Academic journal article Attention, Perception and Psychophysics

Gaze Direction and the Extraction of Egocentric Distance

Academic journal article Attention, Perception and Psychophysics

Gaze Direction and the Extraction of Egocentric Distance

Article excerpt

Published online: 14 June 2014

# The Psychonomic Society, Inc. 2014

Abstract The angular declination of a target with respect to eye level is known to be an important cue to egocentric distance when objects are viewed or can be assumed to be resting on the ground. When targets are fixated, angular declination and the direction of the gaze with respect to eye level have the same objective value. However, any situation that limits the time available to shift gaze could leave to-be-localized objects outside the fovea, and, in these cases, the objective values would differ. Nevertheless, angular declination and gaze declination are often conflated, and the role for retinal eccentricity in egocentric distance judgments is unknown. We report two experiments demonstrating that gaze declination is sufficient to support judgments of distance, even when extraretinal signals are all that are provided by the stimulus and task environment. Additional experiments showed no accuracy costs for extrafoveally viewed targets and no systematic impact of foveal or peripheral biases, although a drop in precision was observed for the most retinally eccentric targets. The results demonstrate the remarkable utility of target direction, relative to eye level, for judging distance (signaled by angular declination and/or gaze declination) and are consonant with the idea that detection of the target is sufficient to capitalize on the angular declination of floor-level targets (regardless of the direction of gaze).

Keywords Distance perception . Angular declination . Gaze direction . Blind walking

A fundamental aim in the study of visual space perception is the identification of the sources of information that support judgments of distance from oneself to objects in the world. Angular declination, or the angular direction of the target with respect to eye level (Ooi, Wu, & He, 2001), is a reliable source of information about distance in the intermediate distance range (Cutting & Vishton, 1995). Accordingly, it plays an important role in several accounts for the perception of dis- tance, particularly when objects can be seen or assumed to be resting on the ground (e.g., Durgin & Li, 2011; Ooi, Wu, & He, 2006; Rand, Tarampi, Creem-Regehr, & Thompson, 2011; Sedgwick, 1986; Wu, Ooi, & He, 2004). Recent studies from our laboratory have further shown that the egocentric distance can be extracted quite quickly when angular declina- tion is informative (Gajewski, Philbeck, Pothier, & Chichka, 2010). Because of its reliability and speed of extraction, we have proposed a dynamic framework wherein angular decli- nation is the primary functional cue when viewing time is limited to the time frame of a typical eye fixation (Gajewski, Philbeck, Wirtz, & Chichka, 2014a). Although additional sources of useful information can be extracted when viewing time is extended, these presumably influence the computation of distance from angular declination by supporting a more accurate representation of the ground surface (He, Wu, Ooi, Yarbrough, & Wu, 2004; Wu, He, & Ooi, 2008;Wuetal., 2004) and/or by providing a more elaborate representation of the scale of the contextual space (Gajewski, Wallin, & Philbeck, 2014b). The weight of evidence suggests that angu- lar declination is important at all time frames when objects are resting on a level ground surface but that this directional cue most completely drives localization performance when view- ing time is limited. Because objects that require localization are often fixated, the angular declination of the target and the direction of gaze to the target typically provide the same angular value. Is the direction of gaze alone sufficient to support a judgment of distance? Real-world situations, such as navigating busy city sidewalks, arguably limit the time available to shift gaze toward objects that require localization. Are there systematic errors associated with judging the dis- tance to objects that are not directly fixated? …

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