The size of the primary visual cortex in the brain correlates with how people see two common visual illusions, reports a study published online this week in Nature Neuroscience. This brain area is known to be important for visual perception, but this work suggests its size also modulates conscious visual experience.
Samuel Schwarzkopf and colleagues used functional magnetic resonance imaging in a group of volunteers to map out a set of visual areas, including the primary visual cortex (V1). They then worked out the V1 surface area of each person, and showed their volunteers two common visual illusions, where the size of simple geometrical shapes appears to be different from what it really is.
The researchers found that the larger the primary visual cortex in each individual, the smaller the magnitude of illusion. This correlation was specific to the primary visual cortex, and was not there for other visual areas tested. These results therefore suggest that the variability in conscious visual experience may partially be down to variability in the size of V1.