Effect of Visual Angle on the Head Movement Caused by Changing Binocular Disparity

It has been shown that vertical binocular disparity has no or little effect on the perception of visual direction (Banks et al., 2002). On the other hand, our previous study has reported that a continuous change of vertical disparity causes an involuntary sway of the head (Maekawa et al., 2009). We predict that the difference between those results attributes to the dissociation between the processes for perception and action in the brain. The aim of this study is to investigate in more details the condition that influences the process of disparity information. The present experiment particularly varied the visual angle of stimulus presentation and measured the head movement and body sway caused by changing vertical disparity. Results showed that the head movement was greater as the visual angle of the stimulus was smaller. It has been reported that stimulus of only small visual angle affect depth perception (Erklens et al., 1995). Thus, our result suggests that perception and action produced by vertical disparity are consistent as far as the effect of the stimulus size is concerned