HOW ACCURATE IS SIZE AND DISTANCE PERCEPTION FOR VERY FAR TERRESTRIALOBJECTS - FUNCTION AND CAUSALITY

This study investigated absolute estimation of size and distance for n atural and artificial objects at viewing distances of 1.1-15.3 km (Exp eriments 1 and 2) and 0.4-5.0 m (Experiment 3). The main results were that, regardless of distance range, size and distance estimates (S' an d D') were related to objective size and distance (S and D), respectiv ely, by a power function with an exponent of unity, but great individu al differences in exponent were obtained for the far objects. The rati o S'/D' was reasonably represented by S'/D' = Ktheta(n) and S'/D' = ta n(atheta + b), rather than S'/D' = tantheta, where theta is the visual angle. Partial correlations were obtained to examine whether (1) appa rent size is determined by taking apparent distance into account or (2 ) both apparent size and apparent distance are determined directly by external stimuli. The combined data for the far objects and the data f or the close objects showed that there were high correlations between S and S' and between D and D' and a low correlation between D' and S'. The data of Experiment 2 showed that both D' and S' were highly corre lated with S, D, and theta, and there was a high positive correlation between D' and S'. It was suggested that the direct-perception model i s valid under some situations, but the taking-into-account model is no t supported in any set of data.