Why both halves of your brain share the work of 'seeing' moving objects

A moving object slides across your view and nothing feels choppy. Your brain splits the scene between two halves (left brain and right brain), yet your overall vision experience stays smooth.

The new peer-reviewed study shows that both brain hemispheres briefly share the same object in your vision at the moment it crosses from left to right, or right to left.

That overlap is timed by distinct brain rhythms that first prepare the transfer, then confirm it happened.

Lead author Matthew Broschard is a Picower Fellow at the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology (MIT).

His team wanted to understand how the two sides coordinate when a tracked target moves across the midline.

Each half of the visual world is called a hemifield, and signals that cross between the hemispheres are called interhemispheric transfers.

Behavioral evidence shows people often do better when items are split across hemifields, hinting that the halves can work somewhat independently.

Studying how brains handle vision

The researchers recorded from the lateral prefrontal cortex, a decision making hub, while two adult rhesus macaques tracked dots moving on a screen.

The animals kept their eyes on a fixation point and made a final saccade to the target when cued, which confirmed attention without letting eye movements drive the results.

About 80 percent of trials forced the object to cross the vertical midline so a handoff was required, and performance stayed near 90 percent correct.

Handoff timing was carefully controlled, with the crossing occurring roughly 720 milliseconds after motion began.

Arrays sampled two neighboring regions, the dorsolateral and ventrolateral prefrontal cortex, in both hemispheres.

That layout allowed the team to compare sensory driven signals to task control signals as the target approached and passed the midline.

Brain rhythms guide objects

Neural rhythms carry labels you may know from physics class. Gamma (about 30 to 80 hertz) carried fine grained sensory information and rose when the screen appeared and again when the target was cued in the sending hemisphere.

Beta (about 15 to 30 hertz) moved opposite to gamma, dropping when gamma rose, which fits a role in gating when detailed sensory encoding turns on.

This push pull pattern was strongest in ventrolateral sites that sit closer to input from the visual system.

Alpha (about 10 to 15 hertz) ramped up in both hemispheres about a quarter second before the cross, then peaked just after.

A classic attention review links alpha increases to suppressing distractors, especially in the hemisphere that needs to stand down.

Theta (about 4 to 10 hertz) peaked only in the receiving hemisphere after the cross, signaling the transfer was complete. A rhythmic attention theory ties theta rhythms to shifting where attention should point next.

Brain hemispheres’ vision overlap

Spike decoding showed the sending hemisphere encoded the object as soon as the color cue marked the target.

As the object neared the midline, the receiving side began to carry the same code, so both sides held the object for a short window.

Alpha increases in dorsolateral sites tracked the buildup to transfer, and theta increases there marked completion on the receiving side.

Meanwhile, gamma influences tended to flow from ventrolateral to dorsolateral regions, while alpha and beta influences flowed back in the opposite direction.

That pattern fits a sensible division of labor. Ventral prefrontal sites emphasize incoming sensory details, while dorsal sites impose task rules about when to release and when to accept the object.

Brain keeps objects seamless

The brain does not drop one representation and then create another from scratch. It eases the target across, which prevents gaps in what you see as a single continuous object.

The finding also helps explain why your conscious experience feels unified even though the architecture is split.

Two halves coordinate in advance, then verify the handoff afterward, keeping perception stable while the target crosses the midline.

“It’s surprising to some people to hear that there’s some independence between the hemispheres, because that doesn’t really correspond to how we perceive reality. In our consciousness, everything seems to be unified,” said Earl K. Miller, Picower Professor in the Picower Institute and MIT’s Department of Brain and Cognitive Sciences.

Brain uses objects for learning

Attention is not a steady spotlight that never changes. It pulses, and those pulses appear in distinct frequency bands that enable preparation, encoding, and confirmation at the right moments.

Learning and working memory rely on keeping track of where things are and what they are. The study shows that spatial updates across hemifields recruit alpha and theta in a reproducible way that minimizes information loss.

Those details give educators and clinicians concrete timing targets for interventions that aim to support attention. They also suggest why certain demanding tasks get harder when coordinating the hemispheres is impaired.

Hints for brain health and disease

Interhemispheric communication is not always intact. In schizophrenia, diffusion imaging studies report reduced white matter integrity in callosal pathways that connect the hemispheres, and those changes relate to symptoms.

Multiple sclerosis often damages the corpus callosum, the main bridge between hemispheres. Interhemispheric connectivity measured at rest shows reductions in patients, and those changes map to motor and sensory areas.

Insights about when and how the handoff succeeds may guide future tests that probe these rhythms directly.

They may also clarify which frequency bands best index recovery when therapies improve communication across the midline.

Left brain, right brain, and vision

The study used two adult macaques and arrays limited to prefrontal regions, so it did not survey every area involved in vision.

Still, the combined spike and rhythm signatures offer a precise roadmap for testing human attention with noninvasive methods.

Future work can ask how the handoff behaves when several objects cross at once, or when a distractor becomes a target mid-flight.

It can also probe whether training can tighten the timing so the overlap window shrinks without sacrificing accuracy.

The handoff is measurable and active, not passive. That makes it a promising biomarker for tracking attention in both health and disease.

The study is published in the Journal of Neuroscience.

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