Pronunciation by Analogy in Normal and Impaired Readers

In: Proceedings of CoNLL-2000 and LLL-2000, pages 13-18, Lisbon, Portugal, 2000. Pronunciation by Analogy in Normal and Impaired Readers R.I. Damper Image, Speech and Intelligent Systems Research Group, Department of Electronics and Computer Science, University of Southampton, Southampton SO17 1B J, UK Y. Marchand Cognitive/Clinical Neuroscience Unit, Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1 Abstract The prevailing dual-route model of oral read- ing claims that a lexical route is used for the pronunciation of words and a non-lexical route processes nonwords. Neurological data from pa- tients with acquired dyslexias have been high- lighted to support this claim. Models using a lexicon alone are generally held to be incapable of explaining these data. However, by selec- tively impairing its component parts, it is easily possible to account for phonological and surface dyslexias using a single-route model based upon pronunciation by analogy. 1 Introduction We have previously developed pronunciation by analogy (PbA) as a model of reading aloud and as a method for automatic phonemisation in text-to-speech synthesis (Sullivan and Damper, 1993; Damper and Eastmond, 1997; Marchand and Damper, 2000). We have also demon- strated (Damper et al., 1999) that the perfor- mance of PbA in producing correct pronunci- ations is vastly superior to manually-written rules and significantly better than the competi- tor data-driven techniques of back-propagation (Sejnowski and Rosenberg, 1987; McCulloch et al., 1987) and the IBloIG method based on information gain weighting (Daelemans et al., 1997). Although we cannot claim that PbA is absolutely the best method for pronunciation generation, it must be taken seriously. This view is clearly shared by other workers who are actively developing analogical methods for natural language processing tasks (Pirrelli and Federici, 1995; Jones, 1996; Yvon, 1996; 1997; Bagshaw, 1998; Pirrelli and Yvon, 1999). Explicit analogy (e.g., Dedina and Nusbaum, 1991; Damper and Eastmond, 1997) retains the lexicon in its entirety, typically as a list of words and their spellings. PbA requires a dictionary in which text and phonemics have been aligned, so that pronunciations corresponding to matching orthographic substrings can be identified. How- ever, many of the necessary computational steps to assemble a pronunciation can be carried out in advance. Thus, in implicit analogy (e.g., Sul- livan and Damper, 1993), the lexical database is precompiled to yield a generalised phonological knowledge base which is consulted during pro- nunciation generation. This done, the (explicit) dictionary can be discarded. Implicit analogy may also attempt to compress the training data, so that some proportion is discarded. Here, we extend earlier work on modelling pronunciation by normal readers to impaired readers with acquired dyslexias. There are sev- eral forms of this: two of the most important are phonological and surface dyslexia. Cases of phonological dyslexia display good ability to read words (both regular and irregularly- spelled) aloud but poor nonword reading abil- ity (Beauvois and D~rouesn~, 1979). In surface dyslexia, however, patients misread irregularly spelled words, which tend to be regularised in their pronunciation (Coltheart et al., 1983). To simulate these dyslexias, we use …

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