From the most fleeting of glimpses: on the time course for the extraction of distance information

Abstract

An observer's visual perception of the absolute distance between his or her position and an object is based on multiple sources of information that must be extracted during scene viewing. Research has not yet discovered the viewing duration observers need to fully extract distance information, particularly in navigable real-world environments. In a visually directed walking task, participants showed a sensitive response to distance when they were given 9-ms glimpses of floor- and eye-level targets. However, sensitivity to distance decreased markedly when targets were presented at eye level and angular size was rendered uninformative. Performance after brief viewing durations was characterized by underestimation of distance, unless the brief-viewing trials were preceded by a block of extended-viewing trials. The results indicate that experience plays a role in the extraction of information during brief glimpses. Even without prior experience, the extraction of useful information is virtually immediate when the cues of angular size or angular declination are informative for the observer.

Figure 1

Mean walked distance to floor-level targets as a function of target distance and viewing duration a) when the block of 113-ms trials was first; and b) when the block of 5-sec trials was first.

Figure 2

Mean walked distance to floor-level targets as a function of target distance and viewing duration. Data are shown for the 9-ms-first group, though performance in no way depended on block order.

Figure 3

Mean walked distance to eye-level targets as a function of target distance and viewing duration.

Figure 4

Mean walked distance as a function of target distance and viewing duration for eye-level and floor-level targets.