The influence of perceptual stabilisation on perceptual grouping of temporally asynchronous stimuli.

Even during fixation, our eyes constantly make small, involuntary eye movements that cause the retinal image to be swept across our retinae. Despite this, our world appears completely stable, due to powerful perceptual stabilisation mechanisms. Whether these mechanisms are of functional consequence for visual performance remains largely unexplored, however. We directly tested this by using a perceptual grouping task, where physically aligned alternate grid elements were presented with an imperceptible temporal offset. Observers' abilities to reliably group the grid into rows (or columns) is posited to arise from the failure in compensation of retinal slip arising from the small eye movements that occur during the temporal offset, effectively introducing a spatial shift in the arrangement of grid elements. We incorporated this perceptual grouping task within the on-line jitter illusion, which temporarily disables perceptual stabilisation mechanisms through a 10 Hz flickering annulus of random noise (Vision Res 43 (2003) 957-969). Observers' abilities to correctly group the grid stimulus were measured with and without perceptual stabilisation mechanisms engaged (i.e. non-flickering vs. flickering annulus). Grouping performance was better when eye movements were perceived, suggesting that the influence of retinal slip is increased when perceptual stabilisation mechanisms are disabled. We therefore find that perceptual stabilisation can measurably influence visual function, in addition to its perceptual effects.