Abstract
Horizontal binocular disparity, the horizontal difference of the retinal images in our two eyes, is widely known to produce depth perception. Vertical disparity with an appropriate pattern has also been shown to produce the perception of depth (Ogle, 1952, Howard & Kaneko, 1995, Backus, Banks van Ee & Crowell, 1999, Ito, 2005). In the developmental studies, infants aged over 4 months were shown to perceive depth from horizontal disparity (Fox & Aslin, 1980, Held, Birch & Gwiazda, 1980). However, infants' ability to perceive depth from vertical disparity has not been clear. This study examined whether infants aged 20 to 27 weeks could detect vertical disparity for the perception of depth as well as horizontal disparity using a preferential looking method. Our stimuli consisted of an oblique line and random-dot background, and uniform vertical disparity was added into the background only. When observing the stimulus, the line is perceived to separate in depth from the background for adults. The stimulus was presented together with a comparison stimulus with zero disparity side by side. Infants are known to prefer the displays with difference in depth to the displays without such three-dimensional difference (Fantz, 1963). If infants showed a preference of the stimulus with vertical disparity to the stimulus without such a disparity, we would conclude that infants could perceive depth from the vertical disparity. As a result, the significant preference for the stimulus with vertical disparity relative to the stimulus with zero disparity was observed. Our results showed the first clear evidence of the infants' ability to detect vertical disparity for the perception of depth.
This study was supported by Grants-in-Aid for scientific research (No. 20539004 to Aki Tsuruhara, No. 21243041 to Masami K. Yamaguchi) from Japan Society for the Promotion of Science (JSPS).