Signed Language Working Memory Capacity of Signed Language Interpreters and Deaf Signers

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Empirical Article

Signed Language Working Memory Capacity of Signed

Language Interpreters and Deaf Signers

Jihong Wang*, Jemina NapierMacquarie University

Received June 4, 2012; revisions received November 12, 2012; accepted November 30, 2012

This study investigated the effects of hearing status and age of signed language acquisition on signed language working memory capacity. Professional Auslan (Australian sign lan-guage)/English interpreters (hearing native signers and hear-ing nonnative signers) and deaf Auslan signers (deaf native signers and deaf nonnative signers) completed an Auslan working memory (WM) span task. The results revealed that the hearing signers (i.e., the professional interpreters) sig-nificantly outperformed the deaf signers on the Auslan WM span task. However, the results showed no significant differ-ences between the native signers and the nonnative signers in their Auslan working memory capacity. Furthermore, there was no significant interaction between hearing status and age of signed language acquisition. Additionally, the study found no significant differences between the deaf native sign-ers (adults) and the deaf nonnative signers (adults) in their Auslan working memory capacity. The findings are discussed in relation to the participants’ memory strategies and their early language experience. The findings present challenges for WM theories.

Although many deaf people use a signed language as their primary or preferred language in adulthood, they vary widely as to when they were first exposed to the language (Emmorey, 2002). Deaf children of signing deaf parents acquire a signed language as their first language from birth, in much the same way as hear-ing children of hearing parents acquire a spoken lan-guage (Emmorey, 2002; Johnston & Schembri, 2007; Marschark, 2002). However, less than 10% of deaf children are born to signing deaf parents (Emmorey, 2002; Johnston & Schembri, 2007). It is more common

for deaf children to be born to hearing parents who do not know a signed language. Deaf children of hearing parents either acquire a signed language as a delayed first language in childhood when they are exposed to other signing deaf children and adults at school, or they may learn it as a second language later in life when they socialize with other signing deaf people (Johnston & Schembri, 2007). Unlike deaf (and hearing) children of signing deaf parents and hearing children of hear-ing parents who acquire language relatively naturally, deaf children of hearing parents typically have delayed exposure to language, which may affect their language acquisition and cognitive development (Emmorey, 2002; Marschark, 2002).

Auslan (Australian sign language) is the natural signed language of the Australian Deaf community (Johnston & Schembri, 2007). Since the late 1980s, when Auslan became recognized as an Australian community language (Dawkins 1991; Lo Bianco 1987), deaf people have gained increased access to the use of interpreters in Australia’s public and private spheres. Auslan/English interpreters may be hearing native signers who typically have signing deaf parents, or they may be hearing nonnative signers who often have no family connections to the Deaf community but learn Auslan as a second language later in life.

Baddeley (1992, p. 556) defines the term working memory (WM) as “a brain system that provides tem-porary storage and manipulation of the information necessary for such complex cognitive tasks as lan-guage comprehension, learning, and reasoning.” WM

*Correspondence should be sent to Jihong Wang, Department of Linguistics, Macquarie University, Sydney NSW 2109, Australia (e-mail: [email protected])

doi:10.1093/deafed/ens068Advance Access publication January 9, 2013

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is different from short-term memory (STM), which is typically conceptualized as a unitary storage buffer that stores information passively and temporarily (e.g., remembering a phone number; Hall & Bavelier, 2010). In light of these definitions, we may consider STM as the storage-only subset of WM. A body of evidence suggests that working memory capacity (WMC) is better than STM span at predicting higher order cog-nitive abilities such as reading comprehension and general fluid intelligence (Conway, Cowan, Bunting, Therriault, & Minkoff, 2002; Daneman & Carpenter, 1980; Engle, Tuholski, Laughlin, & Conway, 1999; Masson & Miller, 1983).

While a large number of previous studies have focused on deaf people’s STM span, few studies have examined hearing and deaf signers’ signed language WMC. This empirical study partially bridges this gap by investigating Auslan WMC of professional Auslan/English interpreters and deaf Auslan signers. Before describing the method and findings of this study, the relevant literature is first presented in order to set the scene for the study.

Background

This section reviews previous research into WM the-ories for speech and sign, STM span of deaf signers versus hearing speakers, WMC of deaf signers versus hearing speakers, WMC of professional interpreters, and native signers versus nonnative signers.

WM Theories for Speech and Sign

Based on solid evidence from hearing speakers, Baddeley (2002, 2007) proposes a WM model com-prising four components: (a) the central executive that focuses, divides, and switches attention; (b) the pho-nological loop that holds and manipulates verbal infor-mation; (c) the visuospatial sketchpad that stores and processes visual and spatial information; and (d) the episodic buffer that integrates the various types of infor-mation in WM and long-term memory into coherent chunks by using a multidimensional code. The pho-nological loop comprises a phonological store and an articulatory rehearsal mechanism. Auditory memory traces within the phonological store decay over a period of approximately 2 s unless refreshed by articulatory

rehearsal. The phonological loop is particularly suited for serial retention of verbal information and facilitates native language acquisition in hearing children and second language learning in hearing adults (Baddeley, 2002, 2007). Empirical support for the phonological loop comes mainly from four signature effects on hear-ing speakers’ immediate serial recall (i.e., STM) of ver-bal stimuli: the phonological similarity effect (Baddeley, 1966); the word length effect (Baddeley, Thomson, & Buchanan, 1975); the articulatory suppression effect (Baddeley et al., 1975); and the irrelevant speech effect (Salamé & Baddeley, 1982).

Interestingly, Wilson and Emmorey (1997, 1998, 2003) also observed the four signature effects on deaf signers’ immediate serial recall of signs, and hence proposed a sign-based phonological loop (also called a sign loop) in deaf signers, which is parallel to hearing speakers’ speech-based phonological loop. The sign-based phonological loop comprises two components: a phonological store that retains information using sign-based phonological codes (e.g., handshape, orientation, location, and movement), and a manual articulatory rehearsal mechanism that refreshes information in the phonological store. Nevertheless, the relation between the visuospatial sketchpad and the sign-based phono-logical loop remains unclear in the existing literature.

STM Span of Deaf Signers versus Hearing Speakers

Numerous studies have compared deaf signers with hearing speakers in terms of their linguistic STM span and their nonlinguistic spatial STM span. Linguistic STM span tasks typically include the digit (or letter, word) span task, in which a participant is required to recall lists of digits in the exact order of presentation (presented as 1, 2, 3, 4, 5; recalled as 1, 2, 3, 4, 5). The length of the longest list perfectly recalled is typically considered to be the participant’s linguistic STM span.

It has been well documented that deaf native sign-ers’ signed language STM span is significantly shorter than native speakers’ spoken language STM span (Bavelier, Newport, Hall, Supalla, & Boutla, 2006, 2008; Bellugi, Klima, & Siple, 1974; Boutla, Supalla, Newport, & Bavelier, 2004; Wilson, Bettger, Niculae, &

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Klima, 1997). Similarly, deaf nonnative signers’ signed language digit span is significantly poorer than their hearing peers’ spoken language digit span (Falkman & Hjelmquist, 2006; Wilson et al., 1997). Possible expla-nations for these consistent findings include the follow-ing: signs take longer to articulate than speech (Wilson et al., 1997; Wilson & Emmorey, 2006a, 2006b); speech-based encoding leads to a larger serial STM span than does sign-based encoding (Hall & Bavelier, 2011); visu-ally encoded information decays faster than speech-like information (Boutla et al., 2004); and visual encoding is less effective than auditory encoding in maintaining serial order information (Bavelier et al., 2006; Boutla et al., 2004). Comparing the STM span in the native language of different populations has both advantages (e.g., different populations can be matched for lan-guage proficiency and age of language acquisition) and disadvantages (e.g., the actual test items are different; the tests are different in language and modality).

An alternative research design compares hearing signers’ signed language STM span with their spo-ken language STM span. Recent evidence shows that hearing native signers’ signed language STM span is substantially shorter than their spoken language STM span (Bavelier et al., 2006; Boutla et al., 2004; Rönnberg, Rudner, & Ingvar, 2004). Furthermore, James and Gabriel (2012) found that American Sign Language (ASL)/English interpreting students’ ASL STM span was significantly shorter than their English STM span. All of the interpreting students were hear-ing nonnative signers of ASL. Similarly, Hall and Bavelier (2011) found that ASL/English interpreters and bimodal bilinguals’ ASL STM span was consider-ably shorter than their English STM span. Participants of the Hall and Bavelier study consisted of hearing native signers and hearing nonnative signers. Hall and Bavelier found no significant differences between the hearing native signers and the hearing nonnative sign-ers in their STM span. However, van Dijk, Christoffels, Postma, and Hermans (2012) found no significant dif-ferences between experienced Sign Language of the Netherlands (SLN)/Dutch interpreters’ SLN STM span and their Dutch STM span. These contradictory findings may have resulted from participant selection, different test materials, and/or different statistical analyses.

Another research design compares hearing sign-ers with deaf signers on the same STM span task. This design also has strengths (e.g., the actual test items are the same) and weaknesses (e.g., the groups are no longer matched on several potentially impor-tant variables such as proficiency in the test language). Logan, Maybery, and Fletcher (1996) found that hear-ing signers significantly outperformed deaf signers on both written English STM span tasks and Auslan STM span tasks. They specified that the hearing sign-ers included Auslan/English interpreters and bimodal bilinguals; however, they omitted to indicate whether the deaf signers were native or nonnative signers. They claimed that the hearing signers’ English phonological coding was considerably more effective than that of the deaf signers and that the hearing signers’ English pho-nological coding was intrinsically more suitable than the deaf signers’ Auslan phonological coding for serial retention of linguistic information. By instructing all their participants to recall Auslan signs in written English, Logan et al. may have required the deaf sign-ers to make an extra mental translation that was almost spontaneous in the hearing signers (Hall & Bavelier, 2011). In addition, the requirement for written recall may have caused English interference in retaining Auslan signs and thus biased all participants’ Auslan STM span.

In order to avoid possible confounding variables relating to sensory modality, several studies compared deaf signers with hearing speakers in terms of their serial recall of gestures or pictures. Geraci, Gozzi, Papagno, and Cecchetto (2008) found no significant differences between deaf signers and hearing speakers in their STM span for emblems. Furthermore, Rudner and Rönnberg (2008a) found no significant differences between deaf signers, hearing signers, and hearing nonsigners in their STM span for easily nameable pictures. These results suggest that deaf signers and hearing speakers are similar in their STM span for nonlinguistic materials.

Nonlinguistic spatial STM span is typically measured using the Corsi block task, in which the experimenter touches a sequence of identical blocks on a board, and the participant is required to exactly replicate the sequence. The participant’s score typi-cally is the length of the longest sequence correctly

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recalled. Despite deaf signers’ shorter linguistic STM span, they appear to have an increased, or at least equal, nonlinguistic spatial STM span compared with hearing speakers (Alamargot, Lambert, Thebault, & Dansac, 2007; Falkman & Hjelmquist, 2006; Geraci et al., 2008; Logan et al., 1996; Wilson et al., 1997). This increased or equal nonlinguistic spatial STM span is likely due to deaf signers’ experiences with a signed language.

WMC of Deaf Signers versus Hearing Speakers

To date, only two studies have compared deaf signers with hearing speakers in terms of their WMC. Boutla et al. (2004) and Alamargot et al. (2007) found no sig-nificant differences between deaf signers’ signed lan-guage WMC and hearing speakers’ spoken language WMC. In both studies, signed language WMC was measured using a signing span task, in which deaf sign-ers were required to retain sets of signs and then recall each sign by producing a sentence containing the sign. Similarly, spoken language WMC was tested using a speaking span task, in which hearing speakers were instructed to remember sets of words and then recall each word by articulating a sentence containing the word. Boutla et al. specified that their deaf participants were deaf native signers; Alamargot et al. omitted to specify whether their deaf participants were deaf native or nonnative signers. More research is needed to verify these findings.

WMC of Professional Interpreters

Many studies have measured spoken language interpret-ers’ WMC using reading (or listening) span tasks. In a reading (or listening) span task (Daneman & Carpenter, 1980), participants typically read aloud (or listen to) sets of sentences, verify the truthfulness or sensibility of each sentence, and remember the final word of each sentence for later recall. So far, the results are mixed. Some studies found that professional spoken language interpreters significantly outperformed student inter-preters and/or noninterpreters on a reading span task (Christoffels, De Groot, & Kroll, 2006; Padilla, Bajo, Cañas, & Padilla, 1995; Signorelli, 2008; Zhang, 2007). Other studies found that professional spoken language

interpreters performed similarly to student interpret-ers and/or noninterpreters on a listening span task (Köpke & Nespoulous, 2006; Liu, Schallert, & Carroll, 2004; Stavrakaki, Megari, Kosmidis, Apostolidou, & Takou, 2012; Timarová, 2007). Together, these findings suggest that professional spoken language interpreters’ WMC is significantly greater than, or at least equal to, that of the general population.

While many studies have focused on spoken lan-guage interpreters’ WMC, only five studies have measured signed language interpreters’ WMC. Gran Tarabocchia and Kellett Bidoli (2001) reported that one professional Italian Sign Language (LIS)/Italian interpreter obtained similar results on an LIS WM span task as five spoken language interpreting students did on an Italian listening span task. In the LIS WM span task, the signed language interpreter watched sets of LIS sentences and retained sentence-final signs for later recall. More recently, Macnamara, Moore, Kegl, and Conway (2011) found no significant differences between highly skilled and less skilled ASL/English interpreters in their WMC, suggesting that interpret-ers’ WMC may not predict their interpreting skill level. Macnamara et al. measured their participants’ WMC with a (nonlinguistic) symmetry span task, which required the participants to judge whether black-and-white matrix patterns were symmetrical along the ver-tical axis while remembering red-square locations for subsequent recall.

Additionally, Rudner, Fransson, Ingvar, Nyberg, and Rönnberg (2007) used two-back tasks to measure bilingual WMC of Swedish Sign Language (SSL)/Swedish interpreters and bimodal bilinguals. All participants were native users of both SSL and Swedish. In the two-back task, the participants were required to judge whether the currently shown item matched an item presented two steps back. Rudner et al. found no significant differences between all participants’ SSL WMC and their Swedish WMC. However, Rudner et al. treated all participants as one group for statistical analyses and did not compare the interpreters’ SSL WMC with their Swedish WMC. Similarly, van Dijk et al. (2012), in their study mentioned earlier, measured the experienced SLN/Dutch interpreters’ bilingual WMC using three-back tasks. The interpreters comprised hearing




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native signers and hearing nonnative signers. van Dijk et al. found no significant differences between all interpreters’ SLN WMC and their Dutch WMC. Moreover, van Dijk et al. found no significant differences between the hearing native signers’ WMC and the hearing nonnative signers’ WMC.

Furthermore, Wang (2012) required professional Auslan/English interpreters (hearing native sign-ers and hearing nonnative signers) to complete an English listening span task and an Auslan WM span task. She found no significant differences between the hearing native signers and the hearing nonnative signers in their English WMC, and no significant differences between the two groups in their Auslan WMC. In addition, Wang found no significant differ-ences between each group’s English WMC and their Auslan WMC. Wang therefore replicated van Dijk et al.’s findings with different participants and differ-ent WM span tasks. In sum, all studies reviewed in this section reported null effects. However, none of these studies compared professional signed language interpreters with noninterpreters in terms of their WMC, which is a critical gap in the current literature. It also remains unclear whether different WM span tasks used in these various studies measure the same WMC construct.

Native Signers versus Nonnative Signers

Research has found that deaf native signers are bet-ter than deaf nonnative signers in various aspects of signed language processing (see Emmorey, 2002, for a review). Deaf native signers (adults) invariably out-performed deaf nonnative signers (adults) on ASL morphology use (Newport, 1990), ASL sentence shad-owing (Mayberry & Eichen, 1991), and ASL gram-maticality judgment (Emmorey, Bellugi, Friederici, & Horn, 1995). In addition, Napier (2006) noted that a professional Auslan/English interpreter and a deaf signer who were both native signers used mouthing and fingerspelling appropriately and effectively in their English-to-Auslan interpreting and Auslan presenta-tion in academic contexts, respectively. She also found that a professional interpreter and a deaf signer who were both nonnative signers exhibited more English interference and used more marked mouthing and

fingerspelling in their English-to-Auslan interpreting and Auslan presentation in similar academic settings, respectively (e.g., in terms of inclusion of function words). Based upon these findings, Napier suggested that the hearing and deaf nonnative signers might be still thinking in English during their English-to-Auslan interpreting and Auslan presentation, which may have influenced their Auslan output. In sum, late exposure to a signed language appears to have an impact on deaf signers’ signed language proficiency.

Several studies have compared deaf native sign-ers with deaf nonnative signers in terms of their STM span. Wilson et al. (1997) found that deaf native signers (children) significantly outscored deaf nonnative sign-ers (children) on ASL digit span tasks. This finding suggests that late acquisition of a signed language con-siderably affects the development of effective rehearsal strategies in deaf children, consequently affecting their STM span. However, Krakow and Hanson (1985), and Mayberry and Eichen (1991), found that deaf native signers (adults) performed similarly to deaf nonna-tive signers (adults) on ASL digit span tasks. In rela-tion to deaf nonnative signers, Emmorey (2002, p. 221) speculated that “unlike linguistic effects, the cognitive effects of late language exposure may not continue into adulthood.”

To summarize, while a large number of studies have contrasted hearing speakers with deaf signers in terms of their STM span, few studies have compared hearing speakers with deaf signers in terms of their WMC. It is worth noting that many previous studies on deaf signers’ STM span differed in participant profile, STM span test methodology (e.g., test stimuli, and recall order requirement), scoring methods, and statistical analyses. To date, there have been no studies comparing professional signed language interpreters’ WMC with noninterpreters’ WMC. Only a few studies have compared native signers with nonnative signers in terms of their signed language WMC. The aims of this study include exploring the effects of hearing status (hearing, deaf) and age of signed language acquisition (native signer, nonnative signer) on Auslan WMC and comparing deaf native signers with deaf nonnative signers in terms of Auslan WMC. The method and findings of this study are presented in the following sections.




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Method

Participants

To recruit participants, a research flyer was emailed to the Australian Sign Language Interpreters’ Association, the major interpreter employers through-out Australia, Deaf Australia (the national peak organization for Deaf people in Australia) and Deaf community service organizations in major cities across Australia, who then distributed the flyer to profes-sional interpreters and deaf signers in their databases. All NAATI-accredited professional-level Auslan/English interpreters1 and deaf Auslan signers between 18 and 65 years of age were eligible and could self-select to participate in the study. Data were collected in four major cities across Australia: Sydney, Melbourne, Brisbane, and Perth.

A total of 31 NAATI-accredited professional-level Auslan/English interpreters participated. This group comprised 14 hearing native signers and 17 hearing nonnative signers. The hearing native signers acquired Auslan from birth from their signing deaf parents and at the same time acquired English through interaction with the surrounding hearing population. According to participants’ self-reports, the hearing nonnative signers acquired English from birth from their hear-ing parents and started to learn Auslan at or after age 10 through receiving formal education in Auslan and/or associating with deaf signers through work or social networks. The participants’ demographic information is shown in Table 1.

A total of 26 deaf signers participated. This group comprised 6 deaf native signers and 20 deaf nonnative signers. The deaf native signers acquired Auslan from

birth from their signing deaf parents. Despite great efforts, only a small number of deaf native signers could be recruited. This may be reflective of the fact that the population of severely and profoundly deaf Auslan signers is relatively small—approximately 6,500 (Johnston, 2006), of which only a small subset would represent deaf native signers. According to their demographic information, the deaf nonnative signers were born to hearing parents; used spoken English, lip reading, cued speech2, and/or Signed English3 rather than Auslan at home up until age six; and started to learn Auslan at or after age eight by associating with deaf signers in school and/or through social networks4. As a result, the deaf nonnative signers were considered as late learners of Auslan. The deaf nonnative signers were highly variable in their demographic characteristics such as age of hearing loss, age of Auslan acquisition, Auslan proficiency, degree of hearing loss, use of hearing aids or cochlear implants, and educational background. Although these differences in demographic characteristics reflected a real-life profile of deaf nonnative signers in Australia, they may be considered to be confounding variables in the study. Seven deaf nonnative signers reported that they were not born deaf; nevertheless, the exclusion of their data did not change the pattern of results in this study.

Materials

Auslan WM span task. Given the paucity of literature on measuring signed language WMC, executive decisions had to be reached on how to create and administer the Auslan WM span task. The task was adapted from the LIS WM span task in Gran

Table 1 Demographic information of the professional interpreters and deaf signers

Demographic information

Professional interpreters (N = 31) Deaf signers (N = 26)

Hearing native signers (N = 14)

Hearing nonnative signers (N = 17)

Deaf native signers (N = 6)

Deaf nonnative signers (N = 20)

Female/male 11/3 16/1 3/3 15/5Mean age (SD) 40 (14) 40 (9) 34 (12) 40 (11)Mean age of hearing loss (SD) — — 0 (0) 1.1 (2.4)Mean age of acquiring Auslan (SD) 0 (0) 19 (6) 0 (0) 16 (5)Mean years of using Auslan (SD) 40 (14) 21 (11) 34 (12) 24 (12)Participants with a BA or MA degree 6 14 1 8Mean years of professional interpreting

experience (SD) 13 (8) 8 (7) — —




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Tarabocchia and Kellett Bidoli (2001) but modified to include a sentence verification component. The task incorporated concurrent storage and processing and served to measure the Auslan WMC of the professional interpreters and the deaf signers.

The Auslan WM span task instructed participants to watch sets of Auslan sentences on a video, verify the sensibility of each sentence (sign yes if it made sense or no if not), memorize the final sign of each sentence, and at the end of each set reproduce all sentence-final signs in serial order. Participants were not allowed to say any-thing, write anything down, use signed language, or use gesture as memory aids. The task consisted of four sets each of two, three, four, five, six, and seven unrelated Auslan sentences, 108 sentences in total. Each partici-pant watched four sets of two sentences, then four sets of three sentences, until four sets of seven sentences (i.e., in ascending order). Each participant completed the task by watching all 108 sentences. The time for verifying each sentence was 1 s, and the time for recall-ing each sentence-final sign was 4 s. Serial recall was prompted by a question mark at the end of each set.

The second set of three sentences in the Auslan WM span task may serve as an example.

1. Participants saw the Auslan phrase three sen-tences on a computer screen followed by a white screen lasting for half a second.

2. Then they saw the set number 3.2 followed by a white screen lasting for half a second.

3. Then they saw the first sentence point country many people work with animals (Many people who live in rural areas work with animals) fol-lowed by a white screen lasting for 1 s for seman-tic verification (sign yes).

4. Then they saw the second sentence me plane discuss decide go shopping tomorrow (A plane and I decided to go shopping tomorrow) followed by a white screen lasting for 1 s for semantic verification (sign no).

5. Then they saw the third sentence couple recent marry determine save + buy house new (The newly-wed couple are determined to save and buy a new house) followed by a white screen lasting for 1 s for semantic verification (sign yes).

6. And then they saw a question mark staying on the computer screen for 12 s, prompting serial reproduction of the three sentence-final signs animals, tomorrow, and new.

All Auslan test sentences were created by a female deaf near-native signer rather than being created in English and translated into Auslan. This was done in order to ensure that they were idiomatic in Auslan without inter-ference from English. The signer referred to Auslan dic-tionary resources to ensure that standard Auslan signs were used, the full range of available handshapes was represented, and dialectal differences were minimized when the sentences were filmed. Test sentences varied from 6 to 10 Auslan signs and were easy to understand. Although all sentences were grammatically correct, 86 (80%) sentences made sense and 22 (20%) sentences were purposefully nonsensical. The sentence-final signs were simple and commonly used. Given that the Auslan sentences were idiomatically created, the sentence-final signs varied from nouns, verbs to adjectives and were not controlled for articulation length. However, the sentence-final signs were controlled for handshape, orientation, location, and movement, in order to avoid the phonological similarity effect on STM of signs (see Wilson & Emmorey, 1997). All Auslan test sentences were articulated by the deaf near-native signer, filmed using an Ultra HD Flip camera, edited5, and saved as an mp4 video with all the necessary white screens and question marks inserted. The articulation length of each Auslan test sentence varied from 5 to 9 s.

Procedure

Participants were tested individually either at their homes or in a Deaf community service organization in their respective cities. Each participant filled in an informed consent form and a demographic question-naire and then completed the Auslan WM span task. Upon completion of the task, the professional inter-preters engaged in a brief interview, whereas the deaf signers filled in another questionnaire, in order to report their memory strategies and give comments. At the time, no other options were available to col-lect memory strategy data from the deaf signers, due to communication barriers between the experimenter




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and the deaf signers. Task instructions were filmed and shown to the participants by the same deaf near-native signer who had articulated the test sentences. Participants received the task instructions, then prac-ticed with three sets of two sentences and three sets of three sentences, and then proceeded to the real task, which took approximately 24 min to complete. Task materials were presented on a 2.7 GHz Core i7 13.3″ MacBook Pro computer. The participants were filmed during the real task and the interview for later analysis.

Data scoring

As the existing literature on WM span tasks lacks con-sensus on recall order requirements (serial vs. random), recall order acceptance, and scoring methods (see Wang & Napier, 2012, for a review), we had to make executive decisions on how to score the participants’ WMC data. The data-scoring process entailed deciding whether recall of a sentence-final sign was correct and then apply-ing two scoring methods to obtain WMC scores.

Deciding whether recall of a sentence-final sign was correct. Recall of a sentence-final sign was considered correct irrespective of its recalled position/order because the recalled position/order was not always clear. Regarding recalled position/order, when participants used indexing (serially placing the sentence-final signs on their fingers while watching each set of sentences and then referring to their fingers at recall) to memorize the sentence-final signs, the recalled position might be different from the recalled order. Take for instance the set of seven sentence-final signs nine, present, hat, delicious, crash-down, library, and silver. A hearing native signer with seven years of professional interpreting experience first recalled six signs in the following order: nine, present, delicious, crash-down, silver, and library. Then, she referred to her thumb and repeated nine; then she touched her index finger and repeated present; then she referred to her middle finger and recalled hat; she then referred to her ring finger and recalled crash-down. In this example, the participant’s recalled position/order of the signs hat, delicious, silver, and library was unclear. However, given that the participant actually

reproduced all seven sentence-final signs, we decided to give credit to all seven sentence-final signs.

Sometimes a participant recalled variants of a sentence-final sign rather than exactly replicating the sentence-final sign. In such cases, decision-making surrounding whether recall of the sentence-final sign was correct was conducted first in a generous way then in a strict way (for further detail see Wang & Napier, 2012). In the generous way of decision-mak-ing, a sentence-final sign was considered correctly recalled if a participant either exactly replicated the sentence-final sign or produced any variant of the sentence-final sign, for the participant remembered the concept of the sentence-final sign. In the strict way of decision-making, a sentence-final sign was considered accurately recalled only if a participant exactly replicated the sentence-final sign or produced a phonological variant of the sentence-final sign. Since both the generous and strict ways of decision-making yielded the same pattern of results for this study, this article reports only on results arising from the generous way of decision-making. Problematic signs produced by the participants in the Auslan WMC data were checked with four different native signers (three hearing and one deaf), with the major-ity opinion adopted.

Applying two scoring methods. The participants’ Auslan WMC scores were calculated using two scoring methods (for more detail see Wang & Napier, 2012): total items (i.e., the total number of correctly recalled items across all sets, the maximum possible score being 108) and proportion items (i.e., the average proportional recall for each set, the maximum possible score being 1). Because both scoring methods produced the same pattern of results for this study, this article reports only on results arising from the total item measure.

Results

There were no significant differences in Auslan sen-tence verification accuracy among any of the four subgroups: the hearing native signers, the hearing nonnative signers, the deaf native signers, or the deaf nonnative signers. This section thus concentrates on




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results of the participants’ Auslan WMC and their memory strategies.

Auslan WMC

A two-way between-groups analysis of variance was conducted to explore the effects of hearing status (hearing, deaf) and age of signed language acquisi-tion (native signer, nonnative signer) on Auslan WMC. There was a significant main effect for hearing status, F(1, 53) = 5.63, p = .021, partial η2 = .10 (a moder-ate effect size). That is, the hearing signers (M = 70.65, SD = 20.62, collapsing the hearing native and nonna-tive signers) significantly outperformed the deaf sign-ers (M = 55.69, SD = 16.97, collapsing the deaf native and nonnative signers) on the Auslan WM span task. However, there was no significant main effect for age of signed language acquisition, F(1, 53) = .04, p = .85. Namely, the native signers (M = 64.65, SD = 17.98, col-lapsing the hearing and deaf native signers) were simi-lar to the nonnative signers (M = 63.38, SD = 21.70, collapsing the hearing and deaf nonnative signers) in their Auslan WMC. There was no significant interac-tion between hearing status and age of signed language acquisition, F(1, 53) = .98, p = .33. In other words, there was no significant difference in the effect of hear-ing status on Auslan WMC for the native signers and the nonnative signers6.

Figure 1 shows the mean Auslan WMC for the four subgroups: the hearing native signers, the hear-ing nonnative signers, the deaf native signers, and the deaf nonnative signers. We also conducted the follow-ing t-tests to explore simple effects.

1. The hearing nonnative signers (M = 73.65, SD = 21.18) significantly outperformed the deaf nonnative signers (M = 54.65, SD = 18.44) on the Auslan WM span task, t(35) = 2.92, p = .006, η2 = .20 (a large effect size).

2. The hearing native signers (M = 67.00, SD = 20.08) were similar to the deaf native signers (M = 59.17, SD = 11.34) in their Auslan WMC, t(18) = .89, p = .39.

3. The hearing native signers (M = 67.00, SD = 20.08) performed similarly to the hearing nonnative signers (M = 73.65, SD = 21.18) on the Auslan WM span task, t(29) = −.89, p = .38.

This result is reported in Wang (2012) but pre-sented here for completeness.

4. The deaf native signers (M = 59.17, SD = 11.34) were similar to the deaf nonnative signers (M = 54.65, SD = 18.44) in their Auslan WMC, t(24) = .56, p = .58.

Participants’ Memory Strategies in the Auslan WM Span Task

To examine the strategies implemented in the Auslan WM span task, participants were asked how they memorized the sentence-final signs. The professional interpreters were asked this question in the posttask interview. In the questionnaire used with the deaf sign-ers, this question was followed by four choices: rehearse the English words for the sentence-final signs; visualize the sentence-final signs in your mind; make a story from the sentence-final signs; or employ other strategies. In addition to these strategies, it was observed that partici-pants used mouthing (rehearsing the English words for the sentence-final signs on their lips during each set) and indexing during the Auslan WM span task.

Table 2 shows the percentage of professional inter-preters who used each memory strategy in the Auslan WM span task. Due to time constraints, eight profes-sional interpreters were not interviewed; as a result, Table 2 may not provide a full picture of all the pos-sible memory strategies. The professional interpret-ers who were interviewed (N = 23) typically reported

010

Hearing Deaf

2030405060708090

100110

Ausl

an W

MC

Native signers Non-native signers

Figure 1 Mean Auslan working memory capacity (WMC) for the four subgroups: the hearing native signers, the hearing nonnative signers, the deaf native signers, and the deaf nonnative signers. Error bars denote one standard deviation (SD) around the mean (M).




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rehearsing the English words for the sentence-final signs and using visual strategies (e.g., visualizing the object, the sentence-final sign, or the written English word of the sentence-final sign; picturing the whole sentence; or spatial ordering). Table 2 shows that the hearing nonnative signers, compared with the hearing native signers, relied more heavily on English subvocal rehearsal but used less indexing. Furthermore, three hearing nonnative signers reported that they found Auslan phonological coding (e.g., associating different signs that share a similar handshape) and other visual strategies (e.g., visualizing different objects interacting with each other in a particular way) ineffective and/or visually confusing, and thus switched to English sub-vocal rehearsal as their main memory strategy.

Table 3 shows the percentage of deaf signers who used each memory strategy in the Auslan WM span task. In contrast to the deaf native signers, the deaf nonnative signers relied more heavily on English subvocal rehearsal and used more mouthing but used less indexing to memorize the sentence-final signs. This pattern parallels that of the professional interpreters. Recall errors produced by some deaf signers (as well as some professional interpreters), which involved a different sign that was phonologically similar to the sentence-final sign7, suggested that the deaf signers (as well as the professional interpreters) used Auslan phonological coding to retain the sentence-final sign. The memory strategy of making a story from the sentence-final signs indicated that the deaf signers used a semantic code and an episodic code to memorize the sentence-final signs. Observations of participants’ mouthing further revealed that many professional interpreters and deaf signers activated the English translations of the to-be-remembered signs even

though the task instructions did not explicitly require the use of English. Integrating phonological surface representations of lexical items with their underlying semantic representations shows the involvement of the episodic buffer in language processing (Baddeley, 2002, 2007; Rudner et al., 2007; Rudner & Rönnberg, 2008b). In this study, the memory strategy of binding phonological features of Auslan signs to their underlying semantic representations and to their English equivalents indicated that the episodic buffer was involved in the Auslan WM span task.

Discussion

The primary goal of this study was to examine the effects of hearing status (hearing, deaf) and age of signed language acquisition (native signer, nonnative signer) on Auslan WMC. The results reveal that the hearing signers have a significantly larger Auslan WMC than the deaf signers. Given that the hearing signers in this study are professional signed language interpreters, this finding parallels some prior evidence that profes-sional spoken language interpreters have a remarkably larger spoken language WMC than noninterpreters (Christoffels et al., 2006; Padilla et al., 1995; Signorelli, 2008; Zhang, 2007). This finding may be explained by a number of factors. First, the hearing signers, due to their hearing ability, are likely to use English subvo-cal rehearsal more frequently and effectively than the deaf signers in the Auslan WM span task. As speech-based subvocal rehearsal is particularly facilitative for serial recall of linguistic information (Baddeley, 2007;

Table 2 Percentage of professional interpreters (who were interviewed, N = 23) for each memory strategy in the Auslan working memory span task

Memory strategiesHearing native signers (N = 10)

Hearing nonnative signers (N = 13)

English subvocal rehearsal (%)

40 77

Visual strategies (%) 40 54Mouthing (%) 60 62Indexing (%) 90 62

Table 3 Percentage of deaf signers for each memory strategy in the Auslan working memory span task

Memory strategiesDeaf native signers (N = 6)

Deaf nonnative signers (N = 20)

English subvocal rehearsal (%)

50 65

Visualize the sentence-final signs (%)

50 55

Make a story from the sentence-final signs (%)

17 40

Mouthing (%) 50 55Indexing (%) 83 60




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Emmorey, 2002; Hall & Bavelier, 2010), it is not sur-prising that the hearing signers substantially outscored the deaf signers on the Auslan WM span task. Second, the hearing signers may perform better than the deaf signers on allocating attention between concurrent storage and processing during the Auslan WM span task. Five professional interpreters (two hearing native signers and three hearing nonnative signers) reported that they had devoted more attention to the storage component than to the processing component of the Auslan WM span task. In contrast, a number of deaf signers commented that concurrent storage and pro-cessing was the major difficulty for them during the task. The professional interpreters exercise their WM on a daily basis in their professional interpreting prac-tice; whereas the deaf signers rarely need to do this on a consistent basis. Nevertheless, it is unclear from this study if interpreting experience itself accounts for the professional interpreters’ superior Auslan WMC, because interpreting experience is completely con-founded with hearing status in the current research design. Possible alternative factors include participant self-selection, individual differences, verbal/nonverbal intelligence, differences in top–down memory strate-gies, and differences in meta-awareness of effective strategies for rote-memory tasks. Further research is necessary to identify whether the professional inter-preters’ superior Auslan WMC is due to their hear-ing status, interpreting experience, or other factors. For instance, a future study may compare the profes-sional interpreters with English monolinguals in terms of their English WMC and compare the professional interpreters with deaf signers in terms of their Auslan WMC. However, due to time limitations, this was not possible for this study.

Another interesting finding was that the hearing nonnative signers scored significantly higher than the deaf nonnative signers in terms of their Auslan WMC. The majority of the hearing and deaf nonnative signers self-reported that they rehearsed the English translations of the to-be-remembered signs. The hearing nonnative signers tended to be the best performers of the Auslan WM span task, probably because English subvocal rehearsal of signs is particularly effective for serial recall of signs (Hall & Bavelier, 2011). It was interesting to note that the hearing nonnative signers

predominantly resorted to their native and dominant language (i.e., English) to memorize Auslan signs. Translating the to-be-remembered signs into English words would be automatic and spontaneous in the hearing nonnative signers but attention-consuming in the deaf nonnative signers, due to the fact that the hearing nonnative signers were professionally qualified interpreters who were used to searching for meaning and equivalents between English and Auslan.

This finding may also be because English subvo-cal rehearsal is far more frequent and effective in the hearing nonnative signers than in the deaf nonnative signers. According to our observations of participants’ mouthing during the Auslan WM span task, the hear-ing nonnative signers’ English subvocal rehearsal was faster and more frequent and involved adding new words to the constant repetition of a string of previ-ous words. In contrast, the deaf nonnative signers’ English subvocal rehearsal was slower and less frequent and involved repeating only a single word or several words. For example, for six sentence-final signs in the set sleep, third, problem, tie, sister, and society, a hearing nonnative signer rehearsed “sleep” when she saw the sign sleep; rehearsed “sleep, third, sleep, third” when she saw the sign third; rehearsed “sleep, third, problem, sleep, third, problem, sleep, third, problem” when she saw the sign problem; rehearsed “tie, sleep, third, problem, tie, sleep, third, problem, tie” when she saw the sign tie; and rehearsed “sleep, third, problem, tie, sister, sleep, third, problem” when she saw the sign sister; and managed to recall all the six sentence-final signs. In stark contrast, a deaf non-native signer rehearsed “sleep” when she saw the sign sleep; rehearsed “third” when she saw the sign third; rehearsed “problem” when she saw the sign problem; rehearsed “tie” when she saw the sign tie; rehearsed “sister” when she saw the sign sister; rehearsed “soci-ety” when she saw the sign society; and only managed to recall sleep and tie.

Additionally, we found that the hearing native sign-ers and the deaf native signers were similar in their Auslan WMC. This finding may relate to the fact that Auslan is the first and native language for these par-ticipants. The Auslan test stimuli may have encouraged the hearing native signers and the deaf native signers to think in Auslan, and to use sign-based phonological




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coding to memorize the to-be-remembered signs. Furthermore, a high percentage of the hearing native signers and the deaf native signers used indexing to remember the signs or the order of the signs, indicating that they were coping with the Auslan WM span task in a ‘deaf ’ way. Similar memory strategies used by the hearing native signers and the deaf native signers may lead to their similar performance on the Auslan WM span task. Our finding echoes the prior result that hear-ing adults and deaf adults are similar in their native lan-guage WMC (Boutla et al., 2004). The findings from this study and Boutla et al.’s study may suggest that hearing adults and deaf adults are comparable in their WMC, provided that they have been exposed to a natu-ral language since birth. Further investigation in this area is warranted.

Furthermore, when the participants were grouped into native signers and nonnative signers, we found no significant differences between the two groups in Auslan WMC. Also, there was no significant interac-tion between hearing status and age of signed language acquisition. We also found no significant differences between the hearing native signers and the hearing nonnative signers in their Auslan WMC. This finding is consistent with the result obtained by van Dijk et al. (2012). This finding extends Hall and Bavelier’s (2011) result of no significant differences between hearing native signers and hearing nonnative signers in their STM span to also include WMC. This finding may be attributable to the major similarities between the hear-ing native signers and the hearing nonnative signers in this study: both subgroups were professionally certified interpreters with considerable interpreting experience; both subgroups were hearing people who could effec-tively implement English subvocal rehearsal to retain the to-be-remembered signs; and both subgroups were able to resort to their first and native language to mem-orize the to-be-remembered signs. This finding may also be due to other possible factors such as the small sample of professional interpreters in this study, par-ticipant self-selection, and individual differences.

The second goal of this study was to compare deaf native signers with deaf nonnative signers in terms of their Auslan WMC. We found no significant differences between the deaf native signers and the deaf nonnative signers in their Auslan WMC, suggesting that age of

signed language acquisition has no significant impact on deaf adult signers’ WMC. A number of factors may explain this finding. The deaf native signers in this study, compared with the deaf nonnative signers, may have used Auslan phonological coding more frequently and effectively because they acquired Auslan from infancy. Nevertheless, sign-based phonological coding might not be very effective for serial retention of linguistic information (Logan et al., 1996). The deaf nonnative signers in this study may largely have relied on English phonological coding to retain the to-be-remembered signs, possibly due to the following reasons: they used spoken English, cued speech, lip reading, and/or Signed English rather than Auslan at home up until age six and were relatively late learners of Auslan; some of the deaf nonnative signers wore hearing aids or cochlear implants and may have used their residual hearing to adopt speech-based phonological coding; and some of the deaf nonnative signers had completed a university degree and thus achieved reasonably good English literacy, which may have influenced their use of English. Previous studies have shown that different memory strategies employed by deaf people often lead to quantitatively similar performance on memory tasks (Marschark, 1993; Marschark & Mayer, 1998).

Given the probable advantage of speech-based encoding for serial recall of signs (Hall & Bavelier, 2011), it may seem surprising that the deaf nonnative signers did not outperform the deaf native signers on the Auslan WM span task. However, as evident in the aforementioned example of a deaf nonnative signer’s mouthing during the Auslan WM span task, the deaf nonnative signers’ English subvocal rehearsal of signs seemed not to be effective. Given that deaf nonnative signers are generally less proficient in a signed lan-guage than deaf native signers (Emmorey et al., 1995; Mayberry & Eichen, 1991; Napier, 2006; Newport, 1990), the deaf nonnative signers in this study may have had to devote more attention to the Auslan sen-tence verification component and less to the storage component of the Auslan WM span task. However, this finding may also have resulted from other possible factors such as the small number of deaf native sign-ers in the study, individual differences in demographic characteristics, and individual differences in general fluid intelligence. Even so, this finding is consistent




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with prior evidence that deaf native signers (adults) are similar to deaf nonnative signers (adults) in their STM span (e.g., Krakow & Hanson 1985; Mayberry & Eichen 1991). This finding also supports Emmorey’s (2002) claim that delayed exposure to a signed language does not appear to affect the cognitive abilities of deaf adults.

Analysis of the qualitative data revealed that both the professional interpreters and the deaf signers implemented English subvocal rehearsal, visual strat-egies (including sign-based phonological coding), semantic strategies, and indexing to retain the to-be-remembered signs. The professional interpreters and deaf signers’ use of sign-based phonological coding provides further evidence that hearing signers and deaf signers may have a sign-based phonological loop (Wilson & Emmorey, 1997, 1998, 2003). However, our results suggest that deaf signers’ WM for signs not only utilizes a sign-based phonological code but also involves a spoken language translation, a semantic code, spatial ordering, and/or indexing. This finding not only lends some evidence to Baddeley’s (2002, 2007) multicompo-nent model of WM but also indicates the involvement of the episodic buffer in the Auslan WM span task. In addition, this finding supports the multiple-coding hypothesis (Hall & Bavelier, 2010), which proposes that memory traces of a stimulus are strongest when people recode the stimuli into as many mental codes as pos-sible and integrate the codes.

The limitations of this study may lead some readers to question the validity of the research. However, although the results of this study do not provide conclusive evidence, they at least demonstrate the need for more research into the WMC of hearing signers and deaf signers. The small and varied sample in this study may limit the statistical power and generalizability of the results. Future studies should include a larger sample of deaf native signers, and should recruit deaf nonnative signers who are relatively homogeneous in demographic characteristics. Second, the Auslan WM span task could be improved methodologically. In order to avoid potential confounding variables (e.g., strategy use) when measuring individual differences in signed language WMC, future studies should require participants to remember isolated signs (nouns in particular) that follow the test sentences; control the

proportion of semantically correct test sentences as 50%; administer different set sizes in a random order rather than in the ascending order; and require and score serial recall. A test format of five sets each of two, three, four, five and six sentences would be adequate for most people. In order to minimize sign variation in recalled signs, each to-be-remembered sign should be cautiously selected as a standardized, established, national sign with only one sign choice for one concept. Articulation length, part of speech, and phonological similarity of the to-be-remembered signs and their spoken language translation equivalents are also worth considering. In addition, we recommend that future studies use the same research tool (e.g., questionnaires) to collect memory strategy data from hearing signers and deaf signers.

Conclusion

This study explored the effects of hearing status (hear-ing, deaf) and age of signed language acquisition (native signer, nonnative signer) on Auslan WMC of profes-sional Auslan/English interpreters and deaf Auslan signers. The results reveal that the hearing signers (i.e., the professional interpreters) have a remarkably larger Auslan WMC than the deaf signers, even though both groups use multiple codes to memorize Auslan signs. Also, the results showed no significant differences between the native signers and the nonnative signers in their Auslan WMC. In addition, there was no sig-nificant interaction between hearing status and age of signed language acquisition. Among the native signers, hearing status did not significantly influence Auslan WMC; that is, the hearing native signers and the deaf native signers were similar in their Auslan WMC. However, among the nonnative signers, the hearing nonnative signers scored significantly higher than the deaf nonnative signers in terms of their Auslan WMC. Finally, there was no significant difference between the deaf native signers and the deaf nonnative signers in their Auslan WMC, indicating that age of signed lan-guage acquisition has no significant impact on deaf adult signers’ WMC. It appears that delayed exposure to a signed language may affect deaf children’s WMC, but the deficits may be reduced or eventually overcome during adolescence and adulthood.




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The results of this study have implications for WM theories. The evidence that signed language interpret-ers and deaf signers use both English subvocal rehearsal and sign-based phonological coding to remember signs demonstrates a need to integrate Baddeley’s (2002, 2007) multicomponent WM model with Wilson and Emmorey’s (1997, 1998, 2003) sign-based phonologi-cal loop theory. This evidence also suggests that deaf signers (including profoundly deaf native signers) may think both in English and Auslan even when the test stimuli are Auslan.

Hearing and deaf signers’ WMC is still an underex-plored topic that merits further investigation. Further research is needed to compare professional signed language interpreters, signed language interpreting students, bimodal bilinguals, hearing monolinguals, deaf relay interpreters8, and deaf signers (noninter-preters) on a variety of WMC measures, in order to examine the influence of hearing status and interpret-ing experience on WMC. To explore the impact of interpreter education on WMC, a longitudinal study could be undertaken to monitor signed language inter-preting students’ WMC at regular intervals throughout the interpreter education program. To investigate the effects of different memory strategies on deaf sign-ers’ memory performance, researchers may explicitly instruct the deaf signers to adopt particular memory strategies and then compare their memory scores. In addition, it would be of interest to investigate possible correlations between deaf children’s WMC and their reading skills, academic attainment, and general fluid intelligence, so as to inform deaf education principles.

Author Note

Jihong Wang is currently working toward a PhD in Linguistics in the Department of Linguistics, Macquarie University. Jemina Napier is an Associate Professor in the Department of Linguistics, Macquarie University. Correspondence concerning this article should be addressed to Jihong Wang, Department of Linguistics, Macquarie University, NSW 2109, Australia (mobile: +61 430437361; e-mail: [email protected]).

This paper presents selected findings from Jihong Wang’s PhD research project under the primary supervision of Jemina Napier. The authors thank all professional Auslan/English inter-preters and deaf signers for their participation in this research. We thank Trevor Johnston, Andy Carmichael, Della Goswell and Linda Warby for sharing with us their views on Auslan sign

variation. We would also like to thank Lindsay Ferrara, Gabrielle Hodge, and two anonymous reviewers for their helpful com-ments on earlier drafts of this article. We are also grateful to Peter Petocz for his constructive statistical consultancy.

Notes

1. In Australia, all interpreters and translators are accredited through the National Accreditation Authority for Translators and Interpreters (NAATI). Only two accreditation levels are available for Auslan/English interpreters—Paraprofessional Interpreter and Professional Interpreter. For a full description of accredi-tation levels offered by NAATI, see http://www.naati.com.au/PDF/Misc/Outliness%20of%20NAATI%20Credentials.pdf 2. Cued speech is a manual means of disambiguating spoken language by using handshapes and placements in combination with mouth movements and speech. For more information, see http://www.cuedspeechmaine.org/whatis.html 3. Signed English is a manual means of representing English by combining signs and fingerspelling in English word order. 4. One deaf nonnative signer had a deaf mother and deaf siblings, used cued speech at home before age six, and started to learn Auslan at age 10 from signing deaf friends. 5. Each sentence was edited in a way that it began when the signer lifted her hands into the air and ended when she put her hands in her lap. 6. µHearing, Native signers − µDeaf, Native signers = µHearing, Nonnative signers − µDeaf, Nonnative signers. In this equation, µ represents mean Auslan WMC, and = means no significant difference. 7. For example, a hearing nonnative signer (with 10 years of interpreting experience) recalled lucky for the sentence-final sign delicious. The two signs have the same handshape, orienta-tion, and movement; and they only differ in location—delicious touches the mouth, while lucky touches the nose. 8. A deaf relay interpreter typically works with a hearing interpreter, interpreting for a foreign signed language user, an International Sign user, a deafblind person, or a deaf person with limited language skills.

Funding

The research described in this article was supported by Research Enhancement Fund HDR in the Department of Linguistics, Macquarie University.

Conflicts of Interest

No conflicts of interest were reported.

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