Comparison between Monocular and Binocular Observation on Continuous-Motion Perception

In several psychophysical functions, thresholds may be lower when the test is performed binocularly than when performed monocularly. We evaluated binocular advantage on continuous motion perception at and above threshold. Firstly, thresholds of motion direction were determined under monocular and binocular conditions. Stimuli were briefly presented Gabor patches with translation of a sinusoidal carrier. Subjects observed the stimuli using a mirror stereoscope. The apparent contrasts of stimuli were equivalent between monocular and binocular conditions. The observer's task was to decide if the stimulus moved rightward or leftward. We found a binocular advantage of approximately 1.3. Secondly, binocular advantage on motion perception at suprathreshold levels was determined by measuring point of subjective equality (PSE) between monocular and binocular conditions. Monocular condition was the reference and binocular one was the test. Two Gabor patches with carrier translation were presented in succession in random order. The observer's task was to decide if the second stimulus was faster or slower than the first. We found a binocular influence of approximately 1.5 at three times the speed of the motion threshold, no influence at ten times the speed of the threshold.