Humans began to develop systems of reading and writing only within the past few thousand years. Our reading abilities set us apart from other animal species. Still, a few thousand years is much too short a timeframe for our brains to have evolved new areas specifically devoted to reading. […]
Humans began to develop systems of reading and writing only within the past few thousand years. Our reading abilities set us aside from other animal species, but a couple of thousand years is far too short a timeframe for our brains to possess evolved new areas specifically dedicated to reading.
To account for the event of this skill, some scientists have hypothesized that parts of the brain that originally evolved for other purposes are “recycled” for reading. together example, they suggest that a neighborhood of the sensory system that’s specialized to perform visual perception has been repurposed for a critical component of reading called orthographic processing – the power to acknowledge written letters and words.
A new study from MIT neuroscientists offers evidence for this hypothesis. The findings suggest that even in nonhuman primates, who don’t skills to read, a neighborhood of the brain called the inferotemporal (IT) cortex is capable of performing tasks like distinguishing words from nonsense words or picking out specific letters from a word.
“This work has opened a possible linkage between our rapidly developing understanding of the neural mechanisms of visual processing and a crucial primate behavior — human reading,” says James DiCarlo, the top of MIT’s Department of Brain and Cognitive Sciences, an investigator within the McGovern Institute for Brain Research and therefore the Center for Brains, Minds, and Machines, and therefore the senior author of the study.
Rishi Rajalingham, an MIT postdoc, is that the lead author of the study, which appears in Nature Communications. Other MIT authors are postdoc Kohitij Kar and technical associate Sachi Sanghavi. The research team also includes Stanislas Dehaene, a professor of experimental psychology at the school de France.
Word recognition Reading may be a complex process that needs recognizing words, assigning aiming to those words, and associating words with their corresponding sound. These functions are believed to be opened up over different parts of the human brain.
Functional resonance imaging (fMRI) studies have identified a neighborhood called the visual form area (VWFA) that lights up when the brain processes a word. This region is involved within the orthographic stage: It discriminates words from jumbled strings of letters or words from unknown alphabets. The VWFA is found within the IT cortex, a neighborhood of the visual area that’s also liable for identifying objects.
DiCarlo and Dehaene took an interest in studying the neural mechanisms behind word recognition after cognitive psychologists in France reported that baboons could learn to discriminate words from nonwords, during a study that appeared in Science in 2012.
Using fMRI, Dehaene’s lab has previously found that parts of the IT cortex that answer objects and faces become highly specialized for recognizing written words once people learn to read.
“However, given the restrictions of human imaging methods, it’s been challenging to characterize these representations at the resolution of individual neurons, and to quantitatively test if and the way these representations could be reused to support orthographic processing,” Dehaene says. “These findings inspired us to ask if nonhuman primates could provide a singular opportunity to research the neuronal mechanisms underlying orthographic processing.”
The researchers hypothesized that if parts of the primate brain are predisposed to process text, they could be ready to find patterns reflecting that within the neural activity of nonhuman primates as they simply check out words.
To test that concept, the researchers recorded neural activity from about 500 neural sites across the IT cortex of macaques as they checked out about 2,000 strings of letters, a number of which were English words and a few of which were nonsensical strings of letters.
“The efficiency of this system is that you simply don’t get to train animals to try to anything,” Rajalingham says. “What you are doing is simply record these patterns of neural activity as you flash a picture ahead of the animal.”
The researchers then fed that neural data into an easy computer model called a linear classifier. This model learns to mix the inputs from each of the five hundred neural sites to predict whether the string of letters that provoked that activity pattern was a word or not. While the animal itself isn’t performing this task, the model acts as a “stand-in” that uses the neural data to get a behavior, Rajalingham says.
Using that neural data, the model was ready to generate accurate predictions for several orthographic tasks, including distinguishing words from nonwords and determining if a specific letter is present during a string of words. The model was about 70 percent accurate at distinguishing words from nonwords, which is extremely almost like the speed reported within the 2012 Science study with baboons. Furthermore, the patterns of errors made by model were virtually like those made by the animals.
Neuronal recycling The researchers also recorded neural activity from a unique brain area that also feeds into IT cortex: V4, which is a component of the visual area. once they fed V4 activity patterns into the linear classifier model, the model poorly predicted (compared to IT) the human or baboon performance on the orthographic processing tasks.
The findings suggest that the IT cortex is especially well-suited to be repurposed for skills that are needed for reading and that they support the hypothesis that a number of the mechanisms of reading are built upon highly evolved mechanisms for visual perception, the researchers say.
The researchers now decide to train animals to perform orthographic tasks and measure how their neural activity changes as they learn the tasks.
Reference Rajalingham et al. (2020). The inferior temporal cortex may be a potential cortical precursor of orthographic processing in untrained monkeys. Nature Communications. DOI: https://doi.org/10.1038/s41467-020-17714-3
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