sophisticated than that used by the Oral subjects because the two signing groups always recalled the rhyming items better than the Lipsim lists, indicating that they were less affected by the phonological segmentation requirements inherent in rhyme recognition.
This phonological code was probably based on lipread features, since the retention o f both signing groups was worst for the difficult-to-lipread list. Several observations support this view. Facial expression has been identified by Johnston (1989) as one o f the five underlying parameters o f Auslan, so signers would be expected to pay some attention to lip shape. The interrelationship between sign language and facial perception was also stressed by Emmorey (1993) and Reilly, Mclntire, and Bellugi, (1990). Caccamise (1989) and Montgomery, Miller, Mitchell, Jordan, and M ontgomery (1983) observe that most signs are displaced away from the lips because facial expressions and lip movements are significant in sign perception. Lawson (1983) and Vogt-Svendsen (1983) emphasise "multi-channel signs", in which non-manual aspects, such as mouth and cheek movements, are important ingredients. Additionally, the regularities o f letter-to-articulation coding encourage articulatory responses more than the arbitrary print-to-sign relation invites cherological coding. This is all the more likely given the omnipresence o f the language o f the majority hearing culture. Translation services are not always readily available to interpret the spoken word in conversation, TV or film, and most deaf people attain a modicum o f lipreading skill, by necessity even if not by choice.
An orthographic code?
Another coding alternative is that the deaf subjects were using a visual code based on the letter shapes o f the printed stimuli.
An inspection o f the items in the three master lists can provide support for this interpretation. These items are relisted below.
C-list: cart kangaroo motorbike pastry
pram sheet sock trolley
R-list: brain chain crane drain
fram e lane plane rain
L-list: cook cord cork dirt
door goat toad toe
On several criteria, the Rhyme and Lipsim lists contained more orthographically similar items than the Cherological list. The latter had a more varied word length and employed more different letters than the phonologically similar lists. The similarly signed list incorporated words with 4, 5, 6, 7, 8 and 9 letters, taken from a pool o f 17 different letters. The Rhyme list used words which were all 4 or 5 letters long, made up from 14 different letters whilst the Lipsim list used 3- or 4-letter words, and only 10 different letters.
Additionally, an analysis o f ascenders and descenders, which has been found to influence judgements o f orthographic similarity (Bouma, 1971; Geyer, 1977), indicates that the Lipsim list was more visually similar than the Cherological list. On this criterion, the C-list had only two words with similar word envelopes (these being cart, sock), the R-list contained three {brain, drain, fram e) whilst the L-list incorporated five {cook, cord, cork and dirt, toad).
Therefore, the finding that the two signing groups produced a relatively flat profile o f memory scores could be explained by assuming that they were impaired by cherological similarity on the C-list, and by orthographic similarity on the R-list and the L-list. The Oral group could also have relied on an orthographic code to some extent.
One line o f research which demonstrates the salience o f orthography concerns the impact o f spelling on the performance o f deaf subjects. Campbell and W right (1988) showed that rhyme judgements for pictured stimuli by orally-trained deaf youngsters were less accurate and more spelling sensitive than was the case with hearing subjects who were matched for reading-age. Hanson and Fowler (1987), using signing deaf college students, noted an error rate o f 70% on incongruent written word rhyme judgements as opposed to 28% for congruent spellings. Blanton, Nunnally, and Odom (1967) also showed that deaf subjects were more influenced by orthography in rhyme judgements than were hearing subjects.
Evidence that deaf subjects rely on orthographic and non-orthographic strategies in rhyming tasks has been obtained by Blanton et al. (1967), Hanson (1980), and Hanson and Fowler (1987). Hanson and M cGarr (1989) examined the rhymes generated to word stimuli by college level deaf subjects o f reading age grade 10.1 (that is, they were exceptional readers, given that the median reading comprehension grade level o f profoundly deaf students graduating from high school is 3.2, according to Karchmer, Milone, & Wolk, 1979). Analysis o f the responses showed that 70% could have been generated by an orthographic strategy (e.g. TIE-lie) and 30% by alternative strategies (e.g. TIE-fly). Evidence was also obtained for speech-based strategies - either how the words looked on another's lips (suggested also by Dodd & Hermelin, 1977) or how the words were produced by the subject.
Overall performance
Little can be made o f the observation that the three groups reached the same level o f overall performance. This result does not demonstrate that the three groups were equally matched on ability, because the degrees o f similarity within each master list could not be matched with any other. Moreover, even if this had been achieved, the result might represent nothing more than that some groups relied on more codes than did others, or were more heavily reliant on particular codes, and hence were (dis)advantaged to a greater extent.
Communication speed
The timed measures were included to control for the possibility that the temporal length o f the items, rather than their similarity, may have affected the outcome.
The three coding modes were not associated with different production speeds. For example, on the reading task, the Oral subjects' reading times were always faster than those o f the Auslan and SE subjects, who did not differ from each other. This suggests that the effects o f item similarity were not due to speed o f expression. Similar evidence can be found in the recall o f hearing persons: Hulme and Tordoff (1989) and Schweickert, Guentert, and Hersberger (1990) concluded that the effects o f acoustic similarity in recall do not depend upon differences in speech rate, because sequences of acoustically similar items were not necessarily harder to articulate rapidly despite the fact that spans were much higher for lists containing dissimilar items.
4.5.2 Memory codes and underlying processes
The Cherological, Rhyme and Lipsim lists were associated with a different pattern o f results for the three subject groups, leading to the following conclusions.
First, the deleterious impact o f cherological similarity upon the performance of the Auslan and SE groups but not upon the Oral group confirmed that the recall o f the two signing groups was mediated by a sign code, whereas the Oral group's retention was not.
Secondly, as anticipated, the Oral subjects appeared to be using a speech code, because their worst recall scores were obtained on the two phonologically similar lists. Orthographic coding by the Oral group could also not be discounted, because the two phonologically similar lists were also similar orthographically. To the extent that the Auslan and SE groups employed speech coding at all (some exposure to speech can be assumed, since-it is the language o f the dominant culture), the Oral group seemed to be using more sophisticated phonological representations, because they were relatively more affected by rhyming stimuli than the other subjects.
When combined with the strong indications that the subjects were rehearsing, we may conclude that:
Subjects were rehearsing in their preferred communication mode.
Thirdly, the fact that the group differences on the two phonologically similar lists were few in number and small in magnitude, is consistent with two interpretations, which are not necessarily mutually exclusive.
One possibility is that the cherological code o f the tw o signing groups was less efficacious for serial recall than the speech code o f the Oral group. Comparable performance levels could have occurred for all groups with the Rhyme and Lipsim lists, because the effects o f the inefficient sign code used by the Auslan and SE subjects could have been matched by the effects o f an indistinct speech code (caused by the phonological similarity o f the two lists) which the Oral group relied upon.
~ "Alternatively, the Auslan and SE groups may have used sign in conjunction with other codes during serial recall. Due to the confounding between phonological and visual similarity, it is not possible to judge whether these ancillary codes were based upon visual/kinaesthetic lipread traces, or upon the written shape o f the word to be remembered, or both.