Publications

Abstract

Spoken language is one of the most compact and structured ways to convey information. The linguistic ability to structure individual words into larger sentence units permits speakers to express a nearly unlimited range of meanings. This ability is rooted in speakers’ knowledge of syntax and in the corresponding process of syntactic encoding. Syntactic encoding is highly automatized, operates largely outside of conscious awareness, and overlaps closely in time with several other processes of language production. With the use of positron emission tomography we investigated the cortical activations during spoken language production that are related to the syntactic encoding process. In the paradigm of restrictive scene description, utterances varying in complexity of syntactic encoding were elicited. Results provided evidence that the left Rolandic operculum, caudally adjacent to Broca’s area, is involved in both sentence-level and local (phrase-level) syntactic encoding during speaking.

Abstract

In language comprehension a syntactic representation is built up even when the input is semantically uninterpretable. We report data on brain activation during syntactic processing, from an experiment on the detection of grammatical errors in meaningless sentences. The experimental paradigm was such that the syntactic processing was distinguished from other cognitive and linguistic functions. The data reveal that in syntactic error detection an area of the left dorsolateral prefrontal cortex, adjacent to Broca’s area, is specifically involved in the syntactic processing aspects, whereas other prefrontal areas subserve general error detection processes.

Abstract

An event-related brain potential experiment was carried out to investigate the time course of contextual influences on spoken-word recognition. Subjects were presented with spoken sentences that ended with a word that was either (a) congruent, (b) semantically anomalous, but beginning with the same initial phonemes as the congruent completion, or (c) semantically anomalous beginning with phonemes that differed from the congruent completion. In addition to finding an N400 effect in the two semantically anomalous conditions, we obtained an early negative effect in the semantically anomalous condition where word onset differed from that of the congruent completions. It was concluded that the N200 effect is related to the lexical selection process, where word-form information resulting from an initial phonological analysis and content information derived from the context interact.

Abstract

Lexical-semantic processing impairments in aphasic patients with left hemisphere lesions and non-aphasic patients with right hemisphere lesions were investigated by recording event-related brain potentials (ERPs) while subjects listened to auditorily presented word pairs. The word pairs consisted of unrelated words, or words that were related in meaning. The related words were either associatively related, e.g. 'bread-butter', or were members of the same semantic category without being associatively related, e.g. 'churchvilla '. The latter relationships are assumed to be more distant than the former ones. The most relevant ERP component in this study is the N400. In elderly control subjects, the N400 amplitude to associatively and semantically related word targets is reduced relative to the N400 elicited by unrelated targets. Compared with this normal N400 effect, the different patient groups showed the following pattern of results: aphasic patients with only minor comprehension deficits (high comprehenders) showed N400 effects of a similar size as the control subjects. In aphasic patients with more severe comprehension deficits (low comprehenders) a clear reduction in the N400 effects was obtained, both for the associative and the semantic word pairs. The patients with right hemisphere lesions showed a normal N400 effect for the associatively related targets, but a trend towards a reduced N400 effect for the semantically related word pairs. A dissociation between the N400 results in the word pair paradigm and P300 results in a classical tone oddball task indicated that the N400 effects were not an aspecific consequence of brain lesion, but were related to the nature of the language comprehension impairment. The conclusions drawn from the ERP results are that comprehension deficits in the aphasic patients are due to an impairment in integrating individual word meanings into an overall meaning representation. Right hemisphere patients are more specifically impaired in the processing of semantically more distant relationships, suggesting the involvement of the right hemisphere in semantically coarse coding.