The role of eye movements in motion detection

The roles of small eye movements of fixation, and of different kinds of background in motion detection were studied. Minimum detectable displacement for a luminous line oscillating either in a blank field or in the presence of three types of background was measured under two viewing conditions: normal, when eye movements generate normal movements of the image on the retina, and stabilized when these retinal image movements were nearly eliminated. It was demonstrated that eye movements enhance motion detection for a sinusoidally moving target when the target is superimposed on a patterned background; they are detrimental when there is no background. In addition, it was found that the function relating threshold amplitude to frequency of movement is band-pass when the image is stabilized or when the bar moves on a blank field, and is more low-pass when both the background and the test target are subject to the effects of eye movements.