Mechanisms underlying illusory motion induced position shifts

Motion and position information interact within the visual cortex in such a way that creates the perception that a stimulus is shifted in position. This displacement in position is referred to as a motion induced position shift. Multiple theories have attempted to explain the underlying mechanisms of these perceived shifts in motion stimuli. One of the dominant theories suggests that the position of motion stimuli is extrapolated forward in an attempt to compensate for the internal and external delays in processing. An alternative theory suggests that there is a simple cell summation at all sides of a motion stimulus, however it is selectively reduced at the trailing edges. Thus, an inhibitory process selectively occurs for signals that trail motion rather than advance on it. The current project aims to tease apart these theories by examining the relationship between sensitivity at the leading and trailing edges of a drifting grating and the magnitude of the perceived motion induced shift. Experiment 1 attempted to confirm this relationship within both first and second order motion stimuli. Results revealed that there was a negative correlation between sensitivity at the trailing edge and the magnitude of illusory shift. Experiment 2 attempted to replicate these findings using a standardised measure of the magnitude of illusory shift. The results consistently revealed that sensitivity was selectively reduced at the trailing edge relative to the leading edge. However, no relationship was found between sensitivity and the magnitude of illusory shifts. Thus, the results revealed inconclusive findings concerning the relationship between sensitivity at the leading and trailing edges and the magnitude of the illusory shifts