Abstract

Extending a method of van Doorn and Koenderink,¹ I have examined visibility of spatial modulations of image motion. The stimulus was the sum to two moving bandpass noise images with different velocities. Over the vertical extend of the stimulus, the two noise images were contrast modulated in antiphase by the square root of a stationary sinusoid. For large modulation amplitude, the typical appearance is alternating horizontal stripes of differing velocity. At smaller amplitudes, the stripes disappear. The experimental task was forced-choice discrimination between zero and some nonzero modulation amplitude. A staircase measured the threshold amplitude for various modulation frequencies to determine a velocity-modulation sensitivity function. Data were collected for several noise spatial frequencies and velocities. For each noise frequency tested, modulation sensitivity falls off steeply about one octave below the noise frequency. In certain conditions, sensitivity also declines at low modulation frequencies, consistent with differentiation of motion estimates, as might be employed in a motion-edge sensor.

© 1991 Optical Society of America