Monocular and binocular rivalry between contours.

The temporal characteristics of binocular and monocular rivalry between orthogonal gratings of the same or complementary colours were investigated. Rivalry was measured in terms of the dominance of either grating or the visibility of composites comprised of parts of both gratings. The total duration for which either grating was dominant was significantly longer in binocular rivalry between gratings of complementary colours. A comparison of binocular and monocular rivalry indicated considerable phenomenal differences between them. Dominance in binocular rivalry corresponds to the visibility of one grating alone; this occurs rarely in monocular rivalry, which is characterized by fluctuations in the distinctiveness of the gratings. The changes in distinctiveness are influenced by colour in a similar manner to that in binocular rivalry, and the frequencies of fluctuations are higher for gratings of complementary colours.     

Possible monocular predictors of binocular rivalry of contours

An analysis of contour disappearances in conflicting patterned stereograms is made from the knowledge of two monocular events: contrast effects associated with contours and phasic local adaptation. It is argued that the percepts resulting from these monocular processes are combined simply by some more central process and that a suppression mechanism may not be necessary to account for contour rivalry. Predictions were tested in three experiments and the results tend to support the argument given.     

Haploscopic colour mixtures with and without contours in subjects with normal and disturbed binocular vision

Binocular mixtures of equiluminous components of different wavelengths were matched with additive monoptic mixtures of the same components. After a satisfactory match had been achieved, the luminance of each colour in the monoptic mixture was measured photometrically. After presentation of an orthogonal grating superimposed on the colour shown to one eye, the colour matching was repeated. The grating induced a strong dominance of the colour with which it was combined. Yet the uncontoured colour was not entirely suppressed, but contributed to the binocular colour to various degrees. In three subjects with anisometropic amblyopia in one eye the colour presented to the amblyopic eye contributed little or nothing to the haploscopic colour mixture, depending on the degree of amblyopia. This diminished contribution could not be enhanced by a grid. In three cases with strabismic amblyopia and in one case with strabismus alternans no haploscopic colour mixture effects could be demonstrated. The observations are discussed in the context of neurophysiological findings in the visual system of primates, and it is suggested that colour and contour are not transmitted through independent channels from the retina to the cortex.     

A simple device for producing synchronous and asynchronous binocular flicker

Many studies on binocular integration have compared in-phase and out-of-phase flicker stimulation. A new method of producing such stimulation is described. It differs from previous designs in that a combination of polarizers is used rather than mechanical light choppers or electronic flashers. The arrangement produces sinusoidal luminance pulses that can be presented with any degree of asynchrony between the two eyes.     

The relationship between binocular brightness matches and luminance difference discriminability of successively presented light flashes1

Measurements of monocular ΔI and PSE as a function of the ISI between two 2-deg foveal fields successively presented to the same retinal area were obtained for two Standard durations, using the method of constant stimuli. Binocular brightness matches of the stimuli revealed that detection of a difference occurred whenever a constant difference (in log mL) in matching luminance existed. The implication of the results was that ΔI is related to the rate of change of brightness with changes in test-field luminance.     

Effect of ramp-like contours upon perceived size and detection threshold

Perceived widths and detection thresholds were measured for foveally viewed stimuli which were edged on two sides by luminance ramps. Perceived width approximated the distance between the midpoints of the ramps. It varied with the width of the ramps, but was unaffected by a five-fold change in the luminance of the stimulus. The detection threshold was higher for a ramp stimulus than for a normal stimulus of the same apparent width. The relationship between perceived width and detectability is consistent with a theoretical treatment based upon receptive-field mechanisms.     

Effect of prolonged monocular deprivation (homogeneous illumination) on the CFF of the nonoccluded and occluded eye

Since previous research has shown that the exposure of one eye to a prolonged period of darkness produces an initial depression followed by an enhancement of the CFF in the nonoccluded eye, an attempt was made to determine whether a similar phenomenon could be demonstrated by using diffuse, homogeneous illumination as the monocular condition. Two experiments were conducted, in which the CFFs of the nonoccluded and the occluded eyes were measured before and then at various intervals during 3 days of unpatterned visual stimulation. No significant changes in performance were observed in either eye. It was concluded that the production of this unusual interocular effect is dependent upon an absence of visual stimulation per se rather than upon an absence of pattern vision. The results were related to Sharpless’s (1964) concept of “disuse of neural pathways,” a revision of the law of denervation.     

Focusing attention on overlapping and non-overlapping figures with subjective contours

In a series of five experiments we investigated whether observers could focus attention on a restricted visual area that was demarcated by Kanizsa-like subjective contours, and whether this effect also occurred in the case of overlapping figures. The task was a simple reaction time to a luminance increment and the basic finding was that reaction time was faster when the imperative stimulus fell inside the focus of attention than when it fell outside. The first two experiments showed that the extent of the attentional focus could be adapted to a region that was demarcated by subjective contours, thus extending the results of previous studies that used regions demarcated by real contours. The last three experiments showed that, regardless of the type of margins, focusing was more efficient for the figure that was perceived as lying in front in a pair of overlapping figures. Received: 21 December 1999  / Accepted: 23 August 2000     

Investigations of Flicker and Fusion: I. The Effect of Practice,Under the Influence of Various Attitudes,on the CFF

Hunt, J. M., Ed. Personality and the Behavior Disorders. (2 vols.) New York: Ronald Press, 1944. Pp. 1242. Reviewed by H. J. Eyesenck     

Binocular detection of positive and negative flashes

Binocular forced-choice detection rates were measured under conditions where both eyes received positive flashes, both eyes received negative flashes, and one eye received a positive flash while the other received a negative flash. When both eyes received the same kind of flash, both positive or both negative, detection rates were,greater than probability summation. When one eye received a positive flash while the other received a negative flash, detection rates were near a level expected on the basis of probability summation. It is concluded that, at the level of forced-choice detection. positive and negative flashes are detected as though they were separate, independent events.     

Simultaneous detection and recognition of chromatic flashes

Studies of simultaneous detection and recognition were performed to test alternative models of the detection process, signal detection theory and low-threshold theory. Sensitivity in a detection experiment was independent of whether the type of signal (red or green light flash) was known in advance, because only one type of s trial was possible, or was unknown because either stimulus could occur. When a recognition judgment was added to either a binary or rating-scale detection response, Ss were able to report the nature of the stimulus at better than chance levels even when they indicated that the stimulus was not detected. Since such performance occurred when Ss used detection responses likely to have been given only in the nondetect state, the data lead to the rejection of low-threshold theory.     

Effects of flicker-induced depth on chromatic subjective contours

Two experiments examined the dependence of illusory colors on boundary salience and depth stratification by using flicker-induced depth. The first used a subjective-contour stimulus that appeared as a translucent colored rectangle covering a set of inducing circles and a dark background. The circles were then flickered so as to be perceived as background, and the previously dark background moved forward and appeared as foreground. Simultaneously, the chromatic subjective contour was eliminated. In the second experiment, a subjective-contour (faces/vase-concentric squares) figure was tinted with the McCollough effect, which produced a strong subjective color edge. This edge was visible only with the faces/vase percept and not in the squares percept. Flickering the target locked it into the square configuration because in this case the flicker held the entire pattern in the same depth plane. This eliminated the subjective color edge. Depth stratification and subjective color blockage were maximal at a flicker rate of 6 Hz.     

Dichoptic interaction of visual structure and light flashes

Perceptual interaction between monocular flashes and different amounts of continuously visible target structure shown to the other eye was investigated. A response variable called dominance of the flashes is defined and found to be a direct function of flash intensity and an inverse function of contraocular target structure. The dominance variable is distinguished from subjective brightness of the flashes and subjective complexity of the targets. The observed effects are attributed to limited central processing capacity with increased informational load.