Phonological Mismatch Negativity Research Articles

Semantic processing of spoken words in Alzheimer's disease: an electrophysiological study.

Patients suffering from Alzheimer's disease (AD) have severe difficulties in tasks requiring the use of semantic knowledge. The semantic deficits associated with AD have been extensively studied by using behavioral methods. Many of these studies indicate that AD patients have a general deficit in voluntary access to semantic representations but that the structure of the representations themselves might be preserved. However, several studies also provide evidence that to some extent semantic representations in AD may in fact be degraded. Recently, a few studies have utilized event-related brain potentials (ERPs) that are sensitive to semantic factors in order to investigate the electrophysiological correlates of the semantic impairment in AD. Interest has focused on the N400 component, which is known to reflect the on-line semantic processing of linguistic and pictorial stimuli. The results from studies of N400 changes in AD remain somewhat controversial: Some studies report normal or enlarged N400 components in AD, whereas others report diminished ones. One issue not reported in previous studies is whether word-elicited ERPs other than N400 remain normal in AD. In the present study our aim was to find out whether the ERP waveforms N1, P2, N400, and Late Positive Component (LPC) to semantically congruous and incongruous spoken words are abnormal in AD and whether such abnormalities specifically reflect deficiencies in semantic activation in AD. Auditory ERPs from 20 scalp sites to semantically congruous and incongruous final words in spoken sentences were recorded from 17 healthy elderly adults and 9 AD patients. The early ERP waveforms N1 and P2 were relatively normal for the AD patients, but the N400 and LPC effects (amplitude difference between congruous and incongruous conditions) were significantly reduced. We interpret the present results as showing that semantic-conceptual activation and other high-level integration processes are defective in AD. However, a word congruity effect earlier than N400 (phonological mismatch negativity), reflecting lexical selection processes, is at least to some extent preserved in AD.

Event-Related Potential Components Reflect Phonological and Semantic Processing of the Terminal Word of Spoken Sentences

Abstract An event-related brain potential (ERP) reflecting the acoustic-phonetic process in the phonological stage of word processing was recorded to the terminal words of spoken sentences. The peak latency of this negative-going response occurred between 270 and 300 msec after the onset of the terminal word. The independence of this response (the phonological mismatch negativity, PMN) from the ERP component known to be sensitive to semantic violations (N400) was demonstrated by manipulating sentence endings so that phonemic and semantic violations occurred together or separately. Four conditions used sentences that ended with (1) the highest Cloze probability word (e.g., "The piano was out of tune."), (2) a word having the same initial phoneme of the highest Cloze probability word but that was, in fact, semantically anomalous (e.g., "The gambler had a streak of bad luggage."), (3) a word having an initial phoneme different from that of the highest Cloze probability word but that was, in fact, semantically appropriate (e.g., "Don caught the ball with his glove."), or (4) a word that was semantically anomalous and, therefore, had an initial phoneme that was totally unexpected given the sentence's context (e.g., "The dog chased our cat up the queen"). Neither the PMN nor the N400 was found in the first condition. Only an N400 was observed in the second condition while only a PMN was seen in the third. Both responses were elicited in the last condition. Finally, a delayed N400 occurred to semantic violations in the second condition where the initial phoneme was identical to that of the highest Cloze probability ending. Results are discussed with regard to the Cohort model of word recognition.