Visuo-motor development which causes detection of visual depth from motion and density cues 1The article is based on a presentation given by the first author at the Joint Swiss-Japanese Scientific Seminar Human Motion Perception, Eye Movements, and Orientation in Visual Space, supported by the Swiss National Science Foundation in cooperation with the Japanese Society for the Promotion of Science, in Gunten (Switzerland) May 19-21, 1999. The research was supported by a Grant-in-Aids for Scientific Research from the Ministry of Education, Science and Culture of Japan. The experiments were conducted as a joint research project supported by the Institute for Primate Research of Kyoto University.

This study examines the effectiveness of cues of visual depth and distance in the course of development and how this process depends on visuo-motor development. In the visual pitfall situation, i.e. a modification of Gibson 's visual cliff, eight Japanese monkeys (macaca fuscata) were observed with respect to their depth avoidance and visuo-motor activity. The tests were run once a week from the first until the sixteenth week after birth. Binocular parallax, motion parallax and texture density rates were manipulated to examine their effectiveness as cues. It was shown that for the first two months depth perception depended exclusively on motion parallax, whereas in the third month cues of motion and texture were added. Binocular cues did not have any effect in this age range. Three items of behaviour, i.e. visual regard of depth, head movement, and body movement, were checked and measured to obtain information which could explain the process of development of the cue function. The three items showed different developmental curves. During the first month, visual regard closely concurred with head and body movements, then visual activity suppressed motor behaviour and, after the end of the second month, the two became almost independent of each other. These analyses demonstrated that at a later stage pictorial cues produced an effect additional to the primary motion cues and that the effective cue function was based on the development of visuo-motor activity.