The Importance of the Visual Background

If the selected rest frame is picked in such a way as to minimize calculations, we would expect it to be heavily influenced by what is perceived to be the visual background. The reason is that the visual background generally defines the largest set of coherent spatial cues in the environment. Consequently, calculations performed by the nervous system may be simplified by assigning this set of cues to be the rest frame, and thus as forming the comparator for spatial judgments.

One should note, however, that the primary issue is simplifying calculations, not an inherent need to make use of the visual background. For cases in which one's task involves the visual foreground one would expect this foreground to determine the selected rest frame. One example of this is that while the night stars are clearly in the visual background, one usually perceives a change in the position of the stars, not the Earth. The reason, presumably, is that the task of concern to the nervous system is navigating with respect to the surface of the Earth, not with respect to the stars. Hence, it is much more practical to take a rest frame aligned with the surface of the Earth. The relative motion between the Earth and the stars is therefore interpreted as a motion of the stars. Similarly, when checking the instrument panel of an aircraft, one will tend to perceive the panel as being at rest (defining the selected rest frame). It is only when one again looks out the window and switches to a task of navigating visually with respect to the Earth's surface that one again perceives the aircraft (and the panel) as moving.

The ``induced motion'' of the visual background reported in Pilot Study AIIIP2 (Appendix D, involving a driving simulator) is also of interest in this regard. In this case, a conflict between the motion of the visual background and of the visual foreground was perceived as a motion of the background, even though it was the background which was in agreement with the inertial cues. The driving-simulator task under study required the participant to navigate with respect to the visual foreground. Apparently, this was sufficient to result in the foreground being selected as the rest frame, even in the presence of conflicting rest frame cues from the background and from inertial cues.

Human Interface Technology Lab

Human Interface Technology Lab