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Speech Comprehension (speech + comprehension)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

The neural response to changing semantic and perceptual complexity during language processing

HUMAN BRAIN MAPPING, Issue 3 2010
David J. Sharp
Abstract Speech comprehension involves processing at different levels of analysis, such as acoustic, phonetic, and lexical. We investigated neural responses to manipulating the difficulty of processing at two of these levels. Twelve subjects underwent positron emission tomographic scanning while making decisions based upon the semantic relatedness between heard nouns. We manipulated perceptual difficulty by presenting either clear or acoustically degraded speech, and semantic difficulty by varying the degree of semantic relatedness between words. Increasing perceptual difficulty was associated with greater activation of the left superior temporal gyrus, an auditory-perceptual region involved in speech processing. Increasing semantic difficulty was associated with reduced activity in both superior temporal gyri and increased activity within the left angular gyrus, a heteromodal region involved in accessing word meaning. Comparing across all the conditions, we also observed increased activation within the left inferior prefrontal cortex as the complexity of language processing increased. These results demonstrate a flexible system for language processing, where activity within distinct parts of the network is modulated as processing demands change. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. [source]

A comparison of five fMRI protocols for mapping speech comprehension systems

EPILEPSIA, Issue 12 2008
Jeffrey R. Binder
Summary Aims:, Many fMRI protocols for localizing speech comprehension have been described, but there has been little quantitative comparison of these methods. We compared five such protocols in terms of areas activated, extent of activation, and lateralization. Methods:, fMRI BOLD signals were measured in 26 healthy adults during passive listening and active tasks using words and tones. Contrasts were designed to identify speech perception and semantic processing systems. Activation extent and lateralization were quantified by counting activated voxels in each hemisphere for each participant. Results:, Passive listening to words produced bilateral superior temporal activation. After controlling for prelinguistic auditory processing, only a small area in the left superior temporal sulcus responded selectively to speech. Active tasks engaged an extensive, bilateral attention, and executive processing network. Optimal results (consistent activation and strongly lateralized pattern) were obtained by contrasting an active semantic decision task with a tone decision task. There was striking similarity between the network of brain regions activated by the semantic task and the network of brain regions that showed task-induced deactivation, suggesting that semantic processing occurs during the resting state. Conclusions:, fMRI protocols for mapping speech comprehension systems differ dramatically in pattern, extent, and lateralization of activation. Brain regions involved in semantic processing were identified only when an active, nonlinguistic task was used as a baseline, supporting the notion that semantic processing occurs whenever attentional resources are not controlled. Identification of these lexical-semantic regions is particularly important for predicting language outcome in patients undergoing temporal lobe surgery. [source]

Mirror Neurons, the Motor System and Language: From the Motor Theory to Embodied Cognition and Beyond

LINGUISTICS & LANGUAGE COMPASS (ELECTRONIC), Issue 6 2009
Jonathan H. Venezia
The motor theory of speech perception states that phonetic segments in the acoustic speech stream activate stored motor commands in the brain that give rise to perception of discrete speech sounds. The motor theory fell out of favor when growing evidence from lesion and behavioral studies led aspects of the theory to appear untenable. However, with the recent discovery of mirror neurons and their potential role in action understanding, interest in the motor theory of speech perception is renewed. We review the function and properties of mirror neurons in monkeys, and briefly describe the current literature that focuses on the role of a putative human mirror system in cognition and language processing. Further, we describe proposed evidence for the involvement of the motor system in perceptive speech processing, and point out ambiguities in the literature that arise from the tight coupling of sensory and motor processes in speech comprehension. An alternative theory proposing that sensory representations in superior temporal cortex are mapped onto frontal production networks is offered. We cite evidence that confirms the failure of the motor theory to accurately describe perceptive processes in speech, and promote the conclusion that speech representations are fundamentally sensory in nature. [source]

Retrieving meaning after temporal lobe infarction: The role of the basal language area

ANNALS OF NEUROLOGY, Issue 6 2004
David J. Sharp MRCP
During speech comprehension the auditory association cortex in the superior temporal cortex is involved in perceptual analysis of the speech signal, whereas the basal language area in the inferior temporal cortex mediates access to word meaning. Disruption of the interaction between the superior and inferior temporal cortices is one factor that may determine recovery from aphasic stroke. We used positron emission tomography to investigate semantic processing within inferior temporal cortex in control subjects and after infarction involving the superior temporal cortex. In the control group, semantic decision making on clear speech activated both anterior fusiform gyri. Chronic aphasic patients were impaired at the task and demonstrated reduced activation within the left anterior fusiform gyrus. A similar pattern of impaired performance and reduced left anterior fusiform gyrus activation was observed when control subjects heard perceptually degraded speech. Performance in both groups predicted activity in the right anterior fusiform gyrus and the temporal poles, where accuracy linearly correlated with activity. These results demonstrate that the function of the basal language area is sensitive to changes in the quality of perceptual input. In addition, different profiles of response observed in each hemisphere suggest distinct contributions of both left and right inferior temporal cortices to the semantic processing of speech. Ann Neurol 2004 [source]