Perceiving distance accurately by a directional process of integrating ground information

Abstract

By itself, the absolute distance of an object cannot be accurately judged beyond 2-3 m (refs 1-3). Yet, when it is viewed with reference to a flat terrain, humans accurately judge the absolute distance of the object up to 20 m, an ability that is important for various actions. Here we provide evidence that this is accomplished by integrating local patches of ground information into a global surface reference frame. We first show that restricting an observer's visual field of view to the local ground area around the target leads to distance underestimation, indicating that a relatively wide expanse of the ground surface is required for accurate distance judgement. Second, as proof of surface integration, we show that even with the restricted view, the observer can accurately judge absolute distance by scanning local patches of the ground surface, bit by bit, from near to far, but not in the reverse direction. This finding also reveals that the surface integration process uses the near-ground-surface information as a foundation for surface representation, and extrapolation to the far ground surface around the target for accurate absolute distance computation.

Does Energy Expenditure Affect the Perception of Egocentric Distance? A Failure to Replicate Experiment 1 of Proffitt, Stefanucci, Banton, and Epstein (2003)

“…Based on the previous work of Creem-Regehr et al (2005) and Wu et al (2004), it was expected that reducing the participant's field of view would cause a reduction of the perceived distances of the different targets. This result was obtained with both direct measures of perceived distance, verbal report and the distance to the stopping points in the indirect blind walking task; the ratios of the slopes of the regression functions (RFOV/control) were 0.83 and 0.86 for verbal report and blind walking, respectively.…”

“…Consequently, for a constant angular size, increases in perceived distance should result in proportional increases in the perceived size. Because of the reported reduction of perceived distance produced by restricting the field of view (Creem-Regehr et al, 2005;Wu et al, 2004), we expected proportional decreases in estimated target size. Similarly, if wearing a backpack increases perceived distance, there should be proportional increases in estimated target size.…”

“…Therefore, we chose to use instead a manipulation for reducing perceived distance. To effect this reduction, we greatly restricted the field of view on the participants, a manipulation found to decrease perceived egocentric distance, as measured using variants of blind walking (Creem-Regehr, Willemsen, Gooch, & Thompson, 2005;Wu et al, 2004) 2 . Thus, participants in the present reduced field of view (RFOV) condition viewed targets through a restrictive aperture and made the same estimates as in the other two conditions.…”

“…Action based measures of perceived egocentric distance include ball throwing, blind walking, triangulation methods, and more recently a measure based on a response in 3-D space consisting of blind walking and a pointing gesture by the hand (Ooi, Wu, & He, 2001). Non-action based measures include verbal report of perceived distance, an estimate of perceived distance derived from distal size judgments by way of size-distance invariance (e.g., Gogel, Loomis, Newman, & Sharkey, 1985), and estimates of distance derived from judgments of shape by way of the coupling observed between perceived shape and perceived distance (Ooi, Wu, & He, in press;Wu, Ooi, & He, 2004).…”

Toward a new theory of stereopsis.

“…Monocular viewing eliminates two important distance cues (vergence and vertical disparity) as well as eliminating the precision depth cue 24 This would correspond to the point beyond which only depth order can be conceivably be discriminated on the basis of disparities, but without the impression of stereopsis (what Ogle(1950) (Wu et al, 2004), which suggests that depth could, in principle, be scalable under monocular viewing well into action space. However, the depth cues specifying the relative separation between objects are themselves considerably less reliable than disparity.…”