Dichoptic Motion Research Articles

Dichoptic activation of the early motion system

The short range or early motion system has long been considered incapable of binocular integration. We have developed dichoptic motion stimuli which are based upon the decomposition of traveling sinewave gratings into the sum of two standing waves in spatial and temporal quadrature. The monocular views of such displays appear as counterphase flicker but when presented dichoptically the perception is of movement in a unique direction. Two lines of evidence are presented for the binocularity of early motion mechanisms in human vision. First, adaptation to dichoptic motion sinewave gratings is found to result in a motion aftereffect. Second, random texture motion displays based on the quadrature decomposition are found to support dichoptic perception of motion direction, but not figure/ground. Unlike random dot kinematograms, these displays do not necessitate alternating the direction of motion during dichoptic presentation. This encumbrance, and the reliance on figure/ground discrimination, may have been responsible for prior failure to achieve dichoptic motion perception with short range stimuli.

Monocular motion sensing, binocular motion perception

The two-process account of motion perception and its binocular organization were addressed in experiments on apparent movement (AM) with three types of grating: sinusoidal; random bar width; and square-wave with missing fundamental (MF). Monocular MF gratings sampled four times per cycle of drift always appeared to move backwards. Here AM was unrelated to the spatial appearance of the pattern, and followed the motion of the dominant spatial frequency component (the third harmonic). We take this reversed AM to be characteristic of “short-range” motion sensors. It did not occur dichoptically, implying that the direction-selective mechanism of motion sensors is purely monocular. AM was seen with dichoptic presentation for all three types of grating. Performance improved with the length of the stimulus sequence, as predicted by probability summation. This result reconciles previous positive and negative findings on dichoptic AM. The perceived direction of dichoptic AM was consistent with polarity-selective matching of features over time (the “long-range process”). The most telling effect supporting featurematching in dichoptic motion was that dichoptic MF motion reversed direction with a change in the visible features of the pattern (induced by changes in contrast and pulse duration); monocular apparent motion did not. Two routes from spatial frequency channels to the perception of object motion are discussed.

Monoptic and dichoptic signals do not cooperate in the perception of a bistable motion display

Two new conditions of presentation of a bistable motion display are studied, where a competition between monoptic and monoptic plus dichoptic information is supposed to be involved. Data contradict the expectation that a dichoptic motion signal could cooperate with a monocular one. A different interpretation of the combination of monoptic and dichoptic signals is proposed. According to it, the clarity of rotational motion is based upon the evidence, even conflicting, which the two “peripheral” low-level processes separately provide.

Motion aftereffects: Evidence for parallel processing in motion perception

Interocularly transferred motion aftereffects occur immediatelv after exposure to moving stimuli but are no longer demonstrable 7 min later. By contrast, opposite dichoptic motion aftereffects occur both immediately after exposure and 7 min later, with no evidence of a decrease over time. The results imply that the processing of motion aftereffects and hence, by extension, motion perception occurs in parallel systems.