A ground surface based space perception in real and virtual environments
Department of Psychological & Brain Sciences
University of Louisville
Louisville, KY 40292
Time and Place
Mauldin Auditorium (NSH 1305)
With reference to a flat terrain, humans can judge distance accurately up to about 20m an ability important for various actions. Here we explored how this feat is achieved and what is information provided for accurate distance perception. Subjects distance judgment was examined in real, altered and virtual environments using perceptual tasks or actions to assess the role of a variety of intrinsic and environmental depth cues. We found: (1). The perception of direction is largely veridical (direction constancy). A target in the dark was seen along its projection line from the observer even if the perceived location was erroneous (Ooi et. al., 2001). This highlights the role of the angular declination, or height in the visual field, in distance judgment. (2). A continuous and homogeneously-textured ground is critical for veridical distance perception. Texture variations, gaps in the ground, or the partial occlusion of the ground will lead to errors in judging distance (Sinai et al., 1998; Yarbrough et al., 2002). The results underscore the notion that the ground is used as the reference frame for coding objects locations. (3). Distance is underestimated if an observers view is restricted to the local ground area about the target. This suggests that accurate distance judgment relies on a process that takes in information about the target as well as that faraway from it to build an accurate ground surface representation. We thus propose the sequential surface integration process (SSIP) model that a ground surface representation is formed by sampling and combining information across space and time and the computation starts from near space where rich depth cues can provide for a reliable initial representation and then progressively extends to distant areas. Confirming this, our results found that subjects could judge distance accurately by scanning local patches of the ground from near to far, but not in the reverse direction (Wu et al., 2003).
Sinai, M. J., Ooi T. L., He J. Z., (1998). Terrain influences the accurate judgment of distance, Nature, 395, 497-500.
Ooi, T.L., Wu, B. & He, Z.J. (2001). Distance determined by the angular declination below the horizon. Nature, 414, 197-200. Yarbrough, G. L., Wu, B., Wu, J., He, Z. J., & Ooi, T. L. (2002).
Judgments of object location behind an obstacle depend on the particular information selected. Journal of Vision, 2(7), 625a, http://journalofvision.org/2/7/625/.
Wu, B., Ooi, T.L., & He Z.J. (2003). Perceiving distance accurately by a directional process of integrating ground information, Nature (In press).
Bing Wu is a Ph.D. student in Dept. of Psychological & Brain Sciences at the Univ. of Louisville, majored in Experimental Psychology. Prior to his arrival at the University of Louisville in 1999, he received a B.A. in Biomedical Engineering from Huazhong University of Technology & Sciences in 1994 and a M.S. degree in Neurobiology in 1997 from Shanghai Institute of Physiology, Chinese Academy of Sciences. Currently, he is working with Dr. Zijiang He. His research area is human space perception. More specifically, his research aims at understanding what information in the environment enable people to judge distance accurately and how this feat is achieved by the visual system. Bing Wu has five papers published or accepted, including two in Nature.
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