Static scene analysis for the perception of heading

In the current study, we explored observers ’ use of two distinct analyses for determining their direction of motion, or head-ing: a scene-based analysis and a motion-based analysis. In two ex-periments, subjects viewed sequentially presented, paired digitized images of real-world scenes and judged the direction of heading; the pairs were presented with various interstimulus intervals (ISIs). In Ex-periment 1, subjects could determine heading when the two frames were separated with a 1,000-ms ISI, long enough to eliminate appar-ent motion. In Experiment 2, subjects performed two tasks, a path-of-motion task and a memory-load task, under three different ISIs, 50 ms, 500 ms, and 1,000 ms. Heading accuracy decreased with an increase in ISI. Increasing memory load influenced heading judgments only for the longer ISI when motion-based information was not available. These results are consistent with the hypothesis that the scene-based analysis has a coarse spatial representation, is a sustained temporal process, and is capacity limited, whereas the motion-based analysis has a fine spatial resolution, is a transient temporal process, and is capacity un-limited. Gibson (1966, 1979) argued that a fundamental source of informa-tion for locomotion is optic flow—the perspective transformation of the optic array (see Fig. 1). According to Gibson, flow of the optic ar-ray, or flow perspective structure, specifies locomotion, whereas the lack of flow, or a frozen perspective structure, specifies that the ob-server is at rest. Since Gibson’s initial research on optic flow, research-ers have proposed a number of models by which observers might determine their motion from flow fields (e.g., Bruss & Horn, 1983; Hee