Academic journal article Attention, Perception and Psychophysics

Short-Lived Effects of a Visual Inducer during Egocentric Space Perception and Manual Behavior

Academic journal article Attention, Perception and Psychophysics

Short-Lived Effects of a Visual Inducer during Egocentric Space Perception and Manual Behavior

Article excerpt

Published online: 8 May 2013

®> Psychonomic Society, Inc. 2013

Abstract A pitched visual inducer has a strong effect on the visually perceived elevation of a target in extrapersonal space, and also on the elevation of the arm when a subject points with an unseen arm to the target's elevation. The manual effect is a systematic function of hand-to-body distance (Li and Matin Vision Research 45:533-550, 2005): When the arm is folly extended, manual responses to perceptually mislocalized lumi- nous targets are veridical; when the arm is close to the body, gross matching errors occur. In the present experiments, we measured this hand-to-body distance effect during the presence of a pitched visual inducer and after inducer offset, using three values of hand-to-body distance (0, 40, and 70 cm) and two open-loop tasks (pointing to the perceived elevation of a target at true eye level and setting the height of the arm to match the elevation). We also measured manual behavior when subjects were instructed to point horizontally under induction and after inducer offset (no visual target at any time). In all cases, the hand-to-body distance effect disappeared shortly after inducer offset. We suggest that the rapid disappearance of the distance effect is a manifestation of processes in the dorsal visual stream that are involved in updating short-lived representations of the arm in egocentric visual perception and manual behavior.

Keywords 3-D perception · Space perception Perception and action · Visual perception · Sensory-motor interactions

Introduction

The pitch of a visual field (the rotation of a frontoparallel plane around a horizontal axis in the frontal plane of the observer) systematically influences the elevation of a vi- sual target that appears to be at eye level (Matin & Fox, 1986, 1989; Poquin, Ohlmann, & Barraud, 1998; Post & Welch, 1996; Stoper & Cohen, 1989). When the field is pitched top-backward (as in Fig. 1, left panel), a small round target that is actually lower than trae eye level appears to be at eye level; when the field is pitched top- forward, a target that appears to be at eye level is higher than true eye level. These inducing effects can be mea- sured by using the subject's reports about a visual target's height relative to perceived eye level (too high or too low) to allow the experimenter to obtain a null point for the visually perceived eye level (VPEL). The effects are very large and vary linearly with the pitch of the inducer over a wide range. Furthermore, they are not limited to a target that appears to be at eye level-targets above and below VPEL undergo a similar translation, as if the VPEL established a zero-point on a subjective elevation dimen- sion (Li, Dallai, & Matin, 2001; Li & L. Matin, 2005; Robison, Li, & Matin, 1995).

It might seem that a complex visual structure (e.g., the "pitchroom" in Fig. 1, left panel) would be necessary to produce such profound effects on the subject's VPEL. However, that is not the case. The effect is only slightly less (88 %) when the highly structured pitched visual field is replaced by two long, eccentrically placed pitched lines (Matin & Li, 1992a, 1992b). When the inducing structure is still further reduced, to one long line (as in Fig. 1, right panel), the effect is still 82 % of its magnitude with the highly structured field (Matin & Li, 1994a, 1994b). These results rule out the possibility that some aspect of perspective-related complexity is central to the induction. Moreover, the effects with monocular viewing are indistinguishable from the effects with binocular viewing, ruling out stereopsis as a critical factor (Stoper & Cohen, 1989; also cf. Matin & Fox, 1989 [binocular], with Matin & Li, 1992a, 1992b [monocular]).

These laboratory-studied effects reflect processes that also occur in naturalistic settings. For example, inexperi- enced climbers habitually underestimate the height of a mountain when they look up at the mountain from its base (lowered-peak illusion; MacDougall, 1903). …

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