The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


Cerebral hemisphere dominance and craniofacial constraint of the visual system: Evidence for the development of astigmatism and reduced visual acuity in humans

MICHAEL P. MASTERS1 and SCOTT RISSER2.

1Anthropology, Montana Tech, 2Psychology, Montana Tech

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This study examined the relationship between cerebral hemispheric dominance and reduced vision in humans to assess the impact of greater lateral brain development on the visual system. Encephalization and reduced facial prognathism in hominin evolution have circumscribed the orbits between the neurocranium and viscerocranium. Expansion and anterior placement of the brain has repositioned the frontal cortex atop the eyes, and resulted in the juxtaposition of two different functional systems in modern humans. This study aimed to investigate if greater cerebral lateralization, measured by hemispheric dominance, correlated with side-dependent reduced vision.

750 participants (55% female) were asked to report astigmatism (left, right, both eyes, and no astigmatism), uncorrected visual acuity (measured in dioptres), and hemispheric dominance, which was derived from a 15-item dominance test. This hemicity scale, ranging from 7.5 (very right-hemisphere dominant) to -7.5 (very left-hemisphere dominant), was used to investigate how lateral dominance varies in association with vision in each eye.

Results indicated that astigmatism occurred more frequently on the side of the dominant cerebral hemisphere, and that those with no astigmatism or with astigmatism in both eyes, fell between these disparate groups. A significant relationship also existed between a participant’s worse eye (difference > .5 dioptres) and hemisphere dominance, even after accounting for the effect of astigmatism. These results suggest that side-dependent cerebral and neurocranial development contribute to reduced visual acuity by constraining the hard and soft tissue of the eye and orbit, situated between an outsized brain and orthognathic face in modern humans.

This research was funded by a faculty seed grant from Montana Tech

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