Electrophysiological studies of formal, derivational and repetition priming
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ERPs have been found to be sensitive to formal (i.e. orthographic and phonological) and semantic relationships between words, as well as to word repetition. Such effects have been used to argue that the N400 component of the ERP may reflect processing of the representations of words, i.e. 'lexical processing'. If ERPs do reflect lexical processes then they may also be sensitive to morphological relationships between words which are thought to be lexically represented. The first three experiments investigated the sensitivity of ERPs to morphological relationships between words. Modulations of the ERP resulting from derivational, formal and repetition priming were compared. In each case, there was a positive-going shift in the ERP compared to the ERP elicited by unprimed words. However there was little evidence to suggest that the effects found in the derivational priming condition differed from those found when words were formally but not morphologically similar. A subsequent three experiments focused on these ERP formal priming effects. Formal priming effects were found when the proportion of related items was relatively low, with non-words and with words which were only orthographically similar and with words which were both orthographically and phonologically similar. In each case formal and repetition priming were initially of similar magnitude, with the repetition effect subsequently becoming greater in amplitude than the formal effect. Whilst the distribution of the repetition effect for non-words and the formal priming effects for words and non-words tended to be greatest over the right hemisphere, the word repetition effect was largest over the midline. It is concluded that the N400 does not reflect lexical processing, nor is it specific to semantic processing. Instead the N400 may reflect the operation of a similarity-sensitive mechanism which is sensitive to orthographic, phonological and/or semantic similarity and which may operate in an all-or-none fashion.
Thesis, PhD Doctor of Philosophy
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