There are high concentrations of the male sex hormone (androgen) receptors throughout the cerebral cortex in the brain, particularly in the visual cortex, which is in charge of processing images.
Guys have 25% more neurons in the visual cortex than females because, during embryogenesis, androgens are responsible for controlling the development of those neurons.
The vision of men and women was compared by a team of researchers from Brooklyn and Hunter Colleges of the City University of New York. The experts observed people over the age of 16 from both college and high school, including students and faculty. Both sexes needed to have normal color vision and 20/20 sight (with glasses or contacts was considered fine), in order to participate.
Scientists learned that the color vision of men was shifted, after they asked the volunteers to describe colors shown to them across the visual spectrum. It also became clear that male subjects needed a slightly longer wavelength to experience the same hue as the female subjects.
It was not as easy for men to discriminate between colors as it was for women, meaning that the males had a broader ranger in the center of the spectrum.
In order to measure contrast-sensitivity functions (CSF) of vision, the researchers used an image of light and dark bars that were either horizontal or vertical, asking the participants to decide which one they saw. When the light and dark bars were alternated in each image, the image appeared to flicker.
The investigators found, by varying how quickly the bars alternated or how close together they were, that at moderate rates of image change, volunteers lost sensitivity for bars that were close together, and gained sensitivity when the bars were farther apart.
Both males and females had a harder time resolving the images over all bar widths when the image change was faster. However, men had an easier time resolving more rapidly changing images that were closer together than the women.
Professor Israel Abramov, lead author, explained:
"As with other senses, such as hearing and the olfactory system, there are marked sex differences in vision between men and women. The elements of vision we measured are determined by inputs from specific sets of thalamic neurons into the primary visual cortex.
We suggest that, since these neurons are guided by the cortex during embryogenesis, that testosterone plays a major role, somehow leading to different connectivity between males and females. The evolutionary driving force between these differences is less clear."