Conditions for view invariance in the neural response to symmetry revisited: The case of real and drawn perspective.

Visual symmetry activates the extrastriate visual cortex and generates an Event Related Potential (ERP) called the Sustained Posterior Negativity (SPN). SPN amplitude is often reduced when stimuli are presented in perspective. We call this reduction SPN perspective cost . Previous research has shown that SPN perspective cost is flexible. We examined flexibility in SPN perspective cost by comparing three experimental conditions in three separate blocks. In the frontoparallel block , the stimuli were seen face on. In the real perspective block , the physical monitor was rotated with respect to the participant’s line of sight, so the stimuli were viewed from an unconventional angle. In the drawn perspective block , the physical monitor was not rotated, but the stimuli were drawn as if viewed from the same unconventional angle. The same group of 72 participants completed all three blocks. As predicted, the SPN was selectively reduced in the drawn perspective block. We conclude that when sufficient visual depth cues are available, the brain can construct a view invariant representation. This is an important step forward in the wider research project to determine when different forms of perceptual organization happen.