Abstract
We have developed three types of binocular motion stimuli whose monocular components are dynamic random-dot patterns (1) without coherent motion, (2) patterns moving in the same direction as binocular motion, (3) those moving in the opposite direction to binocular motion (e.g., motion after binocular fusion moves downward while visual input to each eye is upward motion). Here we utilize such novel stimuli to investigate how our visual system processes monocular and binocular motions. Exp. 1: Seven observers were instructed to view 6 motion stimuli whose monocular and binocular motions were in opposite directions with variable intensity ratio (M/B stimuli) under 5 different stimulus durations. Then the observers reported which motion direction was perceived as dominant. The results showed that monocular motion perception becomes more dominant as stimulus duration becomes shorter, indicating that our ability to detect binocular motion over time is poor compared with detection of monocular motion. Exp. 2: To examine the time course of motion processing in detail, we measured ocular-following responses (OFR) elicited by 27 motion stimuli (n=3). The onset latency of the OFR elicited by monocular motion is faster than that of binocular motion by 20–50 ms, and the amplitude of initial OFR is determined by the monocular motion intensity alone. When monocular and binocular motions are in opposite directions, the OFR waveforms elicited by M/B stimuli can be fitted very well with the linear summation of OFR waveforms induced by exclusively monocular and exclusively binocular motions, suggesting that these motions are processed parallel without strong interaction. On the other hand, when monocular and binocular motions move in the same direction, we find nonlinear response enhancement as a result of facilitative interaction between monocular and binocular motion mechanisms. The latency of the enhanced response components is considered to reflect the time delay for the interaction.