effet du nombre des graphèmes en Anglais - Aix Marseille Université

232Appendice Ito an orthographic lexicon of 2494 words (for a detailed description of the cleaning procedure applied on thisdatabase in order to extract the selected lexicon, see the appendix).This multilength lexicon raises the issue of how to code letter-in-word position and the relation betweenword units of different lengths. Some recent empirical studies suggest that the cognitive system uses relativerather than absolute position coding (Grainger & Jacobs, 1993 ; Peressotti & Grainger, 1995 ; see alsoGrainger & Jacobs, present volume). Thus, letters in a word are not supposed to be represented in terms oftheir absolute position in the word (i.e., U at the third position in BLUE), but in terms of their relative position,which is calculated from the word boundaries (e.g., U is one position before the final letter and L isone position after the initial letter in BLUE, i.e. U=final -1 and L=initial +1, respectively). This codingscheme allows us to establish more plausible similarity relations between words of different lengths than theoriginal position coding scheme of the IAM 7 . As an example, the stimulus WORD is encoded as : W ininitial position, O in initial +1, D in final position, and R in final -1. This coding scheme was applied tothe orthographic lexicon and for coding the input stimuli presented to the model. Table 1 gives a generaldescription of our coding scheme for 3 to 5 letter words.OrthographicLexiconPhonologicLexiconLetterLevelPhonologicalUnit LevelVisual StimulusAuditory StimulusFigure 4 : Grainger and Ferrand's model (1994)WHOLE WORD PHONOLOGICAL LEXICON. In MROM-P we assume that each orthographic representationof a word has a corresponding whole-word phonological representation. The phonological lexicon containingthese representations is smaller than the orthographic one because of homophones that have distinctorthographic entries but share the same phonological code. This led to 2323 whole word phonological representationsin contrast to the 2494 orthographic word units. Connections were established between eachwhole-word orthographic unit and its corresponding whole-word phonologic unit, and specific values of restinglevel activation (i.e., coding frequency of occurrence) were given to each unit using the CELEX frequencycount (see appendix for a description of the procedure).Table 1 : Relative position coding scheme for 3 to 5 letter wordsWord initial init.+1 init.+2 final-1 finallength5 L1 L2 L3 L4 L54 L1 L2 * L3 L43 L1 L2 * * L3PHONOLOGICAL UNITS. We assume that i) the cognitive system of a reader possesses some elementaryphonological representations or coding units ; ii) these basic phonological units, or phonemes, are grouped7 The evaluation of the plausibility of this coding scheme requires further investigation and, probably, further refinements.The use of a more structured coding scheme, introducing a grapheme level composed of functional pronunciationunits as proposed by Berndt, D'Autrechy and Reggia (1994 ; Berndt, Reggia & Mitchum, 1987 ; Reggia,Marsland & Berndt, 1988) is a possible candidate for such refinements. However, more constraining results areneeded to specify the nature and the boundaries of such units.