Our previous study (Takahashi, Fukuda, Kaneko, 2010) reported that for the perception of the gravitational vertical (up-down) of visual images, the information processed in the early stage of visual system, such as the luminance distribution and edges, seemed to have large effects when the stimulus was presented for a short time. When the presentation time increased, this tendency decreased with the increase of the influence of the information processed in a relatively higher stage of visual system such as knowledge or inference. The information regarding the gravitational vertical is also important in our actions such as walking and standing upright.
In this study, we aimed to identify the visual factors to affect our action related to the gravitational vertical. We manipulated the factors such as the luminance distribution, motion, edges and meaning in natural pictures. As an indicator of action, we measured the observers’ body sway induced by rotating the pictures periodically clockwise and counterclockwise. The results showed the motion and edges had large effects and the luminance distribution had little effect on body sway. We discuss the difference between perception and action in the processing of the information regarding the gravitational vertical.