| Abstract | A visual bar alternately presented in vertical and horizontal orientations appeared to rotate 90.degree. through 1 of 2 pairs of opposite quadrants. Human subjects judged whether a probe dot, interjected at some delay and angular deviation from the vertical bar, appeared before or after the bar passed through the corresponding angular orientation. When the motion was perceived in the probed quadrant, percent before responses dropped abruptly from near 100% to near 0% as delay increased and the drop occurred at longer delays for probes at larger angular deviations. Under physically identical conditions, when the motion was perceived in an unprobed quadrant, percent before responses varied much less with delay and insignificantly with angular position. The accuracy of the judgments in the 1st case suggested the internal generation of an ordered sequence of intermediate representations during each apparent rotation.
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