Perceiving affordances: Visual guidance of stair climbing.

Abstract

How do animals visually guide their activities in a cluttered environment? Gibson (1979) proposed that they perceive what environmental objects offer or afford for action. An analysis of affordances in terms of the dynamics of an animal-environment system is presented. Critical points, corresponding to phase transitions in behavior, and optimal points, corresponding to stable, preferred regions of minimum energy expenditure, emerge from variation in the animal-environment fit. It is hypothesized that these points are constants across physically similar systems and that they provide a natural basis for perceptual categories and preferences. In three experiments these hypotheses are examined for the activity of human stair climbing, by varying riser height with respect to leg length. The perceptual category boundary between "climbable" and "unclimbable" stairs is predicted by a biomechanical model, and visually preferred riser height is predicted from measurements of minimum energy expenditure during climbing. It is concluded that perception for the control of action reflects the underlying dynamics of the animal-environment system.

An Ontology Design Pattern for Referential Qualities

“…The implementation of the use-cases conforms with theory in the domain, but rival theories exist that might require a different pattern. The findings in this paper are compatible with for example the specification suggested in the MONITOR project [19] and in Warren's stair climbing experiment [37].…”

“…One of the most cited investigation of an affordance is Warren's [37] account of the stair-climbing affordance that is provided by a step with a riser height to a person with matching leg-length. The implementation of stair-climbability introduces two new categories for the stair-climbing affordances and for the stair-climbing effectivity.…”

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).…”

Influence of gaze elevation on estimating the possibility of passing under high obstacles during body tilt

“…It was therefore suggested that intrinsic individual characteristics (body size, speed of locomotion and level of motor control) and the position of the point of observation may constitute important properties of the actor-environment fit. Other studies have demonstrated that judgements of ''passability'' through apertures (Mark 1987;Warren and Whang 1987) and ''climbability'' of objects (Warren 1984) were based on affordances for which body-scaled information were also important. As a main reference for this body-scaled information, the observers' eye level appeared determinant in estimating these possibilities of action (Marcilly and Luyat 2008;Mark 1987;Wagman and Malek 2008).…”