Inaccurate Representation of the Ground Surface beyond a Texture Boundary

Abstract

The sequential-surface-integration-process (SSIP) hypothesis was proposed to elucidate how the visual system constructs the ground-surface representation in the intermediate distance range (He et al, 2004 Perception 33 789-806). According to the hypothesis, the SSIP constructs an accurate representation of the near ground surface by using reliable near depth cues. The near ground representation then serves as a template for integrating the adjacent surface patch by using the texture gradient information as the predominant depth cue. By sequentially integrating the surface patches from near to far, the visual system obtains the global ground representation. A critical prediction of the SSIP hypothesis is that, when an abrupt texture-gradient change exists between the near and far ground surfaces, the SSIP can no longer accurately represent the far surface. Consequently, the representation of the far surface will be slanted upward toward the frontoparallel plane (owing to the intrinsic bias of the visual system), and the egocentric distance of a target on the far surface will be underestimated. Our previous findings in the real 3-D environment have shown that observers underestimated the target distance across a texture boundary. Here, we used the virtual-reality system to first test distance judgments with a distance-matching task. We created the texture boundary by having virtual grass- and cobblestone-textured patterns abutting on a flat (horizontal) ground surface in experiment 1, and by placing a brick wall to interrupt the continuous texture gradient of a flat grass surface in experiment 2. In both instances, observers underestimated the target distance across the texture boundary, compared to the homogeneous-texture ground surface (control). Second, we tested the proposal that the far surface beyond the texture boundary is perceived as slanted upward. For this, we used a virtual checkerboard-textured ground surface that was interrupted by a texture boundary. We found that not only was the target distance beyond the texture boundary underestimated relative to the homogeneous-texture condition, but the far surface beyond the texture boundary was also perceived as relatively slanted upward (experiment 3). Altogether, our results confirm the predictions of the SSIP hypothesis.

Egocentric distance estimation on a discontinuous ground surface in the virtual environment

“…The distance underestimation in virtual environments is consistent with the results of a number of studies conducted in the VE (e.g., [Thompson et al 2004;Grechkin et al 2010]) using other methods, e.g., blind walking. However, the texture discontinuity effect of Wu et al [2007] was not found in these experiments.…”

“…Using the adjustment method of Wu et al [2007], distances were underestimated in all of the conditions in Experiments 1 and 2. The distance underestimation in virtual environments is consistent with the results of a number of studies conducted in the VE (e.g., [Thompson et al 2004;Grechkin et al 2010]) using other methods, e.g., blind walking.…”

“…Two experiments were conducted to investigate the effect of a discontinuous ground surface on distance perception in virtual environments (VEs). The first experiment was the replication of Experiment 1 from Wu et al [2007]. The second experiment involved the manipulation of the position of the texture boundary.…”

Frontal extents in virtual environments are not immune to underperception

“…The current project compared the relationship between frontal and depth extents in two VEs: the indoor classroom environment used by Geuss et al (2012) and a barren outdoor environment consisting of a ground plane covered in a grass texture, which has produced relatively large underperception of egocentric distance in our laboratory (Kelly, Hammel, Siegel, & Sjolund, 2014). Similar outdoor VEs have been used in numerous experiments testing distance perception (Kelly, Donaldson, Sjolund, & Freiberg, 2013;Li et al, 2013;Messing & Durgin, 2005;Richardson & Waller, 2005;Waller & Richardson, 2008;Wu, He & Ooi, 2007;Ziemer, Plumert, Cremer & Kearney, 2009). We expected that manipulation of the VE (room vs. grass) would affect judgments of depth extents, with smaller judgments in the grass VE compared to the room VE.…”

Non-visually-guided distance perception depends on matching torso fluctuations between training and test

“…Kinesthesis Distance perception draws on multiple physiological systems. Optical variables inform sighted distance judgments (e.g., Wu, He, & Ooi, 2007), and participants with eyes closed can blindly walk a distance commensurate with distance to that target (Thomson, 1983;Elliott, 1986). Blindwalking participants use haptic information from footfalls and postural corrections to feel their way on "how long" it is to the target (Loomis, Da Silva, Fujita, & Fukusima, 1992;Loomis et al, 1993).…”