993). VisionResearch,33, pp. 1193–1205]. We compare motion sensitivity measured with single-step pixel lifetimes and unlimited pixel Iifetimes. A motion stimulus with a single-step pixel lifetime contains directional motion energy primarily at one combination of spatial displacement and temporal delay. We recorded the responses of complex cells to different combinations of displacement and delay to describe their spatio-temporal correlation characteristics. The response to motion of RPAs with unlimited lifetime is strongest along the preferred speed line in a delay vs displacement size diagram. When using an RPA with a single-step pixel lifetime, the cells are responsive to a much smaller range of spatial displacements and temporal delays of the stimulus. The maximum displacement that still gives a directionally selective response is larger when the preferred speed of the cell is higher. It is on average about three times smaller than the receptive field size. 01997 Elsevier Science Ltd. All rights reserved.