Elucidating the ground-based mechanisms underlying space perception in the intermediate distance range

Human observers can make accurate egocentric distance judgments on the continuous ground surface in the intermediate distance range up to about 25 m (Loomis et al. 1996). What depth information is used by the visual system to accomplish this perceptual feat? About half a century ago, J. J. Gibson (1950) proposed the ground theory of space perception, which emphasizes the eminent role of the ground surface. Recent studies have provided substantial empirical supports for Gibson’s theory, and propelled extended empiricaldriven hypotheses of the ground-based mechanisms underlying space perception (e.g., Sedgwick 1986; Sinai et al. 1998; He et al. 2004; Ooi et al. 2001, 2006; Wu et al. 2004, 2005). Together these mechanisms entail that the visual system constructs a ground surface representation for use as a reference frame to determine the object location. Here, we present our empirical findings that led to the formulation of the proposed ground-based mechanisms. Main contribution