Egocentric and allocentric localization during induced motion

Abstract

This research examined motor measures of the apparent egocentric location and perceptual measures of the apparent allocentric location of a target that was being seen to undergo induced motion (IM). In Experiments 1 and 3, subjects fixated a stationary dot (IM target) while a rectangular surround stimulus (inducing stimulus) oscillated horizontally. The inducing stimulus motion caused the IM target to appear to move in the opposite direction. In Experiment 1, two dots (flashed targets) were flashed above and below the IM target when the surround had reached its leftmost or rightmost displacement from the subject's midline. Subjects pointed open loop at either the apparent egocentric location of the IM target or at the bottom of the two flashed targets. On separate trials, subjects made judgments of the Vernier alignment of the IM target with the flashed targets at the endpoints of the surround's oscillation. The pointing responses were displaced in the direction of the previously seen IM for the IM target and to a lesser degree for the bottom flashed target. However, the allocentric Vernier judgments demonstrated no perceptual displacement of the IM target relative to the flashed targets. Thus, IM results in a dissociation of egocentric location measures from allocentric location measures. In Experiment 2, pointing and Vernier measures were obtained with stationary horizontally displaced surrounds and there was no dissociation of egocentric location measures from allocentric location measures. These results indicate that the Roelofs effect did not produce the pattern of results in Experiment 1. In Experiment 3, pointing and Vernier measures were obtained when the surround was at the midpoint of an oscillation. In this case, egocentric pointing responses were displaced in the direction of surround motion (opposite IM) for the IM target and to a greater degree for the bottom flashed target. However, there was no apparent displacement of the IM target relative to the flashed targets in the allocentric Vernier judgments. Therefore, in Experiment 3 egocentric location measures were again dissociated from allocentric location measures. The results of this experiment also demonstrate that IM does not generate an allocentric displacement illusion analogous to the "flashlag" effect.

Paradoxical stabilization of relative position in moving frames

“…There have been many demonstrations of the effects of frames on position, orientation, and motion decomposition (1-10), but none with effects of this magnitude. What is different here is that the probes are flashed, removing the constraints on perceived location imposed by the continuously present probes used by Duncker (2) and Wallach (8) and others since them (10). The frame-induced shift with flashed probes approaches a 100% effect in several conditions-the shift had virtually the same amplitude as the frame motion that produced it.…”

Conflicting motion information impairs multiple object tracking

“…It is unclear whether representational momentum occurs for objects that do not disappear. Studies of perceived position of visible stimuli in motion seem to suggest that there are many factors that determine the interaction between location and motion information (Kerzel & Gegenfurtner, 2004;Post, Welch, & Whitney, 2008;Whitney, 2006). Thus, the existing evidence of motion influence on target localization after disappearance may or may not address the question of what information is used for tracking visible objects.…”

Spatial localization investigated by continuous pointing during visual and gravitoinertial changes

“…When the visual background was rotated without any Gi modifications (Vis R condition), we found a progressive elevation of continuous pointing which could be interpreted as a consequence of an illusory target elevation. This induced-motion phenomenon has already been described at length in the literature for localization judgments and discrete pointing movements (Bridgeman et al 1981;Post et al 2008). Post and Lott (1990) also suggested that the strength of induced motion is mostly related to the visual background velocity.…”

“…Although de Graaf et al (1998) have already tested the effectiveness of rotating the visual scene in order to reduce the somatogravic illusion, the effect of moving visual cues on target localization during centrifugation has never been investigated, to our knowledge. This may, however, constitute a promising way of investigation since it is well established that, in a nonmodified Gi environment, moving the visual background strongly influences target localization (i.e., induced-motion illusion, Duncker 1929;Post et al 2008). Specifically, when a static visual target is presented, a moving visual background usually produces an illusory perception of target motion, in a direction opposite to the background motion, while the visual background is perceived static.…”