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By The End of This Headline, Your Brain Will Have Shifted Focus 20 Times

Did you notice?

MIKE MCRAE
25 AUG 2018

It may feel like you have a smooth, continuous picture of the world around you. But neuroscientists who study perception have now found our brains actually shift focus at a shocking speed - four times a second.

 

Paying attention requires our brains to balance focus with awareness of activities that might demand greater priority. To get it right, perception seems to behave like an old-fashioned movie, constantly flicking from frame to frame, faster than the blink of an eye.

New studies linking oscillations in neural activity with attention are forcing us to rethink how we make sense of the world, and how primate brains manage – and sometimes fail – to cope with an increasingly distracting landscape.

"Our subjective experience of the visual world is an illusion," says psychologist Sabine Kastner from the Princeton Neuroscience Institute in the US.

"Perception is discontinuous, going rhythmically through short time windows when we can perceive more or less."

Kastner's studies on neurological oscillations and attention have contributed to a growing body of evidence showing how our brains build a seamless perception of our surroundings by editing together snippets of stimuli.

Knowledge about the brain's oscillations has been around for as long as we've been recording the pulse of our nervous system's electrochemistry.

But beyond linking certain brain waves with states of consciousness, we've still got a lot to learn about the nature of its rhythms.

 

"We can now link brain rhythms for the first time to our behaviour, on a moment-to-moment basis," says Kastner.

Kastner and her colleagues performed several experiments involving both humans and other primates in order to better understand the paradox of how a continuous stream of focus manages to construct a story amid a shifting landscape of activity. 

By training macaques to respond to a cue and recording their brain activity, the researchers mapped a group of brain waves characterising interactions between different neurological regions.

This allowed them to pin down the rhythmic properties of attention to a specific part of the macaque's brain – its frontoparietal network.

In itself, this isn't at all surprising. This area's role in visual attention has been well established, making it a natural place to study the dynamics at work. But getting a grip on how the fluctuating brain waves might relate to a changing environment hasn't been so straight forward.

Evidence currently suggests that changes in our surroundings aren't likely to be responsible for setting this rhythm, implying instead that the frontoparietal network marches to the beat of its own drum.

 

It's almost as if the brain is an old fashioned camera, focussing in discrete snapshots and then stringing them together into a scene.

The locations and timing of the macaque's shifting patterns of brain waves revealed details about the nature of the network's oscillations, reinforcing the emerging idea that our brains grab stimuli in chunks.

Not only that, it suggests this sampling method has been a feature of primate brains for quite some time.

Where most researchers might end their study with such this assumption, Kastner went one step further and sought to replicate her work on humans.

Joining forces with Berkeley neuroscientist Robert Knight and his research team, Kastner made use of 15 patients undergoing surgical treatments for epilepsy, using these patients' diagnostic probes to study similar brain wave patterns during periods of focus.

Sure enough, the same strobing effect became apparent.

"We have an assumption that what we find in the monkey will hold up in humans, but it's rarely checked as carefully as it is here," says neuroscientist Ian Fiebelkorn, who was the first author on the macaque study.

 

Putting the evidence into context, the parts of our brain responsible for focussing our attention on specific actions flicker constantly, interrupting the stream of stimuli four times a second.

It doesn't seem to make sense at first. Why not just lock onto an object? It could have something to do with a persistent need to check for danger.

"Every 250 milliseconds, you have an opportunity to switch attention," says Fiebelkorn.

"You don't want to be over-locked on anything. It seems like it's an evolutionary advantage to have these windows of opportunity where you're checking in with your environment."

The researchers don't speculate on the medical implications of their research.

But in a world that's increasingly demanding of our attention, research that explains how our focus works on a fundamental level could become increasingly important.

This research was published in Neuron here and here.

 
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