Kinetic depth effects of unidimensional motion perspective in young children
Heinbuck, Claudia L.
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The purpose of the present study was to determine whether young children get impressions of depth when viewing motion pictures in which motion perspective is confined to a single dimension (horizontal) of that display. Motion perspective refers to those transformations of the optic array which accompany motion of the observer or motion of the object viewed. Displays of two-dimensional motion perspective yield impressions of depth known as "kinetic depth effects." Further, Hershberger and his associates have demonstrated that the motion perspective available in a two-dimensional projection of a plane figure rotating in depth about a vertical axis incorporates two independent components (horizontal and vertical motion perspective) which have independent perceptual effects for adult subjects. The present study was designed to determine whether young children get impressions of depth from such unidimensional motion perspective. Children of four different age groups, preschool, first grade, third grade, and fifth grade, were asked to view individually a computer generated moving picture depicting a horizontal array of 13 vertical pickets rotating in depth about the center picket. Motion perspective was confined to the horizontal dimension of the display: the vertical visual angle subtended by the pickets never changed. The children were asked to describe the perceived motion of the array (rotation with size change, rotation without size change, translation with size change, translation without size change) both verbally and with their hands. With each report of rotation or translation in a frontal plane, the child was asked to indicate whether the vertical pickets appeared to change in size. According to the size-distance invariance hypothesis, a report of rotation in depth should be accompanied by a report of change in the height of the vertical pickets. When a report of rotation in depth was rendered, the child was also asked to indicate the rotation direction. Four manual displays, depicting the possible motions of the stimulus display, were provided after each stimulus presentation so that the child could better represent what he/she had seen. The present study found that children in the assessed age groups are susceptible to kinetic depth effects from unidimensional motion displays. The tendency to report "rotation" was high, 92%, with no significant differences between the age groups or across trial blocks and, 89% of these reports were corroborated by correct judgments of direction of rotation. However, reports of "rotation" which were accompanied by reports of size change were found to increase as a function of the subject's age and as a function of repeated viewing. The ability of these young children to correctly judge rotation direction is discussed as strong evidence of a genuine kinetic depth effect. The tendency to report size change is discussed as possibly reflecting varying degrees of horizontal size constancy. The present study yielded results which differ markedly from those found by Carpenter in a very similar study investigating the perceptual impact of unidimensional motion perspective upon young children. The difference between Carpenter's results and those of the present study are discussed as perhaps artifacts of the size of the elements comprising the stimulus arrays used in the two studies (lines versus dots).