Investigation of visual space using an exocentric pointing task

Abstract

Classically, it has been assumed that visual space can be represented by a metric. This means that the distance between points and the angle between lines can be uniquely defined. However, this assumption has never been tested. Also, measurements outdoors, where monocular cues are abundant, conflict with this model. This paper reports on two experiments in which the structure of visual space was investigated, using an exocentric pointing task. In the first experiment, we measured the influence of the separation between pointer and target and of the orientation of the stimuli with respect to the observer. This was done both monocularly and binocularly. It was found that the deviation of the pointer settings depended linearly on the orientation, indicating that visual space is anisotropic. The deviations for configurations that were symmetrical in the median plane were approximately the same, indicating that left/right symmetry was maintained. The results for monocular and binocular conditions were very different, which indicates that stereopsis was an important cue. In both conditions, there were large deviations from the veridical. In the second experiment, the relative distance of the pointer and the target with respect to the observer was varied in both the monocular and the binocular conditions. The relative distance turned out to be the main parameter for the ranges used (1-5 m). Any distance function must have an expanding and a compressing part in order to describe the data. In the binocular case, the results were much more consistent than in the monocular case and had a smaller standard deviation. Nevertheless, the systematic mispointings remained large. It can therefore be concluded that stereopsis improves space perception but does not improve veridicality.

Matching perceived depth from disparity and from velocity: Modeling and psychophysics

“…Some of these experiments have been conducted in the laboratory with computer-generated displays Brenner & Landy, 1999;Brenner & van Damme, 1999;Collett, Schwarz, & Sobel, 1991;Johnston, 1991;Johnston, Cumming, & Landy, 1994;Norman & Todd, 1998;Todd, Oomes, Koenderink, & Kappers, 2001;Tittle, Todd, Perotti, & Norman, 1995), whereas other studies have been carried out by using real objects in fully illuminated natural environments (Baird & Biersdorf, 1967;Battro, Netto, & Rozestraten, 1976;Bradshaw, Parton, & Glennerster, 2000;Cuijpers, Kappers, & Koenderink, 2000a, Cuijpers, Kappers, & Koenderink, 2000bGilinsky, 1951;Harway, 1963;Koenderink, van Doorn, Kappers, & Todd, 2002;Koenderink, van Doorn, & Lappin, 2000;Loomis, Da Silva, Fujita, & Fukusima, 1992;Loomis & Philbeck, 1999;Norman, Crabtree, Clayton, & Norman, 2005;Norman, Lappin, & Norman, 2000;Norman, Todd, Perotti, & Tittle, 1996 -see their Experiment 4). In most of the cases, however, the psychophysical literature suggests that human observers do not estimate the viewing distance correctly.…”

Effects of Context on a Visual 3-D Pointing Task

“…This task has been used in the horizontal plane at eye-height by several experimenters including Cuijpers et al (2000a), Koenderink et al (2000), and Schoumans et al (2002). During a 2-D exocentric pointing task, an observer has to rotate a pointer with a remote control in the horizontal plane at eye-height.…”

“…The task is to let it point towards a target. Cuijpers et al (2000a) tried to conceal the information normally provided by walls, floor, and ceiling of the experimental room by covering the walls with wrinkled plastic. In addition, they had the observers seated in a cabin with a chin-rest to prevent them from deriving information from head movements.…”

Visual space under free viewing conditions

“…Recently, Cuijpers, Kappers, and Koenderink (2000a, 2000b, 2001 did indoor experiments in a room where most pictorial depth cues were eliminated from the visual field by means of wrinkled plastic that prevented observers from seeing the walls. The floor and ceiling of the room were not visible because the observer was seated in a cabin that restricted the vertical field of view.…”