Rivalry Stimuli Research Articles

Mu rhythm modulation during changes of visual percepts

Cooperation between vision and somatomotor behavior, such as manual exploration of objects, suggests close functional coupling between the visual and sensorimotor systems. We observed this type of interaction in human volunteers during binocular rivalry while following the level of sensorimotor mu rhythm with a whole-scalp neuromagnetometer. The observers viewed a weak vertical grating in the lower visual field of one eye and a strong horizontal grating in the same spatial window of the other eye. When stationary, the weak grating was permanently invisible because of its low contrast and spatial frequency. A sudden brief drifting movement of the weak grating wiped out the dominant grating, and the weak grating became visible for less than the 3-s interval between the movements. The postcentral 8- to 15-Hz mu rhythm was found in six of nine observers, and its level increased transiently by 10–15%, starting about 450 ms after the beginning of the movement. The mu level was also enhanced by the actual disappearance of the stronger stimulus, when it occurred in random order with the rivalry stimuli. Identical visual motion, when not accompanied by a perceptual dominance change, produced only minor effects on the mu rhythm. Our results show that a change in visual percept, even with no real or imagined motor response, is associated with modified activity of the postcentral gyrus. This modification may reflect visuohaptic interactions and/or activity of the distributed cortical network implementing visually guided movements.

Rival ideas about binocular rivalry

Binocular rivalry has been used to investigate neural correlates of visual awareness. For this investigation to succeed, however, it is necessary to know what rivals during binocular rivalry. Recent work has raised questions about whether rivalry is between eyes or between stimuli. We find that stimulus rivalry occurs only within a limited range of spatial and temporal parameters—otherwise eye rivalry dominates.

Interocular Suppression Produced by Rivalry Stimuli: A Comparison of Normal and Abnormal Binocular Vision

This study compares interocular suppression in subjects with early strabismus and/or anisometropia with binocular rivalry suppression in subjects with normal binocular vision. A psychophysical test-probe paradigm was used to measure the changes in luminance-increment detection thresholds associated with periods of phenomenal suppression. In subjects with normal binocular vision, rivalry suppression induced by viewing orthogonally oriented grating pairs produced a distinctive wavelength-dependent change in visual sensitivity; specifically, there was a greater reduction in sensitivity for short (e.g., 450 nm) vs. middle or long wavelength stimuli (e.g., 560 nm). In contrast, subjects with abnormal binocular vision, regardless of the type of early abnormal visual experience, showed more reduction in sensitivity for a 560-nm stimulus than for the short-wavelength, 450-nm stimulus. Moreover, the pattern of sensitivity change in subjects with abnormal binocular vision was the same for suppression induced by either rivalry stimuli or stimuli that would normally promote fusion. The results clearly indicate that interocular suppression in subjects with abnormal binocular vision is qualitatively different from normal binocular rivalry. Evidently, the processes that mediate binocular rivalry are very susceptible to environmental influences during early vision development and can be disrupted easily.

Aftereffects in binocular rivalry.

Five experiments are reported in which the aftereffect paradigm was applied to binocular rivalry. In the first three experiments rivalry was between a vertical grating presented to the left eye and a horizontal grating presented to the right eye. In the fourth experiment the rivalry stimuli consisted of a rotating sectored disc presented to the left eye and a static concentric circular pattern presented to the right. In experiment 5 rivalry was between static radiating and circular patterns. The predominance durations were systematically influenced by direct (same eye) and indirect (interocular) adaptation in a manner similar to that seen for spatial aftereffects. Binocular adaptation produced an aftereffect that was significantly smaller than the direct aftereffect, but not significantly different from the indirect one. A model is developed to account for the results; it involves two levels of binocular interaction in addition to monocular channels. It is suggested that the site of spatial aftereffects is the same as that for binocular rivalry, rather than sequentially prior.

Stimulus complexity and rate of alternation in binocular rivalry.

Pairs of random figures representing four levels of complexity were presented in a binocular-rivalry situation to 12 student volunteer observers. The effect of different levels of complexity on the rate at which complete alternations of the rivalry stimuli occurred was assessed. Rate of alternation was significantly inversely related to the level of stimulus complexity.

Simultaneous disappearances of both images during binocular rivalry of contours and effect on eye-blink rate.

Simultaneous disappearances of both rivalry images were reported by 28 women who reported on the rivalry 3.2 degree diagonal rivalry contours for 10 min. of continuous viewing. The data support the notion that suppression of images during binocular rivalry is independent in both eyes. In a second study, 48 women reported simultaneous disappearances during the rivalry of 3.2 degree vertical and horizontal contours for 10 min. of continuous viewing under one of two blink-rate instruction conditions. Fewer simultaneous disappearances were reported by Ss instructed to blink every 5 sec. than by Ss instructed to blink every 15 sec. Blinking may reduce the probability of simultaneous disappearances in rivalry. In both studies, the fusion squares surrounding the rivalry stimuli were continuously perceived.

Ocular dominance reduced with practice.

Changes of ocular dominance were measured with binocular rivalry tests in 2 groups of Ss after 9 4-min. practice sessions. During the practice sessions one group passively viewed binocular rivalry and the second group attempted to reduce the magnitude of dominance by actively viewing rivalry. Passive viewing was ineffective but the active viewing group showed a significant reduction of ocular dominance when dominance was measured with the rivalry stimuli used in the practice sessions. Although only a single measure of ocular dominance was changed, the experiment suggests that more measures of ocular dominance may be changed by practice of active control of rivalry.

Binocular rivalry suppression: Insensitive to spatial frequency and orientation change

The selectivity of rivalry suppression, defined as sensitivity to new information presented during suppression, was measured by determining the detectability of changes in the suppressed rivalry stimulus. The stimulus was a vertical grating whose spatial frequency or orientation could be changed without altering contrast or mean luminance. Large changes in frequency and orientation were not detectable. Increments in contrast were detectable, but not decrements. Suppression is fundamentally nonselective, remaining insensitive to all classes of stimulus change except those constituting an energy increment.

A DEVELOPMENTAL STUDY OF RETINAL RIVALRY.

In a developmental study of retinal rivalry, 141 Ss were each tested for 3 consecutive minutes. Male and female Ss were selected from kindergarten, 2nd, 4th, 5th, 6th grades, and college students. The rivalry stimulus was a monocular horizontal line and a monocular vertical line (approximately 1 mm. retinal size). Reliability of Ss' report was checked using a simulated rivalry technique. Rivalry rate increased significantly as a function of age, and females' rates were higher at every age tested.