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 direction is easily detected among noise dots in Brownian motion (Watamaniuk et al., Vis Res 1995;35:65-77). In this study we calculated the predictions of a commonly-used psychophysical motion model for a motion trajectory in noise. This model assumes local motion energy detectors optimally tuned to the signal, followed by a decision stage that implements the maximum rule. We first show that local motion detectors do indeed explain the detectability of brief trajectories (100 ms) that fall within a single unit, but that they severely underestimate the detectability of extended trajectories that span multiple units. For instance, a 200 ms trajectory is approximately three times more detectable than two isolated 100 ms trajectories presented together within an equivalent 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 than 1 degree are almost as detectable as linear trajectories. Our data are consistent with a flexible network that feeds forward excitation among units tuned to similar directions of motion.
Verghese
P
P
Smith-Kettlewell Eye Research Institute, San Francisco, CA 94115-1821, USA.
Watamaniuk
S N
SN
McKee
S P
SP
Grzywacz
N M
NM
D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D009039:Motion Perception / Q000502:physiology*; D011601:Psychophysics