Language deficits, localization, and grammar: evidence for a distributive model of language breakdown in aphasic patients and neurologically intact individuals.

Selective deficits in aphasic patients' grammatical production and comprehension are often cited as evidence that syntactic processing is modular and localizable in discrete areas of the brain (e.g., Y. Grodzinsky, 2000). The authors review a large body of experimental evidence suggesting that morpho-syntactic deficits can be observed in a number of aphasic and neurologically intact populations. They present new data showing that receptive agrammatism is found not only over a range of aphasic groups, but is also observed in neurologically intact individuals processing under stressful conditions. The authors suggest that these data are most compatible with a domain-general account of language, one that emphasizes the interaction of linguistic distributions with the properties of an associative processor working under normal or suboptimal conditions.

Mapping from sound to meaning: reduced lexical activation in Broca's aphasics.

Recent studies of lexical access in Broca's aphasics suggest that lexical activation levels are reduced in these patients. The present study compared the performance of Broca's aphasics with that of normal subjects in an auditory semantic priming paradigm. Lexical decision times were measured in response to word targets preceded by an intact semantically related prime word ("cat"-"dog"), by a related prime in which one segment was acoustically altered to produce a poorer phonetic exemplar ("c*at"-"dog"), and by a semantically unrelated prime ("ring"-"dog"). The effects of the locus of the acoustic distortion within the prime word (initial or final position) and the presence of potential lexical competitors ("cat" --> /gaet/versus "coat" --> "goat") were examined. In normal subjects, the acoustic manipulations produce a small, short-lived reduction in semantic facilitation irrespective of the position of the distortion in the prime word or the presence of a voiced lexical competitor. In contrast, Broca's aphasics showed a large and lasting reduction in priming in response to word-initial acoustic distortions, but only a weak effect of word-final distortions on priming. In both phonetic positions, the effect of distortion was greater for prime words with a lexical competitor. These findings are compatible with the claim that Broca's aphasics have reduced lexical activation levels, which may result in a disruption of the bottom-up access of words on the basis of acoustic input as well as increased vulnerability to competition between acoustically similar lexical items.

Effects of subphonetic and syllable structure variation on word recognition.

This study explored whether natural acoustic variations as exemplified by either subphonetic changes or syllable structure changes affect word recognition processes. Subphonetic variations were realized by differences in the voice-onset time (VOT) value of initial voiceless stop consonants, and syllable structure variations were realized by vowel deletion in initial unstressed syllables in multisyllable words. An auditory identity priming paradigm was used to determine whether the amount of facilitation obtained to a target stimulus in a lexical decision task was affected by the presence of these acoustic variations in a prime stimulus. Results revealed different patterns for the two types of variability as a function of lexical status. In the case of subphonetic variations, shortening of VOT resulted in reduced facilitation for words but not for nonwords, whereas in the case of syllable structure variation, vowel deletion in an unstressed syllable resulted in reduced facilitation for nonwords and increased facilitation for words. These findings indicate that subphonetic variability interferes with word recognition, whereas syllable structure variability does not, and that this effect is independent of the magnitude of the acoustic difference between a citation form and its variant. Furthermore, the results suggest that the lexical status of the target item plays a crucial role in the processing of both types of variability. Results are considered in relation to current models of word recognition.

Effects of local speaking rate context on the perception of voice-onset time in initial stop consonants.

This study explored the prediction that local speaking rate context affects the perception of voice-onset time (VOT) in initial stop consonants not only for ambiguous stimuli at the category boundary, but also for good exemplars from the category center [Volaitis and Miller, J. Acoust, Soc. Am. 92, 723-735 (1992)]. Naturally produced exemplars of the voiceless phonetic category were presented in the context of syllables produced at fast or slow speaking rates in a series of perceptual tasks, including phonetic discrimination, identification, and goodness rating. The results from all three tasks revealed no effects of speaking rate context on the perception of VOT in initial stop consonants. Rather, it appears that listeners perceive longer VOTs as better exemplars of the voiceless phonetic category, irrespective of the rate context. Further, an additional condition, in which the instructions and familiarization tasks presented prior to the administration of the perceptual tests were similar to those used by Volaitis and Miller [J. Acoust. Soc. Am. 92, 723-735 (1992)], revealed that the previous results may have been influenced by the experimental design.

Selective acoustic phonetic impairment and lexical access in an aphasic patient.

The relationship between acoustic-phonetic disturbances and lexical access was explored in an aphasic patient. M.L. had a restricted disturbance of phonemic discrimination that affected the discrimination of voicing contrasts in nonword stimuli. Despite this impairment, her discrimination of voicing contrasts in words and her comprehension of auditorily presented words containing voiced segments was excellent. Performance on lexical decision was impaired: M.L.'s rejection of nonwords was poor and her reaction times and error rates for word stimuli showed a trend toward being influenced by the lexical status (word or nonword) of the item that would be formed by a change in voicing. The results are consistent with a role for a phonemic code in auditory word recognition, coupled with lexical-to-acoustic/phonetic feedback, but are also compatible with the view that other access codes for the Phonological Input Lexicon are also available.

The influence of language on the acoustic properties of phonetic features: a study of the feature [strident] in Ewe and English.

This study explored the extent to which the acoustic manifestation of a phonetic feature is influenced by the linguistic role that the feature plays in the sound inventory of the particular language. To this end, we investigated the acoustic property associated with the feature [strident] in the production of bilabial and labiodental fricatives in Ewe, and labiodental and alveolar fricatives in English, and explored whether the acoustic manifestation of the feature [strident] varied in the instantiation of [f] in Ewe and English. In Ewe, the feature [strident] plays a contrastive role distinguishing labiodental from bilabial fricatives, whereas in English the feature [strident] does not play a contrastive role. Results showed that a measure of turbulence noise was able to distinguish bilabial and labiodental fricatives in Ewe and labiodental and alveolar fricatives in English. Moreover, the range of values associated with defining the amplitude characteristics for [f] was similar in the two languages. Nevertheless, differences emerged in the acoustic fine structure of the noise amplitude for [f v] in the two languages, with the frequency distribution for the labiodental fricative in Ewe being skewed towards the high amplitude range relative to English. These results suggest that while the fundamental manifestation of the acoustic property is the same across languages, its instantiation may be influenced by the functional role that its associated feature plays in the language.