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The previous sections in this chapter have been concerned with the different types of STM codes available to deaf people. This forms the main focus of this thesis. However, this is not simply of theoretical interest. At the beginning of this chapter it was pointed out that, in comparison to hearing peers, deaf people show poorer recall of linguistic but not non-linguistic stimuli. It was suggested that this was due to differences in the efficiency of use of linguistic STM codes. That is, the STM code used, how well specified the code is and proficiency in the use of this code, may

influence overall STM performance. Differences between deaf and hearing people in

performance on different types of immediate recall tasks will now be considered.

It is a common assumption that deaf people have a specific deficit in the recall of serial order o f linguistic stimuli (e.g., see Conrad, 1979, pg. 135 for discussion), th e studies often cited in support of this position are those by O’Connor and Hermelin (1972; 1973b). In their tasks digits were presented one at a time in one of three horizontally arranged windows. The digits never appeared in a left to right order. Subjects were then asked to recall the numbers they had seen. The type of STM code used was inferred from whether the subject recalled items in a left to right order (spatial coding) or in the order that they appeared (temporal coding). Deaf subjects

were more likely to use a spatial code than a temporal, speech-based, code. In contrast, hearing subjects were more likely to use a temporal code.

However, this finding does not appear to have been replicated (Beck, Beck & Gironella, 1977; see also Das, 1983). Hanson (1990) conducted a similar study using

letters. However, here deaf college students were asked to recall spatially or

temporally, rather than leaving the subject to interpret what was required, as in O’Connor and Hermelin’s study. In contrast to O’Connor and Hermelin’s study there was no difference in accuracy between deaf and hearing subjects in either task. That is, even when hearing subjects were able to use a robust speech-based code in a SOR task, deaf and hearing people performed equally well when the items were presented

spatially. This is an important finding since deaf people are generally found to be poor at SOR of linguistic stimuli. However, it could be that these results are specific to well-educated deaf people, tested by Hanson. Furthermore, subjects were only required to recall three items on any trial. Therefore, it is possible that subjects’ performance was at ceiling. However, a study with deaf children by Sterne (1996 - Experiment 3) confirmed that these results might generalise to the deaf population as a whole.

Sterne’s study was complex and only selected findings are reported here. Sterne tested deaf and hearing twelve-year-olds on a computerised version o f the Corsi blocks task. This uses a 3 X 3 grid in which different squares are illuminated in a sequence. The subject’s task was to point to the squares in the serial order in which they were illuminated. Recall by deaf twelve-year-olds (mean number of correctly recalled sequences = 9.12) was significantly greater than that o f hearing chronological age (CA) matched controls (mean = 7.08). This pattern was reversed in a traditional visual span test using letters (letters presented in the same location): recall by hearing CA controls (mean = 7.08) was significantly greater than that o f deaf subjects (mean = 2.35). The crucial task involved spatial presentation of letters in the Corsi 3 X 3 grid. The nine letters in each of the squares were visible at all times. Subjects were

required to point to the letters or repeat the letters aloud in serial order. There was no

difference between deaf and hearing subjects in either of these tasks (deaf; pointing = 9.53, spoken = 10.00; hearing: pointing = 8.92; spoken = 10.75). Thus, spatial cues may enhance SOR of linguistic stimuli by deaf children bringing them to a level equivalent to that of their hearing peers.

However, deaf subjects’ performance in the spatial linguistic tasks did not differ from that in the purely spatial Corsi blocks task. As the grid of letters was present throughout recall of the linguistic stimuli it is possible that deaf subjects were not recalling the phonological properties of the item. Rather they may have identified the appropriate spatial location and then named the letter at that position from the screen in front of them. It would be interesting to repeat this study using a signed/ spoken response in the absence of the stimulus grid requiring the child to make a response based on retrieved phonology, not on recognition of a letter in a particular spatial location. This would determine whether recall of linguistic stimuli truly is enhanced by spatial presentation or whether the effect is, in part at least, due to the presence of a cue grid at recall.

Whatever the detailed analysis eventually shows, when spatial cues are not present, as when stimuli are presented in the same location, SOR by deaf subjects is typically worse than that of hearing subjects (e.g., Blair, 1957; Campbell & Wright, 1990;

Hanson, 1982; Krakow & Hanson, 1985; Pintner & Patterson, 1917). ,

Hanson (1982) argues that since a speech-based code is temporal in nature it is particularly suited to SOR of stimuli. She argues, since deaf people are generally less skilled at using a speech-based code, their SOR skills are impaired. Hanson further argued that this deficit should be specific to SOR in contrast to free recall (FR - recall of items without order), which should be similar in deaf and hearing CA controls.

Hanson (1982) tested this hypothesis in two different experiments. In Experiment 1 deaf college students were tested on probed recall of printed English words. A list of words was presented. One of the words was then shown as a cue. The subjects’ task was to identify the word that followed the cue in the original sequence. The word lists were speech-similar, sign-similar or orthographically similar. Each of these stimulus sets had its own control set of dissimilar stimuli, which were matched on frequency to the target set. The effects of similarity of recall in this experiment were discussed in detail in section 3.3.Ü. O f importance to the present discussion was subjects’ overall accuracy. Hanson measured this as the percentage of dissimilar items correctly recalled across the three control sets of stimuli. Probed recall of control stimuli by hearing subjects was significantly better than that of deaf subjects.

In Experiment 2 Hanson (1982) tested written FR of sign similar and speech similar words. Again, each experimental set of stimuli had its own control set of dissimilar words matched on frequency. In contrast to Experiment 1, deaf subjects’ recall of the

two control sets of stimuli was equivalent to that of hearing controls. Hanson

therefore claims that the STM deficits of deaf people are limited to SOR, due to inefficient use of a speech-based code.

Very few studies have examined the FR abilities of deaf subjects. This illustrates how the focus within mainstream research with hearing people on serial processing has influenced deafness research. However, studies that have tested FR by deaf subjects show little support for Hanson’s results. Deaf subjects tend to perform less well than hearing subjects in tests of FR (Bonvillian, 1983; Koh, Vernon & Bailey, 1971; Liben, 1979; Siedlecki, Votaw, Bonvillian & Jordan, 1990). Hanson’s results may be restricted to her deaf college student subjects, with high levels of reading proficiency. Furthermore, Hanson tested different subjects on FR and SOR. Given the importance

of subject characteristics on STM performance the same subjects should be compared.

This would be a more direct test of the hypothesis that deaf people have a specific deficit in the recall of ordered but not unordered information.

In summary, it is not yet clear whether deaf people have a general deficit in immediate recall of linguistic stimuli or whether they have a specific deficit in SOR of linguistic stimuli. This issue is addressed in the first experiment in this thesis.