Kenzo Sakurai

Auditory induced bounce perception persists as the probability of a motion reversal is reduced.

When two identical targets move toward one another from opposite sides of a display and continue past one another along collinear trajectories, they can be perceived to either stream past or bounce off of one another. Streaming is the dominant perception in motion displays free of additional transients, while bouncing predominates when a transient (eg auditory or visual) is presented at the point of coincidence. We investigated whether the auditory induced bias towards bouncing would persist as the probability of a motion reversal was reduced by introducing a spatial offset either vertically in a 2-D display or in depth in a 3-D display. Offset conditions were combined with two auditory conditions (tone or no-tone at the point of coincidence) in the presence or absence of a central occluder. In conditions with no sound, streaming was reported on a clear majority of trials, regardless of spatial offset. When a transient tone was presented, reported motion reversals dominated and persisted for increasing verbal offsets up to 17.9 min of arc and for 3-D trajectory offsets up to 25.6 min of arc. The bounce-promoting effect of an auditory tone at the point of coincidence in stream/bounce displays persists in spite of rendering the visual motion sequence unambiguous and more consistent with streaming.

A new variant of the Ouchi illusion reveals Fourier-component-based processing.

We report that anomalous motion illusion in a new variant of the Ouchi figure is well predicted by the strength of its Fourier fundamentals and harmonics. The original Ouchi figure consists of a rectangular checkerboard pattern surrounded by an orthogonal rectangular checkerboard pattern, in which illusory relative motion between the two regions is perceived. Although this illusion has been explained in terms of biases in integrating one-dimensional motion signals to determine the two-dimensional motion direction, the physiological mechanism has not been clarified. With our new stimuli, which consisted of thin lines instead of rectangles, we found that the perceived illusion is drastically reduced when the position of each line element is randomly shifted. This is not predicted by simple models of local motion integration along the visible edges. We demonstrate that the relative amplitude of the relevant Fourier fundamentals and harmonics leads to a quantitative prediction. Our analysis was successfully applied to other variants of the Ouchi figure (Khang and Essock 1997 Perception 26 585–597), closely predicting the reported rating. The results indicate that the underlying physiological mechanism is sensitive to the Fourier components of the stimuli rather than the visible edges.

Depth perception, motion perception, and their trade‐off while viewing stimulus motion yoked to head movement

Observers viewed monocularly and binocularly a motion parallax display that simulated a vertically or horizontally corrugated sine wave surface. The stimulus consisted of an expanding/contracting dot motion that was yoked to a leftward/rightward or forward/backward head movement. The extent of perceived depth in the binocular condition was smaller than that in the monocular condition, but the extent of perceived motion was larger. We argue that any retinal motion produced by a head movement that the visual system is unable to convert into depth is seen as motion, and that a depth/motion trade-off occurs to a varying extent across different conditions, depending upon the amount of retinal motion that can be converted into depth.

Perceptual continuation and depth in visual phantoms can be explained by perceptual transparency

We try to explain perceptual continuation and depth in the visual-phantom illusion in terms of perceptual transparency. Perceptual continuation of inducing gratings across the occluder in stationary phantoms could be explained with unique transparency, a notion proposed by Anderson (1997 Perception 26 419–453). This view is consistent with a number of previous reports including that of McCourt (1994 Vision Research 34 1609–1617) who criticized the stationary phantom illusion from the viewpoint of his counterphase lightness induction or grating induction, which might involve invalid transparency. Here we confirm that the photopic phantom illusion (Kitaoka et al, 1999 Perception 28 825–834) really gives in-phase lightness induction and involves bistable transparency. It is thus suggested that perceptual continuation and depth in the visual-phantom illusion depend on perceptual transparency.

Last but Not Least

Here we draw attention to similarity between Petters effect and the visual phantom illusion. Phantoms are visible when the spatial frequency of the inducing grating is low or the occluder is thin, whereas phantoms are invisible when the spatial frequency of the inducing grating is high or the occluder is thick. Moreover, phantoms are perceived in front of the occluder when they are visible, whereas the occluder is seen in front of the inducing gratings when phantoms are invisible. These characteristics correspond to Petters effect, in which the thicker region tends to be perceived in front of the thinner region when two regions of the same lightness and of different sizes overlap, since ‘thick’ corresponds to low spatial frequency of the inducing grating or a thick occluder while ‘thin’ corresponds to high spatial frequency of the inducing grating or a thin occluder.

Two competing mechanisms underlying neon color spreading, visual phantoms and grating induction

Neon color spreading is closely related to the photopic visual phantom illusion, since these two completion phenomena are characterized by in-phase lightness induction, and the only difference in the stimulus configuration is the difference in the inducer height. This idea was supported by the present study. Neon color spreading showed almost the same function of critical spatial frequency as photopic visual phantoms (Experiment 1), and the critical spatial frequency was constant as the inducer height was changed (Experiment 2). We also examined the relationship between neon color spreading and grating induction (characterized by counterphase lightness induction) in critical spatial frequency (Experiment 3) and in magnitudes of lightness induction (Experiment 4) as a function of the inducer height. The inducer height at which in-phase (neon color spreading) appearance gave way to counterphase (grating) induction was approximately 0.1 deg. These results suggest that neon color spreading shares a common neural mechanism with the photopic visual phantom illusion and that this mechanism is different from, and competes with, the mechanism of grating induction.

Tactile Flow Overides Other Cues To Self Motion

Vestibular-somatosensory interactions are pervasive in the brain but it remains unclear why. Here we explore the contribution of tactile flow to processing self-motion. We assessed two aspects of self-motion: timing and speed. Participants sat on an oscillating swing and either kept their hands on their laps or rested them lightly on an earth-stationary surface. They viewed a grating oscillating at the same frequency as their motion and judged its phase or, in a separate experiment, its speed relative to their perceived motion. Participants required the phase to precede body movement (with or without tactile flow) or tactile flow by ~5° (44 ms) to appear earth-stationary. Speed judgments were 4–10% faster when motion was from tactile flow, either alone or with body motion, compared to body motion alone (where speed judgments were accurate). By comparing response variances we conclude that phase and speed judgments do not reflect optimal integration of tactile flow with other cues to body motion: instead tactile flow dominates perceived self-motion – acting as an emergency override. This may explain why even minimal tactile cues are so helpful in promoting stability and suggests that providing artificial tactile cues might be a powerful aid to perceiving self-motion.

Erratum: Tactile Flow Overrides Other Cues To Self Motion

A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.

Shape distortion illusion of flashed circles can be induced by dichoptic stimulation

Flash presentation of a circle alternating with its inward gradation pattern induces an illusory shape distortion: the circle appears as a polygon (e.g. hexagon) in a short period (Sakurai, 2014 VSS, ECVP). We investigated whether this shape distortion illusion occurs before or after binocular combination in the visual pathway by measuring the induction time (latency) of the illusion in dichoptic and monoptic stimulation conditions. Stereoscopic stimuli consisted of a circle of 3.5 deg in diameter and its inward gradation pattern on a white background, alternating at 2 Hz and located at 4.5 deg on the left or right side of a central fixation cross surrounded by a 15 deg square frame for fusion lock. In the dichoptic condition, the circle was presented to one eye and the gradation pattern was presented to the other eye. In the monoptic condition, both the circle and the gradation pattern were presented to the same eye. In the control condition, the circle was solely presented to one eye flashing at 2 Hz. Observers had their head fixed on a chin-and-forehead rest and viewed the display through a mirror stereoscope. They were asked to press a response key as soon as they noticed the shape distortion in each trial. Results showed that the latencies of this illusion in both dichoptic and monoptic conditions were shorter than that in the control condition. No significant difference in latency was found between the dichoptic and monoptic conditions. These results suggest that the shape distortion illusion occurs after binocular combination and that some cortical process responsive to curvatures is involved in this illusion. Meeting abstract presented at VSS 2015.

Seeing Further Than Your Nose

Among monocular depth cues, ocular parallax (first described formally by Brewster in 1844) remains mostly unknown, its role in perception still not investigated scientifically. Given that every single eye movement induces ocular parallax, it is a potentially useful depth cue. This paper is an attempt to revive interest in the topic. As a monocular depth cue, ocular parallax naturally leads us to consider its benefit for a monocularly enucleated individual. Throughout history, numerous illustrious personalities coped with this fate in various ways. Here, we consider some historical insights into the visual life of the erstwhile duke of Urbino, Federico da Montefeltro (1422–1482), warlord and patron to the painter Piero della Francesca, and the Japanese warlord, Masamune Date (1567–636), a vocal patron of exploration and the arts.