A study examining visual processing in the brain found that men have greater sensitivity to detail and rapidly moving stimuli, while women are better at discriminating between colors. The findings, from researchers at the City University of New York, appear in the latest edition of Biology of Sex Differences.
In one experiment, volunteers with normal color vision and 20/20 sight were required to describe colors shown to them across the visual spectrum. The results, say the researchers, revealed that the color vision of the men was shifted, and that they required a slightly longer wavelength to experience the same hue as the women. Additionally, the males had a broader range in the center of the spectrum where they were less able to discriminate between colors.
In another experiment, an image of light and dark bars was used to measure the subjects’ contrast-sensitivity. The bars were either horizontal or vertical and the volunteers had to choose which one they saw. In each image, when the light and dark bars were alternated the image appeared to flicker.
By varying how rapidly the bars alternated or how close together they were, the research team found that at moderate rates of image change, observers lost sensitivity for close together bars, and gained sensitivity when the bars were farther apart. When the image change was faster both sexes were less able to resolve the images over all bar widths. Overall, however, male subjects were better able to resolve more rapidly changing images that were closer together than the women.
The researchers believe the relatively high concentration of androgen receptors in the visual cortex is responsible for these variations. Androgens are responsible for controlling the development of neurons in the visual cortex during embryogenesis, meaning that males have 25 percent more of these neurons than females.
“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,” explained lead researcher Israel Abramov.
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