Sensory deprivation can improve perceptual abilities

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First studies on sensory deprivation grew out of a clandestine cold war military experiment on mind control.

In the early 1950s, footage emerged from Korea of American prisoners of war denouncing capitalism and extolling the virtues of communism.

The CIA, convinced that the soldiers had been brainwashed, promptly launched a research initiative – Project Bluebird – on mind-control techniques.

Part of the research team was a psychologist named Donald Hebb, who offered to conduct an experiment on what he called “sensory isolation.”

Hebb was not so interested in actual brainwashing, but had long been curious about the response of the brain to the absence of stimuli.

He wondered about reports, for example, of Royal Air Force pilots who, after many hours of flying in isolation and staring at an unchanging skyline, would suddenly, for seemingly no reason, lose control of the plane and crash.

And of mariners who, after stretches looking out over a static marine horizon, saw mirages.

And of the Inuit who warned against fishing solo, because in the absence of human contact, without visual cues in a white-out Arctic landscape, they would become disoriented and paddle out to sea, never to return.

By examining the neurological response to isolation, Hebb wondered if he might be able to answer questions about the structure of the brain.

For Project X-38, Hebb constructed a grid of four-by-six-by-eight-foot cells, each air-conditioned and sound-proofed, then recruited volunteers, whom he paid twenty dollars a day to lie in the cells, where they were subjected to “perceptual isolation.”

Over their eyes, the subjects wore frosted plastic goggles that prevented “pattern vision.”

To reduce tactile stimulation, they wore cotton gloves and elbow-to-fingertip cardboard cuffs.

Over their ears, a U-shaped foam pillow.

The cells were outfitted with observation windows, as well as an intercom so that the research team could communicate with the subjects. Hebb instructed his volunteers to stay in the cells for as long as they could.

Initially, Hebb had regarded Project X-38 lightheartedly, joking that the worst part of isolation for the subjects would be the meals prepared by his post-docs.

When the results came in, though, he was stunned: the subjects’ disorientation was far more extreme than he’d imagined.

One volunteer, upon completing the study, drove out of the laboratory parking lot and crashed his car.

On several occasions, when subjects took a break to relieve themselves, they got lost in the bathroom, and had to call a researcher to help them find the way out.

Most startling were the hallucinations.

After just a few hours in isolation, nearly all the subjects saw and felt things that weren’t there.

First they would see pulsing dots and simple geometric patterns; these grew into complex isolated images floating about the room, which then evolved into elaborate, integrated scenes playing out before the subjects’ eyes – “dreaming when awake,” as one participant described it.

One participant reported seeing a parade of squirrels marching “purposefully” across a snowy field, wearing snowshoes and backpacks, while another saw a bathtub being steered by an old man in a metal helmet.

In a particularly extreme case, a subject encountered a second version of himself in the room: he and his apparition began to blend together, until he was unable to discern which was which.

“It is one thing,” wrote Hebb, “to hear that the Chinese are brainwashing their prisoners on the other side of the world; it is another to find, in your own laboratory, that merely taking away the usual sights, sounds, and bodily contacts from a healthy university student for a few days can shake him, right down to the base: can disturb his personal identity.”

Today, the neurological mechanism behind these reactions is more or less understood.

At any given moment, our brain is receiving a torrent of sensory information—visual, auditory, tactile, and so on.

We are so accustomed to this stream of input that when it gets cut off, our brain essentially produces its own stimuli.

It identifies its own patterns, combining any scant blip in the visual cortex with images stored in memory to devise scenes that may be intensely vivid, however disconnected from present reality.

During one particularly illuminating experiment in 2007, researchers at the Max Planck Institute for Brain Research in Frankfurt collaborated with a German artist named Marietta Schwarz, who had volunteered to live with a blindfold on for twenty-two days.

Blindversuch (Blind Study), as Schwarz called her project, was part of a larger art project called Knowledge of Space, which incorporated interviews with blind people on perception, image, space, and art. Schwarz sat blindfolded in the laboratory, recording into a Dictaphone a granular, real-time diary of everything that was happening in her brain.

She reported an array of hallucinations, including intricate abstract patterns, such as bright amoebas, yellow clouds, and animal prints.

The researchers, meanwhile, used an fMRI scanner – functional magnetic resonance imaging, which tracks changes in blood flow in the brain – to follow the neurological operations behind her hallucinations.

Despite the total absence of visual input, Schwarz’s visual cortex lit up like a lantern, exactly as it would if she weren’t blindfolded.

That is, in the world of her brain, the hallucinations were as true and real as anything she could touch or taste or smell.

The aupdated study…..

When you wake up in the middle of the night in total darkness, it can feel as if you have auditory superpowers.

Suddenly, you can hear floorboards creak storeys below and the softest rustle of foxes destroying the bins outside, once again.

Indeed, it is common wisdom that when you lose one sense, the remaining senses heighten.

Research with people experiencing long-term sensory deprivation, such as blindness or deafness, appears to support this notion. People born without sight can indeed feel and hear things significantly beyond the range of the sighted.

Brain data initially seemed to explain these sensory superpowers.

When a major sensory input is lost, the brain area that would have supported the missing sense now becomes active to other inputs.

This can happen across sensory systems – like visual areas activating to touch in the blind.

But it can also happen within sensory systems – such as the brain area of an amputated hand becoming more responsive to touch on the opposite hand or the remaining part of the amputee’s arm.

It was long assumed that more brain space meant more processing power and, therefore, should also mean enhanced perceptual powers for the invading sense.

While this is still the consensus across the scientific world, the idea is starting to attract some unexpected controversy.

Our new paper, published in the Journal of Experimental Psychology: General, has shed some light on the problem.

One reason behind the recent controversy is that sensory enhancement in blind individuals may simply result from their dependence on touch to get by, and increased exposure to fine tactile discrimination, such as braille.

Indeed, scientists have been able to train people with intact vision to show similarly impressive touch discrimination as blind people, with sufficient training.

That is, it may not be that case that blind people are using their visual cortex to process touch at all.

Other studies have found no evidence of sensory deprivation boosting sensory perception where it would be expected (for example, in blindness or following amputation).

The experiment

To dig deeper, we experimentally caused temporary sensory deprivation in a group of volunteers and compared the results with those of a control group – a total of 36 participants.

Using a simple anaesthetic – Lidocaine, like you get at the dentist – we blocked touch and movement perception of a single finger of our participants.

The anaesthetic was applied twice (on consecutive days), and lasted about two hours.

We found that this very small period of deprivation lead to significant improvements in touch perception of the finger directly adjacent to the anaesthetised finger, with no changes in the other digits.

Why just the neighbouring finger?

Research with primates shows that when one finger is lost, it’s mostly the neighbouring fingers that claim the missing finger brain territory.

Our results show that the brain immediately boosted touch perception in one of the remaining fingers of our “temporary finger amputees” – suggesting short term deprivation can indeed have functional benefits for perception, without training.

This shows a person reading braille with their fingers

One reason behind the recent controversy is that sensory enhancement in blind individuals may simply result from their dependence on touch to get by, and increased exposure to fine tactile discrimination, such as braille. The image is adapted from The Coversation news release.

What’s more, in another group, we showed that blocking touch perception on the index finger boosted the effect of a sensory training procedure applied to the middle finger – its effects were more widespread across the hand than in a non-anaesthetised group.

Stroke rehabilitation and beyond

These results are exciting as – unlike some past studies – we can actually show that sensory deprivation has different, and separable effects when used by itself, and when used to boost the effects of sensory training.

Crucially, this holds promising implications for rehabilitation following brain damage. For example, sensory function of a hand affected by stroke can be improved by a sensory block of the opposite, unaffected hand.

It also helps us understand a popular therapy for stroke that requires the unaffected arm to be bound, forcing use of the affected arm.

It may be that this works partly thanks to the sensory and motor deprivation resulting from the “good arm” being bound.

If this can be shown to truly be the case, we can use this knowledge to further push what this therapy can achieve.

The research can also help us answer a bigger question in neuroscience. While we show that sensory brain resources can be reallocated within a sensory modality – meaning a finger can use the brain territory of another finger to support touch perception – it remains unclear whether the brain can learn to reuse an area designed to support a different sense.

So we still haven’t shown whether the vision area of the brain could be used for a completely different purpose. 

Very new perspectivessuggest that this kind of reorganisation might be too extreme, and brain areas are limited to the general functions they were designed for.

While nobody denies that there are changes in brain activity after sensory deprivation, it is unclear whether such changes are necessarily “functional” – affecting how we move, think or behave.

But we are certainly edging closer to understanding the complicated brain processes that enable the sensory experiences that ultimately make life worth living.

Source:
The Conversation
Media Contacts: 
Harriet Dempsey-Jones – The Conversation
Image Source:
The image is adapted from The Coversation news release.

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