Robert Fox

The psychophysical inquiry into binocular summation

Experiments that compare monocular and binocular visual performance of human psychophysical Os on a variety of visual tasks are reviewed. The review attempts to include all experiments published in English in this century, excluding work on stereopsis, rivalry, and evoked potentials. The concept of probability summation as a baseline for assessing the presence of neural summation is discussed, and the assumptions of several models for estimating probability summation are considered. Experiments are classified in terms of visual task, major categories being increment detection, flicker fusion, brightness magnitude, and contour resolution. A major conclusion is that binocular performance is superior for essentially all task categories and in most cases by a magnitude greater than that predicted by appropriate probability summation models.

Further developments in binocular summation

This paper reviews experiments that bear on the issue of binocular summation, the superiority of binocular over monocular viewing on various visual tasks covering studies published since the appearance of a previous review of this literature by Blake and Fox (1973). The experiments are grouped into three main categories—those that deal with the specificity of binocular summation (i.e., the extent to which inputs to the two eyes must coincide spatially and temporally), those that study binocular summation on suprathreshold tasks, and those that correlate binocular summation with other aspects of binocular function. The last section of the paper critically reviews several models of binocular summation.

Stochastic properties of binocular rivalry alternations

The extent to which binocular rivalry phases are sequentially related was assessed by theν statistic and by autocorrelation. Both measures indicate that the duration of successive phases are independent. The frequency distributions of suppression phases and of nonsuppression phases can be fitted by gamma distributions. These results are consistent with models of the rivalry process that incorporate independence assumptions.

Binocular rivalry suppression: Insensitive to spatial frequency and orientation change

Abstract 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.

Effect of binocular rivalry suppression on the motion aftereffect.

Abstract The relative loci within the visual system of the site of the motion aftereffect (MAE) and the site of binocular rivalry suppression was inferred by measuring the magnitude of the MAE when the inducing motion was phenomenally suppressed for > 50 per cent of the inspection period. The MAE magnitude was a function of the duration of physical impingement of the inducing stimulus; the state of suppression exerted no effect, thereby implying that the site of suppression does not occur before the site of the MAE. This result, together with other data, is interpreted to mean that the site of suppression is cortical.

Increment detection thresholds during binocular rivalry suppression

In two experiments, two-choice forced-choice duration thresholds for increment test flashes were estimated during phases of rivalry suppression and nonsuppression and for a nonrivalry monocular control condition. In both experiments thresholds of both eyes of each S were measured and, to maximize correct detections, feedback was given after every trial and Ss were relieved of the task of continually reporting changes in rivalry phases. Results of both experiments support the conclusion that suppression constitutes an elevation in threshold, on the order of .5 log units relative to thresholds found during nonsuppression and monocular conditions. These data, in concert with others, reinforce the general conclusion that rivalry suppression is an inhibitory state that nonselectively attenuates all classes of inputs falling within the spatial boundaries of the suppressed target.

Binocular rivalry and reciprocal inhibition

Any explanation of binocular rivalry based on a reciprocal inhibition mechanism would require that unilateral increases in the stimulus strength of the rivalry target in one eye produce increases in the mean nonsuppression duration of that eye and concommitant decreases in the mean nonsuppression duration of the contralateral eye. To test that hypothesis, the stimulus strength (in this case, contrast) of one rivalry target was varied (0.1, 1, 10, and 100 ft-L) while the strength of the target in the other eye remained constant. The data, obtained from six experienced Ss, indicate that variations in stimulus strength do not alter the mean nonsuppression duration of the recipient eye. This outcome offers a fundamental difficulty for the reciprocal inhibition concept. A model that assumes partially independent suppression and dominance mechanisms is suggested as a more adequate alternative.

Optokinetic nystagmus as an objective indicator of binocular rivalry

Abstract When each eye is separately stimulated by moving contours that generate antagonistic optokinetic nystagmus, vigorous phenomenal rivalry results, yet the nystagmus eye movements remain yoked and shift direction in accord with the eye that is phenomenally dominant. The feasibility of using this nystagmus rivalry as an indicator of phenomenal dominance was examined. The high correlation between phenomenal report and nystagmus rivalry, together with stochastic and stimulus similarities between nystagmus rivalry and conventional rivalry, support using nystagmus as an objective indicator.

Depth separation and lateral interference

In four experiments, the perceptual interaction between an annulus and a Landolt C enclosed within it was investigated as a function of their perceived relative depth positions and of the perceived lateral distance between the inner edge of the annulus and the outer edge of the C. To permit facile and unconfounded manipulation of perceived depth, the stimuli were stereoscopic contours formed from dynamic random-lement stereograms. Either one or both stimuli were visible continuously. The effect of the annulus on the Landolt C was assessed by forced-choice recognition thresholds of the C and by judgments of its apparent clarity. The main results were: (1) For both threshold recognition and apparent clarity, perceived depth separation has a strong effect on the strength of perceptual interaction; (2) the effect is asymmetrical in that the stimulus perceived as in front of its partner and closer to the observer has greater perceptual potency; and (3) as spacing between the elements increases, perceptual interaction declines independently of depth position. The implications of these data for general theories of stimulus interaction in three-dimensional space are discussed.

Temporal perturbations of binocular rivalry

Successive durations of binocular rivalry are sequentially independent, random variables. To explore the underlying control process, we perturbed the cycle during a 30-sec viewing period by immediately forcing an eye to return to dominance whenever it became suppressed. During this period of forced dominance, that eye’s individual dominance durations were unusually brief, but immediately following the period of forced dominance that eye’s suppression durations were unusually long. However, no long-term change in the sequential pattern of rivalry occurred, and the stochastic independence of successive durations was maintained during and following the period of forced dominance. The same pattern of results was obtained with even longer periods of forced dominance. These results are consistent with the existence of a short-term adaptation, or fatigue, process responsible for transitions from dominance to suppression.