Summary: Researchers report that handedness determines which hemisphere of the brain is specialized for processing fine visual detail. The new “action asymmetry hypothesis” argues that lateralized visual processing for high- and low-frequency information emerges from the routine ways we use our hands in everyday tasks.
In people who are right-handed, the left hemisphere is specialized for high-spatial-frequency vision; in many left-handers, that specialization is reversed. These results challenge prior ideas that visual frequency asymmetries are determined prenatally or are simply a byproduct of language lateralization.
Key Facts
- Handedness link: High-frequency visual specialization tends to be on the opposite side in left-handers compared with right-handers.
- Language is separate: Both right- and left-handers typically process high-frequency components of spoken language in the left hemisphere.
- Action–perception link: The brain’s perceptual organization may reflect the typical actions performed by the dominant and nondominant hands.
Source: Cornell University
Imagine hammering a nail: your dominant hand swings the hammer while the other hand steadies the nail.
Cornell psychologists propose that everyday hand actions like this shape an important organizational feature of perception: why one hemisphere becomes tuned to high-frequency visual details and the other to lower-frequency, more stable information.
Past research has found that, for most people, the left hemisphere responds more quickly to rapidly changing (high-frequency) visual input, while the right hemisphere is better at processing slower, low-frequency information. Until now, however, explanations for that hemispheric division have been incomplete.
The team’s “action asymmetry hypothesis” offers a functional account: hemispheric specialization for visual frequencies may develop from asymmetries in how we use our hands—dominant hands performing higher-frequency, precise actions and nondominant hands performing steadier, lower-frequency tasks. Importantly, the researchers show for the first time in large samples that the side specialized for high-frequency vision is reversed in many left-handers.
“We observed the expected left-hemisphere advantage for high-frequency vision in right-handers, and an opposite pattern in left-handers,” said Daniel Casasanto, associate professor of psychology and director of the Experience and Cognition Lab. “These findings support the idea that perceptual systems are organized in part by how we perform actions with our hands.”
Casasanto is senior author of the paper “Frequency Asymmetries in Vision: the Action Asymmetry Hypothesis,” published June 27 in the Journal of Experimental Psychology: General. The first author is Owen Morgan, M.A. ’23, a doctoral student in psychology.
Historical explanations for visual frequency asymmetries have ranged from prenatal origins to links with language, since the left hemisphere is dominant for many language functions. The new evidence weakens those accounts: handedness typically does not reverse fetal development patterns or the hemisphere used for language, yet visual frequency specialization does reverse with handedness.
Building on the “body specificity hypothesis”—the idea that bodily attributes influence how the brain and mind are organized—the team examined whether motor-action habits help shape perceptual laterality. Unlike much earlier work that focused primarily on right-handed participants, these experiments deliberately included a substantial number of left-handed participants.
“Testing left-handers alongside right-handers is essential to understanding how perception is actually organized and why,” Casasanto said.
Two preregistered online experiments and a larger combined dataset included nearly 2,000 participants with roughly equal numbers of strong right- and left-handers, plus mixed-handers. Participants judged low- and high-frequency visual shapes presented briefly in the left or right visual hemifield. Stimuli were hierarchical shapes—such as a large diamond made of small triangles placed next to a large triangle composed of small squares—designed to separate high- and low-spatial-frequency processing.
Reaction-time patterns showed the expected hemispheric asymmetry for right-handers and a marked reversal for left-handers: the hemisphere specialized for high-spatial-frequency vision switched sides. A third experiment using dichotic listening confirmed that both groups still typically process high-frequency auditory components of language in the left hemisphere, ruling out language laterality as the cause of the visual reversal.
The authors suggest two nonexclusive mechanisms. First, once a hemisphere becomes dominant for high-frequency actions, it may be advantageous for the brain to link motor, visual and auditory systems on the same side to improve efficiency. Second, frequent use of the dominant hand may bias the visual and auditory input that hemisphere receives—dominant-hand actions often bring high-frequency sights and sounds into the corresponding hemispace.
“Action asymmetries create asymmetries in the sensory input we give ourselves,” Casasanto explained. “Over time, the hemisphere that routinely receives high- or low-frequency input may become specialized for that information.”
The experiments did not show a clear reversal for low-frequency visual processing, which the authors attribute to the fact that low-frequency actions (for example, holding an object steady) are often shared between hands, reducing the magnitude of any lateralized specialization.
With these findings supporting the action asymmetry hypothesis for vision, the researchers plan further studies to test whether handedness similarly affects frequency specialization in audition. They also intend to study stroke patients who lose use of their dominant hand to see whether perceptual specialization reorganizes with changes in habitual hand use.
“Our hypothesis is straightforward: asymmetries in hand action give rise to asymmetries in perception across vision and hearing,” Casasanto said. “How you use your hands influences a range of cognitive functions—including language, emotion and now, clearly, visual perception.”
About this handedness and visual processing research news
Author: James Dean
Source: Cornell University
Contact: James Dean – Cornell University
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Frequency asymmetries in vision: The action asymmetry hypothesis” by Owen Morgan et al., Journal of Experimental Psychology: General
Abstract
Frequency asymmetries in vision: The action asymmetry hypothesis
Extensive prior research indicates that the two cerebral hemispheres differ in their sensitivity to spatial frequencies in both vision and audition, yet the origins of this specialization have been unclear.
We tested whether hemispheric asymmetries in visual perception arise from asymmetries in how people habitually perform high- versus low-frequency actions with their dominant and nondominant hands (the action asymmetry hypothesis).
In two large, preregistered online experiments, participants judged low- and high-spatial-frequency shapes presented to the left and right visual hemifields. The typical hemispheric asymmetry for spatial frequency observed in strong right-handers was significantly attenuated and, across experiments, fully reversed in strong left-handers.
A third dichotic-listening experiment indicates that differences in language lateralization do not account for this reversal. These results offer initial support for the action asymmetry hypothesis: perceptual frequency asymmetries may be driven in part by frequency asymmetries in action.