Is the right brain hemisphere necessary for understanding metaphors?
Injuries to the left hemisphere, rather than the right hemisphere, cause selective difficulties in understanding metaphorical language.
Source
Selective Metaphor Impairments After Left, Not Right, Hemisphere Injury
What they did
To test the neural bases of figurative language, researchers compared 40 patients with chronic, unilateral focal lesions to twenty neurologically healthy older adults. Within the patient group, 20 patients had left hemisphere injuries and 20 patients had right hemisphere injuries. Participants completed a multiple-choice test to match the meaning of 60 literal-metaphor sentence pairs.
What they found
The researchers discovered that only patients with left hemisphere damage exhibited selective impairments in metaphor comprehension, whereas those with right hemisphere damage performed normally. Specifically, four patients with left hemisphere damage showed a classic selective deficit where metaphor comprehension was severely impaired while literal sentence comprehension remained intact. The findings also revealed that metaphors vary in difficulty depending on their grammatical form, with nominal-entity metaphors being the most difficult for patients.
The limits
What it doesn't show
The study cannot rule out the potential involvement of certain brain areas that were not represented in this patient sample, such as the left superior parietal cortex or the right inferior temporal cortex. Additionally, the metaphors utilized in the experiments were only moderately familiar, meaning the results might not apply to highly novel or completely unfamiliar metaphors that could require different neural processing. The study design also relies on patients with chronic, focal injuries, meaning these findings may not generalize to acute-stage stroke patients whose brains have not yet undergone reorganization.
Key terms
- Metaphor
- A figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.
- Left Hemisphere
- The left half of the brain, traditionally associated with dominant control of language and logical processing.
- Right Hemisphere
- The right half of the brain, historically hypothesized to specialize in coarse semantic processing and non-literal language.
- Selective Metaphor Impairment
- A cognitive deficit where an individual struggles to comprehend metaphorical language while maintaining normal comprehension of literal language.
- Nominal Metaphor
- A metaphor that takes the syntactic form of a category assertion, comparing two nouns directly.
- Predicate Metaphor
- A metaphor where an action verb is used in a non-literal way to describe an event or relationship.
Flashcards
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Quiz yourself
According to the paper, approximately how frequently do humans use metaphorical words in typical speech or reading?
Common questions
Why did older studies find that right-hemisphere damage causes metaphor impairments?
Many older studies used tasks with visual-spatial demands that disproportionately affected patients with right-hemisphere injuries, or failed to balance their metaphorical and literal test items for baseline difficulty.
How do researchers prove a true selective deficit for metaphors?
They use statistical tests to show that a patient's metaphorical comprehension is significantly worse than controls, their literal comprehension remains normal, and the difference between the two tasks is statistically meaningful.
Does this mean the right hemisphere plays no role in language?
No, the right hemisphere is still believed to play a supportive role in managing complex language tasks, especially when cognitive and working memory demands are very high.
Are all types of metaphors equally difficult to understand?
No, both healthy controls and patients found predicate metaphors easier to comprehend than nominal metaphors, suggesting that metaphors utilizing action verbs are processed more naturally than those based on nouns.
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