Empirical Support for Object Constancy in 3-Month-Old Infants Using a Memory Reactivation Task.

Object recognition refers to the ability to have stable object representations despite ongoing changes in view, angle, size, retinal images, etc as the observer moves throughout the environment (Gibson, 1979). The development of object recognition in infants is a topic of strong interest to perceptual researchers as well as clinically oriented researchers and clinical practitioners because it demonstrates the presence of functional lower-level perceptual capabilities as well as higher-level memory constructs. Most of what is known about infant remembering and perception has been learned through the use of behavioral techniques (Gerhardstein, Kraebel, & Tse, 2006; Rovee-Collier, & Cuevas, 2006). In studying the presence of functions underlying object recognition, researchers used such techniques, for example, to show that infants can discriminate between items as simple as a horizontal as compared to an oblique line at approximately 6-8 weeks of age (Atkinson & Braddick, 1992; Atkinson, Hood, Wattam-Bell, Anker, & Tickleback, 1988; Bornstein, Krinsky, & Benasich, 1986), and have shown that infants possess a rudimentary capacity for depth perception from motion cues at about the same age (Yonas et al., 1977). Slightly older infants have been found to be capable of discriminating between two different projections of a shape around three months of age (Caron, Caron, & Carlson, 1979; Slater & Morison, 1985). Caron, Caron, and Carlson (1979), for example, found that three-month-old infants, following familiarization with a simple shape (a rectangle, shown in 3D as, essentially, a piece of paper) demonstrated an ability to generalize to a novel projection of the shape, generated by rotating the rectangle in depth about the x-axis, so as to tilt the top of the rectangle backward and the bottom forward at a novel angle. Infants also discriminated the familiar shape from a novel shape (a trapezoid), which was (in its retinal projection) matched to a view used during familiarization of the original object. The findings of Caron et al. (1979) demonstrated the presence of shape constancy, an important component of stable object recognition. That is, infants at this age demonstrated an ability to discriminate between two flat shapes based on their distal, or "objective" properties, as Caron et al. labeled them, and not on the basis of their retinal projections, which overlapped (in some cases completely). Note that the 2D projection of a rectangle face tilted in depth is effectively a trapezoid, thus creating ambiguity at the retinal level. Yet, the three-month-olds were still able to discriminate the tilted rectangle from a veridical trapezoid. The ability to base perception on distal object properties is likely to be crucial to the operation of a successful visual system; if each new retinal projection elicits a novel reaction, then a single simple object, as it rotates in any dimension, will result in a large number of novel views. The ability to base perception on the distal object shape, and not its (proximal) retinal projection (i.e., shape constancy), eliminates this potential need to deal with the many projections that the same shape can produce. A second and related perceptual process is object constancy (or viewpoint invariance), which is the ability to recognize two different views of an object as the same 3D distal object. Object constancy is distinct from shape constancy in that view differences in object constancy are explicitly perceptible, while changes in view resulting in shape constancy are not explicitly perceived. To illustrate this point, imagine a coffee cup is rotated forward from the upright such that the top circular opening becomes more widely visible to an observer. As this happens, the retinal projection of the top opening changes from one ellipse to a differently shaped ellipse. Casual observation, however, reveals that perception is immediately of a circular opening in both cases, not a changing ellipse. …