The results of two types of experiments are reported. In 1 type, Ss matched depth intervals on the ground plane that appeared equal to frontal intervals at the same distance. The depth intervals had to be made considerably larger than the frontal intervals to appear equal in length, with this physical inequality of equal-appearing intervals increasing with egocentric distance of the intervals (4 m-12 m). In the other type of experiment, Ss viewed targets lying on the ground plane and then, with eyes closed, attempted either to walk directly to their locations or to point continuously toward them while walking along paths that passed off to the side. Performance was quite accurate in both motoric tasks, indicating that the distortion in the mapping from physical to visual space evident in the visual matching task does not manifest itself in the visually open-loop motoric tasks.

The question of how perceived extents are related to the corresponding physical extents is a very old question that has not been satisfactorily answered. The common model is that perceived extent is proportional to the product of image size and perceived distance. We describe an experiment that shows that perceived extents are substantially larger than this model predicts. We propose a model that accounts for our results and a large set of other results. The principal assumption of the model is that, in the computation of perceived extent, the visual angle signal undergoes a magnifying transform. Extent is often perceived more accurately than the common model predicts, so the computation is adaptive. The model implies that, although the perception of location and the perception of extent are related, they not related by Euclidean geometry, nor by any metric geometry. Nevertheless, it is possible to describe the perception of location and extent using a simple model.

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Two triangulation methods for measuring perceived egocentric distance were examined. In the triangulation-by-pointing procedure, the observer views a target at some distance and, with eyes closed, attempts to point continuously at the target while traversing a path that passes by it. In the triangulation-by-walking procedure, the observer views a target and, with eyes closed, traverses a path that is oblique to the target; on command from the experimenter, the observer turns and walks toward the target. Two experiments using pointing and 3 using walking showed that perceived distance, averaged over observers, was accurate out to 15 m under full-cue conditions. For target distances between 15 and 25 m, the evidence indicates slight perceptual underestimation. Results also show that observers, on average, were accurate in imaginally updating the locations of previously viewed targets.The term visual space (or visually perceived space) refers to a perceptual representation of the immediate physical environment that exists independently of any of the particular spatial behaviors it helps to control. Much vision research has been devoted to establishing the functional properties of visual space and the mechanisms that underlie it. A major goal of such research has been to characterize the mapping from physical to visual space under different conditions of information availability, but ultimately the goal must be to predict visual space solely in terms of its sensory inputs and internal determinants (e.g., intrinsic noise, observer assumptions, etc.).Because visual direction is perceived accurately, most space perception research has examined the perception of egocentric distance (i-e., the distance from the object to the observer) and the perception of exocentric distance (i.e., the distance between two targets lying in the same visual direction or, more generally, the distance between any two locations). Because we believe that the perception of egocentric Gogel, 1977), our focus here is on the former.It generally is accepted that when visual cues to distance are reduced greatly, egocentric distance is misperceived (e.g., Baird, 1970;Da Silva, 1985;Foley, 1977Foley, ,1980Foley & Held, 1972;Gogel, 1974;Holway & Boring, 1941;Kiinnapas, 1968;Philbeck & Loomis, 1997;Sedgwick, 1986). Under "full-cue" conditions, in which a stimulus-rich environment is viewed under good illumination, however, there is little agreement about whether perception is accurate, mainly because of the diversity of findings stemming from different experimental methods. With respect to egocentric distance, much of the research conducted under full-cue conditions suggests that perceived distance is nearly linear in physical distance and appropriately scaled, at least for targets within 20 m (e.g., verbal reports, Da Silva, 1985;Sedgwick, 1986;Teghtsoonian & Teghtsoonian, 1969, 1970 blind walking to previewed targets, Corlett, Patla, & Williams, 1985;Elliott, 1986Elliott, , 1987Elliott, Jones, & Gray, 1990;Loomis, Da Silva, Fujita, & Fukusima, 1992...

Palavras-chave: percepção da fala, teste de fala em ruído, audição.