Monthly Archives: September 2007

Temporal Dynamics of Adaptation to Natural Sounds in the Human Auditory Cortex

from Cerebral Cortex

We aimed at testing the cortical representation of complex natural sounds within auditory cortex by conducting 2 human magnetoencephalography experiments. To this end, we employed an adaptation paradigm and presented subjects with pairs of complex stimuli, namely, animal vocalizations and spectrally matched noise. In Experiment 1, we presented stimulus pairs of same or different animal vocalizations and same or different noise. Our results suggest a 2-step process of adaptation effects: first, we observed a general item-unspecific reduction of the N1m peak amplitude at 100 ms, followed by an item-specific amplitude reduction of the P2m component at 200 ms after stimulus onset for both animal vocalizations and noise. Multiple dipole source modeling revealed the right lateral Heschl’s gyrus and the bilateral superior temporal gyrus as sites of adaptation. In Experiment 2, we tested for cross-adaptation between animal vocalizations and spectrally matched noise sounds, by presenting pairs of an animal vocalization and its corresponding or a different noise sound. We observed cross-adaptation effects for the P2m component within bilateral superior temporal gyrus. Thus, our results suggest selectivity of the evoked magnetic field at 200 ms after stimulus onset in nonprimary auditory cortex for the spectral fine structure of complex sounds rather than their temporal dynamics. 

What constrains sentence production in agrammatism?

from Brain and Language

No abstract available.

When the grammatical principle of agreement is itself restricted in agrammatism

from Brain and Language

No abstract available.

Who needs Broca’s area? Comparisons from lesion and fMRI methods

from Brain and Language

No abstract available.

Why RHD individuals have more difficulties with direct requests than indirect requests? A theory of mind hypothesis

from Brain and Language

No abstract available.

Verb production in sentences by patients with nonfluent progressive aphasia

from Brain and Language

No abstract available.

Verb argument structure encoding during sentence production in agrammatic aphasic speakers: An eye-tracking study

from Brain and Language

No abstract available.

The temporal analysis of semantic perseverations in blocked-cyclic naming

from Brain and Language

No abstract available.

The role of argument structure in the processing of nouns and verbs: An f-MRI study

from Brain and Language

No abstract available.

The representation of letter position: Evidence from dysgraphia

from Brain and Language

No abstract available.

The processing of compounds in bilingual aphasia

from Brain and Language

Discussion

Our main objective was to investigate whether the individual constituents of a compound are processed differentially across the two languages of bilingual aphasic patients. Both patients tested showed a similar behavioural pattern: a significantly reduced number of errors for the head (the first constituent) as compared to the second constituent in French and an equivalent number of errors for both constituents in English, pointing to the cumulative effects of headedness and first-position-in-the-string in French, and to the mutual cancelling out of these effects in English. In conclusion, our results from the performances of two bilingual aphasic participants, together with those of Jarema et al. (1999) on unimpaired individuals, reveal that headedness and position interact in the processing of compounds and that aphasic patients are sensitive to compound-internal structure. Furthermore, these findings underscore the importance of taking into account cross-linguistic variation in our understanding of the manner in which compound words are processed in both normal and pathological populations.

The neural systems underlying lexical competition in speech production: Evidence from Aphasia

from Brain and Language

Conclusion

The findings of this study address several issues relating to the functional architecture of the language system and the neural systems underlying this architecture. With respect to the functional architecture of the language system, they indicate that the statistical properties of words, as measured by lexical density, have consequences for speech production as well as word recognition and suggest that a common lexical system drives both production and processing streams. The basis for the density effect in production is likely due to the increased activation required to access a word with many phonological competitors and the cascading effects of those processes on articulatory implementation. With respect to the neural systems underlying this architecture, they suggest that the SMG is involved in phonological processing (Paulesu, Frith, & Frackowiak, 1993) and that there are greater processing requirements for words from phonologically similar neighborhoods. Such a deficit provides a potential explanation for conduction aphasics’ production of phonemic paraphasias. Finally, the results suggest that although damage to the IFG results in speech output deficits, lexical access processes remain intact.

The neural correlates of abstract versus concrete words: Evidence from an rTMS study

from Brain and Language

This experiment suggests that right hemisphere structures located in the ITG are involved in processing abstract terms, but are not critical for the processing of concrete words. Further studies need to be performed in order (i) to assess the role of additional sites, such as the left superior and inferior frontal gyri, as suggested by the neuroimaging literature, and (ii) to confirm these preliminary results.

The nature of the processing distinction between regular and irregular verbs: Evidence from an English–German bilingual aphasic speaker

from Brain and Language

Discussion

The results in English and German showed an overall similar pattern: responses were less accurate for those verbs that required memory-based, retrieval processes. That is, performance was worse with irregular than for regular verbs. Furthermore, in German a striking difference was observed between stem-change and no-stem-change irregulars. This difference can be understood if we assume that irregulars differ in the extent to which they require memory-based, retrieval steps for their accurate production. These results support a distinction between memory-based, retrieval and rule-based, assembly processes that will yield different patterns of performance on regulars and irregular verbs within and across languages depending on the degree to which the verbs depend on these two process types.

The manifestation of agrammatic comprehension in a case of crossed aphasia

from Brain and Language

Like comprehension of declarative sentences, comprehension of wh-questions in agrammatism reveals aspects of linguistic architecture. We present an agrammatic speaker with crossed aphasia (CA). In CA the lesion is located in the right hemisphere in a right-handed individual. Unlike the classical and typical syndromes CA is a rare and controversial syndrome and theoretically interesting. Studies of CA have shown diverse and, in some cases, unusual neurobehavioral symptoms. It has been suggested that CA can be a mirror image of classical syndromes or anomalous (Alexander, Fischette, & Fischer, 1989). Our speaker exhibits a classic pattern between canonical (agent-patient) and non-canonical (patient-agent) declarative sentences and, contrary to other reported cases, the same pattern between canonical and non-canonical wh-questions.