Visual guidance of walking through apertures: Body-scaled information for affordances.

Abstract

A necessary condition for visually guided action is that an organism perceive what actions are afforded by a given environmental situation. Warren (1984) proposed that an affordance such as the climbability of a stairway is determined by the fit between properties of the environment and the organism and can be characterized by optimal points, where action is most comfortable or efficient, and critical points, where a phase transition to a new action occurs. Perceiving an affordance, then, implies perceiving the relation between the environment and the observer's own action system. The present study is an extension of this analysis to the visual guidance of walking through apertures. We videotaped large and small subjects walking through apertures of different widths to determine empirically the critical aperture-to-shoulder-width ratio (A/S) marking the transition from frontal walking to body rotation. These results were compared with perceptual judgments of "passability" under static and moving viewing conditions. Finally, we tested the hypothesis that such judgments are based on intrinsic or body-scaled information specifying aperture width as a ratio of the observer's eyeheight. We conclude (a) that the critical point in free walking occurs at A/S = 1.30, (b) that static monocular information is sufficient for judging passability, and (c) that the perception of passability under such conditions is based on body-scaled eyeheight information.

Visual enhancement of touch and the bodily self

“…While several studies have demonstrated effects of the bodily self on higher-level perception (e.g., Longo & Lourenco, 2007;Warren & Whang, 1987), to our knowledge the present results constitute the first evidence of such effects at the level of basic sensory processing.…”

Mapping the internal geometry of tactile space.

“…Longo, Azañón, and Haggard (2010) argued that perceiving the metric properties of objects touching the skin requires that immediate sensory signals be combined with (Berryman, Yau, & Hsiao, 2006), sounds produced by action (Tajadura-Jiménez et al, 2012, 2015, the rubber hand illusion (Bruno & Bertamini, 2010), and tool use (Canzoneri et al, 2013;Miller, Longo, & Saygin, 2014, 2017. Thus, in analogy with the modulation of perceived passability of apertures when apparent eyeheight was altered shown by Warren and Whang (1987), these results show that experimental manipulations of represented body size alter perceived tactile distance.…”

“…By inserting (unbeknownst to participants) a false floor between the participants and an aperture, and thus reducing effective eyeheight, they showed that the perception of the affordance of passability through the aperture was determined as a fixed proportion of perceived eye-height. Warren and Whang (1987) introduced a distinction between two ways in which visual information specifying affordances of the environment might be coded, extrinsically or intrinsically. In the case of extrinsic coding, visual information is first used to specify the dimensions of environmental stimuli in an absolute, viewerindependent metric, which is then subsequently compared to representations of the size of the viewer's body.…”

“…In each of these cases, perceptual maps were constructed directly, in the sense that participants were asked to make overt judgments of perceived location in some external frame of reference. Thus, the tasks were extrinsic in the sense of Warren and Whang (1987).…”

Prehension is really reaching and grasping

“…We agree with Smeets and Brenner (1999) that the distinction between intrinsic and extrinsic object properties is problematic. Not only can we think of properties that are hard to classify as either intrinsic or extrinsic (Smeets and Brenner mentioned object orientation), but also another literature (in the tradition of, so-called, aVordance research; see Gibson 1979;Warren 1984;Warren and Whang 1987) suggests that for the person wishing to pick up an object its size per se is not the relevant variable, but more so its size in relation to relevant body metrics (e.g., Newell 1999, 2000a, b;Van der Kamp et al 1998;Newell et al 1989;Richardson et al, 2007). For instance, the transition for picking up an object with a two or three-Wnger grip happens at the same ratio of object size and hand width for small children and adults, such that this transition happens at other object sizes for persons with diVerently sized hands (Newell et al 1989).…”