Results of a previous study (R-614) suggest that the effect of motion on detectability might be caused entirely by contrast changes as the target moves over a complex background. The test documented in the present study, employing a television display and an artificial background, showed independent effects of both contrast and motion on target detectability. The effects can be accounted for by modifying the exponent in the detection probability function with a linear contrast term and a second-power velocity term. At target speeds greater than about 5 deg/sec, the motion effect was less, probably due to interference of the boundaries of the display. Single-fixation experiments confirmed a larger aperture for moving targets than for static targets, and also demonstrated a gradual increase in the fixation time required to detect a target as a function of its distance from the fixation point.
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