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The alternation of dominance and suppression in a binocular-rivalry situation is involved closely in visual consciousness and unconsciousness. Therefore, binocular rivalry has recently been highlighted as a useful psychophysical phenomenon for the study of consciousness. However, we point out that the conventional method since Breese (1899) that rivalrous stimuli to the two eyes are presented simultaneously and for a long time has a fatal flaw for approaching the fundamental mechanisms underlying rivalry and, at the same time, our new method called "the suppression method" is, however, useful.

The synchronization hypothesis is the likely idea for the binding problem in the brain. Here we tested whether the theory is applicable for the occurrence of either binocular fusion or binocular rivalry. We first showed patterns of activated patches in V1 with proceeding from fusion to rivalry on the basis of Hubel and Wiesel's 1979 illustration. We then assumed that the strength of synchrony between the patches in the left-eye and right-eye ocular dominance columns is a crucial determinant for the divergence between fusion and rivalry. By using the strength of fusion between the paired images as a measure of degree of synchrony, we confirm the assumption about interocular vision and the synchronization hypothesis as well.

Singer's group and we found synchronized oscillatory responses at early stages and at a final stage in visual processing, respectively. However, the former occurs on a millisecond time scale and the latter on a second time scale. We have considered that this results from a difference in scale of something which takes part in the oscillations. From this viewpoint, here we first find suppression effects on both figure and ground of a pattern and on only the ground in a binocular-rivalry situation and then examine, using the effects of two steps, what oscillates and synchronizes at the last stage for form. Finally, we conclude that the synchronous neuronal oscillations depend on firing patterns of neurons at early stages in the visual system and the psychophysical ones on configurations of the spread effect of strength of pattern involved closely in whole processing of the visual system and the latter originates in the former.

When certain elements in a pattern are replaced by colored lines, a spreading of neon-like color can be seen around the lines. Using a variety of neon displaying patterns, we hypothesize that two conditions are critical to the neon effect. One is the occurrence of illusory contours and another a decrease in strength of pattern of the colored lines. On the basis of the two conditions, various phenomena of the neon effect are discussed. Finally, examining the striking characteristics of the neon effect, the vagueness of the colored lines and the spreading of the color of the colored lines over an illusory area wherein the color stimulus does not exist, we conclude that the neon effect is caused by synchronization of strength of pattern.

The generation of illusory contours is closely related to distinct parts of a pattern such as dots, line ends, and corner points. On the other hand, the remarkable property is that gaze at one point of the contours diminishes the illusion and a return of gaze to the whole pattern restores it. Therefore, illusory contours depend on local parts and the whole pattern formed by the parts, and fitting data on the two aspects is necessary to clarify underlying mechanisms. We have obtained such data from the experiments performed to elucidate other visual phenomena. On the basis of the data, the concepts of strength of pattern, strength of its spread effect, ridgelines of the spread effect, and a hollow of the spread effect are introduced and then various phenomena on illusory contours, including the Kanizsa triangle, are explained in terms of these concepts.

Both geometrical illusions and illusory contours were facilitated by slight vibration. This suggests that they are produced by similar mechanisms.

There are two important problems in anorthoscopic perception. The first is how a sequence of parts of a figure viewed through a slit is integrated into a whole. The second is how the distortion of an anorthoscopic image along the direction of its motion occurs. To answer the questions, two experiments and two demonstrations were performed by conceiving compound figures of one horizontal and one curvilinear component and a method which permits seeing anorthoscopic and ordinary images at the same time. From the results, the idea of anorthoscopic motion complementary to apparent motion is introduced as a crucial determinant that permits an integration of the parts into a perception of the whole. As regards the distortion of the percept we agree with Rock, et al.'s 1987 assumption but also consider that the distortion depends on the ratio of speed of anorthoscopic motion to real motion.

Two experiments were performed to examine where anorthoscopic images appear. In Exp. 1, in which a narrow slit was used, the images were seen as spatially compressed, but also as spatially displaced along each direction of movement even when two patterns were moved simultaneously and in different directions. These results are incompatible with the retinal painting hypothesis. In Exp. 2, in which a wider slit was used, anorthoscopic images appeared immediately after a pattern entered and left the slit. The two images were considered to depend on temporal changes of parts of a pattern passing across left and right edges of the slit, respectively.

The experiments in which the strengths of pattern and of fusion differing in kind from brightness were used as measures indicated that the visual system could distinguish between illuminance and reflectance. From this result and an observation of gray papers by a microscope, it is assumed that luminance has two aspects, one refers to the macroscopic density of photons and another to the proportion of the reflected microscopic areas to the absorbed microscopic areas so that brightness constancy occurs in relation to each of the patterns of the various sizes from a macroscopic pattern visible to the naked eye to a microscopic pattern not visible. It is also mentioned that the strength of fusion is rare but promising as a measure for analyzing brightness.

It was assumed that there is a variable, named "strength of fusion," underlying binocular fusion and rivalry. The strength of fusion is the resistance of the fused left- and right-eye patterns to separation. The first task was to obtain a measure of the strength of fusion and the second to examine the strength of fusion as a function of various differences of the patterns. The experiments showed that the angular separation only in the temporalward direction could be used as an appropriate measure of the strength of fusion and its value was maximum when the patterns were identical and decreased as the difference increased. This result supports the assumption about the strength of fusion.

The predominance of the strength of pattern over the strength of suppression during binocular rivalry has generally been defined as the percentage of total time of appearance. Is this fit for an index of the predominance? Theoretically, the strengths of pattern and suppression periodically oscillate throughout the observation period. From this assumption, the best fitting indices of predominance were examined. The simplest model of the visual system was one in which the periodicity of the two originates was expressed by a differential equation. Various indices were examined by the solution of its equation so that a power function of the ratio of the time of appearance to that of disappearance was obtained as the most suitable index of the predominance.

The effect of suppression in binocular rivalry is divided into the effects of boundary and of region. By removing the effect of boundary from the double effects, we examined whether the strength of pattern oscillates throughout duration of suppression phase. Probabilities of appearance of the suppressed test patterns were measured immediately after the removal of the suppressing pattern at various temporal points after onset of suppression. The probabilities decrease, reach a minimum level, and then increase throughout the course of the suppression phase. Immediately after the beginning of the suppression phase, the small test pattern whose duration of suppression is short rarely appears, while the large pattern whose duration of suppression is long certainly appears. These results support our hypothesis for which the key assumption is that the strength of pattern periodically oscillates as a function of duration of observation time.

A method for analyzing the temporal suppression mechanism in binocular rivalry is described. A test pattern was presented to one eye and a suppressing pattern to the other eye after varying time intervals. The subject was instructed to report the frequency of nonsuppression phases of the test pattern immediately after presentation of the suppressing pattern. Analysis indicated that the test pattern was never suppressed at the 0-msec. stimulus onset asynchrony and the nonsuppression probabilities decreased as the onset asynchrony increased. Moreover, resistivity to contralateral suppression was greater when the test pattern was projected to the dominant eye.

A method for measuring the strength of suppression of a suppressing pattern is examined. The test pattern was a black filled circle 1 degree in diameter and suppressing patterns were black outline circles 1, 1.2, 1.5, 2, 3, and 4 degrees in inner diameter, respectively. Each subject (2 men, 2 women) was asked to report the frequency of suppression phases of the test pattern immediately after presentation of the suppressing pattern. Analysis indicated that the method used is effective as a way of analyzing the rivalry process and the effect of eyedness.