A study of interocular motion mechanisms in human visual systems.

摘要

Background. Previous studies have postulated that target motion is processed by two, possibly three, independent visual motion mechanisms. The two motion systems of interest in this dissertation are "first-order systems", which are thought of as low-level, reflexive detectors of spatio-temporal variations in luminance; and feature-tracking or "third-order" systems, which are considered to be high-level, attention driven detectors of feature position changes over time. In the case of interocular motion, where successive images of a moving target appear in alternate eyes, literature has provided conflicting evidence regarding which system is responsible for processing motion signals. The following dissertation presents experiments using psychophysical methods, eye movement recordings and retinal image analysis to investigate the characteristics of interocular motion mechanisms. Methods. In experiment one we used the "motion contrast paradox" effect previously reported, to investigate the level at which such contrast interactions occur in motion processing. We measured two-frame motion thresholds for 1-cpd vertical Gabor patches that were presented binocularly, dichoptically, and interocularly either with matched low, matched high, or mixed contrast sequences. In experiment two, we investigated whether interocular motion processing was dependent on perceiving changes in positions of targets or whether its processing was consistent with position-motion dissociation. This was accomplished by measuring sensory fusion ranges and two-frame motion thresholds for horizontal Gaussian lines presented with various stimulus-onset-asynchronies. In experiment three we derived pursuit eye movement correlograms to investigate reflex and attention-driven response modes in first-order (horizontal luminance gratings), feature tracking (dynamic random dot stereogram) and interocular (spatio-temporal quadrature gratings) motion stimuli. In experiment four we investigated whether fixation eye movements adversely affected monocular motion thresholds. Two frame motion thresholds and simultaneous retinal imaging was accomplished by adapting the scanning raster of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). Results. (i) Mechanisms producing the contrast interactions observed with motion receive input after binocular combination of contrast signals; (ii) Interocular motion exhibited position-motion dissociation for short SOAs; (iii) Interocular motion stimuli produced pursuit eye movement correlograms with distinct reflexive components; (iv) In the presence of spatial references, motion thresholds were not dependent on fixation eye movements, however in the absence of references, fixation eye movements adversely affected motion thresholds. Conclusions. Interocular motion is processed by first-order interocular motion systems. These interocular motion systems are relatively weak and may be limited by binocular fusion mechanisms. Furthermore, it is unlikely that eye movements are solely responsible for the elevation of interocular motion thresholds.