Researchers find the brain processes sight and sound in same manner

April 18, 2018, Georgetown University Medical Center
Credit: Wikimedia Commons

Although sight is a much different sense than sound, Georgetown University Medical Center neuroscientists have found that the human brain learns to make sense of these stimuli in the same way.

The researchers say in a two-step process, neurons in one area of the brain learn the representation of the stimuli, and another area categorizes that input so as to ascribe meaning to it—like first seeing just a car without a roof and then analyzing that stimulus in order to place it in the category of "convertible." Similarly, when a child learns a new word, it first has to learn the new sound and then, in a second step, learn to understand that different versions (accents, pronunciations, etc.) of the word, spoken by different members of the family or by their friends, all mean the same thing and need to be categorized together.

"A computational advantage of this scheme is that it allows the brain to easily build on previous content to learn novel information," says the study's senior investigator, Maximilian Riesenhuber, PhD, a professor in Georgetown University School of Medicine's Department of Neuroscience. Study co-authors include first author, Xiong Jiang, PhD; graduate student Mark A. Chevillet; and Josef P. Rauschecker, PhD, all Georgetown neuroscientists.

Their study, published in Neuron, is the first to provide strong evidence that learning in vision and audition follows similar principles. "We have long tried to make sense of senses, studying how the brain represents our multisensory world," says Riesenhuber.

In 2007, the investigators were first to describe the two-step model in human learning of visual categories, and the new study now shows that the brain appears to use the same kind of learning mechanisms across sensory modalities.

The findings could also help scientists devise new approaches to restore sensory deficits, Rauschecker, one of the co-authors, says.

"Knowing how senses learn the world may help us devise workarounds in our very plastic brains," he says. "If a person can't process one sensory modality, say vision, because of blindness, there could be substitution devices that allow visual input to be transformed into sounds. So one disabled sense would be processed by other sensory brain centers."

How does the brain learn categorization for sounds? The same way it does for images
Functional MRI response from a representative subject during a listening task. Credit: Xiong Jiang, Georgetown University

The 16 participants in this study were trained to categorize monkey communication calls— real sounds that mean something to monkeys, but are alien in meaning to humans. The investigators divided the sounds into two categories labeled with nonsense names, based on prototypes from two categories: so-called "coos" and "harmonic arches." Using an auditory morphing system, the investigators were able to create thousands of monkey call combinations from the prototypes, including some very similar calls that required the participants to make fine distinctions between the calls. Learning to correctly categorize the novel sounds took about six hours.

Before and after training, fMRI data were obtained from the volunteers to investigate changes in neuronal tuning in the that were induced by categorization training. Advanced fMRI techniques, functional rapid adaptation (fMRI-RA) and multi-voxel pattern analysis, were used along with conventional fMRI and functional connectivity analyses. In this way, researchers were able to see two distinct sets of changes: a representation of the monkey calls in the left auditory cortex, and tuning analysis that leads to category selectivity for different types of calls in the .

"In our study, we used four different techniques, in particular fMRI-RA and MVPA, to independently and synergistically provide converging results. This allowed us to obtain strong results even from a small sample," says co-author Jiang.

Processing sound requires discrimination in acoustics and tuning changes at the level of the auditory cortex, a process that the researchers say is the same between humans and animal communication systems. Using monkey calls instead of human speech forced the participants to categorize the sounds purely on the basis of acoustics rather than meaning.

"At an evolutionary level, humans and animals need to understand who is friend and who is foe, and sight and sound are integral to these judgments," Riesenhuber says.

Explore further: After learning new words, brain sees them as pictures

More information: Neuron (2018). DOI: 10.1016/j.neuron.2018.03.014

Related Stories

After learning new words, brain sees them as pictures

March 24, 2015
When we look at a known word, our brain sees it like a picture, not a group of letters needing to be processed. That's the finding from a Georgetown University Medical Center (GUMC) study published in the Journal of Neuroscience, ...

In the brain, one area sees familiar words as pictures, another sounds out words

June 9, 2016
Skilled readers can quickly recognize words when they read because the word has been placed in a visual dictionary of sorts which functions separately from an area that processes the sounds of written words, say Georgetown ...

Researchers identify components of speech recognition pathway in humans

June 22, 2011
Neuroscientists at Georgetown University Medical Center (GUMC) have defined, for the first time, three different processing stages that a human brain needs to identify sounds such as speech — and discovered that they ...

The human brain can 'see' what is around the corner

December 4, 2017
Neuroscientists at the University of Glasgow have shown how the human brain can predict what our eyes will see next, using functional magnetic resonance imaging (fMRI).

Recommended for you

Sensitive babies become altruistic toddlers

September 25, 2018
Our responsiveness to seeing others in distress accounts for variability in helping behavior from early in development, according to a study published September 25 in the open-access journal PLOS Biology by Tobias Grossmann ...

Scientists reverse a sensory impairment in mice with autism

September 25, 2018
Using a genetic technique that allows certain neurons in the brain to be switched on or off, UCLA scientists reversed a sensory impairment in mice with symptoms of autism, enabling them to learn a sensory task as quickly ...

Immune cell pruning of dopamine receptors may modulate behavioral changes in adolescence

September 25, 2018
A study by MassGeneral Hospital for Children (MGHfC) researchers finds that the immune cells of the brain called microglia play a crucial role in brain development during adolescence, but that role is different in males and ...

Why it doesn't get dark when you blink

September 25, 2018
People blink every five seconds. During this brief moment, no light falls on the retina, yet people continue to observe a stable picture of the environment with no intervals of darkness. Caspar Schwiedrzik and Sandrin Sudmann, ...

Researchers identify new cause of brain bleeds

September 25, 2018
A team of researchers including UCI project scientist Rachita Sumbria, Ph.D. and UCI neurologist Mark J. Fisher, MD have provided, for the first time, evidence that blood deposits in the brain may not require a blood vessel ...

Lung inflammation from childhood asthma linked with later anxiety

September 25, 2018
Persistent lung inflammation may be one possible explanation for why having asthma during childhood increases your risk for developing anxiety later in life, according to Penn State researchers.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.