Date of Award
Master of Arts in Psychology
In the mental rotation paradigm, observers are shown two stimulus patterns which differ from each other in angular orientation. It has been found that the time required to recognize that two such patterns are the same is a linear function of the angular disparity in the portrayed orientations of the two patterns. Although it has not been claimed that the internal Process is strictly continuous, it nevertheless appears to be an analog of the corresponding physical process. Observers were shown pairs of perspective line drawings of three-dimensional block figures which differed in orientation from a standard by either 0, 3, 6, 9, 12. 15, 18, 21, 24. 27, 30, 60, 90, 120, 150, or 180°. Since no previous studies have included orientation disparities of less than 20°, such disparities were included in the present study to obtain a more refined idea of the nature of the mental rotation process. Regression analyses revealed that the time required to decide that comparison stimuli were the same as standard stimuli was not a linear but rather a constant function for angular disparities from zero to 18°. Data points above 18° fit a linear function similar in slope and intercept to that originally found by Shepard and Metzler (1971). The finding of a threshold for mental rotation suggests that the template matching mechanism which performs "same-different" comparisons is to some extent flexible. Thus, standard and comparison objects with subthreshold angular disparities are not rotated at all, but are immediately accommodated by the flexible template system. However, the converse proposition, that object with supra-threshold angular disparities need be rotated only into the threshold region for a comparison to occur, was not supported. Although in general males seem to outperform females in cognitive tasks requiring spatial ability, no significant sex differences were found, either in the rate of mental rotation or in the size of the threshold for mental rotation. A second experiment was conducted to insure that the threshold for mental rotation was not simply a sensory threshold. Five observers were shown pairs of sequentially presented stimulus figures and asked to rate their impression of the total orientation of each pair, in accordance with Andersen's (1974) functional measurement paradigm. Analyses of variance showed that a simple additive model for the summation of the angles fit the obtained data well. Furthermore, the psychophysical function relating perceived orientation to physical orientation was flat between zero and 6° for four of five subjects, and roughly linear over the rest of the range. These results indicate that while angular disparities of 6° or less between objects are not apparent to observers, there is no evidence for a sensory threshold in the neighborhood of the mental rotation threshold. These results confirm as a psychological effect the threshold for mental rotation. Furthermore, these results may have important implications concerning the perception of complex forms by the human visual system.
Rossi, Joseph S., "Is There a Threshold For Mental Rotation?" (1979). Open Access Master's Theses. Paper 1563.