Angular declination and the dynamic perception of egocentric distance

Abstract

The extraction of the distance between an object and an observer is fast when angular declination is informative, as it is with targets placed on the ground. To what extent does angular declination drive performance when viewing time is limited? Participants judged target distances in a real-world environment with viewing durations ranging from 36-220 ms. An important role for angular declination was supported by experiments showing that the cue provides information about egocentric distance even on the very first glimpse, and that it supports a sensitive response to distance in the absence of other useful cues. Performance was better at 220-ms viewing durations than for briefer glimpses, suggesting that the perception of distance is dynamic even within the time frame of a typical eye fixation. Critically, performance in limited viewing trials was better when preceded by a 15-s preview of the room without a designated target. The results indicate that the perception of distance is powerfully shaped by memory from prior visual experience with the scene. A theoretical framework for the dynamic perception of distance is presented.

Figure 1

The distance to a target object resting on the ground is trigonometrically related to angular declination below eye level but depends on the perception and/or representation of surface slant.

Figure 2

Mean walked distance to floor-level targets as a function of target distance and the physical size of object in Experiment 1. The targets were of constant size or were varied to hold angular size constant. Size was blocked such that either the varied-size trials were administered first (left) or the constant-size trials were administered first (right). Figures include best-fitting regression lines through the average data. Depicted are the means with standard error bars and best-fitting lines for the fixed effects derived from the model.

Figure 3

Mean walked distance to floor-level targets as a function of target distance and trial number in Experiment 2. The viewing duration was 74 ms. Figure includes best-fitting regression lines through the average data. Depicted are the means with standard error bars and best-fitting lines for the fixed effects derived from the model.

Figure 4

Mean walked distance to floor-level targets as a function of target distance and the viewing condition in Experiment 3. The illuminated targets were monocularly viewed in a darkened room (Dark) for 3 seconds and standard targets were viewed binocularly in a well lit room (Light) for 74 ms. Viewing condition was blocked such that either the Dark trials were administered first (left) or the Light trials were administered first (right). Depicted are the means with standard error bars and best-fitting lines for the fixed effects derived from the model.

Figure 5

Mean walked distance to floor-level targets as a function of target distance and the viewing condition in Experiment 4. Standard targets were at each participant’s brief (Suprathreshold) and long (220 ms) viewing duration. Viewing duration was blocked such that either the Suprathreshold trials were administered first (left) or the 220-ms trials were administered first (right). Depicted are the means with standard error bars and best-fitting lines for the fixed effects derived from the model.

Figure 6

Mean walked distance to floor-level targets as a function of target distance in Experiment 5. A block of blind walking trials with a viewing duration of 74 ms was preceded by a 15-second visual preview of the room (Visual Preview), a set of directed-walking trials (Walking Preview), or no-preview control (None). Depicted are the means with standard error bars and best-fitting lines for the fixed effects derived from the model.