Michele Diaz - US grants

DESCRIPTION (provided by applicant): Metaphors, and other figurative language, occur frequently in language and can provide a succinct and vivid description of an object, person, or event. Failures in understanding figurative language can have a dramatic impact on language comprehension and production, and can lead to social isolation and decreased self-esteem. Even when brain injuries do not result in aphasia, figurative language processing can be impaired. Despite the importance of figurative language in human communication, most language research focuses on literal language, resulting in a limited understanding of the neural foundation that supports figurative language. Clinical, behavioral, and neuro imaging research support right hemisphere involvement in metaphor processing. However, there is debate over whether it is metaphors per se that engage the right hemisphere or if other factors that co-vary along the figurative-literal dimension elicit right hemisphere engagement. The Graded Salience Hypothesis proposes right hemisphere recruitment when processing language that is low in salience, and left hemisphere recruitment when processing language that is high in salience. Two factors that may influence salience and hemispheric recruitment are semantic relatedness and context. The first goal of this proposal is to use functional magnetic resonance imaging (fMRI) to investigate the influence of semantic relatedness on hemispheric recruitment by manipulating novelty in metaphors and literal sentences. Familiar phrases, by nature of their common occurrence can establish close semantic relationships in the lexicon. In contrast, novel phrases require dynamic integration of concepts. Semantic relatedness will be manipulated by examining familiar and novel metaphors, and sentences containing typical and innovative uses of objects. The second goal of this proposal is to use fMRI to investigate the influence of context on hemispheric recruitment during metaphor and literal language processing. Context can provide a framework which facilitates the processing of subsequent text. Salience will be manipulated by adding related and unrelated sentential context to metaphors and literal sentences. PUBLIC HEALTH RELEVANCE: Public health will benefit from the proposed research by improving our basic knowledge of the neural foundations of metaphor processing and language in general. This research will facilitate our ability to understand and treat children with specific language impairments and adults with acquired language impairments that result from brain damage.

DESCRIPTION (provided by applicant): Adult development is often associated with the concept of physical and cognitive decline. However, semantic processes related to the meaning of words are largely preserved: vocabulary increases as we age, and semantic word associations and category membership judgments are preserved, for example. Not only does semantic memory typically remain intact during healthy aging, but the number of associations among lexical items may also increase. In addition, these abilities are maintained despite age-related changes that affect brain structure. Despite the preservation of semantic processes specific deficits in phonological processes have been observed. For example, older adults exhibit decreased speed and accuracy in naming objects and increased slips of the tongue. This pattern of aging effects on semantic and phonological processes suggests a fundamental difference in the cognitive organization of these two abilities. The Transmission Deficit Theory provides one theoretical account of these asymmetric patterns of results by proposing fundamental differences in the cognitive architecture of the semantic and phonological systems. The proposed research tests contrasting predictions of the Transmission Deficit theory and other theories for age differences in semantic and phonological processes. The overarching goal of this proposal is to use behavioral measures, diffusion tensor imaging (DTI), and functional magnetic resonance imaging (fMRI) to investigate the mechanisms underlying the asymmetry in aging effects on phonological and semantic processes. While this asymmetry has been investigated behaviorally, few studies have investigated the age-related neural changes that are related to these cognitive changes. These combined methodologies will relate the underlying structural changes to functional activation and behavioral performance. The proposed experiments will characterize semantic and phonological processes in the aging brain, investigate the role of task-irrelevant information in language production and language comprehension tasks, and investigate age-related changes in transient and sustained semantic and phonological processes. This research will improve the current scientific understanding of age-related changes in language, and describe the neural factors that contribute to cognitive decline. The data will be particularly relevant to the concept of plasticity that underlies the maintenance of behavioral functions in older adults. These results will provide essential information for differentiating normal age-related changes in language from the effects of disease, forge advances in our theoretical conceptualization of age-related change in language, and provide insight into rehabilitative therapies for cognitive decline in both healthy aging and clinical patients. PUBLIC HEALTH RELEVANCE: Public health will benefit from the proposed research by improving our basic knowledge of the neural and behavioral foundations of age-related change in language. This research will facilitate our ability to differentiate healthy aging from clinical conditions, and provide insight into rehabilitative therapies for cognitive decline.