Visual space perception and visually directed action.

Abstract

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.

Manipulation of visual information does not change the accuracy of distance estimation during a blindfolded walking task

“…Here we demonstrate that humans can navigate blindfolded to a target up to 20 m away relatively successfully. While this feat has been generally demonstrated previously (Corlett et al, 1985;Fukusima et al, 1997;Glasauer et al, 1994;Loomis et al, 1992;Mittelstaedt & Mittelstaedt, 2001;Rieser et al, 1990;Steenhuis & Goodale, 1988), we demonstrate that the accuracy decreased steadily in the blindfolded group as the distance increased, with this group taking longer to complete the task at every distance tested (Experiment 1). Conversely, the visual group remained relatively accurate by comparison, completing the task faster and with lower error scores.…”

“…While many studies have shown, similar to Thomson, that blindfolded humans are able to navigate relatively successfully towards a target, his suggestion of a time limiting component has not been replicated (Fukusima, Loomis, & Da Silva, 1997;Rieser, Ashmead, Talor, & Youngquist, 1990), with many authors finding that participants become less accurate in their estimation if the distance is increased (Corlett, Patla, & Williams, 1985;Fukusima et al, 1997;Glasauer, Amorim, Vitte, & Berthoz, 1994;Loomis, Da Silva, Fujita, & Fukusima, 1992;Mittelstaedt & Mittelstaedt, 2001;Rieser et al, 1990;Steenhuis & Goodale, 1988). Indeed, there is good evidence to suggest that other factors apart from time can contribute to successful non-visual distance estimation.…”

The perception of length on curved and flat surfaces

“…The probable reason this distortion was not noticed previously is that it appears to be limited to situations in which observers are estimating lengths on a surface with a significant amount of curvature; it was not evident in our experiments when the observers made similar judgments on a flat planar surface. The studies cited above (e.g., Baird & Biersdorf, 1967;Loomis et al, 1992) required observers to estimate the magnitude ofextents in depth on a flat surface (e.g., a flat table or a ground plane).…”

“…But this is not necessarily the case. Gilinsky (1951), Harway (1963), Wagner (1985), and Loomis, Da Silva, Fujita, and Fukusima (1992) all found that distances or lengths in depth appeared to their observers as increasingly smaller and compressed at farther and farther distances. Gilinsky's experiment took place in an indoor archery range, whereas the experiments ofHarway, Wagner, and Loomis et al were conducted outdoors in grassy fields.…”

Toward a new theory of stereopsis.

“…This translates to a nearly linear increase in CVs from 3% to 12% for distances from 2.5 to 20m. However, other data has shown near-veridical distance judgements (bling walking) to 12m with little change in standard deviations (averaged over 7 observers) for these distances, which translates to an effective reduction in CVs with distance (Loomis et al, 1992).…”