Implications

8.5.1 Implications for the working memory model

This study confirms that the notion o f serial recall driven by rehearsal o f a decaying trace has considerable generality, for it can be extended to a memory representation in speech devoid o f acoustics, and another representation founded on visuo-spatial features. The rehearsal speed account o f deaf people's memory deficit can resolve many o f the apparent differences between hearing subjects and the three deaf groups in this study as accommodations by the different sensory modalities to similar underlying principles (e.g. the abbreviation o f long signs, which actually reduced the sign length effect, testifies to the importance o f rehearsal speed).

This research is also consistent with a recent demonstration that the phonological loop's functioning can extend to any discrete and changing sounds (Jones & Macken, 1993), and accords with Reisberg, Rappaport, and O'Shaughnessys (1984) suggestion that in principle, the working memory system can be fractionated in any number o f ways. Based on the improved memory performance contingent on a "finger loop" mnemonic they argue:

the properties o f working memory would not be fixed, but would depend on the constituents o f working memory that a subject chooses to employ in accomplishing a given task. But beyond this, what constituents would be available, and thus what properties working memory could reveal, would then be an accident o f the individuals learning history, so that, in a strong sense, working memory would have no fixed properties, (p. 219).

In a continuation o f Reisberg et al.'s (1984) theme, this research contributes to Baddeley's model by emphasising the notion o f efficiency. Phonological rehearsal in hearing subjects occurs because it produces the best memory performances, whereas the deaf subjects in this study demonstrate that communication-based coding will be used in proportion to its effectiveness, to be supplemented by other strategies as the need arises.

8.6.2 Implications for communication

This study demonstrates that rehearsal speed contributed to the serial recall o f deaf subjects. It also confirms previous reports that deaf subjects usually rehearse words faster in speech than sign. However, these results cannot be used directly to adjudicate between Auslan and speech in everyday use because the relative speeds o f signs and words observed in this experimental situation do not represent their production rates during "normal" conversations.

It is only during serial recall that individual items generally take longer to sign than to speak. In such memory tasks, therefore, overall recall in a sign-based memory code is less effective than in one based on speech (using rehearsal speed as the criterion o f effectiveness). Nevertheless, as explained in Section 8.3.1, although individual items take longer to sign than to speak, Auslan and other sign languages are structured so that propositions can be expressed at equal rates. In these circumstances, the rehearsal speed account predicts that no difference should exist between deaf and hearing people's ability to recall signed and spoken propositions, as is indeed the case (Kyle, 1983). This means that the sequential memory deficit o f the Auslan group - if based on rehearsal rate - is largely irrelevant in everyday situations.

The same may not be true when sign and speech are produced simultaneously, however. Compared to Auslan, the production rate o f SE during serial recall is a better indicator o f its "typical" rate o f expression, for SE must use the sequential inflexional morphology o f spoken English, not the time-saving grammar o f sign language. Combined with a relatively slow sign-rate o f individual words, this means that it takes longer to complete a proposition in this hybrid mode than in either sign or speech alone. The requirement to communicate in SE thus places a barrier to achieving the optimum processing rate (Baker, 1979) and gives a new emphasis to "cognitive overload". This term usually connotes the difficulty o f integrating two modalities experienced by SE users; the current research suggests that the relatively slow rehearsal rate o f SE items may also prove to be cognitively taxing. D eaf people might therefore attempt to reduce the production time o f signs-plus-speech. This would explain the reduced complexity and/or accuracy o f utterances by SE users (Hyde & Power, 1991; M arm or & Pettito, 1979; W ood, W ood, & Kingsmill, 1991), and their reversion to sign language structures (Gee & Mounty, 1991; Kluwin, 1981; Livingston, 1983; Supalla, 1991; Suty & Friel- Patti, 1982). Additionally, the relatively slow rehearsal rate o f SE items may contribute to the less-than-expected language progress o f deaf people who communicate in this mode (given that speech input should be more accessible to them). Indeed the extra demands imposed on serial short-term memory by SE may actually act to dimmish the comprehensibility o f the message. Significantly, several writers have questioned the

advisability o f receiving "spoken" English in a mode other than the auditory one in which it was intended (e.g. Gee & Goodhart, 1985; Sacks, 1989; Suty & Friel-Patti, 1982).11

As well as highlighting some o f the difficulties inherent in SE, this study also suggests ways o f alleviating them. The data support the ongoing practice o f using preexisting signs when devising or expanding the manually-coded English vocabulary, since such signs are likely to have nativised to short forms which are easy to articulate. It also suggests caution in introducing "initialised signs", which are new signs formed by making the handshape o f the sign correspond to the first letter o f its English translation. These signs are driven by English characteristics rather than signed ones. Being invented from outside the sign system, these signs may not lead to a conjunction o f handshape, movement and location which is optimal for memory processing. This study shows that when signs are invented, those which are quick, discriminable, and easy to execute should be given priority over those which merely reflect certain English characteristics.

This does not imply that vocalisations or lip movements are discounted in Auslan, however. D eaf people's reliance on lipshape as an integral part o f the sign was evident in these experiments, suggesting that attention be paid to manual and non-manual components when using or analysing current signs or devising new ones.

The present research may also throw some light on the interplay between memory for speech and linguistic accomplishment. The performance o f the deaf groups in this study indicated that they used an imperfect phonological memory representation. In Baddeley and Wilson's (1993) terms, the "phonological awareness" o f these subjects was relatively poor. Impaired performance on this factor may have far-reaching ramefications since recent research suggests that phonological awareness may affect both short-term memory and language. Low phonological awareness may constrain deaf people's ability to retain and analyse sounds, which in turn is crucial in forming words, and in mastering the alphabetic principle o f letter-sound correspondence (Liberman & Shankweiler, 1991).

It has also been suggested that there is a direct interactive relationship between language and the phonological component o f memory. Not only may temporary auditory representations o f unfamiliar words help build up the more permanent traces required for vocabulary acquisiton (Baddeley, 1993; Gathercole, 1990; Gathercole & Baddeley, 1990a, 1990b), but linguistic familiarity may support phonological memory (Gathercole, Willis, Emslie, & Baddeley, 1991) and the learning o f new words (Snowling, Chiat, & Hulme, 1991). Therefore, some deaf individuals who rely solely on speech input may become locked in a cycle where their imprecise speech representations lead to relatively slow rates o f vocabulary learning which in turn retard their memory performance. Furthermore, the present study, showing both that deaf individuals recalled lengthy items relatively poorly and that the SE items were the most slowly executed, casts doubts on whether appending signs to speech would actually assist this temporary memory representation. Instead, deaf people may need to capitalise on their visual skills if they are to escape the cycle o f poor language performance. For example, as Campbell (1992) suggests, vocabulary expansion via orthographic strategies may in turn promote memory development.

11 International differences occur in the severity of these problems; recent research suggests that Australasian Signed English may experience some of these difficulties to a lesser degree (Hyde & Power, 1991; Leigh & Hyde, 1994).

To the extent that orally educated deaf people have shorter memory spans than hearing people because their recall is based on an indistinct trace, we might expect an association between memory performance and spoken vocabulary development. For these deaf subjects, poor short-term memory may predict a smaller spoken vocabulary even after intervention. However no comparable expectations can be held for sign language users regarding their acquisition o f signs. D eaf people who sign may indeed have shorter spans than hearing people, but this study links the performance discrepancy to the slower production o f signs, not their discriminability. Therefore, a short span in sign does not necessarily indicate poor "cherological awareness", and should not be used to predict a smaller sign vocabulary. Expectations about deaf people's progress in sign language should be based on their memory performance relative to other deaf signers, not relative to hearing people whose recall is assisted by speech.

As the preceding example shows, the results o f this study are significant for those assessing the capabilities o f the deaf population. D eaf peoples' communication modes are a part o f their culture. This study indicates that these modes have dissimilar temporal and discriminability characteristics from the speech mode used by hearing people, and that both these characteristics affect recall. Assessments o f a deaf person's immediate memory must take these factors into account in order to minimise cultural bias. The deaf person's recall should be compared not only with the performance o f other deaf people (matched on age, etiology, onset, and severity), it should also be considered in relation to those who use the same communication mode and whose exposure and fluency are at appropriate levels.

In these experiments, ease o f expression in sign was only one o f several components o f fluency which were important during the memory task. Assessment, and by implication remediation, must also consider reading competence. W ritten material was recalled less well than signed information by the Auslan and SE subjects. The fluency with which printed words were decoded into sign was a powerful determinant o f subjects' performance, and all groups remembered the "easy" (short) words better than the long ones. In view o f the reading difficulties o f the deaf popuation as a whole, it is clear that simply presenting the to-be-remembered-items orthographically will not necessarily put deaf and hearing subjects on an equal footing during a test o f their recall.

This study is based on the premise that the memory performance o f deaf people may be best understood as consequence o f using different communication modes, rather than an outcome o f a deficient ability to remember. Thus, memory performance is seen as an expression o f difference rather than deficit. Different implications for intervention arise according to whether a difference-based or a deficit-based approach is adopted. For example, in the former approach the question o f how deaf people may most effectively remember items for a short time seems best answered by the deaf subjects themselves, who displayed a talent for optimising their skills. In this study, subjects used several methods concurrently to improve their memory performance. Maintenance rehearsal occurred in Auslan, Signed English, and spoken English, supplemented by other strategies including one with an orthographic component. This "multiple methods" approach seems the best route to memory enhancement for these subjects - even though it involved a decreased emphasis on communication-based memory codes and an increased reliance on visual and other strategies, compared to hearing individuals. The data shows that the contrasting approach, encouraging deaf people to be "the same" as hearing people by relying almost completely on maintenance rehearsal, would in fact be

counter-productive (because such rehearsal by deaf subjects would be relatively inefficient).