Detection and contrast discrimination of moving signals in uncorrelated Gaussian noise

We investigate human visual detection and contrast discrimination of a moving Gabor signal in spatiotemporal white noise. We measure performance as a function of signal contrast for detection and contrast discrimination in a 4 alternative forced choice task. Observers were instructed and trained to maintain their gaze on a fixation point at all times during the experiment. The effect of signal contrast on human detection and contrast discrimination performance (d') for a moving signal in spatiotemporal noise is similar to that found for the case of a stationary signal in spatial noise. It can be described by a linear function with a positive x-intercept for detection and a 0 intercept for contrast discrimination. The difference in x-intercepts for the detection and contrast discrimination tasks are consistent with signal uncertainty. The improvement in performance with increasing number of frames is different for the detection and contrast discrimination tasks. Results show performance improvement with number of frames that saturates much later (750 - 800 msec) than would be expected from the early temporal filters (100 - 150 msec). Observers are more efficient detecting a stationary signal than a moving signal (when no eye tracking is allowed) in spatiotemporal noise. In an additional experiment where the signal interframe displacement was increased, observer performance (d') decreased with increasing interframe signal displacements dropping 50% for an interframe displacement of 70 min. of arc showing that human performance for detection of a moving signal is affected by the specific characteristics of the signal motion.