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Tomoko Imura, Masami K. Yamaguchi, Masaki Tomonaga, Akihiro Yagi; Perception of motion trajectory from the moving cast shadow in human infants. Journal of Vision 2005;5(8):329. doi: 10.1167/5.8.329.
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© ARVO (1962-2015); The Authors (2016-present)
Moving cast shadow affects perception of an object's trajectory in adults (Kersten et al., 1997). A ball is perceived to recede in depth when a cast shadow moves diagonally on a parallel with a ball, and float above the floor when a cast shadow trajectory is horizontal. In the present study, we investigated whether infants at 4- to 7-month-old discriminate the motion trajectory of the ball from the moving cast shadows using habituation-dishabituation procedure. In Experiment 1, we tested 12 4–5-month-olds and 12 6–7-month-olds' discrimination between ‘depth’ display containing a ball and a cast shadow with diagonal trajectory and ‘up’ display containing a ball with diagonal trajectory'@and a cast shadow with horizontal trajectory. Infants were habituated to ‘depth’ display and presented both ‘up’ and ‘depth’ displays during test. Six- and 7-month-old, but not 4- and 5-month-old, infants looked significantly longer ‘up’ display than ‘depth’ display. These results suggest that 6- and 7-month-old infants perceive the ball as moving in depth during habituation. In Experiment 2, we tested whether infants would perceive ‘up’ motion as categorically different from ‘depth’ depending on the object's 3-D trajectory. Nine 4–5-month-olds and 12 6–7-month-olds infants were habituated to and tested with the displays containing a ball and a cast shadow with the same trajectory as Experiment 1 except that cast shadows were attached above the ball. These displays did not produce 3-D impressions in adults. Both age groups of infants did not exhibit significant differences between ‘up’ and ‘depth’ displays. These results suggest that infants did not discriminate these displays. When the results from two experiments are considered, 6- and 7-month-old infants discriminated the motion trajectory of the ball from the moving cast shadows. This developmental emergence of depth perception from moving cast shadow at 6 months of age is consistent with that of other pictorial depth cues.
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