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We investigated 3- and 4-month-old infants’ sensitivity to differences defined by shading using a paired-comparison familiarity/novelty preference procedure. Infants were familiarized with a pair of displays consisting of homogeneous shaded disks, and then were tested with two displays: the familiar display and a novel one containing shaded disks with reversed polarity (defined as the target). Experiment 1 examined two assumptions on discerning shapes from shading in infants by manipulating the orientations in the shading gradient of stimuli. When the orientation of the shading gradient was vertical, 4-month-old infants looked at the novel display for a longer time during the test trial. However, they failed to detect differences when the orientation of shading gradients was horizontal. Three-month-old infants did not detect differences in either orientation of the shading gradient. Experiment 2 examined asymmetry in the detection of convex versus concave shapes. Four-month-old infants failed to detect the target when the orientation of the shading grating was vertical and the target was convex. Taken with the results of Experiment 1, concave shapes were much easier to detect than convex shapes for 4-month-olds. This asymmetry suggests that 4-month-old infants process shading information in the same manner as adults.

When a movie presents a person walking, the background appears to move in the direction opposite to the person's gait. This study verified this backscroll illusion by presenting a point-light walker against a background of a random-dot cinematogram (RDC). The RDC consisted of some signal dots moving coherently either leftward or rightward among other noise dots moving randomly. The method of constant stimuli was used to vary the RDC in motion coherence from trial to trial by manipulating the direction and percentage of the signal dots. Six observers judged the perceived direction of coherent motion in a two-alternative forced-choice procedure. Response rates for coherent motion perception in the direction opposite to walking were evaluated as a function of motion coherence. The results showed that the psychometric function shifted toward the direction determined by a bias in the opposite direction to the walker. The mean threshold was about half as high as that in a control condition in which the positions of the point-lights were scrambled to impair the recognition of the walker. The results demonstrate that biological motion noticeably affects the appearance of motion coherence in the background.

When we measure the visual event-related potential (ERP), a subject has to fix eyes to a point on the display in an experimental situation or in a diagnosis on the visual function. Therefore, it is very hard to apply the event-related potential (ERP) to assessment of sensation and attention at clinical fields or at industrial settings. We developed a system to analyze the brain potential associated with offset of saccadic eye movements. The potential is called eye fixation-related potential (EFRP). EFRP is identical with the so-called visual ERP. We can measure the topographical change of EFRP in real time. The first system with a UNIX (Version 1) was very fast, but very expensive. However, the new system (Version 2) is more economical, because it can be used in a notebook computer with Windows XP. EEG and EOG data can be sampled in real time, although the data are analyzed offline. The new system will be useful to study cognitive factors under eye movement conditions.

When subjects made a saccade across a single-flashed dot, a flickering dot or a continuous dot, they perceived a dot, an array (phantom array), or a line (phantom line), respectively. We asked subjects to localize both endpoints of the phantom array or line and calculated the perceived lengths. Based on the findings of Matsumiya and Uchikawa (2001), we predicted that the apparent length of the phantom line would be larger than that of the phantom array. In Experiment 1 of the current study, contrary to the prediction, the phantom line was found to be shorter than the phantom array. In Experiment 2, we investigated whether the function underlying the filled-unfilled space illusion (Lewis, 1912) instead of the function underlying the saccadic compression could explain the results. Subjects were asked to localize both endpoints of a line or an array while keeping their eyes fixated. Although the results of Experiment 2 showed that the perceived length of a line was shorter than that of an array, the function underlying the filled-unfilled illusion could not fully account for the results of Experiment 1. To explain the present results, we proposed a model for the localization process and discussed its validity.

When observers make a saccade across a flickering light dot at the same location, they usually perceive an array of dots (Hershberger, 1987). This phenomenon can be exploited for presenting two-dimensional images using only a single dimensional light source such as a single column of LEDs or laser projectors. In the present study, we investigated whether the perceived length of saccade-induced images is modulated by relative position of the light source and the observer. Participants were presented with a continuous laser-lit dot at several different locations adjacent to a saccade target. On each trial, they were required to make a saccade from a fixation point to the saccade target and then to localize the two endpoints of perceived line induced by the saccade. The results showed that the perceived length of the saccade-induced lines was approximately a half of the distance between the fixation point and the saccade target regardless of the light source location.

Sixteen subjects sat in a rotating optokinetic drum and were instructed to stare moving vertical stripes inside of the optokinetic drum. Speeds of the stripes were five visual angles (12, 24, 36, 48, 60 deg/s). EEGs and EOGs were measured. EEG epochs were averaged at onset of slow phases (pursuits) of the optokinetic nystagmus (OKN). The positive component of latency of about 100 ms appeared predominantly at the occipital region of 15 subjects in all conditions. The positive component might be the same as the lambda response that appears in EFRP to a stationary object.

The variations of eye fixation related potentials (EFRPs) were examined in two tasks under three lighting conditions for assessment of lighting environments. Sixteen subjects participated in two tasks; a difficult and an easy reading task under three lighting conditions: Spot light (S), General light (G) and Mixed light (M). EEG (Oz) and EOG were recorded. EEG epochs time-locked to onset of eye fixations were collected at random and averaged separately in two arrays to obtain a pair of EFRPs. Two wave forms under the S were similar, although those under the G showed the disparity, the largest disparity being in the easy task under the G. Under the S, wave forms of EFRPs were stable in the difficult task. The amplitude changed with the task load. The results suggested that EFRPs might be an index of the work load under lighting conditions.

本実験では, 単調作業が事象関連電位の一種である眼球停留関連電位へ及ぼす影響について検討した. 10名の被験者に, 5分のトラッキングと3分の主観評価からなるブロックを12回, 計96分間の単調な作業を課した. その作業前後に特定の刺激に対して眼を動かすサッケイド課題を課し, 眼球停留関連電位を求めた. 眼球停留関連電位は, サッケイド終了時点を基準にして脳波を加算平均することにより得られる. その結果, 時間経過に伴って, エラー数増大などの行動量と覚醒感, 集中感の低下, 倦怠感, 疲労感の増加などの主観量に変動が認められた. さらに, 単調作業前後のサッケイド課題時の眼球停留関連電位を比較した結果, 作業後には潜時が約100msの正の電位のピーク振幅の減少が認められた. 以上の結果から, VDT作業による精神作業負荷を評価する指標として眼球停留関連電位が有効であることが示唆された.

The Craik-O’Brien-Cornsweet (COC) effect demonstrates that perceived lightness depends not only on the retinal input at corresponding visual areas but also on distal retinal inputs. In the COC effect, the central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. To investigate the underlying mechanisms of the effect, we examined whether the subjective awareness of the COC edge is necessary for the generation of the effect. We manipulated the visibility of the COC edge using visual backward masking and continuous flash suppression while monitoring subjective reports regarding online percepts and aftereffects of adaptation. Psychophysical results showed that the online percept of the COC effect nearly vanishes in conditions where the COC edge is rendered invisible. On the other hand, the results of adaptation experiments showed that the COC edge is still processed at the early stage even under the perceptual suppression. These results suggest that processing of the COC edge at the early stage is not sufficient for generating the COC effect, and that subjective awareness of the COC edge is necessary.

Human observers see a single mixed color (yellow) when different colors (red and green) rapidly alternate. Accumulating evidence suggests that the critical temporal frequency beyond which chromatic fusion occurs does not simply reflect the temporal limit of peripheral encoding. However, it remains poorly understood how the central processing controls the fusion frequency. Here we show that the fusion frequency can be elevated by extra-retinal signals during smooth pursuit. This eye movement can keep the image of a moving target in the fovea, but it also introduces a backward retinal sweep of the stationary background pattern. We found that the fusion frequency was higher when retinal color changes were generated by pursuit-induced background motions than when the same retinal color changes were generated by object motions during eye fixation. This temporal improvement cannot be ascribed to a general increase in contrast gain of specific neural mechanisms during pursuit, since the improvement was not observed with a pattern flickering without changing position on the retina or with a pattern moving in the direction opposite to the background motion during pursuit. Our findings indicate that chromatic fusion is controlled by a cortical mechanism that suppresses motion blur. A plausible mechanism is that eye-movement signals change spatiotemporal trajectories along which color signals are integrated so as to reduce chromatic integration at the same locations (i.e., along stationary trajectories) on the retina that normally causes retinal blur during fixation.

Background Observers misperceive the location of points within a scene as compressed towards the goal of a saccade. However, recent studies suggest that saccadic compression does not occur for discrete elements such as dots when they are perceived as unified objects like a rectangle. Methodology/Principal Findings We investigated the magnitude of horizontal vs. vertical compression for Kanizsa figure (a collection of discrete elements unified into single perceptual objects by illusory contours) and control rectangle figures. Participants were presented with Kanizsa and control figures and had to decide whether the horizontal or vertical length of stimulus was longer using the two-alternative force choice method. Our findings show that large but not small Kanizsa figures are perceived as compressed, that such compression is large in the horizontal dimension and small or nil in the vertical dimension. In contrast to recent findings, we found no saccadic compression for control rectangles. Conclusions Our data suggest that compression of Kanizsa figure has been overestimated in previous research due to methodological artifacts, and highlight the importance of studying perceptual phenomena by multiple methods.

Shadow information, which not only is available in the real world but is also a useful cue for depth perception in two-dimensional pictures or photographs, is categorized as one of the pictorial depth cues. Shadows are classified into two types depending on how they are formed on surfaces: one is “attached” shadow and the other is “cast”shadow.Attached shadows are formed when a surface itself obstructs the light falling on it. Attached shadows provide three-dimensional shapes of objects such as convexity or concavity (Ramachandran 1988a,b; Kleffner and Ramachandran 1992). In contrast, cast shadows occur when one surface occludes another surface from the light source. The shape of a cast shadow can be used for identification of an object shape (Mamassian et al. 1998; Norman et al. 2000; Berbaum et al. 1984; but see Erens et al. 1993). Spatial relationships between cast shadows and casting objects provide effective information about spatial arrangements of objects (Yonas et al. 1978). Especially, motion of the cast shadow improves perception of the spatial layout by adults (Kersten et al. 1997). This chapter initially reviews studies concerning pictorial depth perception from shadows for human adults and then describes findings from two different approaches: human developmental studies, and studies from a comparative and developmental standpoint. Based on the findings, we discuss issues to be explored in the future.

We found a novel motion illusion; when a video clip presents a moving person, the background image appears to move incorrectly. We investigated this illusion with psychophysical experiments using a movie display that consisted of a human figure and a vertical grating pattern. The grating periodically reversed its light-dark phase so that it was ambiguous in terms of motion directions. However, when the human figure presented a walking gait in front of the grating, the grating appears to move in the opposite direction of her/his locomotion. This illusion suggests that human movements modulate perception of video images, and that creators of entertainment images need to pay attention to background images in videos used in animation and computer graphics.

An expanding object, which may represent an approaching motion, is easier to detect than a contracting one, which mayrepresent 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 anapproaching 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 isspecialized to detect approaching motion defined by cast shadows, as well as other three-dimensional cues such asexpanding motion and shading.Keywords: asymmetry, cast shadow, motion in depth, visual searchCitation: Imura, T., Shirai, N., Tomonaga, M., Yamaguchi, M. K., & Yagi, A. (2008). Asymmetry in the perception of motion indepthinducedbymovingcastshadows. Journal of Vision, 8(13):10, 1

The backscroll illusion refers to the apparent motion perceived in the background of a movie image that presents a locomotive object such as a person, an animal, or a vehicle. Here, we report that the backscroll illusion can occur in far peripheral visual fields at retinal eccentricity of more than 30 degrees. In psychological experiments, we presented a walking person in profile against an ambiguously moving background of vertical counterphase grating. This stimulus, which subtended 30 degrees of visual angle in width and height, was projected onto a hemispheric screen and positioned at horizontal eccentricity between 0 degrees and 50 degrees at intervals of 10 degrees. The eccentricity was changed randomly trial by trial, and stimulus duration was as short as 350 ms so that observers could not effectively move their eyes to the stimulus. Six observers viewed the stimulus either monocularly or binocularly and reported their perceptual impression for the grating in a three-alternative forced-choice procedure: drifting left, drifting right, or flickering. Results showed that the grating appeared to move in the opposite direction of walking at high probabilities even in the far periphery. Additional experiments confirmed that walking action could be recognized from the far peripheral stimulation. Our findings suggest that the visual system uses high-level object-centered motion signals to disambiguate retinal motion signals in the whole visual field.

A moving cast shadow of the object affects the perception of the object’s trajectory in adults [Kersten, D., Mamassian, P., & Knill, D. C. (1997). Moving cast shadow induce apparent motion in depth. Perception, 26, 171–192]. In the present study, we investigated by using a habituation–dishabituation procedure whether infants at 4- to 7-months old discriminate the motion trajectory of a ball from the moving shadow it casts. In Experiment 1, 4- to 5-month-old and 6- to 7-month-old were tested for ability to discriminate between a “depth” display containing a ball and a cast shadow with a diagonal trajectory and an “up” display containing a ball with a diagonal trajectory and a cast shadow with a horizontal trajectory. Six- and 7-month-old, but not 4- and 5-month-old, infants looked significantly longer at the “up” display than at the “depth” display. In Experiment 2, we tested whether 4- to 5-month-old and 6- to 7-month-old infants would perceive “up” motion as categorically different from “depth” depending on the object’s 3-D trajectory. We used displays containing a ball and a cast shadow with the same trajectories as those in Experiment 1 except that the cast shadows appeared above the ball. These displays did not produce 3-D impressions in adults. Neither age group of infants exhibited significant differences between “up” and “depth” displays. When the results from the two experiments are considered, 6- and 7-month-old infants discriminated the motion trajectory of the ball from the moving cast shadows. This developmental emergence of depth perception from a moving cast shadow at 6 months of age is consistent with that of other pictorial depth cues.