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At least 19 recordsLinked to original sources
PubMed2006

Dissociable effects of phonetic competition and category typicality in a phonetic categorization task: an fMRI investigation.

The current study used fMRI to explore the extent to which neural activation patterns in the processing of speech are driven by the quality of a speech sound as a member of its phonetic category, that is, its category typicality, or by the competition inherent in resolving the category membership of stimuli which are similar to other possible speech sounds. Subjects performed a phonetic categorization task on synthetic stimuli ranging along a voice-onset time continuum from [da] to [ta]. The stimulus set included sounds at the extreme ends of the voicing continuum which were poor phonetic category exemplars, but which were minimally competitive, stimuli near the phonetic category boundary, which were both poor exemplars of their phonetic category and maximally competitive, and stimuli in the middle of the range which were good exemplars of their phonetic category. Results revealed greater activation in bilateral inferior frontal areas for stimuli with the greatest degree of competition, consistent with the view that these areas are involved in selection between competing alternatives. In contrast, greater activation was observed in bilateral superior temporal gyri for the least prototypical phonetic category exemplars, irrespective of competition, consistent with the view that these areas process the acoustic-phonetic details of speech to resolve a token's category membership. Taken together, these results implicate separable neural regions in two different aspects of phonetic categorization.

Acoustic Stimulation↗
PubMed2003

Electrophysiological indicators of phonetic and non-phonetic multisensory interactions during audiovisual speech perception.

We studied the interactions in neural processing of auditory and visual speech by recording event-related brain potentials (ERPs). Unisensory (auditory - A and visual - V) and audiovisual (AV) vowels were presented to 11 subjects. AV vowels were phonetically either congruent (e.g., acoustic /a/ and visual /a/) or incongruent (e.g., acoustic /a/ and visual /y/). ERPs to AV stimuli and the sum of the ERPs to A and V stimuli (A+V) were compared. Similar ERPs to AV and A+V were hypothesized to indicate independent processing of A and V stimuli. Differences on the other hand would suggest AV interactions. Three deflections, the first peaking at about 85 ms after the A stimulus onset, were significantly larger in the ERPs to A+V than in the ERPs to both congruent and incongruent AV stimuli. We suggest that these differences reflect AV interactions in the processing of general, non-phonetic, features shared by the acoustic and visual stimulus (spatial location, coincidence in time). The first difference in the ERPs to incongruent and congruent AV vowels peaked at 155 ms from the A stimuli onset. This and two later differences are suggested to reflect interactions at phonetic level. The early general AV interactions probably reflect modified activity in the sensory-specific cortices, whereas the later phonetic AV interactions are likely generated in the heteromodal cortices. Thus, our results suggest that sensory-specific and heteromodal brain regions participate in AV speech integration at separate latencies and are sensitive to different features of A and V speech stimuli.

Acoustic Stimulation↗
PubMed2004

Phonetic perceptual identification by native- and second-language speakers differentially activates brain regions involved with acoustic phonetic processing and those involved with articulatory-auditory/orosensory internal models.

This experiment investigates neural processes underlying perceptual identification of the same phonemes for native- and second-language speakers. A model is proposed implicating the use of articulatory-auditory and articulatory-orosensory mappings to facilitate perceptual identification under conditions in which the phonetic contrast is ambiguous, as in the case of second-language speakers. In contrast, native-language speakers are predicted to use auditory-based phonetic representations to a greater extent for perceptual identification than second-language speakers. The English /r-l/ phonetic contrast, although easy for native English speakers, is extremely difficult for native Japanese speakers who learned English as a second language after childhood. Twenty-two native English and twenty-two native Japanese speakers participated in this study. While undergoing event-related fMRI, subjects were aurally presented with syllables starting with a /r/, /l/, or a vowel and were required to rapidly identify the phoneme perceived by pushing one of three buttons with the left thumb. Consistent with the proposed model, the results show greater activity for second- over native-language speakers during perceptual identification of /r/ and /l/ relative to vowels in brain regions implicated with instantiating forward and inverse articulatory-auditory articulatory-orosensory models [Broca's area, anterior insula, anterior superior temporal sulcus/gyrus (STS/G), planum temporale (PT), superior temporal parietal area (Stp), SMG, and cerebellum]. The results further show that activity in brain regions implicated with instantiating these internal models is correlated with better /r/ and /l/ identification performance for second-language speakers. Greater activity found for native-language speakers especially in the anterior STG/S for /r/ and /l/ perceptual identification is consistent with the hypothesis that native-language speakers use auditory phonetic representations more extensively than second-language speakers.

Adult↗
PubMed1979

Phonetically mediated recall in the phonetically disordered child.

Children with phonology disorders frequently show reduced performance in short-term recall, inviting the assumption that impairment of memory may cause or help to cause the speech disorder. Ten children with marked phonology disorders were compared to 10 correctly speaking children on a test of short-term memory for sets of pictures whose names rhymed or did not rhyme. The phonologically disordered children performed significantly worse than those with correct speech and provided less evidence of phonetic mediation, a process commonly associated with enhanced levels of recall. Attention is drawn to the possibility that the disorder of phonology operated indirectly to reduce the efficiency of memory, though the question is complicated.

Age Factors↗
PubMed2005

The perception of voice onset time: an fMRI investigation of phonetic category structure.

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.

Acoustic Stimulation↗
PubMed2005

Effects and modeling of phonetic and acoustic confusions in accented speech.

Accented speech recognition is more challenging than standard speech recognition due to the effects of phonetic and acoustic confusions. Phonetic confusion in accented speech occurs when an expected phone is pronounced as a different one, which leads to erroneous recognition. Acoustic confusion occurs when the pronounced phone is found to lie acoustically between two baseform models and can be equally recognized as either one. We propose that it is necessary to analyze and model these confusions separately in order to improve accented speech recognition without degrading standard speech recognition. Since low phonetic confusion units in accented speech do not give rise to automatic speech recognition errors, we focus on analyzing and reducing phonetic and acoustic confusability under high phonetic confusion conditions. We propose using likelihood ratio test to measure phonetic confusion, and asymmetric acoustic distance to measure acoustic confusion. Only accent-specific phonetic units with low acoustic confusion are used in an augmented pronunciation dictionary, while phonetic units with high acoustic confusion are reconstructed using decision tree merging. Experimental results show that our approach is effective and superior to methods modeling phonetic confusion or acoustic confusion alone in accented speech, with a significant 5.7% absolute WER reduction, without degrading standard speech recognition.

Decision Trees↗
PubMed1991

The relation between phonetics and phonology.

It is the goal of this paper to consider how phonetics may interface with phonology. The role phonetics plays in phonological analysis is considered with respect to features, segments, phonological processes, and the abstractness of phonological solutions. Phonetic evidence is reviewed concerning the feature [strident] that questions the defining properties of this feature, its place in the distinctive feature framework, and its role in the analysis of natural classes for fricatives. The extent to which a sound segment is analyzed as a single unit or a cluster is considered with reference to prenasalized stops in Moru. The phonetic data are neutral with respect to the unitary or complex status of such segments, suggesting that the decision is more properly a phonological one. Phonetic evidence for the phonological process of neutralization is reviewed. Acoustic analysis of word-final devoicing in German, Polish and Catalan provides support for the reality of the process of neutralization in phonological solutions. Finally, phonetics helps provide a set of constraints or limiting conditions on the abstractness of phonological solutions. While phonetics cannot inform phonology about the appropriateness of a particular underlying form, there should be some phonetic transparency between the underlying form and its ultimate phonetic instantiation.

Attention↗
PubMed1983

Comparison of alphabetic and phonetic retrieval of online drug information.

Alphabetic, phonetic, and combined alphabetic and phonetic methods of retrieving online drug information were compared. Twenty-four volunteers participated in the study representing four user groups: physicians, nurses, pharmacists, and nonhealth-care hospital staff. Each subject performed 150 searches, 50 by each retrieval method. Using the alphabetic method, drug information was retrievable only if the drug name was spelled correctly. Using the phonetic method, searches were conducted based on the phonetic spelling of requests (e.g., "symetadine" for cimetidine). The combined method used a phonetic search only after an initial alphabetic search was unsuccessful. The elapsed time between the first entry and an indication that the information had been found or could not be found was determined, and the number of drug names not found and the number of excess tries were counted. There were no significant differences in elapsed time among the three methods. Pharmacists had the shortest mean elapsed time and physicians the longest. The average number of excess tries using the phonetic system was a third of the number required using the alphabetic method. The number of drugs not found showed only slight differences among the three methods. The subjects found the desired information on the first try 67% of the time with the alphabetic method, 66% with the combined method, and 90% with the phonetic method. The phonetic method had an average of 75 matches versus 20 for the alphabetic and combined methods. These results support use of a combined alphabetic and phonetic system for retrieving drug information.

Drug Information Services↗
PubMed1993

Attentional modulation of the phonetic significance of acoustic cues.

Four experiments addressing the role of attention in phonetic perception are reported. The first experiment shows that the relative importance of two cues to the voicing distinction changes when subjects must perform an arithmetic distractor task at the same time as identifying a speech stimulus. The contribution of voice onset time to phonetic labeling decreases when subjects are distracted, while that of FO onset frequency increases. The second experiment shows a similar pattern for two cues to the distinction between the vowels /i/ (as in "beat") and /I/ (as in "bit"). Under low attention conditions, formant pattern has a smaller effect on phonetic labeling while vowel duration has a larger effect. Together these experiments indicate that careful attention to speech perception is necessary for strong acoustic cues (voice-onset time and formant patterns) to achieve their full impact on phonetic labeling, while weaker acoustic cues (FO onset frequency and vowel duration) achieve their full impact on phonetic labeling without close attention. Experiment 3 shows that this pattern is obtained when the distractor task places little demand on verbal short-term memory. Experiment 4 provides a data set for testing formal models of the role of attention in speech perception. Attention is shown to influence the signal-to-noise ratio in the phonetic encoding of acoustic cues; the sustained phonetic contribution of weak cues without close attention stems from reduced competition from strong cues. This principle is instantiated in a network model in which the role of attention is to reduce noise in the phonetic encoding of acoustic cues. Implications of this work for understanding speech perception and general theories of the role of attention in perception are discussed.

Acoustic Stimulation↗
PubMed1991

Speech and language production at age 2: evidence for tradeoffs between linguistic and phonetic processing.

The purpose of this study was to explore how 2-year-old children manage the relationship between phonetic production and production of word combinations in their spontaneous speech. The subjects were 5 normally developing 2-year-olds who were participants in an ongoing longitudinal study of speech and language acquisition. Three measures were used to estimate phonetic production skills in the children's spontaneous speech samples. These included a measure of the accuracy of consonant production (Percentage of Consonants Correct), and two estimators of phonetic complexity (phonetic products for utterance and word length units). Regression analyses were used to determine the relationship between complexity of word combinations, as measured by length of utterance in morphemes and a propositional complexity analysis, and utilization of phonetic production skills. The results revealed modest tradeoffs between complexity of word combinations and accuracy of consonant production for 2 of the 5 children. The results also showed tradeoffs between complexity of word combinations and phonetic complexity of individual lexical items (phonetic product for words) for 4 of the 5 children. As the complexity of these 4 children's multiword combinations increased, the phonetic complexity of individual lexical items decreased. These results are consistent with synergistic theories of language acquisition and language processing that emphasize dynamic tradeoffs in interactions among language processing levels in a limited capacity production system.

Child Language↗