How the Brain Handles Sentences with Multiple Meanings
Resolving sentences with ambiguous quantifiers depends not just on core language areas but also on executive-control brain networks like the prefrontal cortex.
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Converging evidence for the processing costs associated with ambiguous quantifier comprehension
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How the Brain Handles Sentences with Multiple Meanings
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
16 healthy young adults analyzed
One participant was excluded from all analyses for responding with the same button-press for every experimental trial and therefore all analyses include 16 participants.
16 patients with behavioral variant frontotemporal dementia (bvFTD) recruited
We recruited 16 bvFTD patients from the Frontotemporal Degeneration Center at the University of Pennsylvania.
What they did
In the initial experiment, researchers used fMRI to scan 16 healthy young adults while they judged whether sentences with ambiguous quantifiers matched a series of pictures. In the subsequent experiment, they tested 16 patients with a neurodegenerative disease called behavioral variant frontotemporal dementia (bvFTD) and 16 healthy seniors using the same task. Additionally, 11 of the patients underwent brain imaging to correlate their gray matter density with their behavioral response times.
What they found
Healthy young adults took an average of 93 milliseconds longer to process ambiguous sentences compared to unambiguous ones, activating both core language areas and prefrontal executive regions. Healthy seniors also showed a clear processing cost, taking an average of 393 milliseconds longer on ambiguous trials, whereas patients with bvFTD showed no such processing cost. Within the patient group, greater tissue loss in the left dorsolateral prefrontal cortex strongly correlated (r = -0.68) with slower response times for ambiguous sentences.
The limits
What it doesn't show
The study does not rule out whether the prefrontal activity is specific to language ambiguity or represents general working memory and decision-making demands. Additionally, because the researchers did not test patients with parietal lobe disease, they could not verify the exact causal role of the parietal lobe activation seen in healthy adults. Finally, the findings are limited by relatively small sample sizes, particularly the subset of only 11 patients who had neuroimaging data available.
Key terms
- quantifier
- A word or phrase, such as 'all' or 'some', that indicates the quantity of a referent.
- collective interpretation
- An interpretation of a sentence where individuals act together as a single group to perform an action.
- distributive interpretation
- An interpretation of a sentence where each individual performs the action independently.
- behavioral variant frontotemporal dementia (bvFTD)
- A neurodegenerative disease characterized by progressive changes in personality, social behavior, and executive function.
- dorsolateral prefrontal cortex (dlPFC)
- A brain region crucial for executive control, working memory, and decision-making.
- peri-Sylvian language network
- The core areas of the left hemisphere of the brain, including Broca's and Wernicke's areas, traditionally associated with language processing.
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Quiz yourself
Which brain regions traditionally make up the core peri-Sylvian language network involved in sentence processing?
Common questions
What makes a sentence like 'All the dogs jumped in a puddle' ambiguous?
This is a doubly-quantified sentence containing both 'all' and 'a'. It can mean all dogs jumped into a single shared puddle (collective) or that each dog jumped into its own separate puddle (distributive).
Why do healthy adults take longer to process ambiguous sentences?
The processing delay, or processing cost, occurs because the brain must evaluate multiple potential interpretations, recruiting additional executive and decision-making brain regions beyond the normal language network to resolve the ambiguity.
Why didn't patients with frontotemporal dementia (bvFTD) show a processing delay for ambiguous sentences?
Due to damage in prefrontal networks like the dorsolateral prefrontal cortex, these patients have impaired executive resources, rendering them insensitive to the subtle alternative interpretations of the ambiguous sentences.
Does this study mean language processing happens entirely outside of traditional language areas?
No, the traditional peri-Sylvian language network is still highly active during these tasks, but the brain must recruit additional, extra-Sylvian executive networks to handle the extra cognitive load of resolving ambiguity.
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