Surface perception in pictures JAN

Subjects adjusted a local gauge figure such as to perceptually " fit " the apparent surfaces of objects depicted in photographs. We obtained a few hundred data points per session, covering the picture according to a uniform lattice. Settings were repeated 3 times for each of 3 subjects. Almost all of the variability resided in the slant; the relative spread in the slant was about 25% (Weber fraction). The tilt was reproduced with a typical spread of about 100. The rank correlation of the slant settings of different observers was high, thus the slant settings of different subjects were monotonically related. The variability could be predicted from the scatter in repeated settings by the individual observers. Although repeated settings by a single observer agreed within-5%, observers did not agree on the value of the slant, even on the average. Scaling factors of a doubling in the depth dimension were encountered between different subjects. The data conformed quite well to some hypothetical fiducial global surface, the orientation of which was " probed " by the subject's local settings. The variability was completely accounted for by single-observer scatter. These conclusions are based upon an analysis of the internal structure of the local settings. We did not address the problem of veridicality, that is, conformity to some " real object. " We addressed the problem of the internal consistency of data structures generated via the visual inspection of pictures, in the presence of these pictures. We used photographs of existing objects, but made no further references to these objects. Many previous investigators have used local probes to measure the internal representation of three-dimensional (3-D) surfaces from looking at pictures. For instance, BUlthoff and Mallott (1992) have measured depth maps, whereas Stevens (1983a, 1983b), Stevens and Brookes (1987), and Todd and Akerstrom (1987) have developed methods to probe the slant and tilt distribution. These authors also address the important problem of conformity to the real (3-D) object, on the basis of shape from shading , texture gradients, disparity, and so forth. In the present study, we used a method related to that proposed by Mingolla and Todd (1986). The aim here was to test, by quantitative means, whether observers sample some coherent surface. In order to do so, it was necessary to obtain somewhat more extensive data than usual. METHOD Stimuli The stimuli were photographs of rigid objects, displayed on a CRT tube measuring …