Abstract
Size perception in a 3D scene is known to be affected by distance perception. Two objects with the same physical size appear to have very different sizes if they are perceived to be at different distances. The primary visual cortex area (V1) has been demonstrated to be a critical area to process the 3D size illusion. However, when the representation of the size illusion starts to manifest in V1 remains largely unknown. Here we used the methods of psychophysics and event-related potentials (ERPs) to investigate the time course of brain activity related to the size illusion processing. Psychophysically, we measured the magnitude of the 3D size illusion by asking participates to adjust the size of a ball on a uniform background to match the perceived size of a ball (either near or far) in a 3D scene. The perceived size of the far ball was larger than that of the near ball. Electrophysiologically, we acquired EEG data while participates were asked to detect a small dot occurred on the balls with a small probability (20% of trials). We manipulated the position and contrast of the ball to construct four experimental conditions (high contrast far, low contrast far, high contrast near and low contrast near condition), which enabled us to isolate the ERPs for the balls only by subtracting the ERPs elicited by the low contrast stimuli from those elicited by the corresponding high contrast stimuli. We focused on the earliest visual ERP component C1 that normally peaked around 80 ms post-stimulus onset and has been demonstrated to originate in V1. We observed a significantly greater amplitude of C1 in the far condition than the near condition. These results suggest that the V1 area starts to represent the 3D size illusion as early as less than 100 ms.
Meeting abstract presented at VSS 2013