Judging Egocentric Distance on the Ground: Occlusion and Surface Integration

Abstract

On the basis of the finding that a common and homogeneous ground surface is vital for accurate egocentric distance judgments (Sinai et al, 1998 Nature 395 497–500), we propose a sequential-surface-integration-process (SSIP) hypothesis to elucidate how the visual system constructs a representation of the ground-surface in the intermediate distance range. According to the SSIP hypothesis, a near ground-surface representation is formed from near depth cues, and is utilized as an anchor to integrate the more distant surfaces by using texture-gradient information as the depth cue. The SSIP hypothesis provides an explanation for the finding that egocentric distance judgment is underestimated when a texture boundary exists on the ground surface that commonly supports the observer and target. We tested the prediction that the fidelity of the visually represented ground-surface reference frame depends on how the visual system selects the surface information for integration. Specifically, if information is selected along a direct route between the observer and target where the ground surface is disrupted by an occluding object, the ground surface will be inaccurately represented. In experiments 1–3 we used a perceptual task and two different visually directed tasks to show that this leads to egocentric distance underestimation. Judgment is accurate however, when the observer selects the continuous ground information bypassing the occluding object (indirect route), as found in experiments 4 and 5 with a visually directed task. Altogether, our findings provide support for the SSIP hypothesis and reveal, surprisingly, that the phenomenal visual space is not unique but depends on how optic information is selected.

The ground dominance effect in the perception of relative distance in 3-D scenes is mainly due to characteristics of the ground surface

“…This integration process hypothesis was supported by Z. J. He et al (2004). They found that when there was an occluding box between a participant and a target object on the ground, the distance of the target object was underestimated.…”

“…In recent years, a number of investigators have proposed similar ideas (Z. J. He, Wu, Ooi, Yarbrough, & Wu, 2004;McCarley & Z. J. He, 2000;Nakayama, Z. J.…”

“…Z. J. He et al (2004) proposed that the discontinuity effect results from a sequential surface integration process (SSIP), through which the ground surface is represented in the visual system. The SSIP hypothesis assumes that the ground surface is perceived accurately only at near distance, where sufficient depth cues, such as vergence, binocular disparity, and so on, are present.…”

How high is visual short-term memory capacity for object layout?

“…Our manipulation of an organizational factor was motivated by recent work in perception that has implicated surfaces-and ground surfaces, in particular-as structures for integrating object and scene information (e.g., He, Wu, Ooi, Yarbrough, & Wu, 2004;Ni, Braunstein, & Andersen, 2005;Vecera & Palmer, 2006; see also Gibson, 1979). Stimulus elements were selected from an organized pair of surfaces (ground and sky, Figure 1A) or an unorganized pair of surfaces (random arrangement of the same elements, Figure 1B).…”

Action-Specific Effects Underwater

“…Researchers attribute this overestimation to optical factors such as reduced brightness contrast or seemingly increased aerial perspective. However, above ground, reduced cue settings can result in distance compression (eg He et al 2004), so distance underestimation may have been expected underwater where optical cues are reduced. In the current experiment, participants viewed the same environment, so all optical cues were held constant across conditions.…”