Semantic Priming In Schizophrenia - The N400 In A Picture Verification Task

• Semantic memory access has been characterized as abnormal in schizophrenia, but findings concerning automatic spreading activation at short stimulus onset asynchronies (SOA) have been inconsistent. Using the N400 as an indicator of semantic priming, a recent study (Mathalon, Faustman, & Ford, 2002) found evidence of hyperpriming in schizophrenic patients in a picture verification task. The present study replicates the Mathalon et al. study and extends the paradigm to a third stimulus condition. Pictures of common objects were shown, followed at short SOAs by words with three types of semantic relation to the picture: (a) matching, e.g. dog-dog, (b) related, e.g. dog-cat, or (c) unrelated, e.g. dog-bicycle. We expected patients to show a smaller N400 than controls in the related condition, indicating hyperpriming of semantic relations. Eighteen medicated patients and twenty-four controls participated. Behavioral results revealed slowed reaction times in patients, but no interaction with stimulus condition. The P300 in the matching condition was normal. The N400 in the related condition was, as predicted, reduced in patients. Unexpectedly, the unrelated condition showed the same difference between patients and controls, suggesting that reduced N400 was not caused by activation spreading along normal pathways. Subtraction waveforms (related - unrelated) were equivalent in amplitude between groups, but peak latency was longer in patients. The results indicate slowed processing, and an atypical pattern of semantic activation in schizophrenia.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Neurologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Neurology (hsv//eng)

Publikations- och innehållstyp

kon (ämneskategori)

vet (ämneskategori)