A computational and psychophysical study of motion induced distortions of perceived location
In this thesis I begin by extending previous psychophysical research on the effects of visual motion on spatial localisation. In particular, I measured the perceived spatial shift of briefly presented static objects adjacent to a moving stimulus. It was found that the timing of the presentation of static objects with respect to nearby motion was crucial. I also found a decrease of this motion induced spatial displacement with the increasing distance of static objects from motion, suggesting a local effect of motion. The induced perceptual shift could also be reduced by introducing transient stimuli (flickering dots) in the background of the display. The next stage was to construct a computational model to provide a mechanism that could facilitate such shifts in position. To motivate our combined model of motion computation and spatial representation we considered what functions could be attributed to V1 cells on the basis of their contrast sensitivity functions. I found that functions based on sums of differential of Gaussian operators could provide good fits to previously found V1 data. The properties of V1 cells as derivatives of Gaussian kernel filters on an image were used to build a spatial representation, where position is represented in the weighting of these filter outputs, rather than in a one-to-one isomorphic representation of the scene. This image representation can also be used along with temporal derivatives to calculate motion using the Multi-Channel Gradient Model scheme (Johnston et al, 1992). 1 demonstrate how this framework can incorporate motion signals to produce "in place" shifts of visual location. Finally a combined model of motion and spatial location is outlined and evaluated in relation to the psychophysical data.