Nobu Shirai

Asymmetry in the perception of motion-in-depth

We investigated the anisotropic responses between the detection of motion toward and motion away from the observers with expanding/contracting shaded circles. Our experiments followed visual search paradigm with two exceptions: (1) the stimulus presentation time was fixed for 300 ms and (2) the mean error rates were adopted as a dependent variable. In Experiment 1, targets and distractors were defined by expanding (or contracting) convex/concave circles. Results of Experiment 1 suggested that the human visual system is more sensitive to expanding convex circles (which create the impression of approaching objects) than others. In Experiment 2, the targets and distractors were defined by expanding (or contracting) step gradient (top-lighting/bottom-lighting) circles. The results of Experiment 2 suggest that the anisotropy for the perception of motion-in-depth should not be caused by change of luminance polarity but by change of shading cue.

Asymmetrical cortical processing of radial expansion/contraction in infants and adults

We report asymmetrical cortical responses (steady-state visual evoked potentials) to radial expansion and contraction in human infants and adults. Forty-four infants (22 3-month-olds and 22 4-month-olds) and nine adults viewed dynamic dot patterns which cyclically (2.1 Hz) alternate between radial expansion (or contraction) and random directional motion. The first harmonic (F1) response in the steady-state VEP response must arise from mechanisms sensitive to the global radial motion structure. We compared F1 amplitudes between expansion-random and contraction-random motion alternations. F1 amplitudes for contraction were significantly larger than those for expansion for the older infants and adults but not for the younger infants. These results suggest that the human cortical motion mechanisms have asymmetrical sensitivity for radial expansion vs. contraction, which develops at around 4 months of age. The relation between development of sensitivity to radial motion and cortical motion mechanisms is discussed.

Sensitivity to linear-speed-gradient of radial expansion flow in infancy.

A radial expansion flow having a linear-speed-gradient (linear-grad) creates robust perception of a rigid object moving-in-depth [Perception 19 (1990) 21]. It has been reported that sensitivity to a linear-grad of radial expansion emerges at 2 months of age [Infant Behavior and Development 17 (1994) 165]. In the present study, we examined the development of sensitivity to the linear-grad of radial expansion after 2 months of age with three experiments. A total of 197 2- to 5-month-old infants participated. The results showed that sensitivity to the linear-grad improves between 2 and 3 months of age (Experiment 1), and that the infants may discriminate between an expansion having linear-grad and that having zero-grad based on their perception of motion-in-depth (Experiments 2 and 3).

Infants' sensitivity to shading and line junctions.

We examined the sensitivity to shading and line junction cues in human infants aged 5-8 months using computer-generated displays containing a rectangular-wave grating and a serrated aperture. In Experiment 1, infants were presented with a pair of displays: a two-dimensional to three-dimensional (2D-3D) display, alternating between 2D and 3D images, and a 2D-2D display, alternating between two 2D images. The 3D image consisted of black-and-white borders aligned with the peaks of a serrated aperture, creating the appearance of a 3D folded surface. The 2D image consisted of the black-and-white borders misaligned with the peaks of a serrated aperture, which does not create a 3D impression for adults. Seven- and 8-month-old infants looked longer at the 2D-3D display than the 2D-2D display. In contrast, 5- and 6-month-old infants did not exhibit a looking preference. In Experiment 2, we used images with double-cycle rectangular-wave gratings to impair shading information. These images consisted of black-and-white borders aligned with half of the peaks and misaligned with latter half of the peaks of a serrated aperture, giving the appearance of surface markings. Seven- and 8-month-old infants did not exhibit a significant difference in preference between the two test displays. These results could not be explained by the young infants failure of discrimination due to the experimental procedure (Experiment 3). These results showed that the sensitivity to shading and line junctions change between 5-6 and 7-8 months of age.

More rapid and stronger vection in elementary school children compared with adults.

We compared vection (visually induced illusory self-motion perception) among elementary school children and adults by measuring latency to onset, cumulative duration, and estimated strength of vection. Significantly stronger vection with shorter latency was observed in children compared with adults. Several possible causes (eg size-difference of the effective visual field) of the age-related differences are discussed.

Asymmetry in the perception of motion in depth induced by moving cast shadows

An expanding object, which may represent an approaching motion, is easier to detect than a contracting one, which may represent a receding object. To confirm the generality of asymmetry in the detection of approaching and receding motions, we focused on the perception of apparent motion in depth created by moving cast shadows. The visual search for an approaching target among receding distractors was more efficient than for the opposite condition (Experiment 1). However, this asymmetry disappeared when a light shadow was added (Experiments 2 and 3). This suggests that the visual system is specialized to detect approaching motion defined by cast shadows, as well as other three-dimensional cues such as expanding motion and shading.

Perception of Elasticity in the Kinetic Illusory Object with Phase Differences in Inducer Motion

Background It is known that subjective contours are perceived even when a figure involves motion. However, whether this includes the perception of rigidity or deformation of an illusory surface remains unknown. In particular, since most visual stimuli used in previous studies were generated in order to induce illusory rigid objects, the potential perception of material properties such as rigidity or elasticity in these illusory surfaces has not been examined. Here, we elucidate whether the magnitude of phase difference in oscillation influences the visual impressions of an objects elasticity (Experiment 1) and identify whether such elasticity perceptions are accompanied by the shape of the subjective contours, which can be assumed to be strongly correlated with the perception of rigidity (Experiment 2). Methodology/Principal Findings In Experiment 1, the phase differences in the oscillating motion of inducers were controlled to investigate whether they influenced the visual impression of an illusory objects elasticity. The results demonstrated that the impression of the elasticity of an illusory surface with subjective contours was systematically flipped with the degree of phase difference. In Experiment 2, we examined whether the subjective contours of a perceived object appeared linear or curved using multi-dimensional scaling analysis. The results indicated that the contours of a moving illusory object were perceived as more curved than linear in all phase-difference conditions. Conclusions/Significance These findings suggest that the phase difference in an objects motion is a significant factor in the material perception of motion-related elasticity.

Looking Away Before Moving Forward Changes in Optic-Flow Perception Precede Locomotor Development

Voluntary locomotion is one of the most important motor actions performed by animals, including humans, and vision plays an important role in controlling such action. We conducted cross-sectional (Experiment 1) and longitudinal (Experiment 2) investigations and found that the perception of visual motion (optic flow), a critical cue for perceiving and controlling the direction of locomotion, drastically changes just before the emergence of locomotion in infancy. The results suggest that developmental change in particular visual perceptions precedes and potentially promotes the emergence of related motor actions in early development. Our findings offer a new perspective on the development of visuomotor coordination, which has long been thought to derive from the development of motor actions rather than from changes in visual perceptions.

Perception of Motion Transparency in 5-Month-Old Infants

We investigated the perceptual development of motion transparency in 3- to 5-month-old infants. In two experiments we tested a total of 55 infants and examined their preferential looking behaviour. In experiment 1, we presented transparent motion as a target, and uniform motion as a non-target consisting of random-dot motions. We measured the time during which infants looked at the target and non-target stimuli. In experiment 2, we used paired-dot motions (Qian et al, 1994 Journal of Neuroscience 14 7357 – 7366) as non-targets and also measured target looking time. We calculated the ratio of the target looking time to the total target and no-target looking time. In both experiments we controlled the dot size, speed, the horizontal travel distance of the dots, and the motion pattern of the dots. The results demonstrated that 5-month-old infants showed a statistically significant preference for motion transparency in almost all stimulus conditions, whereas the preference in 3- and 4-month-old infants depended on stimulus conditions. These results suggest that the sensitivity to motion transparency was robust in 5-month-olds, but not in 3- and 4-month-olds.

Infants’ perception of curved illusory contour with motion

Recently, Masuda et al. (submitted for publication) showed that adults perceive moving rigid or nonrigid motion from illusory contour with neon color spreading in which the inducer has pendular motion with or without phase difference. In Experiment 1, we used the preferential looking method to investigate whether 3-8-month-old infants can discriminate illusory and non-illusory contour figures, and found that the 7-8-month-old, but not the 3-6-month-old, infants showed significant preference for illusory contour with phase difference. In Experiment 2, we tested the validity of the visual stimuli in the present study, and whether infants could detect illusory contour from the current neon color spreading figures. The results showed that all infants might detect illusory contour figure with neon color spreading figures. The results of Experiments 1 and 2 suggest that 7-8-month-old infants potentially perceive illusory contour from the visual stimulus with phase-different movement of inducers, which elicits the perception of nonrigid dynamic subjective contour in adults.