NRSC 4132 Blog

As people we all vary in personality, thought and emotion. We all know that. But, when it comes to the world we live in, does everyone see the same things? If I look at a beautifully orange colored flower, does the person sitting next to me see what I see? According to a study by Dr. Samuel Schwarzkopf the answer to this question may be no.

In Dr. Schwarzkopf's recent study, a negative correlation was found between the size of an individual?s central visual field, as defined as the surface area of a person's primary visual cortex (V1), and the magnitude of illusory perceptual effect of two different optical illusions. The first optical illusion is the Ebbinghaus illusion where two central circles are identical in size but appear to be different sizes to the viewer because of the surrounding circles. One circle is surrounded by 6 larger circles and the other surrounded by 8 smaller circles. The second illusion come from Ponzo and is an illusion in which two checkerboard circles are identical in design and size but appear different because of the three dimensional background.

The two illusions may have different mechanisms behind their perception. The article predicts that the Ebbinghaus illusion may be associated with the lateral connections in V1 and the Ponzo illusion mediated by "feedback projections from the areas that extract the three dimensional context of the background".

The subjective experience of how large the circles looked varied between subjects. As I previously stated, in a large sample population, Schwarzkopf found a significant negative correlation between the magnitude of both illusions and the surface area of V1. Using standard retinotopic mapping procedures with functional magnetic resonance imaging (fMRI), participants with a small functionally defined V1 surface area were found to have stronger perceptual illusion than subjects with a large V1. There was no significant correlation found between the V2 or V3 visual regions and magnitude of the size illusions.

The study mentions that future work will look into whether the individual differences found can be attributed only to V1 surface area size or whether other mechanisms such as the concentration of the inhibitory neurotransmitter GABA or possible differences in actual brain structure. Furthermore, individual differences in size perception exist but are there commonalities among similar populations? For example: do people with autism see sizes more similarly than when an autistic person is compared to a person with brain activity attributed with normality? What about the effect of color blindness on size perception?

Schwarzkopf's study helps remind us of the variations in brain structure that contribute to each of us being who we are. If we all see things differently, how does the way we see something affect how we feel about it?

The article detailing Schwarzkopf?s study can be found in Nature Neuroscience at http://www.nature.com/neuro/journal/v14/n1/full/nn.2706.html