Abstract
A widely accepted theory of vision is that optical flow provides information for the perception and control of locomotion. In the present study we examined the availability of a different source of information—static scene layout and landmarks. We propose that this second source of information can be used without the presence of apparent motion and involves the recovery of a high level description of the scene that requires attention. To examine these issues we presented observers with displays of digitized images of real scenes depicting a receding space in depth with landmarks. On each trial observers were shown two successive frames produced by displacing the viewer's position to the left or right. The observer's task was to indicate whether the viewer's position change was to the left or to the right. The independent variables included the magnitude of displacement and the ISI of the two frames (0, 500, and 1000 msec). We also manipulated attentional load by requiring observers to solve a digit and an alphabet arithmetic task while performing the displacement judgment. The results indicated that accuracy in determining the direction of displacement increased with the magnitude of the displacement. Accuracy decreased with an increase in ISI, but was clearly above chance at the 1000 msec ISI for large displacements. We also observed a decrease in direction accuracy for high load as compared to low load conditions for long ISIs. These results provide evidence that scene layout information is used to determine position change in the absence of apparent motion and is dependent on attentional processes.
Supported by NIH Grant 1R01EY12437.