Optic illusions are fascinating. Sparking curiosity, intrigue and doubt in minds gazing at the impossibilities spawned by them. Most people have been exposed to a variation of the famous "which object is bigger" illusion. If you don't know what I'm talking about, there are two objects of equal size physically, surrounded by various contextual components. These various components give the viewer a false sense of subjectivity in which one object appears larger than the other, even though both objects are identical. It turns out neuroscientists want to better understand the cause behind these false perceptions and even predict human subjectivity in object size.
Your brain contains a primary visual cortex, let's call this thing V1. The size and surface area of V1 has a large range of variability from person to person. Scientists have correlated the surface area of V1 to the subjectivity in object size. Experimentation took place during September 2010 with 30 subjects with the hypothesize correlating V1 surface area and conscious perception differences via FMRI technology. Subjects viewed a "Ebbinghaus" illusion as well as a "Ponzo" illusion. Both are forms of physically identical objects appearing different sizes due to contextual differences surrounding the objects. The Ebbinghaus illusion appears larger due to different size circles surrounding the center circle. While the Ponzo illusion appears larger due to the 3-D context surrounding the images. The resulting data showed a strong and negative correlation between V1 surface area and subjective object size. Meaning: The less V1 surface area, the bigger the difference between the identical objects perceived by subjects. It should be noted that the Ebbinghaus illusion yielded better data for relation than the Ponzo illusion. "The ability to judge fine visual differences in physical stimuli (Vernier acuity) is correlated with the degree of cortical magnification in primary visual cortex".
The article also addressed V1 surface area and brain size do not have a direct relationship. Meaning a bigger brain doesn't constitute greater V1 surface area. Therefore having a larger brain doesn't mean a person is better at correctly determining visual stimuli. V1 actually tended to be smaller in larger brains.
Consider the possibilities of predicting human behavior, opinions and subjectivities by knowing who is more susceptible to illusions and visual stimuli based on brain structure. Knowing exactly how well people can perform certain tasks depending on their brain structure may be far off in the future but it's roots seem to have a firm plantation in the field of research.
Most people like to believe they are in total control of their thoughts, subjectivities and opinions. Yet in this experiment, it showed that people having less surface area of the V1, perceptions of object size were distorted. Your perspective and opinions may not be as genuine as you original believed them to be. Rather just by products of the human brain analyzing stimuli. As neuroscience continues to unravel the mysteries of the human mind ideas such as free will, consciousness and perception may need to be redefined.
(All information was taken from http://www.nature.com/neuro/journal/v14/n1/full/nn.2706.html)