Why the Brain Splits Visual Processing Across Hemispheres
Splitting visual tasks between hemispheres boosts attention and memory while preventing perceptual overload.
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A longstanding principle of neuroscience is that the brain processes visual stimuli from each side of the visual field in the opposite hemisphere: stimuli from the right side are processed in the left hemisphere, and vice versa. While often cited in popular culture with substantial inaccuracy, this anatomical reality plays a critical functional role in how the brain manages its limited perceptual resources.
“People hear all these myths about the left brain being more analytical and the right brain being more artistic, or people being right-brained vs left-brained. Ninety-nine percent of that is nonsense.”
Dr. Earl K. Miller.
A new review article in Neuropsychologia by researchers at the Massachusetts Institute of Technology (MIT) outlines how this division of labor not only reflects the brain’s physical structure but also supports cognitive efficiency. The authors detail how splitting visual spatial perception across hemispheres helps avoid attentional overload and blind spots, particularly when multiple objects must be tracked at once.
“Perceptual capacity is limited—you can only take in so much at once. If you’re your capacity is fully tied up on the right side of your gaze, you might miss a threat approaching on the left. Splitting resources between both sides helps avoid dangerous perceptual blind spots”.
Dr. Scotrr Brincat.
Contralateral processing extends into high-level functions
Earlier theories suggested that although the visual cortex processes each visual hemifield in opposite hemispheres, the prefrontal cortex integrates this information into a unified whole. However, evidence from studies over the past two decades – including work by the review’s authors – has shown that this integration remains partial. Even in the prefrontal cortex, neural activity related to spatial information is more robust in the hemisphere contralateral to the stimulus.
Prefrontal cortex
The front part of the brain’s frontal lobes involved in complex behaviors including planning, attention and decision-making.Contralateral
A term describing how the brain processes sensory input from the opposite side of the body or visual field.This contralateral bias is measurable in neural oscillations, such as increases in gamma-frequency power in the hemisphere corresponding to the opposite visual field. Functional independence between the hemispheres has also been observed during tasks involving attention and working memory, where split presentations of visual items across hemifields result in improved memory performance compared to items clustered within a single hemifield. This phenomenon is referred to as the “bilateral advantage.”
Gamma-frequency oscillations
A pattern of neural activity in the brain typically associated with attention, memory and perception; usually involves brain waves in the 30–100 Hz range.Bilateral advantage
The cognitive benefit observed when visual or spatial information is divided between the brain’s hemispheres rather than presented to a single hemisphere.
Working memory
A limited-capacity system for temporarily holding and manipulating information necessary for complex tasks such as reasoning and learning.Cognitive advantages and constraints
While the bilateral advantage supports better recall of spatial information, the benefit has clear boundaries. Tracking multiple items, even when split between hemispheres, does not match the performance of focusing on a single object. Individual variation in perceptual capacity across the visual field further underscores the complexity of this system.
To explore practical applications of these findings, one of the review authors has launched a company aiming to use individual perceptual capacity profiles to enhance performance in visually demanding tasks.
Notably, this lateralization of processing appears specific to spatial information. Non-spatial features, such as color or shape, are processed bilaterally.
Coordinated handoffs across hemispheres
Despite the lateralization of processing, human perception feels seamless. Objects that move across the visual field – from left to right, for instance – do not appear to “jump” between hemispheres. Neural studies show this continuity is maintained by overlapping activity during handoffs. As an object approaches the central visual midline, the receiving hemisphere ramps up activity in advance, while the sending hemisphere sustains its engagement after the transition. This overlapping activity can last up to a second.
This neural coordination ensures continuity but comes at a small cost. Studies indicate a slight decline in tracking performance at the moment of transition between hemispheres.
Implications for understanding neurological disorders
Disruptions in communication or synchronization between hemispheres have been linked to several neuropsychiatric conditions, including Alzheimer’s disease, schizophrenia, autism spectrum disorders and anxiety and mood disorders. The review suggests that a better understanding of how interhemispheric processing supports attention and working memory may offer new directions for intervention strategies targeting brain network function.
Reference: Brincat SL, Miller EK. Cognitive independence and interactions between cerebral hemispheres. Neuropsychologia. 2025;212:109153. doi: 10.1016/j.neuropsychologia.2025.109153
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