Using individual differences in morphological priming to distinguish between theories of morphological representation

Andrews, S. & Lo, S.

University of Sydney, Australia

We used the masked priming lexical decision task to address previous contradictory evidence about the relative strength of priming for (i) Transparent pairs (e.g., worker WORK) which are morphologically and semantically related; (ii) Opaque pairs (e.g., corner CORN) that have the same apparent morphological structure but are not semantically related; and (iii) Form pairs (e.g., turnip TURN) that are only orthographically related. The average data for 92 university students showed a graded effect of morphological structure with stronger priming effects for Transparent than Opaque or Form pairs, which gradually increased across the reaction time (RT) distribution. However, these average effects were significantly modulated by individual differences in independent measures of spelling and vocabulary. Individuals with higher spelling than vocabulary showed priming for Transparent pairs across the entire RT distribution but virtually no priming for Opaque or Form pairs. In complete contrast, those with higher spelling than vocabulary showed priming for Opaque pairs across the entire distribution while priming for Transparent pairs gradually developed for slow responses.
This evidence of systematic individual differences amongst skilled readers has important implications for models of morphological priming. ‘Morphographic’ models, (Rastle & Davis, 2008) cannot explain the very early semantic influence shown by individuals with relatively higher vocabulary than spelling ability. Emergentist models provide a principled account of how differences in the ‘morphological richness’ of languages modulate the ‘division of labour’ between different network components. This approach can be extended to individual differences in morphological priming by assuming that individuals who are relatively better at orthographic processing than semantic processing are less sensitive to morphological structure than those with the reverse pattern of strengths and weaknesses. However, this analogy predicts that higher spelling than vocabulary should be associated with reduced priming for opaque pairs - the opposite of the pattern of results we observed.