ISCA Workshop on Plasticity in Speech Perception (PSP2005)
Senate House, London, UK
Learning a new word involves the acquisition of form and meaning, and at some point the integration of this information with existing knowledge in the learner's mental lexicon. In human speech perception, the latter "lexicalisation" stage is characterized by the engagement of the novel word in a competition process, in which it is able to inhibit identification of existing words (Gaskell & Dumay, 2003). Here we show that although the simple acquisition of a spoken form is swift, the impact of the novel item on lexical competition is more delayed and associated with sleep.
Two participant groups were familiarised with a set of nonwords either in the morning or the evening. The effects of familiarisation were then tested immediately afterwards, and retested 12 and 24 hours later in order to examine the effects of delays with and without sleep. Our tests were designed to assess knowledge of the form of the novel items (2AFC judgements and free recall measures), and also the engagement of the items in lexical competition (a pause detection task, in which delayed responses indicate increased lexical competition; Mattys & Clark, 2002; Gaskell & Dumay, 2003).
Tests of direct recognition immediately after exposure showed that both groups had learnt the novel items well, with further sleep-related improvements in recall at later time points. However, for the lexical competition test, there were strong delayed effects, correlated with the presence of sleep. Words learnt in the evening did not induce inhibitory effects in pause detection immediately after exposure, but did so after a 12-hour interval including a night's sleep, and this effect remained after 24 hours. Conversely, words learnt in the morning did not show such effects immediately or after 12 hours of wakefulness, but these effects emerged after 24 hours, following a night's sleep. We interpret these results in terms of the differing plasticity of two types of storage for novel items: a highly flexible episodic representation, and a more stable representation in which lexical competition occurs. This dissociation fits well with neural and connectionist models of learning in which sleep provides an opportunity for hippocampal information to be fed into the long-term neocortical store.
Gaskell, M. G., & Dumay, N. (2003). Lexical competition and the acquisition of novel words. Cognition, 89, 105-132.
Mattys, S. L., & Clark, J. H. (2002). Lexical activity in speech processing: evidence from pause detection. Journal of Memory and Language, 47, 343-359.
Bibliographic reference. Gaskell, Gareth / Dumay, Nicolas (2005): "Plasticity in lexical competition: the impact of vocabulary acquisition", In PSP2005, 108.