日髙 聡太

The alternation of sounds in the left and right ears induces motion perception of a static visual stimulus (SIVM: Sound-Induced Visual Motion). In this case, binaural cues were of considerable benefit in perceiving locations and movements of the sounds. The present study investigated how a spectral cue - another important cue for sound localization and motion perception - contributed to the SIVM. In experiments, two alternating sound sources aligned in the vertical plane were presented, synchronized with a static visual stimulus. We found that the proportion of the SIVM and the magnitude of the perceived movements of the static visual stimulus increased with an increase of retinal eccentricity (1.875-30 degrees), indicating the influence of the spectral cue on the SIVM. These findings suggest that the SIVM can be generalized to the whole two dimensional audio-visual space, and strongly imply that there are common neural substrates for auditory and visual motion perception in the brain. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Background: Vision provides the most salient information with regard to stimulus motion, but audition can also provide important cues that affect visual motion perception. Here, we show that sounds containing no motion or positional cues can induce illusory visual motion perception for static visual objects. Methodology/Principal Findings: Two circles placed side by side were presented in alternation producing apparent motion perception and each onset was accompanied by a tone burst of a specific and unique frequency. After exposure to this visual apparent motion with tones for a few minutes, the tones became drivers for illusory motion perception. When the flash onset was synchronized to tones of alternating frequencies, a circle blinking at a fixed location was perceived as lateral motion in the same direction as the previously exposed apparent motion. Furthermore, the effect lasted at least for a few days. The effect was well observed at the retinal position that was previously exposed to apparent motion with tone bursts. Conclusions/Significance: The present results indicate that strong association between sound sequence and visual motion is easily formed within a short period and that, after forming the association, sounds are able to trigger visual motion perception for a static visual object.

We used a questionnaire to investigate how non-researchers conceptualize sense of presence. Respondents were 108 students with no professional education related to engineering or virtual reality. More than 90% of the respondents knew of the term, but they tended to use sense of presence not only to refer to a subjective experience of being there in a mediated environment, but also to refer to an experience that makes them feel excited or as having an extraordinary experience in an actual environment. Factor analysis revealed four sense of presence components: evaluation, impact, activity, and mechanicalness. Events with high presence were likely to be evaluated as preferred, impressive, and dynamic. Furthermore, the participants estimated that distal and proprioceptive sensors such as vision, audition, equilibrium, and kinesthesis were closely related to a sense of presence. These results suggest that sense of presence is not a single and simple concept for non-researchers, but is instead an ambiguous and the multidimensional construct with modality-selectivity. These aspects of sense of presence must be considered in specifying physical factors for high presence and establishing objective measures of sense of presence.

Background: Audition provides important cues with regard to stimulus motion although vision may provide the most salient information. It has been reported that a sound of fixed intensity tends to be judged as decreasing in intensity after adaptation to looming visual stimuli or as increasing in intensity after adaptation to receding visual stimuli. This audiovisual interaction in motion aftereffects indicates that there are multimodal contributions to motion perception at early levels of sensory processing. However, there has been no report that sounds can induce the perception of visual motion. Methodology/Principal Findings: A visual stimulus blinking at a fixed location was perceived to be moving laterally when the flash onset was synchronized to an alternating left-right sound source. This illusory visual motion was strengthened with an increasing retinal eccentricity (2.5 deg to 20 deg) and occurred more frequently when the onsets of the audio and visual stimuli were synchronized. Conclusions/Significance: We clearly demonstrated that the alternation of sound location induces illusory visual motion when vision cannot provide accurate spatial information. The present findings strongly suggest that the neural representations of auditory and visual motion processing can bias each other, which yields the best estimates of external events in a complementary manner.

In the present research, we investigated the depth information contained in the representations of apparently moving 3-D objects. By conducting three experiments, we measured the magnitude of representational momentum (RM) as an index of the consistency of an object's representation. Experiment 1A revealed that RM magnitude was greater when shaded, convex, apparently moving objects shifted to a flat circle than when they shifted to a shaded, concave, hemisphere. The difference diminished when the apparently moving objects were concave hemispheres (Experiment 1B). Using luminance-polarized circles, Experiment 2 confirmed that these results were not due to the luminance information of shading. Experiment 3 demonstrated that RM magnitude was greater when convex apparently moving objects shifted to particular blurred convex hemispheres with low-pass filtering than when they shifted to concave hemispheres. These results suggest that the internal object's representation in apparent motion contains incomplete depth information intermediate between that of 2-D and 3-D objects, particularly with regard to convexity information with low-spatial-frequency components.

Thus far, it has been pointed out that motion representation is completed in motion trajectory, and that motion representation interferes with a single physical input at a specific time and space in the motion trajectory. However, it has not been fully investigated whether the internal motion representation could interact with multiple physical inputs across time and space in motion trajectory. Thus, the current research investigated whether spatiotemporally coherent motion perception could be established in a situation involving the spatiotemporal reversal of motion sequences. In a five-point motion display, we found that the motion direction perception of the last two stimuli containing the spatiotemporal reversal was consistent with three preceding stimuli. This failure to perceive motion direction reversal occurred when the shapes of motion trajectory (to upper or lower) were randomly changed. Moreover, we con formed that one preceding stimulus (three-point motion) was sufficient to produce the failure to perceive motion direction reversal, and the effect of the prior stimuli saturated when the preceding sequence contained two or more stimuli. These findings suggest that the flexible internal motion representation mechanisms reorganize the spatiotemporal irregularities in motion trajectory and establish spatiotemporally coherent motion perceptions.

Apparent motion is perceived when two objects are presented alternately at different positions. The internal representations of apparently moving objects are formed in an apparent-motion path which lacks physical inputs. We investigated the depth information contained in the representation of 3-D moving objects in an apparent-motion path. We examined how probe objects-briefly placed in the motion path-affected the perceived smoothness of apparent motion. The probe objects comprised 3-D objects which were defined by being shaded or by disparity (convex/concave) or 2-D (flat) objects, while the moving objects were convex/concave objects. We found that flat probe objects induced a significantly smoother motion perception than concave probe objects only in the case of the convex moving objects. However, convex probe objects did not lead to smoother motion as the flat objects did, although the convex probe objects contained the same depth information for the moving objects. Moreover, the difference between probe objects was reduced when the moving objects were concave. These counterintuitive results were consistent in conditions when both depth cues were used. The results suggest that internal representations contain incomplete depth information that is intermediate between that of 2-D and 3-D objects.