Tomoko Imura, Masami K. Yamaguchi, So Kanazawa, Nobu Shirai, Yumiko Otsuka, Masaki Tomonaga, Akihiro Yagi
Perception of motion trajectory of object from the moving cast shadow in infants
Vision Research, 46, 652-657, doi: 10.1016/j.visres.2005.07.028
A moving cast shadow of the object affects the perception of the object’s trajectory in adults [Kersten, D., Mamassian, P., & Knill, D. C. (1997). Moving cast shadow induce apparent motion in depth. Perception, 26, 171–192]. In the present study, we investigated by using a habituation–dishabituation procedure whether infants at 4- to 7-months old discriminate the motion trajectory of a ball from the moving shadow it casts. In Experiment 1, 4- to 5-month-old and 6- to 7-month-old were tested for ability to discriminate between a “depth” display containing a ball and a cast shadow with a diagonal trajectory and an “up” display containing a ball with a diagonal trajectory and a cast shadow with a horizontal trajectory. Six- and 7-month-old, but not 4- and 5-month-old, infants looked significantly longer at the “up” display than at the “depth” display. In Experiment 2, we tested whether 4- to 5-month-old and 6- to 7-month-old infants would perceive “up” motion as categorically different from “depth” depending on the object’s 3-D trajectory. We used displays containing a ball and a cast shadow with the same trajectories as those in Experiment 1 except that the cast shadows appeared above the ball. These displays did not produce 3-D impressions in adults. Neither age group of infants exhibited significant differences between “up” and “depth” displays. When the results from the 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 a moving cast shadow at 6 months of age is consistent with that of other pictorial depth cues.
Cast shadow, Motion, Pictorial depth, Infants