Selective Metaphor Impairments After Left, Not Right, Hemisphere Injury

Abstract

The relative contributions of the left and right hemispheres to the processing of metaphoric language remains unresolved. Neuropsychological studies of brain-injured patients have motivated the hypothesis that the right hemisphere plays a critical role in understanding metaphors. However, the data are inconsistent and the hypothesis is not well-supported by neuroimaging research. To address this ambiguity about the right hemisphere’s role, we administered a metaphor sentence comprehension task to 20 left-hemisphere injured patients, 20 right hemisphere injured patients, and 20 healthy controls. Stimuli consisted of metaphors of three different types: predicate metaphors based on action verbs, nominal metaphors based on event nouns, and nominal metaphors based on entity nouns. For each metaphor (n = 60), a closely matched literal sentence with the same source term was also generated. Each sentence was followed by four adjective–noun answer choices (target + three foil types) and participants were instructed to select the phrase that best matched the meaning of the sentence. As a group, both left and right hemisphere patients performed worse on metaphoric than literal sentences, and the degree of this difficulty varied for the different types of metaphor – but there was no difference between the two patient groups. Tests for literal-metaphor dissociations at the level of single cases revealed two types of impairments: general comprehension deficits affecting metaphors and literal sentences equally, and selective metaphor impairments that were specific to different types of metaphor. All cases with selective metaphor deficits had injury to the left hemisphere, and no known comprehension difficulties with literal language. Our results argue against the hypothesis of a specific or necessary contribution of the right hemisphere for understanding metaphoric language. Further, they reveal deficits in metaphoric language comprehension not captured by traditional language assessments, suggesting overlooked communication difficulties in left hemisphere patients.

The neural basis of metaphor comprehension: evidence from left hemisphere degeneration

“…Functional imaging evidence also implicates areas in the left hemisphere used by the healthy brain in metaphor comprehension (Rapp et al, 2012;Bohrn et al, 2012;Yang 2014). The current study, and other patient studies (Cardillo et al, 2018;Ianni et al, 2014;Gagnon et al, 2003;Tompkins et al, 1990), provide evidence for the importance of left-hemisphere regions for normal metaphor comprehension. Our anatomic analyses included a targeted ROI analysis, an analysis within areas of group degeneration, and a subgroup brain-behavior analysis of patients based on their patterns of performance.…”

“…Patient studies, while more difficult to conduct, offer an important constraint on theorizing based solely on imaging studies (Fellows et al, 2005). Studies with focal lesion patients find evidence of patients with selective metaphor deficits despite normal literal sentence comprehension following left-sided damage (Cardillo McQuire, & Chatterjee 2018;Ianni et al, 2014;Gagnon et al, 2003;Tompkins 1990). These studies implicate left frontal and posterior temporal cortices in metaphor comprehension (Cardillo McQuire, & Chatterjee 2018;Zaidel et al, 2002).…”

“…Studies with focal lesion patients find evidence of patients with selective metaphor deficits despite normal literal sentence comprehension following left-sided damage (Cardillo McQuire, & Chatterjee 2018;Ianni et al, 2014;Gagnon et al, 2003;Tompkins 1990). These studies implicate left frontal and posterior temporal cortices in metaphor comprehension (Cardillo McQuire, & Chatterjee 2018;Zaidel et al, 2002). The traditional view that the right hemisphere plays a privileged role in metaphor comprehension is increasingly difficult to justify, though it remains a staple of clinical and basic neuroscience teaching.…”

Sensitive Measures of Cognition in Mild Cognitive Impairment

“…Assessments of figurative language comprehension also show promise as sensitive measures of cognition and may map onto aspects of semantic knowledge. Figurative language, such as metaphor comprehension, can be impaired despite normal literal language abilities (Cardillo, McQuire, & Chatterjee 2018;Ianni et al, 2014). Successful metaphor processing requires working memory, cognitive flexibility, inhibition of literal meaning, abstract thinking, executive demands, and semantic memory.…”

Context matters: Novel metaphors in supportive and non-supportive contexts (Preprint)

“…Recent patient studies with well controlled linguistic stimuli have not replicated these neuropsychological observations (Cardillo, McQuire, & Chatterjee, 2018;Ianni, Cardillo, McQuire, & Chatterjee, 2014).…”