Speed and accuracy of 3D interpretation of linear stereograms

Stereograms belonging to 10 different textural types were constructed. Each stereogram represented five hemi-ellipsoids, either as bumps or hollows (+, -) and elongated either along the horizontal, or the vertical direction (H, V). The ease with which these stereograms could be interpreted was tested on 70 subjects. The two criteria of speed and accuracy were correlated. The main factors contributing to the ease of interpretation, in the case of the +/- character were: (i) diversity in the orientations of the matching stimuli; (ii) other factors reducing matching ambiguity; (iii) the presence of discontinuous elements; and, to a much lesser extent (iv) the presence of monocular cues. The last two factors exerted a stronger influence on the appreciation of the H-V character. Of the four kinds of objects, the H- and V+ hemi-ellipsoids appeared to be the least and the most error-prone ones respectively. The results further suggest that: (i) stereoscopic interpretation does not proceed from small to large disparities; (ii) the edge detectors of the visual cortex, when activated, speed up interpretation, but are easily saturated; (iii) large surfaces are reconstructed by correlation of horizontal rather than vertical patches.