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Sheila E. Blumstein
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2013) 25 (5): 706–718.
Published: 01 May 2013
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Listeners' perception of acoustically presented speech is constrained by many different sources of information that arise from other sensory modalities and from more abstract higher-level language context. An open question is how perceptual processes are influenced by and interact with these other sources of information. In this study, we use fMRI to examine the effect of a prior sentence fragment meaning on the categorization of two possible target words that differ in an acoustic phonetic feature of the initial consonant, VOT. Specifically, we manipulate the bias of the sentence context (biased, neutral) and the target type (ambiguous, unambiguous). Our results show that an interaction between these two factors emerged in a cluster in temporal cortex encompassing the left middle temporal gyrus and the superior temporal gyrus. The locus and pattern of these interactions support an interactive view of speech processing and suggest that both the quality of the input and the potential bias of the context together interact and modulate neural activation patterns.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2011) 23 (3): 593–603.
Published: 01 March 2011
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The current study examined the neural systems underlying lexically conditioned phonetic variation in spoken word production. Participants were asked to read aloud singly presented words, which either had a voiced minimal pair (MP) neighbor (e.g., cape ) or lacked a minimal pair (NMP) neighbor (e.g., cake ). The voiced neighbor never appeared in the stimulus set. Behavioral results showed longer voice-onset time for MP target words, replicating earlier behavioral results [Baese-Berk, M., & Goldrick, M. Mechanisms of interaction in speech production. Language and Cognitive Processes, 24, 527–554, 2009]. fMRI results revealed reduced activation for MP words compared to NMP words in a network including left posterior superior temporal gyrus, the supramarginal gyrus, inferior frontal gyrus, and precentral gyrus. These findings support cascade models of spoken word production and show that neural activation at the lexical level modulates activation in those brain regions involved in lexical selection, phonological planning, and, ultimately, motor plans for production. The facilitatory effects for words with MP neighbors suggest that competition effects reflect the overlap inherent in the phonological representation of the target word and its MP neighbor.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2010) 22 (2): 213–224.
Published: 01 February 2010
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The present study investigated the neural bases of phonological onset competition using an eye tracking paradigm coupled with fMRI. Eighteen subjects were presented with an auditory target (e.g., beaker ) and a visual display containing a pictorial representation of the target (e.g., beaker ), an onset competitor (e.g., beetle ), and two phonologically and semantically unrelated objects (e.g., shoe , hammer ). Behavioral results replicated earlier research showing increased looks to the onset competitor compared to the unrelated items. fMRI results showed that lexical competition induced by shared phonological onsets recruits both frontal structures and posterior structures. Specifically, comparison between competitor and no-competitor trials elicited activation in two nonoverlapping clusters in the left IFG, one located primarily within BA 44 and the other primarily located within BA 45, and one cluster in the left supramarginal gyrus (SMG) extending into the posterior superior temporal gyrus. These results indicate that the left IFG is sensitive to competition driven by phonological similarity and not only to competition among semantic/conceptual factors. Moreover, they indicate that the SMG is not only recruited in tasks requiring access to lexical form but is also recruited in tasks that require access to the conceptual representation of a word.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2009) 21 (5): 960–975.
Published: 01 May 2008
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The current study investigated the neural correlates that underlie the processing of ambiguous words and the potential effects of semantic competition on that processing. Participants performed speeded lexical decisions on semantically related and unrelated prime–target pairs presented in the auditory modality. The primes were either ambiguous words (e.g., ball ) or unambiguous words (e.g., athlete ), and targets were either semantically related to the dominant (i.e., most frequent) meaning of the ambiguous prime word (e.g., soccer ) or to the subordinate (i.e., less frequent) meaning (e.g., dance ). Results showed increased activation in the bilateral inferior frontal gyrus (IFG) for ambiguous-related compared to unambiguous-related stimulus pairs, demonstrating that prefrontal areas are activated even in an implicit task where participants are not required to explicitly analyze the semantic content of the stimuli and to make an overt selection of a particular meaning based on this analysis. Additionally, increased activation was found in the left IFG and the left cingulate gyrus for subordinate meaning compared to dominant meaning conditions, suggesting that additional resources are recruited in order to resolve increased competition demands in accessing the subordinate meaning of an ambiguous word.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2008) 20 (4): 592–612.
Published: 01 April 2008
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Lexical processing requires both activating stored representations and selecting among active candidates. The current work uses an eye-tracking paradigm to conduct a detailed temporal investigation of lexical processing. Patients with Broca's and Wernicke's aphasia are studied to shed light on the roles of anterior and posterior brain regions in lexical processing as well as the effects of lexical competition on such processing. Experiment 1 investigates whether objects semantically related to an uttered word are preferentially fixated, for example, given the auditory target “hammer,” do participants fixate a picture of a nail? Results show that, like normal controls, both groups of patients are more likely to fixate on an object semantically related to the target than an unrelated object. Experiment 2 explores whether Broca's and Wernicke's aphasics show competition effects when words share onsets with the uttered word, for instance, given the auditory target “hammer,” do participants fixate a picture of a hammock? Experiment 3 investigates whether these patients activate words semantically related to onset competitors of the uttered word, for example, given the auditory target “hammock,” do participants fixate a nail due to partial activation of the onset competitor hammer? Results of Experiments 2 and 3 show pathological patterns of performance for both Broca's and Wernicke's aphasics under conditions of lexical onset competition. However, the patterns of deficit differed, suggesting different functional and computational roles for anterior and posterior areas in lexical processing. Implications of the findings for the functional architecture of the lexical processing system and its potential neural substrates are considered.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2005) 17 (9): 1353–1366.
Published: 01 September 2005
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This study explored the neural systems underlying the perception of phonetic category structure by investigating the perception of a voice onset time (VOT) continuum in a phonetic categorization task. Stimuli consisted of five synthetic speech stimuli which ranged in VOT from 0 msec ([da]) to 40 msec ([ta]). Results from 12 subjects showed that the neural system is sensitive to VOT differences of 10 msec and that details of phonetic category structure are retained throughout the phonetic processing stream. Both the left inferior frontal gyrus (IFG) and cingulate showed graded activation as a function of category membership with increasing activation as stimuli approached the phonetic category boundary. These results are consistent with the view that the left IFG is involved in phonetic decision processes, with the extent of activation influenced by increased resources devoted to resolving phonetic category membership and/or selecting between competing phonetic categories. Activation patterns in the cingulate suggest that it is sensitive to stimulus difficulty and resolving response conflict. In contrast, activation in the posterior left middle temporal gyrus and the left angular gyrus showed modulation of activation only to the “best fit” of the phonetic category, suggesting that these areas are involved in mapping sound structure to its phonetic representation. The superior temporal gyrus (STG) bilaterally showed weaker sensitivity to the differences in phonetic category structure, providing further evidence that the STG is involved in the early analysis of the sensory properties of speech.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2003) 15 (8): 1160–1175.
Published: 15 November 2003
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The neural basis underlying implicit semantic priming was investigated using event-related fMRI. Prime-target pairs were presented auditorily for lexical decision (LD) on the target stimulus, which was either semantically related or unrelated to the prime, or was a nonword. A tone task was also administered as a control. Behaviorally, all participants demonstrated semantic priming in the LD task. fMRI results showed that for all three conditions of the LD task, activation was seen in the superior temporal gyrus (STG), the middle temporal gyrus (MTG), and the inferior parietal lobe, with greater activation in the unrelated and nonword conditions than in the related condition. Direct comparisons of the related and unrelated conditions revealed foci in the left STG, left precentral gyrus, left and right MTGs, and right caudate, exhibiting significantly lower activation levels in the related condition. The reduced activity in the temporal lobe suggests that the perception of the prime word activates a lexical— semantic network that shares common elements with the target word, and, thus, the target can be recognized with enhanced neural efficiency. The frontal lobe reductions most likely reflect the increased efficiency in monitoring the activation of lexical representations in the temporal lobe, making a decision, and planning the appropriate motor response.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2001) 13 (2): 151–170.
Published: 15 February 2001
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The goal of this article is to illustrate the application of self-organizing dynamics in the design of a model of lexical access. We focus particularly on the mapping of sound structure on to the lexicon and the influence of that structure on lexical access. The approach is tested in a series of two sets of simulations that explicate how lexical access might occur in normal subjects and aphasic patients. Both sets of simulations address the behavioral effects of both phonological and phonetic variability of prime stimuli on the magnitude of semantic priming. Results show that the model can successfully account for the behavioral effects associated with several kinds of acoustic manipulation, competitor presence, and the unfolding of those effects over time—primarily because it balances three important control parameters: resting lexical activation, positive feedback, and negative feedback. These simulations are offered as support (in the form of an existence proof) that deficits in the degree of lexical activation can account for the lexical processing impairments shown by Broca's aphasics who have reduced lexical activation, and Wernicke's aphasics who have increased lexical activation. Overall, results suggest that the present approach promises to offer a coherent theoretical framework within which to link empirical evidence in language processing and cognitive neuroscience in terms of possible underlying mechanisms.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (4): 679–690.
Published: 01 July 2000
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Phonological processes map sound information onto higher levels of language processing and provide the mechanisms by which verbal information can be temporarily stored in working memory. Despite a strong convergence of data suggesting both left lateralization and distributed encoding in the anterior and posterior perisylvian language areas, the nature and brain encoding of phonological subprocesses remain ambiguous. The present study used functional magnetic resonance imaging (fMRT) to investigate the conditions under which anterior (lateral frontal) areas are activated during speech-discrimination tasks that differ in segmental processing demands. In two experiments, subjects performed “same/ different” judgments on the first sound of pairs of words. In the first experiment, the speech stimuli did not require overt segmentation of the initial consonant from the rest of the word, since the “different” pairs only varied in the phonetic voicing of the initial consonant (e.g., dip-tip ). In the second experiment, the speech stimuli required segmentation since “different” pairs both varied in initial consonant voicing and contained different vowels and final consonants (e.g., dip-ten). These speech conditions were compared to a tone-discrimination control condition. Behavioral data showed that subjects were highly accurate in both experiments, but revealed different patterns of reaction-time latencies between the two experiments. The imaging data indicated that whereas both speech conditions showed superior temporal activation when compared to tone discrimination, only the second experiment showed consistent evidence of frontal activity. Taken together, the results of Experiments 1 and 2 suggest that phonological processing per se does not necessarily recruit frontal areas. We postulate that frontal activation is a product of segmentation processes in speech perception, or alternatively, working memory demands required for such processing.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1995) 7 (1): 33–50.
Published: 01 January 1995
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Two auditory lexical decision semantic priming experiments were conducted to examine the extent to which the automaticcontrolled processing dichotomy can characterize lexical access deficits in Broca's and Wernicke's aphasics. In Experiment 1, prime-target predictability was varied while the interval between prime and target (ISI) was held constant. In Experiment 2, ISI was varied while prime-target predictability was held constant. The pattern of semantic facilitation and inhibition results for Experiment 1 showed that Broca's aphasics were influenced by prime-target predictability, whereas Wernicke's aphasics were not. In contrast in hperiment 2, manipulations of ISI at 150 and 2000 msec did not affect patterns of semantic facilitation for either Broca's or Wernicke's aphasics. Taken together, the results of these two experiments suggest that Broca's aphasics use heuristic strategies more so than old and young normal subjects. In addition, they seem to have an automatic processing deficit affecting the level of activation of lexical entries, with a spared time course of activation. Wernicke's aphasics show a pattern of results consistent with the view that automatic processing is unimpaired in these patients, while they fail to use heuristic strategies in these tasks.