Broken time reversal symmetry in visual motion detection.

In neuroscience, symmetries can tell us about the computations being performed by a circuit. In vision, for instance, one might expect that when a movie is played backward, one's motion percepts should all be reversed. Exact perceptual reversal would indicate a time reversal symmetry, but surprisingly, real visual systems break this symmetry. In this research, we designed visual stimuli to probe different symmetries in motion detection and identify features that lead to symmetry breaking in motion percepts. We discovered that symmetry breaking in motion detection depends strongly on both the detector's architecture and how it is optimized. Interestingly, we find analytically and in simulations that time reversal symmetries are broken in systems optimized to perform with natural inputs.