How the brain splits vision and puts it back together

While myths about “left-brained” or “right-brained” personalities persist, one long-known division of labor in the brain turns out to be even more significant than people realize.

A new scientific review reveals how the brain maintains separate processing streams for the left and right sides of our visual field – and how it cleverly balances this split to avoid blind spots, all while giving us a seamless experience of the world.

Neuroscientists Earl K. Miller and Scott Brincat of MIT’s Picower Institute for Learning and Memory have synthesized years of research into how this split processing works. Their insights clarify how the brain’s hemispheres divide up visual spatial perception, why this trade-off exists, and how the brain bridges the resulting gap.

Hemisphere myths debunked

Study co-author Earl K. Miller is a professor in the Department of Brain and Cognitive Sciences at MIT.

“People hear all these myths about the left brain being more analytical and the right brain being more artistic, or people being right-brained versus left-brained. Ninety-nine percent of that is nonsense,” said Miller. “You think with your whole brain.”

Despite this, visual spatial perception really is divided. The brain’s right hemisphere processes what we see on the left, and the left hemisphere processes the right. This separation persists even in high-level cognitive processes like attention and working memory.

“It’s for good reason,” Miller said. “Perceptual capacity is limited – you can only take in so much at once. If 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.”

How the brain splits vision

When Miller was a student, he learned that information from the left and right visual fields was neatly split between brain hemispheres until reaching the prefrontal cortex, where it was believed to be fully integrated.

But two decades of research, including Miller and Brincat’s own studies, have painted a more nuanced picture.

Contrary to earlier assumptions, even in the prefrontal cortex, neural activity shows a strong bias toward the “contralateral” hemisphere – the side opposite to where an object appears in view.

The bilateral advantage

Brain wave measurements, particularly in the gamma frequency range, reveal that neurons in the frontal cortex show increased activity when attending to stimuli on the opposite side.

“As a result, the two hemispheres appear to function surprisingly independently, even for high-level cognitive functions like attention and working memory,” wrote the researchers.

This is why, for example, people and animals can remember more items if those items are presented on both sides of their visual field, rather than all on one side – a phenomenon known as the “bilateral advantage.”

But this advantage has limits. People still track multiple objects less effectively than a single object, even if those objects are split between both sides of vision.

What the brain does share

The brain’s division of labor, however, applies only to spatial information – the “where” of visual objects.

Other aspects, such as color and shape, are processed across both hemispheres. This selective separation allows the brain to maximize its limited perceptual capacity for spatial awareness without compromising recognition of what objects are.

Interestingly, people also show individual differences in their visual capacity across the field of view. To explore this variability, Miller has founded a startup called SplitSage, aimed at helping people optimize performance in visually demanding tasks by measuring these perceptual differences.

Bridging the brain gap

Given the persistence of this division, why don’t we encounter any problems when, for instance, a bird flies from the left to the right side of our gaze? Why doesn’t the handoff between hemispheres disrupt our perception of a seamless world?

Studies show that as an object approaches the midline of vision, the hemisphere about to “receive” it ramps up neural activity in anticipation, while the “sending” hemisphere continues to track it for some time after.

“As a tracked target approaches the visual midline, the hemisphere about to receive the target shows a ramp-up of activity well before the crossing time, as if it is anticipating the target,” the experts wrote.

“Further, activity in the sending hemisphere remains high well after the crossing. Thus, for up to a second or more, neural signals reflecting the target are shared across both hemispheres. It is as if both hemispheres are holding the baton.”

This mechanism ensures continuity, much like how a mobile phone switches between cell towers without dropping a call. However, there is a small but measurable performance cost during this “handoff.”

Brain division and disorders

The ability to synchronize hemispheres is crucial. Disruptions in interhemispheric connectivity and synchrony have been linked to neurological and psychiatric disorders, including Alzheimer’s disease, anxiety, depression, schizophrenia, obsessive-compulsive disorder, and autism spectrum disorders.

“A foundational understanding of interhemispheric processing, combined with interventions translatable to human patients, offers hope for developing novel network-level treatments,” the authors wrote.

The better scientists understand how the brain manages this division and handoff, the better equipped they are to develop treatments for disorders where this process breaks down.

Two halves, one picture

The brain’s strategy of splitting visual spatial perception across hemispheres is an elegant solution to a capacity problem.

By managing each side independently, the brain maximizes awareness and minimizes blind spots. And thanks to its anticipatory handoff system, it stitches both halves of the world into the seamless, unified experience we take for granted.

While pop culture myths about “right-brained artists” and “left-brained analysts” remain oversimplified, the real story of how the hemispheres divide and collaborate is far more interesting – and far more relevant to both neuroscience and human health.

The study is published in the journal Neuropsychologia.

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