Bihemispheric foundations for human speech comprehension

Abstract

Emerging evidence from neuroimaging and neuropsychology suggests that human speech comprehension engages two types of neurocognitive processes: a distributed bilateral system underpinning general perceptual and cognitive processing, viewed as neurobiologically primary, and a more specialized left hemisphere system supporting key grammatical language functions, likely to be specific to humans. To test these hypotheses directly we covaried increases in the nonlinguistic complexity of spoken words [presence or absence of an embedded stem, e.g., claim (clay)] with variations in their linguistic complexity (presence of inflectional affixes, e.g., play+ ed). Nonlinguistic complexity, generated by the on-line competition between the full word and its onset-embedded stem, was found to activate both right and left fronto-temporal brain regions, including bilateral BA45 and -47. Linguistic complexity activated left-lateralized inferior frontal areas only, primarily in BA45. This contrast reflects a differentiation between the functional roles of a bilateral system, which supports the basic mapping from sound to lexical meaning, and a language-specific left-lateralized system that supports core decompositional and combinatorial processes invoked by linguistically complex inputs. These differences can be related to the neurobiological foundations of human language and underline the importance of bihemispheric systems in supporting the dynamic processing and interpretation of spoken inputs.brain | language | morphology | inflection C onsidered as a neuroscientific phenomenon, human language comprehension-and human language function in generalis both remarkably specific and remarkably distributed in its neural instantiation. One hundred fifty years of neuropsychological research demonstrate the irreplaceable role of left hemisphere perisylvian networks (linking left inferior frontal and posterior temporal brain areas) in supporting key combinatorial language functions in the domain of inflectional morphology and syntax. At the same time, evidence from lesion studies and neuroimaging of the intact brain shows that dynamic access to lexical meaning, and the ability to rapidly construct semantic and pragmatic interpretations of incoming speech, can remain strikingly intact even when the left perisylvian language areas are destroyed, implying a distributed bihemispheric substrate. We believe that these contrasts reflect a fundamental distinction in the types of processing operations underlying normal language comprehension and in the neural networks that support these functions. In this event-related fMRI study of lexical processing, we test the hypothesis that general purpose processing demands engage both right and left perisylvian systems, whereas linguistically specific processing demands selectively engage left hemisphere systems.A critical element of this account is its emphasis on the bihemispheric foundations of human speech communication. Functional imaging shows that bilateral activation of temporal lobe structures in a...

Does Semantic Context Benefit Speech Understanding through “Top–Down” Processes? Evidence from Time-resolved Sparse fMRI

“…Echoic representations of speech have previously been linked with anterior regions of the STG Buchsbaum et al, 2005) that show Sentence type × Clarity interactions in the present study. Furthermore, echoic storage of unanalyzed material will, as a downstream consequence, also increase the load on later processes of lexical/semantic selection which have been associated with the LIFG (Bozic, Tyler, Ives, Randall, & Marslen-Wilson, 2010;Righi, Blumstein, Mertus, & Worden, 2010;Rodd et al, 2005). These two computational processes may adequately explain both the timing and location of Sentence type × Speech clarity interactions observed in the present study, without necessary recourse to top-down mechanisms.…”

Nodes and networks in the neural architecture for language: Broca's region and beyond

“…Importantly, Broca's region is also involved in unification operations at the word level, as in morphological (de)composition [44][45][46]. Compositional and decompositional operations are spatio-temporally extended and occur at multiple levels and at multiple time-slices in the language processing system.…”

“…Certainly Broca's region as a whole is not an exclusive syntax area. To what extent a sub-parcellation of Broca's region [31,33] might reveal some regions to be more specific for language processing than others [42] remains to be seen.Importantly, Broca's region is also involved in unification operations at the word level, as in morphological (de)composition [44][45][46]. Compositional and decompositional operations are spatio-temporally extended and occur at multiple levels and at multiple time-slices in the language processing system.…”

The Interaction of Lexical Semantics and Cohort Competition in Spoken Word Recognition: An fMRI Study

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