Egocentric Distance Judgments Research Articles

Judging egocentric distance on the ground: occlusion and surface integration.

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.

Perceptual constancy in judgments of egocentric distance: prevailing binocular information

Binocular cues were considered the prevailing information on specifying depth since the beginning of vision research. In the present study, two perceptual responses, the classical verbal report and a more recent method, open-loop walking, were used to assess the role of binocular information for egocentric distance perception. In two cue conditions environments, full- and reduced-cue, observers judged and walked egocentric distances of stimuli presented at eye-level, under binocular or monocular viewing. Results indicated perceptual constancy for open-loop walking and binocular responses, as well as poor performances under strong degradation on visual information (reduced-cue under monocular viewing), thus presenting evidence to support the fundamental role of binocular information on perception of egocentric distances. Besides that, visually directed actions could be adequate measures of perceived distance, with a better reliability than verbal report, since they were quite free of intrusion of inferential processes and perceptual tendencies. In addition, reduced head movements, side-to-side as well as back and forth deflexion movements, could have contributed to a near perfect coupling between binocular disparity information and open-loop walking responses.

Perceptual constancy in judgments of egocentric distance: prevailing binocular information

Perceptual constancy in judgments of egocentric distance: prevailing binocular information

Egocentric Distance Perception in a Virutal Environment Using a Perceptual Matching Task

Objective: To determine whether egocentric distance judgments are accurate in a virtual environment using a perceptual matching task. Methods: Observers were immersed within a virtual environment consisting of an L-shaped room with a test object (a column) located down one corridor and a comparison object (a flagpole) located down the other. Perceived distances were measured by having the observers move the comparison object to match the distance to the test object. Textures in each corridor were independently varied, as was the size of the test object. Results: Significant effects were found for the texture pattern under the test object and for distance, but not for the texture under the comparison object or column size. Performance was best with a regular (brick) pattern. Overall, observers' judgments overestimated distance to the test object by approximately 7%. Conclusions: Egocentric distance judgments were relatively accurate compared to past research. Texture affected performance, with a regular pattern producing highest accuracy.

Familiar size and judgments of distance: Effects of response mode

Two methods of assessing the perceived egocentric distance of a familiar object presented under full-cue conditions were compared. Familiar size modified verbal estimates of distance but did not affect ratio distance judgments, a less direct measure of perceived distance. In addition, familiar size failed to affect size estimates of an unfamiliar target present in the visual field. These results are consistent with the claim that many of the reported findings indicating an effect of familiar size on direct scalar judgments of egocentric distance may represent a cognitive rather than a perceptual response of the distance of the familiar target.

Role of Familiar Size in Spatial Judgments under Natural Viewing Conditions

The purpose of the present experiment was to examine the role of familiar size in judgments of size and egocentric distance under natural (non-reduced) viewing conditions. Independent groups (ns = 14) judged normal and large off-size chairs and control objects presented at a distance of 25.6 m. Subjects also judged the size of unfamiliar objects (adjacent stimuli) attached to the chairs and stakes. The results indicate that the effects of familiar size are specific to spatial judgments of the familiar object itself since judgments of the adjacent stimuli were unaffected by familiar size.