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In four studies we investigated the perception of the affordance for traversal of a supporting surface. The surface presented was either rigid or deformable, and this property was specified either optically, haptically, or both. In Experiment 1A, crawling and walking infants were presented with two surfaces in succession: a standard surface that both looked and felt rigid and a deforming surface that both looked and felt nonrigid. Latency to initiate locomotion, duration of visual and haptic exploration, and displacement activity were coded from videotapes. Compared with the standard, the deforming surface elicited longer latency, more exploratory behavior, and more displacement in walkers, but not in crawlers, suggesting that typical mode of locomotion influences perceived traversability. These findings were replicated in Experiment 1B, in which the infant was presented with a dual walkway, forcing a choice between the two surfaces. Experiments 2, 3A and B, and 4A and B investigated the use of optical and haptic information in detecting traversability of rigid and nonrigid surfaces. Patterns of exploration varied with the information presented and differed for crawlers and walkers in the case of a deformable surface, as an affordance theory would predict.

In this article we provide evidence against a fundamental assumption of traditional theories of orientation—that gravitoinertial force is perceived. We argue that orientation is based on information that is available in patterns of motion of the organism. We further argue that perception and control of orientation depend not only on information about an organism's motions relative to the local force environment but also on information about the surface of support and about the compensatory actions of the organism. We describe these kinds of information and discuss their availability to, and across, different perceptual systems. The use of this information for the control of orientation is emphasized. We conclude with recommendations for research based on the new approach.

Visually induced motion sickness is a syndrome that occasionally occurs when physically stationary individuals view compelling visual representations of self-motion. It may also occur when detectable lags are present between head movements and recomputation and presentation of the visual display in helmet-mounted displays. The occurrence of this malady is a critical issue for the future development and implementation of virtual environments. Applications of this emerging technology are likely to be compromised to the extent that users experience illness and/or incapacitation. This article presents an overview of what is currently known regarding the relationship between visually specified self-motion in the absence of inertial displacement and resulting illness and perceptual-motor disturbances.