Binocular influences on global motion processing in the human visual system

Abstract

This study investigates four key issues concerning the binocular properties of the mechanisms that encode global motion in human vision: (1) the extent of any binocular advantage; (2) the possible site of this binocular summation; (3) whether or not purely monocular inputs exist for global motion perception; (4) the extent of any dichoptic interaction. Global motion coherence thresholds were measured using random-dot-kinematograms as a function of the dot modulation depth (contrast) for translational, radial and circular flow fields. We found a marked binocular advantage of approximately 1.7, comparable for all three types of motion and the performance benefit was due to a contrast rather than a global motion enhancement. In addition, we found no evidence for any purely monocular influences on global motion detection. The results suggest that the site of binocular combination for global motion perception occurs prior to the extra-striate cortex where motion integration occurs. All cells involved are binocular and exhibit dichoptic interactions, suggesting the existence of a neural mechanism that involves more than just simple summation of the two monocular inputs.

Quantifying Sensory Eye Dominance in the Normal Visual System: A New Technique and Insights into Variation across Traditional Tests

“…For the motion coherence threshold test, the average threshold number of signal dots across participants was 11.5 (4.8 dots SD), which is consistent with previous reports of tests with high-contrast dots. 24 There was a bias toward right eye dominance in the motion coherence test results with 27 (61%) of 44 participants having higher motion coherence thresholds when the signal dots were presented to the left eye. This bias was not present in the results of the modified Bagolini striated lens test.…”

“…Traditionally, binocular interaction has been considered to be wholly excitatory 25 ; however, recent studies [21][22][23][24] have highlighted interocular inhibitory signals that interact before or parallel with the standard excitatory combination of left and right eye signals. This pattern has been developed into what is now referred to as a two-stage model for the combination of left and right eye information: one stage of contrast gain control before summation that receives an inhibitory input from the contralateral eye and one stage of contrast gain control after binocular combination.…”

“…Two previous findings suggest that sensory eye dominance is associated with an inhibitory balance before binocular summation, rather than a balance between monocular excitatory signals per se. First, observers with normal binocular vision exhibit imbalances in dichoptic interactions in performing a variety of tasks, 24,26 suggesting a possible inhibitory basis for eye dominance. Second, eye dominance bears no relationship to the relative monocular contrast sensitivity, acuity, or hyperacuity of each eye, 12 suggesting that monocular excitatory signals are not solely responsible.…”

Excitatory binocular interactions in two cases of alternating strabismus

“…16,17 It has recently been shown that this task can be modified to measure excitatory binocular combination by separating the two populations of dots between the eyes, that is, dichoptic presentation. 7,8,18 Within the normal visual system, the noise seen by one eye impairs the observer's ability to report the direction of the signal dots seen by the other eye, 19 but it does not matter which eye sees the signal and which sees the noise as the inhibitory interactions between the two eyes are balanced. However, in the case of complete suppression, if the fixing eye sees the signal and the suppressed (nonfixing) eye sees the noise, then performance will be at ceiling.…”

“…For observers with suppression, the dots presented to the suppressed eye can be shown at a high contrast, while the contrast of the dots presented to the fixing eye can be lowered to reduce the suppression, 7,8 The aim of this procedure is to find the contrast imbalance at which the motion coherence threshold remains constant regardless of which eye sees the signal and which sees the noise, 7,8 which is consistent with normal binocular combination. 19 The magnitude of the required contrast imbalance also provides a measure of the degree of suppression. 7,8 This is the procedure we used with our alternating strabismus participants.…”