Test Stimuli

Figure 5.1 Familiarization and test stimuli used to test adherence to the lightness similarity Gestalt organizational principle in Quinn, Burke, and Rush (1993). The rationale is that if infants can organize familiar stimulus (a) into columns, then the vertical-column test stimulus should be perceived as familiar, and the horizontal-row test stimulus should be preferred. Similarly, if infants can organize the familiar stimulus (b) into rows, then the horizontal-row test stimulus should be perceived as familiar, and the vertical-column test stimulus should be preferred.

Figure 5.1 Familiarization and test stimuli used to test adherence to the lightness similarity Gestalt organizational principle in Quinn, Burke, and Rush (1993). The rationale is that if infants can organize familiar stimulus (a) into columns, then the vertical-column test stimulus should be perceived as familiar, and the horizontal-row test stimulus should be preferred. Similarly, if infants can organize the familiar stimulus (b) into rows, then the horizontal-row test stimulus should be perceived as familiar, and the vertical-column test stimulus should be preferred.

peripheral filtering by the infant's visual system (Banks & Ginsburg, 1985; Banks & Salapatek, 1981). That is, one could argue that immature resolution acuity and contrast sensitivity rendered the dark squares as indistinguishable from other dark squares and the light squares as indistinguishable from other light squares. The representation of familiar stimuli (a) and (b) resulting from such "low-pass" filtering would best be described as "two dark vertical (or horizontal) bars on a light background." Performance of the 3-month-olds could thus be explained by simple generalization from representations of this nature to the vertical (or horizontal bars) used as test stimuli, without invoking any grouping mechanism (cf. Ginsburg, 1986).

Quinn et al. (1993) attempted to choose between the Gestalt grouping and low-pass filtering explanations of the findings with both computer simulation and experimental evidence. First, the images of the familiar stimuli shown in Figure 5.1, and additional stimuli in which either the dark or light elements were changed from square to diamond, were fed into a low-pass spatial frequency filter that removed spatial frequencies above 4 cycles/degree, the cutoff spatial frequency for 3-month-olds as estimated by preferential looking techniques (e.g., Atkinson, Braddick, & Moar, 1977; Banks & Salapatek, 1978). Figure 5.2 shows the resulting patterns. It can be seen that the stimuli have lost some sharpness, but the individual elements comprising the patterns are clearly discernable. Figure 5.2 thus suggests that 3-month-olds have enough resolution acuity and contrast sensitivity to perceive the individual elements of the patterns, and that the initial preference results cannot be explained on the basis of peripheral immaturities in the young infant's visual system.

This suggestion was subsequently confirmed in a discrimination experiment utilizing the familiarization/novelty-preference methodology. Infants were familiarized with stimuli like those shown in the left half of Figure 5.1 and then presented with novel stimuli in which only the dark or light elements were changed from square to diamond. Preference for the novel stimuli was above chance in both cases, indicating that infants were able to process shape information for both the light and dark elements. The combined findings from the simulation and discrimination experiment thus provide strong evidence in favor of a Gestalt interpretation of the original preference results: infants had perceived the individual elements of the patterns and grouped these elements into alternating light and dark columns or rows on the basis of lightness similarity.

Figure 5.2 Patterns with spatial frequencies above 4 cycles/degree removed. While the individual elements of the patterns have lost some "sharpness," their shape (square or diamond) remains clearly discernable. (From Quinn, Burke, & Rush, 1993.)

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