Aki TSURUHARA^1*, Hirohiko KANEKO², So KANAZAWA³, Yumiko OTSUKA⁴, Nobu SHIRAI⁵, and Masami K. YAMAGUCHI⁶

¹Research and Development Initiative, Chuo University, Hachioji, Tokyo 192-0393, Japan
²Department of Information Processing, Tokyo Institute of Technology, Yokohama 226-8502, Japan
³Department of Psychology, Japan Women's University, Kawasaki 214-8565, Japan
⁴School of Psychology, The University of New South Wales, Sydney, NSW 2052, Australia
⁵Department of Psychology, Niigata University, Niigata 950-2181, Japan
⁶Department of Psychology, Chuo University, Hachioji, Tokyo 192-0393, Japan

(Received November 26, 2012; Accepted February 28, 2013)

Both horizontal and vertical binocular disparities produce depth perception in adults. In developmental studies, infants aged around 4 to 6 months were shown to perceive depth from horizontal disparity. However, infants' sensitivity to vertical disparity has not been shown clearly. To examine the sensitivity in infants, this study measured preferential looking behavior of infants aged 20 to 27 weeks. Results showed a significant preference for the stimulus with vertical disparity, providing the first evidence of infants' sensitivity to vertical disparity. The infants in the same age group did not show preference for stimulus with horizontal disparity when the stimulus were comparable to the stimulus with vertical disparity, while their sensitivity to horizontal disparity was confirmed with the stimuli used in a previous study. Our results would suggest that properties in processing horizontal and vertical disparities are different in infancy, and that the sensitivity to horizontal disparity are still premature in 27 weeks after birth.

Key words: vertical disparity, horizontal disparity, infant vision, stereopsis, preferential looking

^*Present address: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan. E-mail address: aki.tsuruhara@gmail.com