Size-distance invariance in perceptual adaptation

Abstract

Objects viewed through a facemask under water appear larger and closer than when viewed in air. Divers' adaptation to this distortion was measured by obtaining estimates of the size and distance of an array of targets before and after a 20-min underwater dive. A negative correlation between size-and distance-adaptation scores indicated that most divers adapted to one dimension by counteradapting to the other. For example, some Ss adapted to size by increasing the distortion of apparent distance and some the other way around. The results were discussed in relation to the size-distance invariance hypothesis. Recent experiments by Rock (1965. 1966) have confirmed Stratton's (1903) prediction of adaptation to a size-distorted retinal image. Rock found thaI viewing objects through a convex mirror, which minified their retinal image but which left distance undistorted, resulted in adaptation in the direction of veridical size perception. Ross, Franklin. Welt man. & Lennie (1970) found size adaptation following a period of underwater viewing in which both size and distance are usually perceived as distorted. Underwater distortion of size and distance occurs when a diver views objects through a facemask which introduces a water-glass-air interface between the eyes and an underwater object. Since the refractive index of water is 4/3 that of air, light rays passing from water into air are refracted away from the normal. This produces a virtual image at approximately 3/4 of the object's physical distance (the location of the virtual image is referred to as the optical distance), with an angular magnification of abou! 4/3 that wh ich occurs in air. These effects obtain for objects viewed normally to the mask; objects in the periphery undergo greater distortion. According to the size-distance invariance hypothesis, there are alternative ways of perceiving the retinal image of an underwater object. An object viewed thr"ugh a facemask under water should appear its correct size if perceived at i ts optical distance (3/4 physical distance), 4/3 enlarged if perceived at the physical distance, and proportionately enlarged if it appears between the optical and physicaI distance. The latter case occurs for most

Distance perception in an open water environment: Analysis of individual differences

“…Indeed, distance perception in situations of cue reduction is challenging because the relationship between the angular extent of objects and perceived size need not necessarily be consistent with the perceived distance (Brenner & Van Damme, 1991;Gogel, 1971). For example, a general tendency for humans to underestimate overland distances up to approximately 25 m was found by Ross (1967) and Franklin, Ross, and Weltman (1970). In relation to larger distances, Fine and Kobrick (1983) asked soldiers to estimate the distance of a military truck placed between 600 and 1,550 m away from them on a large, flat, open grassy area.…”

Absolute Distance Perception under Water and Improvement through Training

“…It is possible that the small improvement is due to visual adaptation to distance distortion. Adaptation under water has been demonstrated for handeye coordination (Kinney, McKay, Luria, & Gratto, 1970), and Franklin, Ross, and Weltman (1970) claim to have demonstrated adaptation for absolute distance. The occurrence of absolute distance adaptation must be further substantiated, however.…”

Why do objects appear enlarged under water?

“…In general the overestimation was very much less than the angular magnification of 1.33, and also much less than would be predicted from the distance judgements according to classical SDI. The discrepancy may have been caused by the methods of measurement, or by previous perceptual learning on the part of more experienced divers, or to rapid adaptation during the course of the measurements (10,(13)(14) . However, the results might be consistent with perceptual SDI, if the perceived angular size was less than the optical magnification (Figure 2b).…”

“…These precautions were to prevent the observer from seeing the true dimensions of the tanks and the true distances at which the targets were suspended from the support rods. Beneath each tank stand was a moveable marker, initially aligned with the (15) Size match 1.12 1.6 2) Ross (11) Numerical ests 1.18 1.25 3) Franklin et al (14) Numerical ests. 1st 1.01…”