Contexto científico en la concepción del estudio GRACIA-3

To assess whether reading skill contributed to the vissim effect, two separate 2 x 3 x 2 ANOVAs (Vissim x Suppression x Reading skill) were performed on the memory scores o f the Auslan and SE groups. The fast Auslan group remembered more items than the slow readers [F (l, 18) = 8.72; p < .01], the vissim list was recalled more poorly overall [F (l, 18) = 10.63; p < .005] and memory span deteriorated overall with the imposition o f manual and English suppression [F(2, 36) = 11.66; p < .0001]. There were no interactions. In the SE analysis, the memory spans o f the fast and slow SE readers did not differ. All SE subjects showed a vissim effect [F (l, 18) = 19.02; p < .0005], and the items were recalled more poorly when suppression was required [F(2, 36) = 15.94; p < .0001], but there were no interactions.

These analyses imply that the visual similarity effect was not caused by rehearsal speed, even though rehearsal speed may have contributed to the fast Auslan group's better overall performance. As shown in Figure 7.4, reading skill did not interact with visual similarity, which implies that the transformation o f items into sign and speech codes was occurring independently o f visual coding. That is, the vissim effect was not due to differences in the amount o f identification/rehearsal time.

7.5 Discussion

The poorer recall o f the Vissim list by the Auslan, SE, and Oral subjects indicated that they were affected by the orthographic similarity o f the items to be remembered. Moreover, the absence o f Group x Similarity interactions in the data indicated that all three groups were disadvantaged to an equal extent by orthographic similarity. This is consistent with research indicating that signing experience does not affect visual memory (Emmorey, Kosslyn, & Bellugi, 1993).

The second major result was that graphemic similarity did not interact with the suppression conditions. The degree o f orthographic similarity neither influenced, nor was influenced by, the occurrence o f cherological and phonological rehearsal. This indicates that subjects were relatively inflexible in their "mix11 of strategies during recall. This is consistent with the results o f Hitch, Halliday, Schaafstal, and Schraagen (1988) who concluded that verbal rehearsal in young hearing children developed concurrently with a pictorial code, rather than replacing such non-verbal storage mechanisms.

7.5.1 Basis of the vissim effect

Further analyses were conducted to determine precisely why all the deaf groups recalled visually similar items more poorly. At least two interpretations appeared feasible. The first emphasises temporal factors: orthographically similar items were harder to identify, therefore less time was available for sign/speech rehearsal. As described below, the predictions o f this temporal account were not supported, so it was rejected in favour o f a "visual memory" interpretation which concentrates on the confusions in manipulating graphemically similar items in a visually-based memory code.

A temporal basis for the vissim effect was implied by the finding that the Vissim list was read more slowly and remembered more poorly by all groups than the Control list. Similarly, the Oral subjects were the fastest readers and the best rememberers; in contrast, the slowest average reading rates o f the Auslan and SE groups barely exceeded the presentation rate o f one item per second. This suggests that the conversion o f print to sign in the Vissim list may have taken up most o f the presentation time, with the result that there was less opportunity to rehearse phonologically or cherologically. Two analyses were performed to test this idea.

The rationale o f the first analysis was if the effects o f orthographic similarity were merely due to the curtailed rehearsal o f the Vissim list, then the elimination o f rehearsal should remove the vissim effect. Thus, manual suppression should eliminate the vissim effect for the Auslan group whilst concurrent articulation should remove it from the Oral group's data. These predictions were not confirmed, suggesting instead that a visual memory code might underlie the effect.

The second analysis focussed on the performance o f fast and slow signers. If the temporal account o f orthographic similarity were true, the fast signers should show a greater effect o f manual suppression, (since they had more time than the slow signers to rehearse manually in the nil suppression condition). The fast signers should also show a reduced visual similarity effect because the repetition rate data (a measure o f rehearsal speed after item identification) indicated the Vissim and Control lists were repeated equally quickly by each group.

Neither o f these predictions was confirmed, indicating that the effects on memory o f orthographic similarity were not totally due to identification/rehearsal factors. By contradicting a temporal account, these results give support for the notion that a visual memory code underlay the vissim effect. This conclusion is consistent with research with hearing subjects, which supports the existence o f visual rehearsal (Morrison, Holmes, & Haith, 1974) and o f visual coding o f linguistic material (Camden, Motley, & Baars, 1982; Heyer & Barrett, 1971; Hitch, 1990; Janata, Joelson, Joss, & Herrmann, 1978; Papagno, Valentine, & Baddeley, 1991; Zhang & Simon, 1985). The evidence is particularly clear when phonological recoding is suppressed (Brandimonte, Hitch, & Bishop, 1992; Vallar & Baddeley, 1982), or difficult, as in the case o f dyslexics (Frith, 1985; Rack 1985; Snowling, 1980).

Studies o f logographic languages which demand relatively more visual proficiency with a consequent reduction in phonological processing, also demonstrate the occurrence o f visual coding (e.g. Mann 1986; Tzeng & Wang, 1983; W oo & Hoosain, 1984). Zhang and Simon (1985) used homophonic Chinese characters during immediate serial recall, and obtained evidence in support o f a nonphonological component o f short­ term memory with a capacity o f about three chunks. The researchers concluded that this component corresponded to Baddeley's VSSP (Baddeley, 1983; Brooks, 1967).