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Information from lip-reading may form the dominant source of phonological knowledge of spoken language in the early years. However, there is substantial evidence to suggest that once a deaf child leams to read, their knowledge of orthography can also influence their speech-based STM representations.

The majority of studies that support this position have not investigated immediate recall but rather have assessed the phonological awareness skills of deaf people. Hanson and McGarr (1989) tested deaf college students on rhyme generation in response to printed target words. Fifty-two per cent of subjects’ responses rhymed. Seventy per cent of these correct responses could be classed as orthographic rhymes (e.g., tie - lie) and thirty per cent non-orthographic rhymes (e.g., tie - fly). Therefore evidence for both speech-based and orthographic strategies was obtained. However, hearing subjects were not tested, therefore it is not clear whether this distribution of responses represent a greater number of orthographic responses than would normally be generated to the target stimuli.

Another way to test awareness of rhyme is to assess rhyme judgment. Campbell and Wright (1988) presented oral deaf teenagers with fifty word pairs. The subject’s task

was to classify the pairs as rhyming or non-rhyming. Deaf subjects were poor at this task, particularly when spelling was incongruent (e.g., hair - bare), indicating that they relied heavily on orthographic information. Importantly, the influence of orthography was still apparent when the task was repeated using picture pairs rather than word pairs. That is, the visual orthographic cue did not have to be present for deaf teenagers to make use of orthographic information.

Both the Hanson & McGarr and Campbell & Wright studies demonstrate the influence o f orthographic information on deaf subjects’ knowledge of rhyme. However, Hanson and Fowler (1987 - Experiment 2) demonstrated that at least for some deaf people, rhyme knowledge is not limited to information derived from orthography. They tested deaf and hearing college students on rhyme judgment of two word pairs matched on orthography, one pair was regular (e.g., cave - gave) the other irregular (e.g., cave - have). Therefore all orthographic cues were removed from the stimuli. The subject’s task was to decide which pairs rhymed. Accuracy by hearing subjects (99.6%) was significantly better than that of deaf subjects (64.1%). However, performance by deaf subjects was significantly above chance (50%). When orthographic information was not available, these deaf college students were able to make use of phonological information possibly derived from lip-reading or some alternative form of speech input. These results support Comad’s (1979) conclusion that some deaf people are able to use a speech-based code, although their use of such

a code is rarely as efficient as that of hearing people. ^

An ‘abstract’ speech-based code

It is possible that a speech STM code, which is mainly based on non-auditory aspects of speech such as lip-reading and even orthography, functions quite differently to a STM code used by hearing people where the main source of information is auditory speech. However, Dodd (1987) argues that this is not the case and that deaf children

use other forms of speech information to develop the use of a speech-based code in the same way as hearing children, albeit delayed. Dodd further argues that “ A phonological code is likely to be a non-modality-specific code that deals with speech, irrespective of whether the phonemes perceived are heard or lip-read” (1987, pg. 188). In support of this, Dodd, Hobson, Brasher and Campbell (1983) found that recency in recall of lip-read digits by deaf and hearing teenagers was impaired by a phonological suffix (mouthing a number) but not a non-phonological suffix (tongue- protrusion). The fact that lip-read and heard speech appear to be processed in the

same way in STM reinforces the idea that a speech-based code is likely to be amodal

in nature for deaf as well as hearing people (see also Leybaert, 1993).

However, in conflict with this, the results of Campbell and Wright’s (1989) study, reviewed earlier, showed that deaf and hearing children were affected differently in their recall of nonsense syllables by lip-readability of stimuli. They therefore concluded that a speech-based code used by deaf people is qualitatively different to that used by the hearing.

One way to reconcile Dodd and Campbell & Wright’s positions is not to think of the use of a speech-based code as all or nothing but rather that a speech-based code may be used to varying levels of proficiency. These levels of proficiency are likely to reflect the stages of phonological awareness that a hearing child goes through in early childhood (see Goswami & Bryant, 1990). Deaf children may have difficulty reaching the higher stages of this developmental progression. For example, a child may have a representation of a word at the syllabic level. In contrast, another child may have a fully specified phonological representation of the word with knowledge of its rhyming and phonemic properties. Therefore, it is useful to describe the levels at which different deaf children may use different STM codes.

These levels of knowledge can be investigated directly using explicit tests of

well-educated deaf people have rhyme abilities inferior to those o f their hearing peers. These tasks, such as rhyme and homophone judgement, require subjects to use a speech-based code to enable the level of their phonological knowledge to be assessed. In contrast, STM tasks are implicit tests of speech-based coding. They explore the type of STM coding that a deaf person uses spontaneously to recode information in STM. It is this spontaneous recoding of linguistic stimuli which is the main concern of this thesis.