Abstract

Moving beat patterns were made by adding together sinusoidal luminance or chromatic gratings of equal contrasts and different spatial frequencies moving in opposite directions. Lower thresholds of motion (the speed required for discriminating the direction of motion of the moving beat) were measured at a contrast 0.5 log unit above the contrast required for detecting the spatial modulation in the beat pattern. At durations below 0.12 s the direction of motion of beat patterns could not be discriminated, even though beats could be discriminated from pure sinusoids. At longer durations the lower thresholds of motion declined with duration. When expressed in terms of temporal frequency, functions relating lower threshold of motion to duration were superimposed for beats made from color gratings and for beats with carrier frequencies from 1 to 10 cycles/degree. This is consistent with the hypothesis that a common mechanism analyzes the motion in all types of second-order patterns for which the motion can be reduced to be one of spatial contrast modulation of a one-dimensional carrier.

© 1996 Optical Society of America

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