The reading aloud of one- and two- syllable words. Different problems that require different solutions? Insights from a quantitative analysis of the print-to-sound relations Marielle Lange (University of Edinburgh) Alain Content (Université Libre de Bruxelles) Correspondence: Marielle Lange University of Edinburgh, School of Informatics Institute for Adaptive and Neural Computation 5 Forrest Hill Edinburgh EH1 2QL (UK) [email protected] Quantitative description - 18/08/05 2 Abstract: Most models of English word recognition limit their domain of simulation to one syllable words and there is little straightforward empirical data to guide the development of more complex models of reading that would simulate the full set of words a reader is usually exposed to. However, typical reading material consists of polysyllabic words that are influenced by factors which are not present in one syllable words, such as the influence of stress on pronunciation, the influence of context, and the impact of segmentation ambiguity. An issue that arises, therefore is whether the present models, eventually very successful at simulating one-syllable words, in fact present a convincing solution to an inappropriately worded problem. In this study, we present an attempt to reach a clearer understanding of polysyllabic word reading. As a result of the lack of empirical or modeling data, corpus analysis seems the most appropriate technique to use to try to systematically investigate the role of different possible factors on performance when reading aloud. A quantitative description of grapheme-phoneme associations of monosyllabic and disyllabic English words (with their British English pronunciations) is provided as well as details of the methodology adopted for segmenting semi-automatically the spelling and pronunciation of the words into graphemes and phonemes. The data obtained on the distribution of the pronunciations of the different graphemes of the language are used to proceed to a comparison of the predictability of the pronunciation of monosyllabic and disyllabic words. We argue that these data indicate that current theories of monosyllabic word reading cannot be taken as satisfying theories of reading for the whole range of words a reader is exposed to. Quantitative description - 18/08/05 3 INTRODUCTION [ Note: Notation conventions: In this study, graphemes are formatted in bold (e.g., ai), phonemes are represented by the set of symbols from the International Phonetic Alphabet and enclosed in slant brackets (/b/, /p/, /a/), a silence is indicated by the symbol /=/, word or part of word exemplars appear in italics (e.g., every), a sequence of letters possibly forming a grapheme but not in that context is underlined (e.g., ph in uphill), a word's phonetic transcriptions are enclosed in square brackets (e.g., [evr!]). When illustrating segmentation into graphemes and phonemes, a “ ' ” is used to separate the grapheme or phoneme units in the strings (e.g., a'b'a'sh')] Unnoticed to many skilled readers is their ability to make a match between some reference in a conversation to the name of a brand new product and the advert they read the day before in the newspaper, or to make a match between the name of a speaker, as introduced at the start of a talk, and the author name that appeared on the program at a conference. This ability to derive the pronunciation of a letter string which has never been encountered before, as well as the fact that skilled readers are quite reliable in their reading of not so familiar letter strings, is usually seen as evidence that readers have some knowledge of the stable print-to-sound relations of their language is their cognitive systems. This hypothesis is at least largely accepted for readers of alphabetic languages, in which quite stable relationships exist between print and sound. After all, labelling such orthographies as alphabetic marks the fact that these languages evolved from a Roman alphabet in which each sound in the language was represented by a code of its own. In the course of history changes imposed in the sound of some words without a simultaneous change in their spelling have sometimes altered the initial one-to-one relationship, but all alphabetical languages retain that characteristic of having fairly stable print-to-sound relations: a letter sequence is frequently pronounced with the same sound (the sequence sh read as /"/) and a sound transcribed by the same letter or letter sequence (the speech sound /"/ written as sh). For instance, even though English has the reputation of being far more chaotic in its pronunciation than other alphabetic languages such as French, German, or Spanish, between 80 and 95 percent of words can be correctly pronounced by the application of letter(s)-to-sound rules [REF]. However, psycholinguists have not reached any consensus yet as to the exact nature of the representations and processes recruited for the conversion of a letter string into speech. This lack of consensus is particularly apparent in the drastically different if not antagonistic hypotheses of the dual-route and connectionist models of readers' performance. The central dogma of dual-route (DR) models is that an explanation of humans' ability to read requires two distinct routes, or procedures: a global process for the correct pronunciation of words which have an arbitrary pronunciation (i.e., have), and an analytic process for deciphering previously unseen words that cannot be processed globally. Both procedures operate in parallel; the global one rapidly retrieves the pronunciation of the words that are already familiar and the analytic one derives the pronunciation by applying print-sound correspondences. The Quantitative description - 18/08/05 4 dominant instance of this theory is the dual-route model introduced by Coltheart and colleagues (Coltheart, 1978, 1985, xxx). In the lexical route, words are identified as wholes, by accessing them via their orthographic address, which is connected in the mental lexicon to both their phonological address and their meaning. In the conversion route, print is mapped onto sound at the level of the phoneme, with graphemes defined as the letter or letter combination that represents a single speech sound (for example, p in print or ph in grapheme). Coltheart's group assume a knowledge limited to the most frequent pronunciation of each grapheme of the language and conversion operates by identifying of the letter or sequence of letters that operate as a grapheme (for example, the sequence ph) and transforming it into its most common pronunciation in the language (i.e., /f/ for ph). When phonological representations have been obtained for every grapheme in the string, they are merged into a phonological code. In the first version of this model, conversion operated in two steps: the isolation of the graphemes was followed by their translation. In the most recent version (DRC-L with L for Letters; Rastle & Coltheart, 1998; Coltheart et al., 2001), graphemes are translated into the corresponding phonemes during a letter-by-letter deciphering of the letter string. In contrast, the single-route theory rejects the hypothesis of two procedures based on different computational principles (global and analytical print-to-sound translation) and the reliance on two separate sources of knowledge (word specific and infra-lexical print-to-sound relations). As stated by Seidenberg and McClelland (1989, p. 525), "The key feature of [this model] is the assumption that there is a single, uniform procedure for computing a phonological representation from an orthographic representation that is applicable to irregular words and nonwords as well as regular words.". That claim however only related to the processes involved in print-to-sound translation; the general theory is that skilled reading more typically requires the combined support of both the semantic and phonological pathways. The most familiar instance of this theory is the parallel distributed processing (PDP) model of Seidenberg & McClelland (1989). In this model the translation of a letter string into its phonology relies on parallel distributed processing (PDP) in a connectionist network made of three fully interconnected adjacent layers of units: an input layer coding the orthographic form, an output layer coding the phonological representations, and an intermediate layer of hidden units. Activation propagates from the units of one layer to the units of the next layer, in a way that depends the value of the weight of the connections that link units from one layer to units from the next layer. All weights are set during a learning phase to encode the quasi-regularities in the spelling-to-sound mapping in a way that reflects the aggregate effect of training on the words that form the vocabulary of the network. Each time a word is presented, an algorithm estimates the discrepancy between the response produced by the network and the response it was expected to produce and uses this estimate to adjust the strength of the connections between the different levels of units (back propagation learning algorithm), such that performance improves gradually as the network discovers a set of connection weights that minimizes the error on the training corpus. This ability to learn its representations is an important property of this class of models because it complements an explanation of skill and impaired reading by an explanation of the way the system structures itself in the course of the development. Quantitative description - 18/08/05 5 In the mid-eighties, Humphreys and Evett (1985) concluded that despite a great deal of research in cognitive psychology and the neuropsychology of language, it proved impossible to disentangle these drastically different explanations. It was therefore hoped that the introduction of computational models in the years that followed would have the potential to settle these theoretical disputes, by separating the realistic from the unrealistic as hypotheses of human processing The use of computational modeling to express a theory in the form of a computer program or a connectionist network presents a number of advantages over a purely verbal model.