Breaking up is never easy: Feature matching in motion perception

Purpose, We examined the role of cature-matching in motion perception. Method. The stimulus sequence wis constructed from a vertical, 1 c/deg sinusoidal grating divided into horizon al strips of equal height, where alternate strips moved leftward and rightward. The initial relative phase of adjacent strips was either 0 deg (aligned) or 45 deg (n>m-aligned), and the motion was sampled at 90 deg phase steps. A blank interval (ISI, 0-117ms) was introduced between each 33ms presentation of the stimulus frames. Observers had to identify the direction of motion of the central strip. Results. Motion was perceived correctly at short ISIs, but at longer ISIs perfoimancc was much worse for the aligned sequence, where features in successive frames were alternately long and short. Conclusions. We argue that to achieve feature-matching over time the long features must be broken up perceptually before the short segments can appear to move in opposite directions. This coirectly predicted that overlaying narrow, stationary, black horizontal lines at the junctions of the grating strips would improve performance in the aligned condition. The results support the view that feature-tracking, as well as motion eiergy, play an important role in motion perception.