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, 3 (1), 20

Sex & Vision I: Spatio-temporal Resolution

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Sex & Vision I: Spatio-temporal Resolution

Israel Abramov et al. Biol Sex Differ.

Abstract

Background: Cerebral cortex has a very large number of testosterone receptors, which could be a basis for sex differences in sensory functions. For example, audition has clear sex differences, which are related to serum testosterone levels. Of all major sensory systems only vision has not been examined for sex differences, which is surprising because occipital lobe (primary visual projection area) may have the highest density of testosterone receptors in the cortex. We have examined a basic visual function: spatial and temporal pattern resolution and acuity.

Methods: We tested large groups of young adults with normal vision. They were screened with a battery of standard tests that examined acuity, color vision, and stereopsis. We sampled the visual system's contrast-sensitivity function (CSF) across the entire spatio-temporal space: 6 spatial frequencies at each of 5 temporal rates. Stimuli were gratings with sinusoidal luminance profiles generated on a special-purpose computer screen; their contrast was also sinusoidally modulated in time. We measured threshold contrasts using a criterion-free (forced-choice), adaptive psychophysical method (QUEST algorithm). Also, each individual's acuity limit was estimated by fitting his or her data with a model and extrapolating to find the spatial frequency corresponding to 100% contrast.

Results: At a very low temporal rate, the spatial CSF was the canonical inverted-U; but for higher temporal rates, the maxima of the spatial CSFs shifted: Observers lost sensitivity at high spatial frequencies and gained sensitivity at low frequencies; also, all the maxima of the CSFs shifted by about the same amount in spatial frequency. Main effect: there was a significant (ANOVA) sex difference. Across the entire spatio-temporal domain, males were more sensitive, especially at higher spatial frequencies; similarly males had significantly better acuity at all temporal rates.

Conclusion: As with other sensory systems, there are marked sex differences in vision. The CSFs we measure are largely determined by inputs from specific sets of thalamic neurons to individual neurons in primary visual cortex. This convergence from thalamus to cortex is guided by cortex during embryogenesis. We suggest that testosterone plays a major role, leading to different connectivities in males and in females. But, for whatever reasons, we find that males have significantly greater sensitivity for fine detail and for rapidly moving stimuli. One interpretation is that this is consistent with sex roles in hunter-gatherer societies.

Figures

Figure 1
Figure 1
Binocular spatial contrast-sensitivity functions, parametric in temporal modulation rate (group geometric means); all participants color and stereo normal: (a) Females (N = 36; 16–38 years); (b) Males (N = 16; 16–37 years). Error bars are not shown because the SEMs are largely encapsulated within the size of each data symbol.
Figure 2
Figure 2
Group comparisons of binocular spatial contrast-sensitivity functions in Figures1a,1b: ratios of mean sensitivities for males to females. Ratios greater than one show that males have higher sensitivity than females.
Figure 3
Figure 3
Contrast-sensitivity functions of males compared to those of females. Mean functions for males scaled to coincide at 5 cy/deg for 1 Hz temporal modulation. Mean functions for females scaled separately to coincide at same rate; scaled female functions then scaled, as a group, to match scaled male functions. Females represented by data points, males by lines.
Figure 4
Figure 4
Limiting acuities of males and females estimated from contrast-sensitivity functions. Each participant’s function for each of the temporal rates was fitted with a model of these functions [42]. The model functions were extrapolated to find the spatial frequency corresponding to 100% contrast. (Width of half a cycle at that frequency is the acuity limit in units of degrees.) Individuals’ estimated acuities were averaged to obtain group means.

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