Motion direction and perceived relative position: A review and psychophysical study into motion integration

Abstract

Perceiving motion relies on neurally complex mechanisms. We review some of the processes preceding the perception of motion, most notable how motion signals can be integrated into a behaviourally useful motion percept by lateral modulatory mechanisms during early visual processing. We show that these motion integration processes can having perceptual manifestations (e.g. motion integration effects) in the localization of moving patterns. In an attempt to further investigate the motion integration process we created a psychophysics experiment to look at the perceptual effects of motion integration by measuring the differences in behavioural responses due to a dissociation between perceived position and actual physical position (e.g., due to mis- localization) of a steady-state moving grating away from the fixation area. The direction of motion in the two displayed bars was either in equal or in opposite directions. We found significant effects when the two moving sine wave patterns were in opposite compared to equal directions, indicating the presence of an influential motion integration process. Because we do not want changes in eye position to be confused with changes in visual field position and hence complicate interpretation, we also assessed the question whether we could enforce ourselves to keep looking on the fixation dot while presented with the same set of stimuli. No significant differences in eye position distributions was found between any of the stimulus configurations.