Development of illusory-contour perception in infants

We investigated whether infants from 8-22 weeks of age were sensitive to the illusory contour created by aligned line terminators. Previous reports of illusory-contour detection in infants under 4 months old could be due to infants' preference for the presence of terminators rather than their configuration. We generated preferential-looking stimuli containing sinusoidal lines whose oscillating, abutting terminators give a strong illusory contour in adult perception. Our experiments demonstrated a preference in infants 8 weeks old and above for an oscillating illusory contour compared with a stimulus containing equal terminator density and movement. Control experiments excluded local line density, or attention to alignment in general, as the basis for this result. In the youngest age group (8-10 weeks) stimulus velocity appears to be critical in determining the visibility of illusory contours, which is consistent with other data on motion processing at this age. We conclude that, by 2 months of age, the infant's visual system contains the nonlinear mechanisms necessary to extract an illusory contour from aligned terminators.     

Infants' perception of illusory contours in static and moving figures

We investigated 3-8-month-olds' (N=62) perception of illusory contours in a Kanizsa figure by using a preferential looking technique. Previous studies suggest that this ability develops around 8 months of age. However, we hypothesized that even 3-4-month-olds could perceive illusory contours in a moving figure. To check our hypothesis, we created an illusory contour figure in which the illusory square underwent lateral movement. By rotating the elements of this figure, we created non-illusory contour figures. We found that: (1) infants preferred moving illusory contours to non-illusory contours by 3-4 months of age, and (2) only 7-8-month-olds preferred static illusory contours. Our findings demonstrate that motion information promotes infants' perception of illusory contours. Our results parallel those reported in the study of partly occluded objects ().     

The role of kinetic information in newborns' perception of illusory contours

Previous research, in which static figures were used, showed that the ability to perceive illusory contours emerges around 7 months of age. However, recently, evidence has suggested that 2-3-month-old infants are able to perceive illusory contours when motion information is available (Johnson & Mason, 2002; Otsuka & Yamaguchi, 2003). The present study was aimed at investigating whether even newborns might perceive kinetic illusory contours when a motion easily detected by the immature newborn's visual system (i.e. stroboscopic motion) is used. In Experiment 1, using a preference looking technique, newborns' perception of kinetic illusory contours was explored using a Kanizsa figure in a static and in a kinetic display. The results showed that newborns manifest a preference for the illusory contours only in the kinetic, but not in the static, condition. In Experiment 2, using an habituation technique, newborns were habituated to a moving shape that was matched with the background in terms of random-texture-surface; thus the recovery of the shape was possible relying only on kinetic information. The results showed that infants manifested a novelty preference when presented with luminance-defined familiar and novel shapes. Altogether these findings provide evidence that motion enhances (Experiment 1) and sometimes is sufficient (Experiment 2) to induce newborns' perception of illusory contours.     

The perception of subjective contours and neon color spreading figures in young infants

The goal of the present habituation—dishabituation study was to explore sensitivity to subjective contours and neon color spreading patterns in infants. The first experiment was a replication of earlier investigations that showed evidence that even young infants are capable of perceiving subjective contours. Participants 4 months of age were habituated to a subjective Kanizsa square and were tested afterward for their ability to differentiate between the subjective square and a nonsubjective pattern that was constructed by rotating some of the inducing elements. Data analysis indicated a significant preference for the nonsubjective pattern. A control condition ensured that this result was not generated by the difference in figural symmetry or by the local differences between the test displays. In the second experiment, infant perception of a neon color spreading display was analyzed. Again, 4-month-old infants could discriminate between the illusory figure and a nonillusory pattern. Furthermore, infants in a control group did not respond to the difference in symmetry and the local differences between two nonillusory targets. Overall, the results show that young infants respond to illusory figures that are generated by either implicit T-junctions (Experiment 1) or implicit X-junctions (Experiment 2). The findings are interpreted against the background of the neurophysiological model proposed by Grossberg and Mingolla (1985).     

Sound enhances detection of visual target during infancy: a study using illusory contours

In adults, a salient tone embedded in a sequence of nonsalient tones improves detection of a synchronously and briefly presented visual target in a rapid, visually distracting sequence. This phenomenon indicates that perception from one sensory modality can be influenced by another one even when the latter modality provides no information about the judged property itself. However, no study has revealed the age-related development of this kind of cross-modal enhancement. Here we tested the effect of concurrent and unique sounds on detection of illusory contours during infancy. We used a preferential looking technique to investigate whether audio-visual enhancement of the detection of illusory contours could be observed at 5, 6, and 7 months of age. A significant enhancement, induced by sound, of the preference for illusory contours was observed only in the 7-month-olds. These results suggest that audio-visual enhancement in visual target detection emerges at 7 months of age.     

The perception of moving subjective contours by 4-month-old infants

We investigated whether 4-month-old infants are capable of perceiving illusory contours produced by the Kanizsa-square display, first introduced by Prazdny (1983, Perception & Psychophysics 34 403-404), which tests whether a viewer perceives the illusory contour in the absence of brightness contrast (illusory brightness). Because the illusory square appears to move across the computer screen and infants are attracted to motion, this display holds their interest. In experiment 1, 4-month-old infants were tested for their ability to distinguish between a continuously moving illusory square and a continuously moving control display in which the pacman elements were rotated so that the perception of subjective contours did not occur. Data analysis revealed a significant preference for the subjective contour display. In experiment 2, habituation-dishabituation was used with 4-month-old infants. They were tested for their ability to discriminate between the illusory Kanizsa square that continuously moved back and forth and an illusory square which changed positions randomly. Although the infants did not show differences in dishabituation as a function of the habituation display, they looked significantly longer at the continuously moving display.     

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.     

Boundary completion in illusory contours: interpolation or extrapolation?

Most computational and neural-style models of contour completion (ie illusory and occluded contours) are based on interpolation: the filling in of an edge between two visible edges. The results of three experiments suggest an alternative conception, that units are formed as a result of extrapolation from visible edges. In three experiments, subjects reported illusory contours between standard illusory-contour inducing elements and forms that do not, by themselves, induce illusory contours. We suggest that these forms are not a special case of inducing elements but that they represent a different class--receiving elements. Receiving elements are forms that can receive an illusory contour but cannot generate one, and they can alter contour formation. In experiment 1, receiving elements increased the judged clarity of illusory contours. In experiment 2, illusory edges were seen to connect to corners, line ends, and even the edges of circles. Boundary formation in motion displays also appears to be based on extrapolation. In experiment 3, subjects reported that small moving dots altered the formation of spatiotemporally defined boundaries. Implications for higher-order operator and network models of boundary formation are discussed.     

The absence of depth constancy in contour stereograms

Stereoscopic surfaces constructed from Kanizsa-type illusory contours or explicit luminance contours were tested for three-dimensional (3-D) shape constancy. The curvature of the contours and the apparent viewing distance between the surface and the observer were manipulated. Observers judged which of two surfaces appeared more curved. Experiment 1 allowed eye movements and revealed a bias in 3-D shape judgment with changes in apparent viewing distance, such that surfaces presented far from the observer appeared less curved than surfaces presented close to the observer. The lack of depth constancy was approximately the same for illusory-contour surfaces and for explicit-contour surfaces. Experiment 2 showed that depth constancy for explicit-contour surfaces improved slightly when fixation was required and eye movements were restricted. These experiments suggest that curvature in depth is misperceived, and that illusory-contour surfaces are particularly sensitive to this distortion.     

Infants' perception of subjective contours from apparent motion

We examined infants' perception of subjective contours in Subjective-Contour-from-Apparent-Motion (SCAM) stimuli [e.g., Cicerone, C. M., Hoffman, D. D., Gowdy, P. D., & Kim, J. S. (1995). The perception of color from motion. Perception & Psychophysics, 57, 761-777] using the preferential looking technique. The SCAM stimulus is composed of random dots which are assigned two different colors. Circular region assigned one color moved apparently, keeping all dots' location unchanged. In the SCAM stimulus, adults can perceive subjective color spreading and subjective contours in apparent motion (http://c-faculty.chuo-u.ac.jp/ approximately ymasa/okamura/ibd_demo.html). In the present study, we conducted two experiments by using this type of SCAM stimulus. A total of thirty-six 3-8-month-olds participated. In experiment 1, we presented two stimuli to the infants side by side: a SCAM stimulus consisting of different luminance, and a non-SCAM stimulus consisting of isoluminance dots. The results indicated that the 5-8-month-olds showed preference for the SCAM stimuli. In experiments 2 and 3, we confirmed that the infants' preference for the SCAM stimulus was not generated by the local difference and local change made by luminance of dots but by the subjective contours. These results suggest that 5-8-month-olds were able to perceive subjective contours in the SCAM stimuli.     

The generic-viewpoint assumption and illusory contours

Visual images are ambiguous. Any image, or collection of images, is consistent with an infinite number of possible scenes in the world. Yet we are generally unaware of this ambiguity. During ordinary perception we are generally aware of only one, or perhaps a few of these possibilities. Human vision evidently exploits certain constraints--assumptions about the world and images formed of it--in order to generate its perceptions. One constraint that has been widely studied by researchers in human and machine vision is the generic-viewpoint assumption. We show that this assumption can help to explain the widely discussed fact that outlines of blobs are ineffective inducers of illusory contours. We also present a number of novel effects and report an experiment suggesting that the generic-viewpoint assumption strongly influences illusory-contour perception.     

The Ames window illusion: perception of illusory motion by human infants

The sensitivity of human infants, 5 1/2-9 months of age, to the illusory oscillation of the Ames window was assessed in three experiments that employed some variant of the habituation-dishabituation and forced-choice preferential looking paradigms. In Experiment 1, three groups--5 1/2, 7 1/2, and 9 months of age--were given a visual choice between rotating rectangular and Ames windows after exposure to a rotating circular form. The two older groups preferred the Ames window. The results of Experiment 2 showed that this preference is not based on structural differences between the two windows. In Experiment 3, familiarization with an Ames window produced a preference for rotary motion while familiarization with a rectangular window produced a preference for oscillatory motion. These results suggest that sensitivity to the illusion emerges around 7 1/2 months of age, an outcome consistent with the emergence, at this time, of sensitivity to pictorial cues to depth.     

Are children with autistic spectrum disorders susceptible to contour illusions?

Children with autism have been shown to be less susceptible to Kanisza type contour illusions than children without autism ( Happé, 1996 ). Other authors have suggested that this finding could be explained by the fact that participants with autism were required to make a potentially ambiguous verbal response which may have masked whether or not they actually perceived the illusory contours ( Ropar & Mitchell, 1999 ). The present study tested perception of illusory contours in children with autism using a paradigm that requires participants to make a forced choice about the dimensions of a shape defined by illusory contours. It was reasoned that accuracy of the participant on this task would indicate whether or not children with autism could perceive illusory contours. A total of 18 children with autistic spectrum disorder, 16 children with special educational needs not including autism and 20 typically developing children completed an experimental task which assessed perception of Kanisza‐style rectangles defined by illusory contours. There were no significant differences between the performance of the children with autism and either of the two control groups, suggesting that perception of illusory contours is intact in autism.     

Sound induces perceptual reorganization of an ambiguous motion display in human infants

Adults who watch an ambiguous visual event consisting of two identical objects moving toward, through, and away from each other and hear a brief sound when the objects overlap report seeing visual bouncing. We conducted three experiments in which we used the habituation/test method to determine whether these illusory effects might emerge early in development. In Experiments 1 and 3 we tested 4‐, 6‐ and 8‐month‐old infants’ discrimination between an ambiguous visual display presented together with a sound synchronized with the objects’ spatial coincidence and the identical visual display presented together with a sound no longer synchronized with coincidence. Consistent with illusory perception, the 6‐ and 8‐month‐old, but not the 4‐month‐old, infants responded to these events as different. In Experiment 2 infants were habituated to the ambiguous visual display together with a sound synchronized with the objects’ coincidence and tested with a physically bouncing object accompanied by the sound at the bounce. Consistent with illusory perception again, infants treated these two events as equivalent by not exhibiting response recovery. The developmental emergence of this intersensory illusion at 6 months of age is hypothesized to reflect developmental changes in object knowledge and attentional mechanisms.     

Late influences on perceptual grouping: illusory figures

Two experiments demonstrate that grouping can be strongly influenced by the presence of figures defined by illusory contours. Rectangular arrays were constructed in which a central column of figures could group either with those on one side, on the basis of perception of figures defined by illusory contours, or with those on the other side, on the basis of physically present inducing elements. In all displays, subjects grouped according to the illusory figures significantly more often than for control displays that contained the same inducing elements, but rearranged so that illusory contours were degraded or eliminated. A second experiment showed that in objectively defined grouping tasks, subjects grouped faster by illusory figures than by inducing elements. These results indicate that grouping can occur after illusory contours have been perceived.     

Do infants recognize the Arcimboldo images as faces? Behavioral and near-infrared spectroscopic study

Arcimboldo images induce the perception of faces when shown upright despite the fact that only nonfacial objects such as vegetables and fruits are painted. In the current study, we examined whether infants recognize a face in the Arcimboldo images by using the preferential looking technique and near-infrared spectroscopy (NIRS). In the first experiment, we measured looking preference between upright and inverted Arcimboldo images among 5- and 6-month-olds and 7- and 8-month-olds. We hypothesized that if infants perceive the Arcimboldo images as faces, they would prefer the upright images to the inverted ones. We found that only 7- and 8-month-olds significantly preferred upright images, suggesting that they could perceive the Arcimboldo images as faces. In the second experiment, we measured hemodynamic responses using NIRS. Based on the behavioral data, we hypothesized that 7- and 8-month-olds would show different neural activity for upright and inverted Arcimboldo images, as do adults. Therefore, we measured hemodynamic responses in 7- and 8-month-olds while they were looking at upright and inverted Arcimboldo images. Their responses were then compared with the baseline activation during the presentation of individual vegetables. We found that the concentration of oxyhemoglobin increased in the left temporal area during the presentation of the upright images compared with the baseline during the presentation of vegetables. The results of the two experiments suggest that (a) the ability to recognize the upright Arcimboldo images as faces develops at around 7 or 8 months of age and (b) processing of the upright Arcimboldo images is related to the left temporal area of the brain.     

Infants' perception of depth from cast shadows

Five- and 7-month-old infants viewed displays in which cast shadows provided information that two objects were at different distances. The 7-month-olds reached preferentially for the apparently nearer object under monocular-viewing conditions but exhibited no reaching preference under binocular-viewing conditions. These results indicate that 7-month-old infants perceive depth on the basis of cast shadows. The 5-month-olds did not reach preferentially for the apparently nearer object and, therefore, exhibited no evidence of sensitivity to cast shadows as depth information. In a second experiment, 5-month-olds reached preferentially for the nearer of two objects that were similar to those used in the first experiment but were positioned at different distances from the infant. This result indicated that 5-month-olds have the motor skills and motivation necessary to exhibit a reaching preference under the conditions of this study. The results are consistent with the hypothesis that depth perception based on cast shadows first appears between 5 and 7 months of age.     

The effects of perceptual set on the shape and apparent depth of subjective contours

Two experiments showed the influence of perceptual set on the perception of subjective contours. In the first, the perceived shape of a subjective-contour figure (a minimal version of the Ehrenstein configuration) was varied by altering the observer’s viewing set. The second experiment showed that apparent depth emerged in subjective-contour figures when observers were set to perceive the illusory contours.     

Perceptual organization based on illusory regions in infancy

Prior research indicates that, like adults, infants use enclosed regions to group elements. It is not clear whether infants or adults can use regions that have to be inferred from illusory contours to group elements. We examined whether 3- to 4-month-olds use illusory regions to group elements and generalize this organization to novel regions. Infants habituated to pairs of shapes in illusory vertical or horizontal regions subsequently discriminated, in novel regions, pairs of elements that had previously shared a region from pairs of elements that had been in different regions. A control group of infants, who had experienced the same stimuli except for the presence of illusory regions, failed to discriminate between within-region and between-region pairs of stimuli. These results reveal that (1) illusory regions can be used to group elements, (2) perceptual organization is sufficiently developed early in life for 3- to 4-month-olds to group on the basis of ecologically relevant illusory contours, and (3) such grouping in infancy generalizes to novel regions.     

Infants’ perception of depth from cast shadows

Five- and 7-month-old infants viewed displays in which cast shadows provided information that two objects were at different distances. The 7-month-olds reached preferentially for the apparently nearer object under monocular-viewing conditions but exhibited no reaching preference under binocularviewing conditions. These results indicate that 7-month-old infants perceive depth on the basis of cast shadows. The 5-month-olds did not reach preferentially for the apparently nearer object and, therefore, exhibited no evidence of sensitivity to cast shadows as depth information. In a second experiment, 5-month-olds reached preferentially for the nearer of two objects that were similar to those used in the first experiment but were positioned at different distances from the infant. This result indicated that 5-month-olds have the motor skills and motivation necessary to exhibit a reaching preference under the conditions of this study. The results are consistent with the hypothesis that depth perception based on cast shadows first appears between 5 and 7 months of age.