Learning to read written text fundamentally changes the pathways the human brain uses to process spoken language. A recent study shows that adults with formal literacy education recruit special regions on the right side of the brain to identify isolated sounds, a neurological response that is absent in people with limited reading education. This study was recently published in the journal cortex.
Spoken language has been a universal human behavior for hundreds of thousands of years. Reading and writing are relatively recent cultural inventions. The brain was not specifically evolved to read, so it must reuse existing visual and linguistic networks to understand written text.
Neuroimaging studies have demonstrated that mastering the written word induces physical and functional changes in the left hemisphere of the brain. This occurs particularly in areas responsible for linking visual shapes to specific sounds. An open question is whether learning to read also fundamentally changes the way people hear and process everyday spoken language.
Reading education explicitly teaches a cognitive skill called phonological awareness. This is the ability to recognize and manipulate the individual auditory elements of words. Common tests of this skill include asking students to identify specific syllables, recognize rhymes, or repeat fully made up words that have no real meaning.
People who know how to read perform much better on tests of phonological awareness than people who can’t read. False word repetition relies entirely on short-term memory for pure sounds, completely separate from short-term memory for semantic meaning. While literate people can easily hold these sound sequences in their heads, illiterate adults generally have a hard time remembering any string of sounds.
To find out whether this learned skill influences brain activity during natural listening, a team of researchers designed a special audio test. Mariana P. Nucci, a cognitive neuroscientist at the University of São Paulo, led the research team. Nucci and her colleagues wanted to observe how brains from widely different educational backgrounds cope with difficult listening tasks.
Finding a group of adults who have no formal education and live near a modern brain scanner is a real challenge. Researchers recruited participants from the city of São Paulo, Brazil. The region has a thriving scientific community, but historically high rates of wealth inequality mean that many older people grew up without consistent schooling.
The researchers recruited three different groups of healthy volunteers. The sample included 23 highly educated young adults, 21 highly educated older adults, and 15 older adults with very low levels of formal education. The last group of volunteers is classified as functionally illiterate. They may be able to recognize basic letters and common names, but they are generally unable to read and understand long texts.
Participants entered a functional magnetic resonance imaging scanner, a machine that tracks blood flow in the brain and measures neural activity. Volunteers listened to an enhanced audio narration through headphones. They held a small device in their left hand and were instructed to press a button each time they heard a specific target word.
Volunteers performed this word monitoring task in two different languages. First, I listened to the story in my native Portuguese. Because they could understand the story, they were able to use the semantic context of the story to predict the arrival of the target word.
Next, we listened to a structurally identical story in Japanese, but none of the participants could understand it. In this state, the listener cannot rely on the context or meaning of the story. They had to consciously monitor a continuous stream of speech in a foreign language to detect specific sequences of unfamiliar sounds. The researchers also included a baseline task that required participants to press a button when hearing a simple sound in a quiet background.
Volunteers with lower levels of formal education performed relatively better when listening to Portuguese. They succeeded in pressing the native target word button approximately 90% of the time. When the language switched to Japanese, performance dropped dramatically.
Functionally illiterate adults were able to understand target words in an unknown language only 17% of the time. By comparison, the success rate for highly educated older adults was 48%. Highly educated young people heard the target words 75% of the time. Both groups of literate adults performed significantly better than the group with no reading education.
Brain imaging data provided a physiological explanation for these behavioral differences. All three groups showed similar patterns of brain activation while listening to their native language. Significant differences in brain activity emerged only during the Japanese listening task.
In highly educated older adults, there was a clear spike in activity in the right inferior frontal gyrus. This area is located on the right side of your head, near your temple. This corresponds directly to Broca’s area, a highly studied area on the left side of the brain that governs speech production and language comprehension.
Older adults with no formal education completely failed to recruit this right-sided region during an unknown language task. The researchers noted that success in finding hidden Japanese words was highly correlated with scores on standard reading proficiency tests. This indicates that the right inferior frontal gyrus is involved in applying explicit phonological analysis to speech sounds. This particular cognitive ability appears to be developed primarily through years of classroom education and literacy training.
The brain scans also revealed expected differences related to the general aging process. Highly educated older adults showed more extensive brain activity than highly educated young adults during both language tasks. Older brains often recruit extra neural pathways to perform basic tasks. Scientists theorize that this hyperactivation helps compensate for age-related changes in general physiological efficiency.
This study includes several known limitations. The group of functionally illiterate adults was relatively small. This is primarily due to strict exclusion criteria and the inherent difficulty in finding qualified volunteers who can safely participate in noisy brain imaging environments. Small study sample sizes may limit the statistical power of neuroimaging findings.
The authors also emphasize that educational attainment is deeply connected to broader life experiences. Functionally illiterate participants generally faced more socio-economic adversity and had fewer occupational opportunities than their more educated counterparts over the course of their lives. Poverty, stress, and poor access to health care can also affect cognitive development and resting brain organization, independent of reading comprehension.
Future studies could test adults with low literacy skills using nonverbal speech tasks to see if the lack of right frontal brain activation is specific to language. Researchers might also look to tasks that require intense visual focus to determine whether socioeconomic disadvantage generally alters how the brain allocates sustained attention. Expanding this research will help clinicians better understand how to structure cognitive therapy and rehabilitation programs for older patients with diverse educational backgrounds.
The study, “Literacy Ability Modulates Right Inferior Frontal Gyrus Involvement in Spoken Word Phonological Processing,” was authored by Mariana P. Nucci, Kelly Kotosuk, Katerina Lukasova, Ricardo Nitorini, Cheryl L. Grady, Edson Amaro Jr., and Jed A. Meltzer.
