LOCAL MOTION DETECTORS CANNOT ACCOUNT FOR THE DETECTABILITY OF AN EXTENDED TRAJECTORY IN NOISE

Previous work has shown that a single dot moving in a consistent direc tion is easily detected among noise dots in Brownian motion (Watamaniu k et al., Vis Res 1995;35:65-77). In this study we calculated the pred ictions of a commonly-used psychophysical motion model for a motion tr ajectory in noise. This model assumes local motion energy detectors op timally tuned to the signal, followed by a decision stage that impleme nts the maximum rule. We first show that local motion detectors do ind eed explain the detectability of brief trajectories (100 ms) that fall within a single unit, but that they severely underestimate the detect ability of extended trajectories that span multiple units. For instanc e, a 200 ms trajectory is approximately three times more detectable th an two isolated 100 ms trajectories presented together within an equiv alent temporal interval. This result suggests a nonlinear interaction among local motion units. This interaction is not restricted to linear trajectories because circular trajectories with curvatures larger tha n 1 degrees are almost as detectable as linear trajectories. Our data are consistent with a flexible network that feeds forward excitation a mong units tuned to similar directions of motion. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.