Shigeru Ichihara

Hearing visual motion in depth

Auditory spatial perception is strongly affected by visual cues. For example, if auditory and visual stimuli are presented synchronously but from different positions, the auditory event is mislocated towards the locus of the visual stimulus—the ventriloquism effect. This ‘visual capture’ also occurs in motion perception in which a static auditory stimulus appears to move with the visual moving object. We investigated how the human perceptual system coordinates complementary inputs from auditory and visual senses. Here we show that an auditory aftereffect occurs from adaptation to visual motion in depth. After a few minutes of viewing a square moving in depth, a steady sound was perceived as changing loudness in the opposite direction. Adaptation to a combination of auditory and visual stimuli changing in a compatible direction increased the aftereffect and the effect of visual adaptation almost disappeared when the directions were opposite. On the other hand, listening to a sound changing in intensity did not affect the visual changing-size aftereffect. The results provide psychophysical evidence that, for processing of motion in depth, the auditory system responds to both auditory changing intensity and visual motion in depth.

Span of attention, backward masking, and reaction time

A test pattern consisting of 0 to 15 dots and a following random dot masking pattern were presented for 5 msec each with SOAs varying between 30 and 200 msec. The subject was asked to report the perceived number of dots in the test pattern as soon as possible and to assign a confidence rating to each report. The span of attention (upper limit for 50% correct numerosity judgments) increased from 2.4 to 9.5 as the SOA increased. Backward masking reduced the reported number of dots from the actual number in the test pattern, especially with small SOAs. Reaction time increased linearly at a low rate (approximately 40 msec/dot) up to 4 dots in the test pattern and then increased linearly at a high rate (approximately 370 msec/dot) as thereported, orperceived, number of dots increased. The two different branches of the reaction time curve were considered to represent two separate processes,subitizing andcounting, as suggested by Klahr (1973), who found similar dual increase rates as a function of the actual number of dots. These findings, as well as causal inference based on partial correlations and path analysis, indicated that the reported (perceived) number of dots and confidence rating were both determined by the number of stimulus dots and the SOA and that the reaction time was determined by the so-determined perceived number of dots and level of confidence. A multistage model is proposed.

Contrast and Depth Perception: Effects of Texture Contrast and Area Contrast

Many objects in natural scenes have textures on their surfaces. Contrast of the texture surfaces (the texture contrast) reduces when the viewing distance increases. Similarly, contrast between the surfaces of the objects and the background (the area contrast) reduces when the viewing distance increases. The texture contrast and the area contrast were defined by the contrast between random dots, and by the contrast between the average luminance of the dot pattern and the luminance of the background, respectively. To examine how these two types of contrast influence depth perception, we ran two experiments. In both experiments two areas of random-dot patterns were presented against a uniform background, and participants rated relative depth between the two areas. We found that the rated depth of the patterned areas increased with increases in texture contrast. Furthermore, the effect of the texture contrast on depth judgment increased when the area contrast became low.

The selective effect of the image of a hand on visuotactile interactions as assessed by performance on the crossmodal congruency task

Seeing one’s own body (either directly or indirectly) can influence visuotactile crossmodal interactions. Previously, it has been shown that even viewing a simple line drawing of a hand can also modulate such crossmodal interactions, as if viewing the picture of a hand somehow primes the representation of one’s own hand. However, factors other than the sight of a symbolic picture of a hand may have modulated the crossmodal interactions reported in previous research. In the present study, we examined the crossmodal modulatory effects of viewing five different visual images (photograph of a hand, line drawing of a hand, line drawing of a car, an U-shape, and an ellipse) on tactile performance. Participants made speeded discrimination responses regarding the location of brief vibrotactile targets presented to either the tip or base of their left index finger, while trying to ignore visual distractors presented to either the left or right of central fixation. We compared the visuotactile congruency effects elicited when the five different visual images were presented superimposed over the visual distractors. Participants’ tactile discrimination performance was modulated to a significantly greater extent by viewing the photograph of a hand than when viewing the outline drawing of a hand. No such crossmodal congruency effects were reported in any of the other conditions. These results therefore suggest that visuotactile interactions are specifically modulated by the image of the hand rather than just by any simple orientation cues that may be provided by the image of a hand.

Vision of a pictorial hand modulates visual-tactile interactions

The participants in this study discriminated the position of tactile target stimuli presented at the tip or the base of the forefinger of one of the participants’ hands, while ignoring visual distractor stimuli. The visual distractor stimuli were presented from two circles on a display aligned with the tactile targets in Experiment 1 or orthogonal to them in Experiment 2. Tactile discrimination performance was slower and less accurate when the visual distractor stimuli were presented from incongruent locations relative to the tactile target stimuli (e.g., tactile target at the base of the finger with top visual distractor) highlighting a cross-modal congruency effect. We examined whether the presence and orientation of a simple line drawing of a hand, which was superimposed on the visual distractor stimuli, would modulate the cross-modal congruency effects. When the tactile targets and the visual distractors were spatially aligned, the modulatory effects of the hand picture were small (Experiment 1). However, when they were spatially misaligned, the effects were much larger, and the direction of the cross-modal congruency effects changed in accordance with the orientation of the picture of the hand, as if the hand picture corresponded to the participants’ own stimulated hand (Experiment 2). The results suggest that the two-dimensional picture of a hand can modulate processes maintaining our internal body representation. We also observed that the cross-modal congruency effects were influenced by the postures of the stimulated and the responding hands. These results reveal the complex nature of spatial interactions among vision, touch, and proprioception.

Influence of the body on crossmodal interference effects between tactile and two-dimensional visual stimuli

We investigated how tactile discrimination performance was interfered with by irrelevant two-dimensional visual stimuli using the crossmodal interference task. Participants made speeded discrimination responses to the location of vibrotactile targets presented to either tip or base of their forefinger, while trying to ignore simultaneously presented visual distractors presented to either side of the central fixation on a front display. The array of visual distractors was presented at four different angles, and the participants rested their stimulated hand on a desk in either a forward-pointing or inward-pointing posture. Although there was apparently no specific spatial relationship between the tactile and two-dimensional visual stimuli arrays and the spatial response requirement was controlled, visuotactile interference effects occurred between them. Moreover, we found that the spatial relationships between the arrays depended on the potential range of movement and the current posture of the vibrotactile-stimulated hand and possibly the stored orientation of our hand representation, even without any explicit cue referring to hands. Our results suggest that the visuotactile spatial interactions involve multiple mechanisms regarding our bodily perception and our internal body representation.

Reduction in sensitivity to radial optic-flow congruent with ego-motion.

Visual motion, such as radial optic flow, is an important cue for perceiving direction during ego-motion. Several previous studies have reported that the perceived speed of a radial optic flow is underestimated when the represented ego-motion direction between radial optic flow and non-visual (such as vestibular or/and proprioceptive) information is congruent. In the present study, we examined whether sensitivity to different types of optic flow (radial vs. laminar) interacts with vestibular input in different ways by using another method: instead of estimating the perceived speed of the visual motion pattern, we measured motion-coherence thresholds. The results indicated that when the heading direction was represented by a radial optic-flow pattern, the radial optic-flow sensitivity was significantly lower under the condition where the visual and vestibular sensory input were congruent with the ego-motion direction than under the condition where the visuo-vestibular input and ego-motion were incongruent. These results indicated that radial optic-flow sensitivity was decreased by the congruent vestibular input during the ego-motion event. On the other hand, when the direction of ego-motion was represented by a laminar optic flow, the results were different from those observed with radial optic flows. These data suggest that vestibular input has some effect on optic-flow sensitivity but that the magnitude of the effect of vestibular input may differ between distinct flow patterns such as radial and laminar optic flows.

Attentional Bias to Direct Gaze in a Dot-Probe Paradigm

Previous research has suggested that a singly presented facial stimulus having a direct gaze holds spatial attention. This study examined whether facial stimulus having a direct gaze can also capture spatial attention in a relative dot-probe paradigm (facial stimulus having a direct gaze was presented concurrently with that having an averted gaze). The results showed that participants oriented their spatial attention to a facial stimulus having a direct gaze rather than to that with an averted gaze. This attentional bias depended on gaze-perception mechanisms as observed in the lack of attentional bias to a direct gaze from unnatural-looking eyes (i.e., white pupil/iris and black sclera). These findings raise the possibility that the attentional effect implicated in the perception of a direct gaze is induced regardless of the stimulus context.

Asymmetric perception of radial expansion/contraction in Japanese macaque (Macaca fuscata) infants.

Visual radial expansion/contraction motion provides important visual information that is used to control several adaptive actions. We investigated radial motion perception in infant Japanese macaque monkeys using an experimental procedure previously developed for human infants. We found that the infant monkeys’ visual preference for the radial expansion pattern was greater than that for the radial contraction pattern. This trend towards an “expansion bias” is similar to that observed in human infants. These results suggest that asymmetrical radial motion processing is a basic visual function common to primates, and that it emerges early in life.

How finger movement speed affects braille pattern recognition

Many researchers indicate the importance of temporal aspects of braille reading (Grunwald, 1966; Millar, 1987).The purpose of this study was to determine whether braille pattern recognition depends on finger movement speed using a learning transfer paradigm. The participants performed the braille recognition task during nine blocks under one finger movement speed condition, and were then tested under the other finger movement speed. The results of this experiment demonstrate that training enhances the performance in spite of finger movement speed. Even if a participant experiences training in the fast condition, performance in the slow condition is improved. Thus, this result is suggested that Braille pattern recognition does not depend on finger movement speed.