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PERCEIVING OBJECTS WHILE ON THE MOVE

Martha E. Arterberry

Department of Psychology, Gettysburg College, Gettysburg, PA 17325

Studies of infants’ sensitivity to motion-carried information have revealed remarkable abilities in young infants. For example, infants within the first six months of life perceive approaching and receding surfaces, the three-dimensional structure of objects, and biomechanical motions. In addition, they are able to perceive moving objects when they themselves are moving. A notable exception to these astonishing capabilities is infants’ perception of objects that are not fully visible all the time. For example, if infants are presented with an object moving behind an aperture, or window, they provide no evidence of perceiving its length based on how long the object takes to pass behind the window until 12 months of age (Arterberry, 1993). Similarly, infants younger than 12 months appear to be unable to determine the number of objects moving behind an aperture (Arterberry, 1995).

This contradiction in developmental trajectories may be due to the aperture- viewing context. Presenting an object behind an aperture constrains the perceiver in ways that he/she would not be constrained in more natural situations. When viewing a scene over time, the observer typically moves instead of the object. The present study investigated lo- and 12-month-old infants’ perception of object length under the condition of observer motion.

In a habituation of looking paradigm, lo- and lZmonth-olds were seated in a swing suspended from a ceiling and were moved left to right in front of a display case containing a stationary rectangle behind an aperture. During the habituation phase, infants viewed either a long (16 cm) or a short (8 cm) rectangle in full view (the aperture was wide enough to see the whole rectangle at one time). Following habituation, infants viewed both the long and the short rectangle, on alternate trials, behind a 5 cm aperture. The aperture restricted the infants’ view of the complete rectangle but as infants were moved from side to side the full rectangle was revealed. It was predicted that infants would look significantly longer to the rectangle of a novel length if they perceived the length of the object over time.

Twelve-month-old infants showed significantly more looking to the novel object whereas lo-month-old infants did not. Ten-month-olds looked equally to the novel and familiar rectangles. This pattern of results is consistent with previous work by Arterberry (1993,1995). Moreover, this pattern of results suggests that even under conditions that approximate more closely a natural viewing context, infants show limitations in their perception of object properties across time. Possibilities for why this limitation exists will be considered.