The Relative Importance of Contrast and Motion in Visual Detection

The relative roles of contrast and motion in the detection of targets were investigated using a television display of an artificial target inserted in several different backgrounds of varying complexity. Independent effects of both contrast and motion on the detectability of targets were found. The magnitude of these effects can be accounted for in the detection probability function by modifying the exponent with a linear contrast term and a second-power velocity term. At target speeds greater than about 5 deg/sec, the detection probability began to level off, probably due to interference of the boundaries of the display. Single-fixation experiments confirmed a larger detection field for moving targets than for static, but also demonstrated a gradual increase in the fixation time required to detect a target as a function of its distance from the fixation point.