The onset of sensitivity to horizontal disparity in infancy: a short-term longitudinal study

The Development of Binocular Suppression in Infants

Little is known about the time of development of binocular suppression. In the present study, we evaluated the emergence of binocular suppression in infants by using continuous flash suppression (CFS, Tsuchiya and Koch, 2005). In our experiment, one eye of infants was presented with a static face image at one side of the screen, while another eye was presented with dynamic Mondrian patterns in full screen. Adult observers confirmed that the static face image was consciously repressed by the changing Mondrian patterns. If binocular suppression was functional, the infants would not perceive the face and thus would not show any preference in the experiment. However, if binocular suppression in the infants was not yet acquired, they would perceive the face and the Mondrian patterns at the same time and would thus show preference for the side where the face was presented. The results showed that infants aged 2-3 months, but not those aged 4-5 months, detected the position of the face. Furthermore, this detection was not due to weak contrast sensitivity to the dynamic Mondrian mask. These results indicated that the immature binocular visual system may perceive different images from different eyes simultaneously and that infants may lose this ability after establishing binocular suppression at 4-5 months of age.

Infants' responsiveness to half-occlusions in phantom stereograms

The present natural preference study investigated infants 4 and 7 months of age for their ability to respond to phantom contoubrs, illusory surfaces generated by half-occlusions in a stereoscopic display consisting of a pair of parallel vertical lines. The left line in the half-image for the right eye and the right line in the half-image for the left eye have a gap in the middle. The visual system accounts for the binocular unmatched gaps by perceiving an illusory contour. Infants in the experimental condition were presented with a standard phantom stereogram displaying a phantom contour versus a non-standard phantom stereogram, the half-images of which were exchanged. This stereogram evokes the impression of two small separate illusory contours. In both stereograms, the gaps moved up and down. The participants aged 7 but not 4 months preferred looking at the standard phantom stereogram. A control condition supported the hypothesis that the infants 7 months of age in the experimental condition indeed responded to the coherent illusory surface instead of simply detecting differences in the geometric arrangement of the half-occlusions. The results hence indicate that infants are able to extract spatial information from monocular regions in a binocular display.

Development of stereo vision in young infants

In this study, infants' visual processing of depth-inducing stimuli was tested using a new method suitable for experimental settings. Stereograms of the Lang-Stereopad^® were presented in a timed preferential-looking paradigm to determine infants' preference for a stereogram as compared to a stimulus not inducing an impression of depth. A total of 80 infants were tested at 7 months of age; of these, a sub-sample of 41 infants were tested longitudinally at 4 and 7 months to characterize the developmental trajectory of their preference. Infants were simultaneously presented with a card showing a random-dot stereogram (800" disparity) and a similar looking dummy card without stereogram. In the total sample, 7-month-olds showed a clear preference for the stereogram regardless of sex. In the longitudinal sample, 7-month-olds but not 4-month-olds looked significantly longer to the stereogram as compared to the dummy card. On individual level, 56% of the 4-month-olds and 85% of the 7-month-olds predominantly looked at the stereogram. The findings yield evidence for a clear developmental progression and show that the test cards of the Lang-Stereopad^® prototype provide a viable instrument to determine the preference for depth-inducing stimuli in young infants when used in a controlled experimental setting.

Infants Perceive Three-Dimensional Subjective Contours

The addition of crossed horizontal disparity enhances the clarity of illusory contours compared to pictorial illusory contours and illusory contours with uncrossed horizontal disparity. Two infant-controlled habituation-dishabituation experiments explored the presence of this effect in infants 5 months of age. Experiment 1 examined whether infants are able to distinguish between a Kanizsa figure with crossed horizontal disparity and a Kanizsa figure with uncrossed horizontal disparity. Experiment 2 tested infants for their ability to differentiate between a Kanizsa figure with crossed horizontal disparity and a two-dimensional Kanizsa figure. The results provided evidence that the participants perceived the two- and the three-dimensional illusory Kanizsa contour, the illusory effect in which was strengthened by the addition of crossed horizontal disparity.

Infants perceive two-dimensional shape from horizontal disparity

Previous studies observed that responsiveness to horizontal disparity as such emerges at approximately 2 months of age. Moreover, 3- to 4-month-old infants utilize stereoscopic information to perceive object variations in depth. The present study investigated infants' ability to respond to crossed horizontal disparity information that defines two-dimensional shape. Infants 4 and 5 months of age were habituated to either a cross or the outline of a square. During the posthabituation period, they were presented with both shapes. The stimuli were dynamic random dot stereograms shown on an autostereoscopic monitor. The participants 5 but not 4 months of age displayed significant novelty preferences for the unfamiliar shape during the posthabituation period. Five-month-old infants are hence sensitive to horizontal disparity information that specifies shape.

Development of Three-Dimensional Perception in Human Infants

The play of light on the retina contains multiple sources of information about the three-dimensional (3D) structure of the world. Some of the best information is derived from differencing operations that act on the images that result from the two eyes’ laterally displaced vantage points. Other information is available in systematic retinal patterns of local texture and motion cues. This article describes what is currently known about the development of sensitivity to these binocular and monocular cues for depth in human infants, and it places the results in the context of what is known about the underlying neural mechanisms from work in nonhuman primates and human neuroimaging studies.

Infants Perceive Three-Dimensional Illusory Contours as Occluding Surfaces

The study assessed the contribution of stereoscopic depth cues to infants' perception of a Kanizsa rectangle as a surface that temporarily occludes a moving object. In Experiment 1, the Kanizsa figure was shifted into the foreground by enriching it with stereoscopic depth information. According to the results, perception of a three-dimensional Kanizsa figure as an occluding surface emerges between 5 (n = 16) and 7 (n = 16) months of age. Experiment 2 demonstrated that 7-month-old (n = 16) infants performed similarly to the 7-month-olds who participated in Experiment 1 if the moving object was shifted into the background. These findings suggest that 7-month-old infants respond to stereoscopic depth cues and that they exploit it to perceive subjective contours as occluders.

Infants' discrimination of crossed and uncrossed horizontal disparity

In a series of preferential-looking experiments, infants 5 to 6 months of age were tested for their responsiveness to crossed and uncrossed horizontal disparity. In Experiments 1 and 2, infants were presented with dynamic random dot stereograms displaying a square target defined by either a 0.5° crossed or a 0.5° uncrossed horizontal disparity and a square control target defined by a 0.5° vertical disparity. In Experiment 3, infants were presented with the crossed and the uncrossed horizontal disparity targets used in Experiments 1 and 2. According to the results, the participants looked more often at the crossed (Experiment 1), as well as the uncrossed (Experiment 2), horizontal disparity targets than at the vertical disparity target. These results suggest that the infants were sensitive to both crossed and uncrossed horizontal disparity information. Moreover, the participants exhibited a natural visual preference for the crossed over the uncrossed horizontal disparity (Experiment 3). Since prior research established natural looking and reaching preferences for the (apparently) nearer of two objects, this finding is consistent with the hypothesis that the infants were able to extract the depth relations specified by crossed (near) and uncrossed (far) horizontal disparity.

Current Understanding of What Infants See

The current understanding of what infants see varies greatly among healthcare and education specialists. Even among ophthalmologists and pediatric neurologists in charge of clinical examinations of infants, opinions vary on what infants perceive, recognize, and use for communication and learning. It is, therefore, of interest to review publications from several specialties to learn whether new information is available on the development of visual functions and use of vision. Ten percent of total publications on this subject are reviewed here based on the usefulness of their content for improving early diagnosis and intervention of vision disorders in infants.