How does using hands vs speech change brain activity for language?
While both sign and spoken languages share a core language network in the brain, they recruit different sensory-motor regions to support hand movements versus vocal articulation and hearing.
Source
How sensory-motor systems impact the neural organization for language: direct contrasts between spoken and signed language
What they did
In the initial study, 14 bilingual participants overtly named 80 pictures in either American Sign Language or English while researchers used PET scans to track brain activity. In the subsequent study, 13 bilingual participants watched and listened to sentences in both languages during fMRI scans to measure brain activity during comprehension. Both studies directly compared the language modalities to see how the physical format of language impacts the brain.
What they found
For language production, signing triggered higher activity in the upper-limb areas of the motor cortex and the cerebellum, while speaking activated mouth-control regions and auditory areas. For comprehension, signed sentences recruited the parietal and premotor cortex, whereas spoken sentences activated auditory processing areas in the temporal lobe. Both languages shared a core bilateral network, showing that the brain adapts to the physical demands of language while using the same underlying linguistic systems.
The limits
What it doesn't show
The study only involved hearing bilinguals who learned both languages from birth, so the findings may not apply to deaf signers or people who learn sign language later in life. Because the experiments examined single-word naming and individual sentences, they cannot show how the brain processes natural, continuous conversation. Additionally, the unexpected finding of reduced visual cortex activity during signing is speculative and requires further research to confirm if the brain actively suppresses visual feedback during self-signing.
Key terms
- Bimodal bilinguals
- Individuals who are fluent in both a spoken language and a signed language.
- Positron emission tomography (PET)
- A brain imaging technique that measures blood flow changes to detect active neural regions.
- Functional magnetic resonance imaging (fMRI)
- An imaging technology that measures brain activity by detecting changes in blood oxygenation and flow.
- Perisylvian regions
- Areas of the brain surrounding the lateral sulcus that are critical for processing and producing language.
- Somatosensory feedback
- Sensory information received from the body's muscles, joints, and skin about touch, position, and movement.
- Action Observation Network (AON)
- A group of brain regions activated both when performing an action and when watching someone else perform that same action.
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Quiz yourself
What is the primary advantage of directly contrasting spoken and signed language processing within the same bimodal bilingual individuals?
Common questions
Why did the researchers study hearing bilinguals instead of deaf signers?
Studying hearing bilinguals allows researchers to directly compare signed and spoken language processing within the exact same brain, avoiding differences that might arise from comparing two different groups of people.
What is a motoric baseline, and why did the authors avoid using one in Experiment 1?
A motoric baseline is a non-linguistic task (like moving fingers or making random mouth sounds) used to subtract basic physical movement from brain scans; the authors avoided this because they wanted to capture the full sensory and motor differences between producing spoken words and signs.
Why does sign language comprehension activate the parietal cortex?
The parietal cortex is heavily involved in tracking physical space and body movements. It may help signers predict the visual movements of a speaker's hands and arms to speed up comprehension.
Does speaking activate the brain's visual areas more than signing does?
Yes, unexpectedly, speaking showed higher activation in visual areas. The researchers hypothesize this is because the brain actually suppresses visual processing during self-signing to prevent the signer's own hand movements from distracting them.
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