Processing of Visual Mirror Symmetry by Human Observers; Mechanisms and Models

Mirror symmetry is an important and common feature of the visual world, which has attracted the interest of scientists, artists, and philosophers for centuries. The human visual system is very sensitive to mirror symmetry; symmetry is detected quickly and accurately and influences perception even when not relevant to the task at hand. Neuroimaging studies have identified mirror symmetry-specific haemodynamic and electrophysiological responses in extra-striate regions of the visual cortex, and these findings closely align with behavioural psychophysical findings when only considering the magnitude and sensitivity of the response. However, as we go on to discuss later, the location of these responses is at odds with where psychophysical models based on early visual filters would predict. In attempts to capture and explain mirror symmetry perception, various models have been developed and refined as our understanding of the factors influencing mirror symmetry perception has grown. The current review provides a contemporary overview of the psychophysical and neuroimaging understanding of mirror symmetry perception in human vision. We then consider how new findings align with predominant spatial filtering models of mirror symmetry perception to identify key factors that need to be accounted for in current and future iterations.