Spoken word recognition : a combined computational and experimental approach.
The research reported in this thesis examines issues of word recognition in human
speech perception. The main aim of the research is to assess the effect of regular
variation in speech on lexical access. In particular, the effect of a type of neutralising
phonological variation, assimilation of place of articulation, is examined. This
variation occurs regressively across word boundaries in connected speech, altering the
sUlface phonetic form of the underlying words. Two methods of investigation are used
to explore this issue. Firstly, experiments using cross-modal priming and phoneme
monitOling techniques are used to examine the effect of variation on the matching
process between speech input and lexical form. Secondly, simulated experiments are
performed using two computational models of speech recognition: TRACE
(McClelland & Elman, 1986) and a simple recun-ent network.
The priming experiments show that the mismatching effects of a phonological change
on the word-recognition process depend on their viability, as defmed by phonological
constraints. This implies that speech perception involves a process of contextdependent
inference, that recovers the abstract underlying representation of speech.
Simulations of these and other experiments are then reported using a simple recurrent
network model of speech perception. The model accommodates the results of the
priming studies and predicts that similar phonological context effects will occur in nonwords.
Two phoneme monitOling studies support this prediction, but also show
interaction between lexical status and viability, implying that phonological inference
relies on both lexical and phonological constraints. A revision of the network model is
proposed which leams the mapping from the surface form of speech to semantic and