PROBING VISUAL-MOTION SIGNALS WITH A PRIMING PARADIGM

The perceived motion of a vertical sine-wave luminance grating which u ndergoes an abrupt 180 deg phase shift (motion step) is ambiguous, The grating sometimes appears to move rightward; sometimes leftward. Howe ver, when the 180 deg step follows closely upon an unambiguous grating step, the 180 deg step appears to be in the same direction as the una mbiguous step, This phenomenon is termed visual motion priming (VMP), and some of the characteristics of the phenomenon were investigated in a series of experiments, The main findings were that priming (1) last ed for hundreds of msec; (2) was at a maximum when the magnitude of th e priming step was 90 deg; (3) was scarcely affected by spatial freque ncy in the range 0.7-2.8 c/deg; and (4) at suprathreshold contrasts de pended upon the relative contrast, not the absolute contrasts, of the frames comprising the priming step, The experiments were conducted wit hin the framework of a motion energy model (Adelson & Bergen, 1985) wh ich possessed an extra stage which summed motion signals over time, So me of the results could be explained by the second-stage integrator, O ther nonlinear relationships between VMP and contrast require some for m of motion signal compression, and perhaps even a mechanism of dynami c contrast processing. (C) 1997 Elsevier Science Ltd.