Minimum displacement thresholds for binocular three-dimensional motion

AbstractThresholds for the detection of motion in depth in the median plane of the head are substantially poorer than those for motion in the frontoparallel plane. This suggests the existence of two independent mechanisms for their detection. Any three-dimensional (3-D) motion can be decomposed into components of motion in the frontoparallel plane and in the median plane of the head. Can human performance for the detection and discrimination of other 3-D motions be predicted by a combination of responses from the two independent mechanisms? Minimum displacement thresholds (dmin) for the detection of 3-D motion and the direction discrimination of 3-D motion were measured for a wide range of 3-D directions. dmin data were modelled in terms of the probability summation of a pair of independent motion mechanisms, one responding to motion in the median plane of the head, the second to motion in the frontoparallel plane. Detection of 3-D motion was well predicted by probability summation across a range of 3-D directions. Direction discrimination of 3-D motion was similarly well fit by the probability summation model for multiframe motion displays for some observers. However for two-frame motion displays, direction discrimination for 3-D motion was best fit by a model using only a motion mechanism in the frontoparallel plane. Detection and direction discrimination thresholds for 3-D motion can therefore be explained on the basis of one or two mechanisms, sensitive to motion in the frontoparallel plane and in the median plane of the head

Vergence effects on the perception of motion-in-depth

When the eyes follow a target that is moving directly towards the head they make a vergence eye movement. Accurate perception of the target's motion requires adequate compensation for the movements of the eyes. The experiments in this paper address the issue of how well the visual system compensates for vergence eye movements when viewing moving targets. We show that there are small but consistent biases across observers: When the eyes follow a target that is moving in depth, it is typically perceived as slower than when the eyes are kept stationary. We also analysed the eye movements that were made by observers. We found that there are considerable differences between observers and between trials, but we did not find evidence that the gains and phase lags of the eye movements were related to psychophysical performance.</p