Location of the interaction between motion and form signals in motion-streak facilitation

Abstract

<p><i>Introduction.</i> Motion streaks are the smeared representation of a moving object produced by the response persistence of cortical cells. They can be treated as form cues by the visual system, and can facilitate motion processing (Geisler, 1999, Nature). Here we investigated where in the visual system this interaction between form and motion signals occurs. Two likely candidates are the local (V1) and global (V5/MT or MSTd) motion levels. <i>Methods.</i> We used a three-frame global-motion stimulus consisting of signal and noise dots. Strong or weak motion streaks were generated by moving a given dot in either the same direction or a different direction on each frame transition, respectively. There were three conditions: 1) No strong motion-streaks (No Streak)" 2) Strong streaks on the signal (Signal Streak)" 3) strong streaks on the noise (Noise Streak). Thresholds were the percentage of signal dots required to perform a 2AFC direction judgement. The Noise-Streak condition was designed to tap differences in the tuning of cells at the local- and global-motion levels. At the global-motion level, cells are tuned to particular signal directions, so motion streaks should enhance the motion response only when they are in that signal direction, so this would not occur in the Noise-Streak condition. At the local-motion level, each cell is tuned to the direction it is extracting, so if the form-motion interaction occurs here, the noise strength in the Noise-Streak condition would be enhanced. <i>Results.</i> Thresholds for the Signal Streak condition were the lowest (consistent with Edwards & Crane, 2007, VisRes) and thresholds for Noise-Streak condition were the highest. <i>Conclusions.</i> Strong streaks in Noise-Streak impaired motion extraction, consistent with those streaks enhancing the strength of those noise motion-signals. This finding supports the form and motion interactions in motion streak facilitation occurring at the local-motion level.</p>