Signal-driven computations in speech processing.
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Learning a language requires both statistical computations to identify words in speech and algebraic-like computations to discover higher level (grammatical) structure. Here we show that these computations can be influenced by subtle cues in the speech signal. After a short familiarization to a continuous speech stream, adult listeners are able to segment it using powerful statistics, but they fail to extract the structural regularities included in the stream even when the familiarization is greatly extended. With the introduction of subliminal segmentation cues, however, these regularities can be rapidly captured. (+info)
Anatomical correlates of learning novel speech sounds.
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We examined the relationship between brain anatomy and the ability to learn nonnative speech sounds, as well as rapidly changing and steady-state nonlinguistic sounds, using voxel-based morphometry in 59 healthy adults. Faster phonetic learners appeared to have more white matter in parietal regions, especially in the left hemisphere. The pattern of results was similar for the rapidly changing but not for the steady-state nonlinguistic stimuli, suggesting that morphological correlates of phonetic learning are related to the ability to process rapid temporal variation. Greater asymmetry in the amount of white matter in faster learners may be related to greater myelination allowing more efficient neural processing, which is critical for the ability to process certain speech sounds. (+info)
Central bottleneck influences on the processing stages of word production.
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Does producing a word slow performance of a concurrent, unrelated task? In 2 experiments, 108 participants named pictures and discriminated tones. In Experiment 1, pictures were named after cloze sentences; the durations of the word-production stages of lemma and phonological word-form selection were manipulated with high- and low-constraint cloze sentences and high- and low-frequency-name pictures, respectively. In Experiment 2, pictures were presented with simultaneous distractor words; the durations of lemma and phoneme selection were manipulated with conceptually and phonologically related distractors. All manipulations, except the phoneme-selection manipulation, delayed tone-discrimination responses as much as picture-naming responses. These results suggest that early word-production stages--lemma and phonological word-form selection--are subject to a central processing bottleneck, whereas the later stage--phoneme selection--is not. (+info)
Visual detection is gated by attending for action: evidence from hemispatial neglect.
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We report observations in patients with visual extinction demonstrating that detection of visual events is gated by attention at the level of processing at which a stimulus is selected for action. In one experiment, three patients reported the identity of numerical words and digits presented either in the ipsilesional field, the contralesional field, or both fields. On the critical bilateral trials, extinction was greater when the competing items shared the same meaning and response, regardless of whether the items were visually different (e.g., ONE + 1), or identical (e.g., 1 + 1). A fourth patient was tested in a second experiment in which the competing items on bilateral trials were either different (e.g., ONE + TWO), identical (e.g., ONE + ONE) or homophones that were visually and semantically different but shared the same response (e.g., ONE + WON). Homophones and identical items caused similar extinction with less extinction occurring on different item trials. (+info)
Naming and categorization in young children: vocal tact training.
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In three experiments, 2- to 4-year-old children, following pretraining with everyday objects, were presented with arbitrary stimuli of differing shapes. In Experiment 1A, 9 subjects were trained one common tact response, "zag," to three of these and a second tact, "vek," to another three. In category match-to-sample Test 1, 4 subjects sorted accurately when required only to look at the sample before selecting from five comparisons. The remaining 5 subjects succeeded in Test 2, in which they were required to tact the sample before selecting comparisons. Experiment 1B showed, for 2 of these subjects, that tact training with 12 arbitrary stimuli established two six-member classes that were still intact 6 weeks later. In Experiment 2, 3 new subjects participated in a common tact training procedure that ensured that none of the exemplars from the same class were presented together prior to the test for three-member classes. Two subjects passed category Test 1 and the third passed Test 2. Tests showed subjects' listener behavior in response to hearing /zog/ and /vek/ to be in place. These experiments indicate that common naming is effective in establishing arbitrary stimulus classes and that category match-to-sample testing provides a robust measure of categorization. (+info)
The effects of familiarization on intelligibility and lexical segmentation in hypokinetic and ataxic dysarthria.
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This study is the third in a series that has explored the source of intelligibility decrement in dysarthria by jointly considering signal characteristics and the cognitive-perceptual processes employed by listeners. A paradigm of lexical boundary error analysis was used to examine this interface by manipulating listener constraints with a brief familiarization procedure. If familiarization allows listeners to extract relevant segmental and suprasegmental information from dysarthric speech, they should obtain higher intelligibility scores than nonfamiliarized listeners, and their lexical boundary error patterns should approximate those obtained in misperceptions of normal speech. Listeners transcribed phrases produced by speakers with either hypokinetic or ataxic dysarthria after being familiarized with other phrases produced by these speakers. Data were compared to those of nonfamiliarized listeners [Liss et al., J. Acoust. Soc. Am. 107, 3415-3424 (2000)]. The familiarized groups obtained higher intelligibility scores than nonfamiliarized groups, and the effects were greater when the dysarthria type of the familiarization procedure matched the dysarthria type of the transcription task. Remarkably, no differences in lexical boundary error patterns were discovered between the familiarized and nonfamiliarized groups. Transcribers of the ataxic speech appeared to have difficulty distinguishing strong and weak syllables in spite of the familiarization. Results suggest that intelligibility decrements arise from the perceptual challenges posed by the degraded segmental and suprasegmental aspects of the signal, but that this type of familiarization process may differentially facilitate mapping segmental information onto existing phonological categories. (+info)
Lip kinematics for /p/ and /b/ production during whispered and voiced speech.
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In the absence of voicing, the discrimination of "voiced" and "voiceless" stop consonants in whispered speech relies on such acoustic cues as burst duration and amplitude, and formant transition characteristics. The articulatory processes that generate these features of whispered speech remain speculative. This preliminary investigation examines the articulatory kinematics differences between whispered /p/ and /b/, which may underlie the acoustic differences previously reported for these sounds. Computerized video-tracking methods were used to evaluate kinematic differences between voiced and voiceless stops. Seven subjects produced the target utterances "my papa puppy" and "my baba puppy" in voiced and whispered speech modes. The results revealed that mean peak opening and closing velocities for /b/ were significantly greater than those for /p/ during whispered speech. No differences in peak velocity for either oral closing or opening were observed during voiced speech. The maximum distance between the lips for oral opening for /b/ was significantly greater than for /p/ during whisper, whereas no difference was observed during voiced speech. These data supported the suggestion that whispered speech and voiced speech rely on distinct motor control processes. (+info)
Imitation of nonwords by hearing impaired children with cochlear implants: suprasegmental analyses.
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In this study, we examined two prosodic characteristics of speech production in 8-10-year-old experienced cochlear implant (CI) users who completed a nonword repetition task. We looked at how often they correctly reproduced syllable number and primary stress location in their responses. Although only 5% of all nonword imitations were produced correctly without errors, 64% of the imitations contained the correct syllable number and 61% had the correct placement of primary stress. Moreover, these target prosodic properties were correctly preserved significantly more often for targets with fewer syllables and targets with primary stress on the initial syllable. Syllable and stress scores were significantly correlated with measures of speech perception, intelligibility, perceived accuracy, and working memory. These findings suggest that paediatric CI users encode the overall prosodic envelope of nonword patterns, despite the loss of more detailed segmental properties. This phonological knowledge is also reflected in other language and memory skills. (+info)