Perceptual dominance during binocular rivalry is prolonged by a dynamic surround.

We examined whether dynamic stimulation that surrounds a rival target influences perceptual alternations during binocular rivalry. We presented a rival target surrounded by dynamic random-dot patterns to both eyes, and measured dominance durations for each eye's rival target. We found that rival target dominance durations were longer when surrounds were dynamic than when they were static or absent. Additionally, prolonged dominance durations were more apparent when the dynamic surround was alternately presented between the two eyes than when it was presented simultaneously to both eyes. These results indicate that dynamic stimulation that surrounds a rival target plays a role in maintaining the current perceptual state, and causes less perceptual alternations during binocular rivalry. Our findings suggest that dynamic signals on the retina may suppress rivalry, and thus provide useful information for stabilizing perceptions in daily life.

[Decline of monocular contrast sensitivity during binocular fixation].

To investigate binocular single vision, we examined monocular contrast sensitivity during binocular fixation by changing the intervals between the beginning of fixation and a probe stimulus, within 10 seconds. Monocular contrast sensitivities were quite stable within 1s of the interval delay in both eyes, but they were reduced in either eye if the interval delay was more than 1s (Experiment 1). In Experiment 2, a similar stimulus was monocularly presented. In this case, decline of contrast sensitivity was not observed in either eye. In Experiment 3, when the stimulus was interrupted briefly before the probe presentation, the contrast sensitivity was recovered. These results suggest that after prolonged viewing the binocular system does not sustain either eye sensitivity equally unless there is interruption of the binocular stimulation.

Recovery from perceptual filling-in is gated by interocular matching.

We examined how the binocular visual system behaves during perceptual filling-in. In these experiments an initial filled-in target was replaced with an interocularly matched (fusible) or unmatched (rivalrous) target immediately after the disappearance of the initial target induced by perceptual filling-in. We measured the times for the target to recover from the filling-in. We found that recovery times were faster when the target was replaced with an interocularly matched target than with an unmatched target: The matched visual input was immediately released from perceptual suppression by filling-in but the unmatched one was not. These results indicate that even during perceptual filling-in our visual system can use the information whether the visual inputs from the two eyes are interocularly matched or not, and the interocular matching stage (the initial stage of binocular fusion or binocular rivalry) is not inhibited by the perceptual filling-in processing. Our findings suggest that the interocular matching processing may serve to gate visual inputs accessing visual awareness.

Local binocular fusion is involved in global binocular rivalry.

We examined whether interocular inhibition in binocular rivalry could occur at the interocular intersection of horizontal and vertical rectangular patches which are locally fusible but globally rivalrous between the two eyes. We measured contrast increment (and decrement) thresholds of a monocularly presented probe which was presented on the horizontal patch corresponding to the intersection. We found that the threshold was higher when the horizontal patch was perceptually suppressed than when it was dominant. In addition, threshold elevation did not occur when both patches were dominant, or when the horizontal patch was viewed in isolation. These results indicate that interocular inhibition occurs at the potentially fusible region, and the determination of binocular fusion or binocular rivalry does not depend on physical stimulus but rather perceptual state at the time.

The role of interword spacing in reading Japanese: an eye movement study.

The present study investigated the role of interword spacing in a naturally unspaced language, Japanese. Eye movements were registered of native Japanese readers reading pure Hiragana (syllabic) and mixed Kanji-Hiragana (ideographic and syllabic) text in spaced and unspaced conditions. Interword spacing facilitated both word identification and eye guidance when reading syllabic script, but not when the script contained ideographic characters. We conclude that in reading Hiragana interword spacing serves as an effective segmentation cue. In contrast, spacing information in mixed Kanji-Hiragana text is redundant, since the visually salient Kanji characters serve as effective segmentation cues by themselves.