Kazumichi MATSUMIYA^* and Hirohiko KANEKO¹

Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
¹Department of Information Processing, Tokyo Institute of Technology, 4259-G2-3 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan

(Received January 8, 2008; Accepted April 22, 2008)

While an object is approaching a particular location, we can make an estimate of the time when the object will arrive at that location. A geometric model predicts that the estimate of time-to-contact (TTC) is greatly improved by using the rate of change of visual direction of the object when the object is moving with a slow velocity toward a point of nearest approach at a distance far from the observer. It has been shown that pursuit eye movements provide the rate of change of visual direction of an approaching object. We conducted psychophysical experiments, and compared TTC estimates during pursuit eye movements to those during fixation. We found that the differences in TTC estimates between fixation and pursuit show a qualitatively similar pattern to the geometric model prediction. However, the results also show that the magnitudes of the TTC estimation errors are greater than the theoretical values from the geometric model, indicating that the human visual system has a perceptual bias in estimating TTC. These results suggest that the human visual system estimates TTC during pursuit eye movements in a different way from the geometric model, although the effect of these eye movements on TTC estimates in human performance is qualitatively consistent with the model prediction.

Key words: time to contact, pursuit eye movements, extra retinal cue, motion in depth, visually timed action

^*E-mail address: kmat@riec.tohoku.ac.jp