Doctor of Philosophy
Department of Psychology
Lethbridge, Alistair, Semantic priming: an event-related potential investigation using pseudohomophone primes, Doctor of Philosophy thesis, Department of Psychology, University of Wollongong, 2001. http://ro.uow.edu.au/theses/1678
The N400 component of the ERP has proven highly sensitive to lexical manipulations involving semantic congruity. This sensitivity is typically manifest as a comparative reduction in N400 amplitude when 'target' items are preceded by semantically related, as opposed to unrelated, 'primes'. The nature of the N400 has been extensively studied, with one of the more dominant theories regarding its functional significance suggesting that the underlying processes reflect mechanisms associated with lexical integration. Models of the visual word-recognition system typically delineate lexical information in terms of orthography, phonology and semantics. In some models, the representation of linguistic information is considered to occur at the sublexical level, in which case, the information utilised in the integration process would also be sub-lexical. Pseudohomophone stimuli are orthographically dissimilar from, but phonologically identical to, legal words and offer a means of examining the roles of phonological and orthographic information in visual word recognition and the integration process. To this end, the effects of semantically related pseudohomophone primes on behavioural and electrophysiological responses to target words were examined across a number of tasks. It was found that the pseudohomophone-primed targets exhibited effects associated with prime-target relatedness similar to those of word-primed targets i.e., compared to targets following unrelated primes, those which were preceded by related pseudohomophones were responded to faster and more accurately, and mean amplitudes across the N400 latency range were less negative-going. These results were consistent with an integration account of the N400 but topographical differences in the relatedness effects in word- and pseudohomophone-primed conditions supported a multi-source account of this component. The observed results were also considered to be consistent not only with a sub-lexical account of the visual wordrecognition system, but also with proposals which ascribe a prominent role for phonological mediation within this system.