Abstract
This thesis addresses the controversy surrounding how language, and visible speech in particular, is coded by orally-educated prelingually deaf children. Three lipreading experiments were conducted with prelingually deaf and hearing children, beginning with a replication of Dodd & Hermelin (1977) and followed by two revised versions of this experiment. The results demonstrated that lipread rhyme judgement is based on visemic coding (pattern-matching of lip movements) rather than abstract phonological coding, as previously assumed (e. g. Dodd, 1987). Three further experiments used picture stimuli rather than lipread speech to approach the phonological coding question and to assess the extent of visemic coding beyond the lipread context. These experiments showed that phonological coding is unavailable to the majority of prelingually profoundly deaf children tested, although it could not be ruled out for a minority of these subjects who were immune to the visemic, orthographic and semantic distractors used in a rhyme judgement task and who showed no evidence of using articulatory coding in a pseudohomophone judgement task. In a study of spelling errors made by profoundly deaf and hearing children, again using picture stimuli, the deaf children made predominantly (70%) graphemic errors, particularly word substitution errors. This is in contrast to younger hearing children, who showed a classic phonetic pattern of spelling errors. The hypothesis of visemic coding in lipreading was supported by the findings, but little evidence was found for visemic coding in picture contexts. An orthographic coding strategy was dominant with picture stimuli for profoundly deaf subjects in spelling picture names, but in making phonological judgements, no dominant coding strategy emerged. This research has implications for the oral method of education of deaf children and for the processes that control the normal perception of speech.