1.3 EVOLUCIÓN HISTÓRICA DE LA REPERFUSIÓN DEL INFARTO
1.3.6 Contexto científico en la concepción del estudio GRACIA-4
8.1
Confirmation o f the rehearsal speed explanation
This study has addressed the question o f why deaf people have poorer immediate serial recall than their hearing peers.
It examined an explanation o f this phenomenon which suggests that the communication modes used by deaf individuals are associated with rehearsal rates which are slower than those o f hearing people. Consequently, deaf people can "re-enter" fewer items before the initial ones decay, and a shorter memory span ensues. The study evaluated four assumptions o f this rehearsal speed account. These assumptions are underlined in the following three paragraphs which summarise the rehearsal speed argument.
D eaf people have shorter memory spans than hearing people because: 1. deaf people rehearse slower than hearing people;
2. deaf and hearing people's recall is determined by rehearsal rate. 1. D eaf people rehearse slower than hearing people because:
(la ) deaf people communicate more slowly than hearing people and (lb ) deaf and hearing; people rehearse in a code based on communication
mode
2. D eaf and hearing people's recall is determined by rehearsal rate because: (2a) their short-term memory is sensitive to item length and
(2b) the item length effect reflects rehearsal rate.
Assumption la was accepted following a review o f the literature; the remaining three assumptions were evaluated in six experiments against the memory performance of deaf subjects who communicated in Auslan, Signed English, or speech. Hearing subjects were not examined, since the assumptions have already been verified for this population.
The main results o f the individual experiments were as follows:
Experiment 1: Signing subjects recalled printed lists o f cherologically similar items more poorly than did the Oral subjects. All groups remembered the Lipsim list equally well (this list was composed o f items which produced similar lipshapes when spoken, and which also tended to be orthographically similar). Lists o f rhyming items produced the best recall in the two signing groups but the worst recall in the Oral group. ~
Experiment 2 : The orally educated subjects recalled significantly fewer lists with long spoken words than short ones. Signing subjects showed a similar but insignificant trend with signs.
Experiment 3 : All subjects had smaller spans for printed lists containing long as opposed to short items in the relevant communication mode. This item length effect was less marked for the Auslan group.
Experiment 4 : Manual suppression reduced the recall o f the Auslan group and eliminated the sign length effect. No group's memory performance was reduced to chance levels under suppression.
Experiment 5: Concurrent articulation decreased the recall o f all groups, although not to chance levels. It also attenuated the English length effect. Further analyses, which used articulation rate as an index o f difficulty, showed that speaking was more taxing for the Auslan subjects than the SE and Oral subjects.
Experiment 6 : All subjects recalled lists with orthographically similar items more poorly than those in which the items were visually distinct. The degree to which subjects relied on a particular memory code was independent o f the availability o f other codes. Additionally, manual suppression produced smaller memory spans in the Auslan group whereas English suppression detracted from the recall o f all groups.
This pattern o f results supports the three remaining assumptions o f the rehearsal speed account. Thus, deaf people rehearse in a code based on communication mode (Assumption lb) because the recall o f each group was specifically affected by manipulations o f various characteristics o f its primary linguistic mode. Lists with confiisable items (Experiment 1) or long items (Experiments 2 and 3) in the relevant mode were poorly retained, and when the opportunity for sign rehearsal was blocked, the Auslan group's span diminished (Experiments 4 and 6). (The absence o f a specific group effect with English suppression in Experiments 5 and 6 was attributed to the variable difficulty level o f the task across the groups). Furthermore, performances on the rhyming list (Experiment 1) indicated that if phonological coding was employed at all by signing subjects, it was more rudimentary than that used by the Oral subjects.
The results also verify that deaf people's short-term memory is sensitive to item length (Assumption 2a) because Auslan subjects tended to remember short-sign items better than long-sign items, Oral subjects remembered lists with short words better than those with long words, and the SE group's best performance was on the short sign/short word list (Experiments 2 and 3).
Finally, it was confirmed that the item length effect obtained with deaf subjects reflects rehearsal rate (Assumption 2b) because when primary linguistic rehearsal was prevented, the item length effect disappeared (Experiment 4) or was substantially reduced (Experiment 5).
Together with the evidence that hearing people communicate, and hence rehearse, faster than their deaf counterparts (reviewed in Chapter 3), these results support the notion that deaf people's serial recall deficit is attributable to their slower rehearsal rate.
However, the pattern o f results also suggests that a qualification be placed on the rehearsal speed explanation: compared to hearing subjects, rehearsal speed may be a less important determinant o f span for deaf subjects, especially those who use sign language. In the particular case o f the Auslan subjects, the reduced salience o f rehearsal rate was
evident in their consistenly smaller response to the relevant experimental manipulations. O f all the deaf subjects, it was the Auslan group which was least affected by variations of item length (Experiments 2 and 3). Additionally, manual suppression influenced these subjects to a lesser extent than English suppression affected the Oral group (Experiments 3, 4, 5, and 6). The smaller dependence on rehearsal in sign as opposed to speech will be discussed in Section 8.3.1.
There were several indications that communication-based rehearsal was not the sole contributor to the memory spans o f the three deaf groups. First, when such rehearsal was suppressed (Experiments 3, 4, 5, and 6), the performance level o f all subjects indicated that they were not simply guessing, but were regularly relying on additional strategies.
Secondly, a robust effect o f orthographic similarity was obtained in Experiment 6, and there was uniformly poor recall in Experiment 1 o f the Lipsim list (which also contained visually similar items). These results agree with reports that deaf subjects may consistently resort to graphemic strategies. In contrast, phonological coding appears to dominate hearing people's recall, even under occasions (e.g. rhyming items) when such coding produces less than optimal performance (Conrad & Hull, 1964; Luce, Feustel, & Pisoni, 1983; Schiano & Watkins, 1981). This suggests that deaf and hearing subjects may employ a different "mix" o f strategies to optimise their performance, with phonological rehearsal relatively more prominent in hearing individuals.
Finally, all o f the communication-based effects obtained in this study were smaller than those commonly reported for hearing subjects. For example, the Rhyme list in Experiment 1 impaired the performance o f the Oral subjects by .76 item when compared to a control list (List 3, the list which best matches it in syllable number, total letters, and canonical form). This is barely half the effect typical o f hearing subjects (Cowan, Cartwright, Winterowd, & Sherk, 1987; Schwerckert, Guentert, & Hersberger, 1990). It was also noted in Experiments 2 and 3 that the manipulation o f item length altered the recall o f deaf subjects by between .1 and .7 item, as opposed to reported increments o f about one item for hearing subjects with matched articulation rates (Hitch, Halliday, & Littler, 1989, 1993). Finally, when manual and English suppression eliminated the communication-based rehearsal o f the Oral and Auslan subjects respectively, their recall dropped by .3 -.45 item (Auslan) and .7 - .8 item (Oral), which is far short o f decrements o f 1.7 - 2.0 items reported for hearing adults (Baddeley & Lewis, 1984; Cowan et al., 1987), and o f 1.0 - 1.1 items reported for hearing children with comparable reading rates (Hitch, Halliday, & Littler, 1989, 1993). All this suggests that rehearsal based on communication mode may be less crucial for those who cannot hear.
8.2
The relative importance o f rehearsal speed
To examine the idea that rehearsal rate only partially determined the memory spans o f the three deaf groups, a precise measure o f the relative importance o f rehearsal to deaf and hearing subjects is required. Simple comparisons o f memory for "short" and "long" stimuli are inadequate, because the strength o f the item length manipulation might vary, (as discussed in the context o f abbreviation in Section 5.5.1 iii). Instead, two other approaches will be considered. The first involves an estimation o f the temporal capacity o f the articulatory loop. This was achieved by dividing the memory span by the
production rate, measured in items per second. Typically, this index ranges between 1.5 and 2.0 seconds with hearing subjects (Baddeley, 1983, 1990
p.
72; Baddeley & Hitch, 1974; Baddeley, Lewis, & Vallar, 1984; Baddeley, Thomson, & Buchanan, 1975; Ellis & Hennelley, 1980; Hitch, Halliday, & Littler, 1989; Morris & Jones, 1987; Schweickert & Boruff, 1986). Baddeley et al. (1975) maintained that "a subject can recall as many words as he can read in 1.6 seconds or can articulate in 1.3 seconds" (p. 581).In contrast, the capacity estimates obtained for the deaf subjects show them to be superior on this measure. (Calculations were based on data from five o f the nine lists used in this study, and refers to Lists 1-4 in Experiments 2 and 3 and List 9 in Experiment 6. Lists 5, 6, 7, and 8 were inapplicable because the items were similar on cherological, rhyme, lipread, or orthographic dimensions respectively). These estimates are summarised in Table 8.1. Naveh-Benjamin and Ayres (1986) obtained essentially the same outcome in a comparison between English, Spanish, Hebrew, and Arabic: although capacity scores clustered around the two seconds predicted by Baddeley et al. (1975), the languages with lengthier words predicted greater capacity than did those languages which could be read more quickly.