,77 Use of the NAL-AB Wordlists as a South African English Speech Discrimination Test Wayne J. Wilson, Beverley Jones and Peter Fridjhon Department of Speech Pathology and Audiology, University of the Witwatersrand Department of Statistics and Actuarial Science, University of the Witwatersrand ABSTRACT South Africa still lacks a South African English specific speech discrimination test. As an alternative, this study investigated the use of the Australian English, National Acoustic Laboratories Arthur Boothroyd (N AL-AB) wordlists to assess the speech discrimination of South African English speakers. Thirty South African English speakers were tested at 0, 5, 10,20 and 25 dBHL (audiometer dial reading) and their performance-intensity functions were compared qualitatively to the NAL-AB wordlist normative data. Results showed three general patterns; similar performance for both groups; poorer performance by the South African English speakers at the low to mid presentation intensities only; and poorer performance by the South African English speakers across most presentation intensities. Use of the NAL-AB wordlists at threshold levels or for site of lesion assessment was therefore concluded to be unwise. Use of these wordlists at supra-threshold levels, however, would provide a valid and reliable option for the speech discrimination assessment of South African English speakers. OPSOMMING Daar bestaan tans nie 'n Engelse spraakdiskriminasie-toets spesifiek vir die Suid-Afrikaanse konteks nie. Hierdie studie was 'n ondersoek na die bruikbaarkeid van die "National Acoustic Laboratories Arthur Boothroyd (NAL-AB}"-woordelyste, wat op Engelssprekende Australianers toegepas word, om die spraakdiskriminasie van Engelssprekende Suid-Afrikaners te toets. Dertig proefpersone is by 0, 5, 10, 20, en 25 dBHL (oudiometerlesing) getoets, en hulle diskriminasie-intensiteitsfunksies is kwalitatief met die normatiewe data van die NAL-AB vergelyk. Daar is drie algemene patrone gevind:geen verskil tussen die twee groepe nie; swakker diskriminasie deur die Suid-Afrikaanse groep by slegs die lae en middel-intensiteite ; en swakker diskriminasie deur die Suid-Atrikaanse Engelssprekendes by die meeste intensiteite. Die NAL-AB-woordelyste is egter geskik om die spraakdiskriminasie Jan Engelssprekende Suid-Afrikaners bo gehoordrempels te toets. . KEYWORDS: Speech discrilination, phonemic scoring, NAL-AB wordlists, Australian English, South African English. I South Africa still lacks al pre-recorded speech discri- mination test specific to Smith African English. With no less than 11 current, official languages, and an unknown number of dialectal variatioris, the development of such a test that is both language and cUlturally appropriate is a formidable task. Of further hindrance is the need for community based definitions of "normal" language and communication (Pakendorf & Alant, 1997), and for ethnographically based research that defines current "South African English" language and culture (Taylor, 1986). Solving these prerequisite problems is proving to be both resource and time consuming (as forewarned by Jordaan, 1989) and the development of original tests remains, for the moment, a developing area. In the absence of the full development of South African English speech discrimination test, South African audiologists have traditionally used the United States of America's Central Institute for the Deaf (C.LD.)W-22 Wordlists, presented using monitored live voice. The use of non-South African speech and speech related tests, both in their orjginal form and in modified forms, has occurred in South Africa for many years with varying degrees of success. Examples include (amongst others); the WI PI and NU-CHIPS speech discrimination tests (Mehl, 1992), the Staggered Spondaic Word test (Collie, 1991; Stevens, 1991; Corke, 1993; Modi, 1995), the Paediatric Speech Intel- ligibility test (Ewen, 1993), the Willeford Battery of Central Auditory Function (Kastner, 1994; Modi, 1995), and the Peabody Picture Vocabulary Test-Revised (Alant & Beukes, 1986; Labuschagne 1990; Koekemoer, 1994; Pakendorf & Alant, 1997). Whilst the reliability and validity of using these tests on South African speakers has been formally assessed, the use of the C.LD. W-22 on South African English speakers appears to be due mainly to its high and well-documented acceptance in the U.S.A only, and not because of any published data validating its use on the South African population. The use of the C.LD. W-22 in South Africa introduces many reliability and validity problems. Firstly, there is the effect of familiarity and context (or expectation). Familiar words (Ostergard, 1983) and phonemes (Lehiste & Peterson, 1959) can be identified up to 15 dB lower than Die Suid-Afrikaanse Tydskrifvir Kommunikasieafwykings, Vol. 45, 1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) 78 those that are unfamiliar (Edgerton & Danhauer, 1979). Secondly, an ideal speech tests should contain an equal phonetic composition representative of everyday speech in the test population (Egan, 1948). In applying the C.LD. W-22 to the South African population, any equal phonetic representation is lost. Tobias (1964) and Campbell (1965) questioned the need for equal phonetic representation, however, by claiming there was overwhelming clinical and experimental evidence that this an interesting, but unnecessary component in speech audiometry testing. Even today, experimental evidence is lacking and the issue remains unresolved (Mendel & Danhauer, 1997)]. Finally, a valid speech discrimination test should contain an equal range and average level of difficulty within and between wordlists. Although this ideal is rarely achieved in reality (Ross & Huntington, 1962), large variations will affect test reliability and sensitivity. These factors all strongly influence, and possibly invalidate, the use of the C.LD. W-22 with its American English normative data on the South Mrican English speaking population. In response to the problems faced by the C.LD. W-22, many South Mrican audiologists make use of monitored live voice (MLV) presentation. Whilst MLV provides a partial solution to speakerilistener accent mismatch, it does not reduce the dialectal differences inherent in the test materials themselves. Added to this is MLV's well- recognised poor test-retest reliability (Carhart, 1965; Brandy, 1966; Kreul, Bell & Nixon, 1969; Northern & Hattler, 1974), and the problem of comparing MLV test results to standardisation information obtained using recorded versions of the stimuli (Mendel & Danhauer, 1997). Considering the problems already faced in using non-South African English speech material, the signifi- cantly greater variability ofMLV could effectively negate any advantages it may offer in overcoming accent differences. If MLV is to be avoided (an opinion not held by all clinicians), this returns the South African audiologist to the option of using the C.LD. W-22 in its pre-recorded form on cassette tape or compact disc. In addition to the previously mentioned problems this introduces, closer inspection of the C.LD. W-22 reveals that it may not be the best option for the South Mrican English speaker in the first place. The C.LD. W-22 was designed as an improvement on one of the first pre-recorded speech tests, the Psycho- acoustic Laboratories phonetically-balanced 50-word lists (PAL PB-50). It improved phonetic balance (Lehiste & Peterson, 1959), equality of difficulty between lists (Brewer & Resnick, 1983) and degree of familiarity (Brewer & Resnick, 1983; Hirsch et aI., 1952). The test consists of 4 lists of 50 monosyllabic words with no repetitions. The words were chosen to be familiar to North American English speakers, and the phonetic composition of each list aims to reflect that of English as a whole (still based, however, on North American English). Each word is preceded by a carrier phrase and each list may be .' presented with one of six different word orders. In its recorded form, it is spoken by an adult male with "general North American" accented English and all its normative values are based on North American English speakers (Hirsch et aI., 1952). Despite the improvements shown by the C.LD. W-22, it still has several faults that will only be worsened when applying the test to the South Mrican English speaking Wayne J. Wilson, Beverley Jones and Peter Fridjhon population. Brewer and Resnick (1983) and Ostergard (1983) question the C.LD. W-22's ability to discriminate effectively among the performance of the hearing impaired, claiming that it is too easy. Ross and Huntington (1962) and Studebaker and Sherbecoe (1991) disclaim equality of difficulty between lists. Mendel and Danhauer (1997) have also claimed that the validity and reliability of the test for certain conditions under which it is used, such as in background noise, are poorly documented. Finally, users recognised almost immediately the benefits of reducing the test-time (Edgerton & Danhauer, 1979) by adminis- tering 25 word half-lists (Martin & Forbis, 1978). However, these shorter lists are prone to higher variability and therefore poorer reliability and are no longer phonetically balanced (Ostergard, 1983). Even considering Cakiroglu and Danhauer's (1992) claim that listener's and talker's linguistic background has statistical, but not clinical, effects on the performance of non-native English-speaking subjects on the C.LD. W-22 (although they do warn that listener's having less experience with English may not perform as well as native-English speakers), these identified problems warrant a search for a better speech discrimination test for the South Mrican English speaker. An alternative which claims to combat many of the problems encountered by whole word tests, such as the C.LD. W-22, is the phonemically scored speech test (Edgerton & Danhauer, 1979). Lehiste and Peterson (1959) argued that as the speech signal is not acoustically invariant, it is impossible to achieve phonetic balance in a speech test. Therefore intelligibility (discrimination) measures should use materials that are phonemically balanced [although again, the need for phonemic balancing in the first place has been queried (Mendel & Danhauer, 1997)]. Phonemic scoring offers advantages of general and specific significance to a South African English speaking population. Generally, factors such as increased reliability, abbreviated test lists, and decreased test time (Edgerton & Danhauer, 1979) are all beneficial. Specifically, factors such as a decrease in the effect ofthe listener's familiarity with the vocabulary used, and the controversial claim that phoneme scoring involves less extrinsic redundan'cy and therefore eliminates the effects of linguisti~ bias (Lyregaard, 1987; contested by Keith, Katbamna, Tawfik & Smolak, 1987), suggest that use of normative '~alues supplied with a phonemically scored wordlist could ~rovide greater test reliability and validity when used on !South Mrican English speakers. \ Following the success of the first phonemically scored wordlists developed in the U.S.A. by Lehiste and Peterson in 1959 (the consonant-nucleus-consonant or CNCilists), and Tillman, Cahart and Wilber in 1963 (the Northwestern University Auditory Tests No.4 and No.6), Arthur Boothroyd of the United Kingdom developed the phone- mically scored Arthur Boothroyd (AB) wordlists (Booth- royd, 1968). Boothroyd's test contains 15 isophonemic lists, each containing 10 words with 30 scorable phonemes. Each list contains the same 20 consonants and 10 vowels, in varying combinations (Der~ody' & Mackie"; 1987). The phonemes chpsen were those found to be most frequent in Boothroyd's vocabulary, and the only'limitations placed on the original word lists were that neither first names nor obscenities would be included (Boothroyd, 1968). The AB wordlists received criticism, however, with suggestions that Boothroyd's Northern English accent / The South African Journal of Communication Disorders, Vol. 45, 1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) Use of the NAL-AB Wordlists as a South African English Speech Discrimination Test 79 impacted on the design of the test's phoneme content, and that the lists did not comprise random samples of phonemes. Despite Boothroyd's reply that the phonemes are altered by changing their word position, and therefore the phoneme arrangements are essentially random (which would appear to undermine his claim of equality of phonetic representation), the AB wordlists were recorded on at least 2 occasions in the United Kingdom using different U.K. accents (Evans, 1987). The success of the phonemically scored AB lists in the U.K.led to their use in Australia by the National Acoustic Laboratories (NAL) (Dermody & Mackie, 1987). NAL produced a revised version specifically for Australian use, with rearranged word orders and several new words to replace those considered to have low familiarity for Australian English speakers (Travers, 1990). According to Bench (1987), Australian English is based on that of the United Kingdom, but includes North American influences and some uniquely Australian expressions, while some words common to both dialects may carry different meanings. The NAL-AB wordlists (appendix one) quickly became the most commonly used speech discri- mination test in Australia (Bench, 1987), resulting mainly from advantages such as short administration time, and the availability of a high number oflists allowing multiple testing to occur in the one session without learning effects or fatigue (Markides, 1987; Mendel & Danhauer, 1997). In view of the success of the pre-recordedAB wordlists in the U.K. and Australia, the possibility that they could offer significant advantages over the present MLV presentation of the C.LD. W-22 wordlists in South Mrica becomes apparent. The problem oflinguistic bias remains, however, and despite claims that phonemic scoring decreases the effect of linguistic bias (Lyregaard, 1987; contested by Keith, Katbamna, Tawfik & Smolak, 1987), and can be used even on clients with limited familiarity with English (Evans, 1987), it is vital to consider the validity of using this test in a multilingual population such as South Mrica's. : AIMS The aims of this study were as follows: I 1) To determine if first language South Mrican English speakers performed differently to first language, Aus- tralian English speakers, bn the pre-recorded NAL-AB wordlists. I /' 2) To determine if the first ten (of fifteen) pre-recorded NAL-AB wordlists were of equal difficulty for first-lan- guage, South African English speakers. 3) To investigate the feasibility of using the pre-recorded NAL-AB wordlists, with the' NAL Australian English normative data, to assess the speech discrimination abilities of first-language South Mrican English speak- ers in South Africa. METHODOLOGY Exact replication of the NAL-AB wordlist normative study proved to be difficult. The normative data on the performance of Australian English speakers on the pre- recorded NAL-AB wordlists is documented in a clinical manual entitled "AB Word Lists: NAL Protocols" prepared by Anne Travers, NAL, Victoria, August, 1990. This document is supplied with theNAL-AB Word List compact disk and outlines graphically all normative data for the 15 wordlists separately, and as a total average, and contains full recommended procedures the test's clinical use. On close inspection, however, the document provides little detail as to the exact procedures used to obtain the normative values. Details of the NAL-AB wordlist study were not published in the literature and the original data has since been removed from NAL archives. The only fact that is clearly stated in the Travers document is that the data was obtained using 120 normally hearing subjects. With this limited information in mind, the following methodology was used. SUBJECTS Subject selection criteria Subjects were selected using a convenience sampling technique according to the following criteria: (i) Subjects should be adults between 17 and 40 years. This controlled for the well-recognised effects of paediatric and geriatric age ranges on performance on speech discrimination tasks (Hall, 1983). (ii) Subjects should be female. This criterion was included for ease of subject selection, as it was deemed unlikely that a sample balanced for gender could be easily obtained. (iii) Subjects should be first-language speakers of South African English. (iv) Subjects should be resident in Gauteng, South Africa as according to Fuller (1987), subjects for research in the area of speech audiometry should be native to the local area. (v) As determined by a pretest audiogram, the test ear should have hearing thresholds no greater than 5dBHL at 250, 500, 1000, 2000, 4000 and 8000 Hz. (v) As determined by self-report on a pretest questionnaire, subjects should have no significant history, past or present, of: hearing impairment; speech or language impairment; tinnitus; ear infections; noise exposure; speech/articulation disorders; the presence of any disorders of language or; family history of hearing problems. (vi) Subjects should have no knowledge or experience with the NAL-AB wordlists specifically. (vii) Subjects should have little or no knowledge or experience of Australian English. Subject description An initial sample of 32 female, first language South African English speaking subjects, all resident in the Gauteng region was collected. Two subjects were excluded when pure tone screening revealed unacceptable hearing thresholds leaving a final 30 subjects ranging in age from 17.5 years to 26.0 years, with a mean age of20.5 years, a standard deviation of 1.8 years, and a median age of21.0 years. Education levels included two subjects with secondary level, and 28 with, or receiving, tertiary level education. 26 ofthe 28 tertiary level subjects were studying in the field of speech pathology and audiology. On the basis of selecting the best hearing ear as the test ear, 12 right and 18 left ears were tested. TEST ENVIRONMENT, EQUIPMENT AND RECORDED MATERIAL Testing took place in a two-room sound treated booth at the University of the Witwatersrand Hearing Clinic in Die Suid-Afrikaanse Tydskrifuir Kommunikasieafwykings, Vol. 45, 1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) 80 Johannesburg, Gauteng, SouthMrica. The booth included a one-way mirror to allow the tester to observe the subjects during testing. The NAL-AB wordlists were presented via a Sanyo compact disc player CDP-41 coupled with a Grayson-Stadler GSI16 audiometer. Presentation was by means ofTDH-50 headphones with MXAR41 cushions. The NAL Speech Recognition Materials (Disc 1) compact disc with intensity levels equated using an A-weighted Long Term Equivalent Level (Leq) procedure provided the speech stimuli. The NAL-AB Wordlist CD provides 15 pre-recordedAB wordlists (appendix one) arranged to be as representative as possible of 'typical' Australian English (Travers, 1990). Lists are spoken by an adult male Australian general English speaker. Each list contains the same 20 consonants and 10 vowels, arranged into various combinations of 10 CVC monosyllables per list. The lists are ordered according to their reliability as measured on the Australian population (Dermody, cited in Travers, 1990). The order reflects a pairing of those lists with the most similar performance-intensity functions. The last three of the 15 lists demonstrate the most widely variant functions and NAL recommends that these be used at the top end of the PI function only. Each of the word lists is preceded by a short warning pip, the inter-stimulus interval is 4 seconds which serves as the subject response period (there is no carrier phrase), and each list is recorded on a separate track. MEASUREMENT PROCEDURES AND DATA COLLECTION On passing the initial hearing and case history questionnaire screening, subjects were assessed on their speech discrimination performance on the first 10 of the 15 pre-recorded NAL-AB wordlists in their better hearing ear. Administration of all 15 lists to both ears was considered to be impracticable for 3 reasons: (1) the duration of testing would be increased to unacceptably high levels possibly leading to subject fatigue; (2) the additional repetitions of each list would induce a greater degree of practise/learning effects; and (3) as lists 13-15 were shown to be more variable in the Australian sample (Dermody, cited in Travers, 1990), it was felt that lists 1-10, the most reliable and commonly used lists, were more pertinent to the aims of this study. An identical set of instructions was given to all subjects, via the headphones, as per NAL recommendations (Travers, 1990, p8). The instructions read as: "You are going to hear some single words. Mter each word there will be a pause for you to repeat the word. Listen carefully and repeat whatever you hear. Some of the words will be very soft and it is important that you have a guess at each word even ifit doesn't make sense or you only hear a part of the word such as 'ee' or 'ch'. Just repeat what you hear." Once subjects had been instructed, list 11 was presented . at 30dBHL (audiometer dial reading), in order to familiarise subjects with the test procedure. The wordlist presentation was pseudorandomised with the initial ten list order being randomly selected, and then repeated five times. This was done to prevent a particular list from occurring several times in succession, or in close proximity. The intensity presentation was then randomised throughqut all 50 presentations such that each of the ten lists was presented once at five different intensity levels. Wayne J. Wilson, Beverley Jones and Peter Fridjhon The whole process of pseudorandom is at ion was conducted separately for each individual subject. Intensity levels of 0, 5, 10, 20 and 25 dBHL (as per the audiometer dial reading) were used, emulating the normative data provided by NAL. All subject's responses were recorded and scored. on- line by a single tester, a student of Speech and Hearing Therapy at the University of the Witwatersrand, under the supervision ofa full member of the Audiological Society of Australia, in fulfilment of that Society's requirements for use of materials. Responses were transcribed using a combination of orthographic and phonetic transcription. Each word was then assigned a score of 0%, ifno phonemes were correctly repeated; 3% for 1 correct phoneme; 7% for 2 correct phonemes; or 10% if the response was completely correct; as per the scoring protocols, suggested by NAL (Travers, 1990). Subject responses were considered to be correct only if they were pronounced exactly as per the Australian English pronunciation on the NAL-AB wordlist CD. It was noted, however, that none of the 15 NAL-AB wordlists contained words where a predicted difference in pronun- ciation between Australian English and South African English should occur (for e.g., there were no words such as "dance", which would be pronounced as /dams/ in Australian English, but as /dans/ in South African English). In cases where single phonemes or nonsense syllables were given as a response instead ofa whole word, the phonemes were scored based on their acoustic similarity to the relevant Australian English phonemes in the stimulus word. In the case of more than one response being given for a single stimulus, the first response was taken irrespective of accuracy. Subjects were allowed the opportunity to rest at any stage during the test procedure. DATA ANALYSIS Comparison between the South Mrican English speaker scores and the NAL-AB wordlist Australian English normative data was done graphically with all NAL normative data values being extrapolated from the graphs provided in Travers (1990) for reanalysis. Plots lof the extrapolated NAL normative data and the South African English speakers data were completed using Mi~rosoft Excel for Windows, Version 5.0©. I Analysis for differences within the South African English speaker discrimination scores, between p~esen­ tation intensities, was conducted separately fot" each wordlist using Kruskal-Wallis ANOVA by Ranks (~cross all intensities at p<0.05) and Mann-Whitney U (between adjacent intensities only, at p0.05) correlations occurred within the wordlists between low and high presentation intensities only. Similar analyses between scores across wordlists, conducted separately for each presentation intensity, showed mild (0.4) to strong (0.9) correlations between scores for all presentation intensities except for 25 dBHL, which showed large numbers (24.4%) of poor «0.4) or non-significant (p>0.05) correlations between wordlists. F Test analysis for differences in the variance of the South African English speakers' discrimination scores between the different presentation intensities, conducted separately for each wordlist, showed the variance at 25 dBHL to be significantly different (p 0;' Q ;:! ~ ~ ~ ~ .s;, f? ;3 ;3 ~ ;:! 0;' Q "'" 0' ;:! t:::; 1;;' o ~ .;;'l ~ ~ SJ"I .... <:0 & LIST 1 100 ~"~'-<~-r~'«1 .r. J;~"':! 1'" , r 75 50 25 o +I--,-..--....--r-' -5 5 15 25 Presentation level (dBHl) LIST 6 1 00 T'~><'~'"'~ ''''''''''_''!*v ..... "'r..: 1 75'\ 1;'/ ! r "~l 50 -l ~ ! J'l ;~~ 25 I ! 01.L ~ -5 5 15 25 Presentation level (dBHl) \ b l!! .. o o ~ -u QI C 0 0 ~ 0 LIST 2 100 75 50 25 o +-=-.,-....... ~-' -5 5 15 25 Presentation level (dBHl) LIST 7 100 TW"""'~---"",,Tm) 75 ... 50· 25 0 -5 5 15 25 Presentation level (dBHl) i o o ~ - ~ 0 0 ~ LIST 3 1 00 t"~'~"~'~W~~ 75 -5 5 15 25 Presentation level (dBHl) LIST 8 ': r--":~1 ! SO 25- 0 ~'"--''''''''l'''""''''' -5 5 15 25 Presentation level (dBHl) 1:3 l!! 8 ~ -U QI .. .. 0 0 ~ LIST 4 75 o +--,,--,-~ -5 5 15 25 Presentation level (dBHl) LIST 9 75' SO 25- 0 -5 5 15 25 presentation level (dBHl) b ~ o o ~ -U QI .. .. 0 0 ~ 100 75 50 25 LIST 5 .-~--'1iWl 1/".L.J..! (I o . , -5 5 15 25 Presentation Level (dBHI LIST 10 100 r-'MM"~M''''''''--l -:t' I!i:' . ,.Il 75 -1 T/7.Ll , SO- 25' o r--" 't I ~ -5 5 15 25 Presentation level (dBH FIGURE 1: Plots, of South Mrican English speakers' mean scores (diamonds) with error bars (1 S.D.) and NAL's Australian English speaker mean scores (squares) for NAL-AB wordlists 1-10. 00 t\:) ~ ~- = t1> ~ ~ .- III o ? t:d t1> < !t t1> '< c.., ~ t1> III ~ = ~ 'tl t1> .... t1> '1 ~ ... 8: ::r o = R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) Use of the NAL-AB Wordlists as a South Mrican English Speech Discrimination Test 83 to investigate the feasibility of using the pre-recorded NAL- AB wordlists, with the NAL-Australian English normative data, to assess the speech discrimination abilities of first- language South African English speakers in South Africa. To achieve these aims, NAL-AB wordlist speech discrimination scores were obtained from 30 first language South African English speaking, female adults with normal hearing. These scores were then compared to the NAL Australian English speaker normative data (as provided by Dermody, in Travers, 1991). In general, the SouthMrican scores were lower, with three qualitative patterns being observed; similar performance between the two groups (lists one and five); South African scores occurring below the Australian scores at the lower and/or mid presentation levels only (lists three, four, seven, eight and nine); and South African scores occurring below the Australian scores across four or all five presentation intensities (lists two, six and ten). Comparisons of South Mrican scores within and between NAL-AB wordlists showed multiple differences and correlations, depending on which lists and presentation intensities were being compared. The qualitative finding that South African scores were generally worse than those of the Australians, indicates the direct llse of the pre-recorded NAL-AB wordlists with their associated normative values cannot be applied to the South African English speaking population without significant modification. The three differing patterns of South African versus Australian results indicates the different NAL-AB wordlists were not of equal difficulty for the two populations. The first category of results showing similar mean scores for the two groups, suggests these lists were equally difficult. The second category showing differences at the low and/or mid-presentation intensities only, suggests both groups were able to hear these wordlists equally well at the higher presentation intensities, but the Australians were able to extract more information at the lower presentation intensities, due most probably to their TABLE 2: Kruskal-WallisANOVA by Ranks and Mann-Whitney U results for differences in South Mrican English speakers' mean scores between presentation intensities, conducted for each NAL-AB wordlist separately (*- highly significant). NAL-AB WORDLIST KRUSKAL-WALLIS ANOVA BETWEEN THE FIVE Mann-Whitney U (n-=60) NUMBER PRESENTATION INTENSITIES FOR results between adjacent EACH WORDLIST presentation levels for worldlist n p level 1,2,3,4,5,6,7,8,9,10 150 <0.005* Sig. diff's (p0.05) correlations occurred between wordlists. This finding supports the earlier suggestion of the beginning of a ceiling at 25 dBHL presentation intensity as scores in a ceiling range should Wayne J. Wilson, Beverley Jones and Peter Fridjhon be more random and therefore have fewer correlations. Minor limitations to this study include the all young, adult female composition of the sample, and the lack of control over right versus left ear selection. With no reports, to the authors knowledge, of significant female/male or right/left ear performance differences in the literature for any ofthe monosyllabic word tests, these points were not considered to have had any significant impact on this study's findings. A more significant limitation was the sample's English first language prerequisite, and predominance of tertiary level education, much of which was in the field of Speech Pathology and Audiology. Davis (1983) (cited in Lutman, 1987) demonstrated a relationship between socio-economic status and type of occupation, and performance in speech audiometry with higher education level implying a certain level of linguistic competence and even sophistication. It might therefore be predicted that a more representative sample ofthe South African English speaking population would not have performed as well as the more educated sample used in this study. Finally, it must be noted a significant factor affecting any interpretation of speech discrimination results is the large amount of variability inherent in speech testing. Mendel and Danhauer (1997) warn that a margin of 16- 20% should be allowed for erroneous scoring alone, because of errors in the scorer's perception. Similarly, Thorton and Raffin (1978), Ostergard (1983) and Green (1987) state that a single score obtained for a particular wordlist is only an indicator of a range of scores in which the true score is likely to be. This inherent variability in speech audiometry diminishes its accuracy in all uses generally, and the strength of the descriptive results of this study specifically. CONCLUSIONS The similarities observed between the Australian English and South African English speakers on the pre- recorded NAL-AB wordlists makes this test a valid option for the speech discrimination assessment of South African English speakers, under certain conditions. The NAL-AB wordlists are most su.itable for use at suprathresholdilevels (where the fewest dIfferences were observed) where the advantages of shorter test times, and more available wordlists, can be accessed without critically compro~ising test reliability or validity. Use ofthe NAL-AB wordli'sts at threshold, or near threshold, levels (where the Imost differences were observed) should be approached! with caution, however, and reliance on these wordlists fo'r site , I of lesion purposes should be avoided. General test reliability and validity could be improved by changing the wordlist presentation order to (5, 1), (3, 9), (7,6), (8, 4), (2, 10) (where brackets indicate interchangeable lists) to suit South African English speakers, and by collecting larger South African normative data bases where possible. Despite this study's findings, the over-riding need for a South African English specific speech discrimination test remains. Whilst the NAL-AB wordlists offer/advantages over the C.I.D. W-22 wordlists such as ph~emic s~oring and, based on this study's results, at least 'some idea of how South African English speakers vary from the normative data (information which is not currently published for the C.I.D. W-22 wordlists), the cdntinued use of non-South African tests must be seen ~s an interim measure only. In view of similarities between the performance of South The South African Journal of Communication Disorders, Vol. 45, 1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) Use of the NAL·AB Wordlists as a South African English Speech Discrimination Test 85 African English and Australian English speakers seen in this study, the option of modifying the NAL-AB wordlists to suit South African English (as per NAUs modification of the original U.K. AB wordlists to suit Australian English) could provide the starting point needed to develop the long awaited South African English specific speech discrimination test. ACKNOWLEDGEMENT The authors wish to thank Nicci Campbell of the Department of Communication Pathology, University of Pretoria, for her work in finding many of the South African studies referenced in this paper. REFERENCES Alant, E. & Beukes, S.M. (1986). The application of the revised version of the Peabody Picture Vocabulary Test (PPVT-R) to non-mainstream children. South African Journal of Commu- nication Disorders, 33: 7-12. Bench, J. (1987). Speech Audiometry in Australia. In M. Martin (Ed.), Speech Audiometry. London: Whurr Publishers Ltd. Boothroyd, A. (1968). Developments in speech audiometry. Sound, 2: 2-10. Brandy, W.T. (1966). Reliability of voice tests of speech discrimi- nation. Journal of Speech and Hearing Research, 9: 461-465. Brewer, C.C. & Resnick, D.M. (1983). A review of tests of speech discrimination. Seminars in Hearing, 4: 205-220. Cakiroglu, S. & Danhauer, J.L. (1992). Effects of listeners' and talkers' linguistic backgrounds on W-22 test perfomance. Journal of the American Academy of Audiology, 3: 186-192. Campbell, RA. (1965). Discrimination test word difficulty. Journal of Speech and Hearing Research, 8: 13-22. Carhart, R. (1965). Problems in the measurement of speech discrimination. Archiues of Otolaryngology, 82(9): 253-260. Collie, L. (1991). The Staggered Spondaic Word (SSW) Test inuestigated in a South African Context. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersrand. Corke, V. (1993). The Staggered Spondaic Word Test: The South African English uersion. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersra~d. Davis, AC. (1983). Hearing disorders in the population .. First phase findings of the MRC National Study of Hearing. In M.E. Lutman & M.P. Haggard (Eds.), Hearing Science and Hearing Disorders, London: Academic Press. I Dermody, P. & Mackie, J. (1987Jl. Speech tests in audiological assessment at the National Acdustic Laboratories. In M. Martin (Ed.), Speech Audiometry. Lon:don: Taylor and Francis Ltd. Edgerton, B.J. & Danhauer, J.L. ;(1979). Clinical Implications of Speech Discrimination Testzng Using Nonsense Stimuli. Baltimore: University Park Ptess. Egan, J.P. (1948). Articulation testing methods. Laryngoscope, 58: 955-991. Evans, P.LP. (1987). Speech audiometry for differential diagnosis. In M. Martin (Ed.), Speech Audiometry. London: Taylor and Francis Ltd. Ewen, C. (1993). The Paediatric Speech Intelligibility Test- Format II: Performance-intensity functions of first language English speaking South African children. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersrand. Fuller, H. (1987). Equipment for speech audiometry and its calibration. In M. Martin (Ed.), Speech Audiometry. London: Taylor and Francis Ltd. Green, R (1987). The uses and misuses of speech audiometry in rehabilitation. In M. Martin (Ed.), Speech Audiometry. London: Taylor and Francis Ltd. Hall, J.W. III (1983). Diagnostic applications of speech audiometry. Seminars in Hearing, 4: 179-204. Hirsh, LJ., Hallowell, D., Silverman, S.R, Reynolds, E.G., Eldert, E. & Benson, RW. (1952). Dev,elopment of materials for speech audiometry. Journal of Speech and Hearing Disorders, 15: 321- 337. Jordaan, H. (1989). Management of language disability in the bilingual, bicultural child. In SAALED Conference Proceedings: Facilitating Learning: An Ecological Perspectiue, July: 217-234. Kastner, C. (1994). The Willeford Battery of Central Auditory Function: The South African English uersion. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersrand. Keith, RW., Katbamna, B., Tawfik, S. & Smolak, L.H. (1987). The effect oflinguistic background on staggered spondaic word and dichotic consonant vowel scores. British Journal of Audiology, 21: 21-26. Koekemoer, H. (1994). Die toepaslikheid uan 'n Noord-Sotho uertaling uan die PPVT-R by 'n groep skoolgaande kinders. Unpublished undergraduate research report, Department of Communication Pathology, University of Pretoria. Kreul, E.J., Bell, D.W. & Nixon, J.C. (1969), Factors affecting speech discrimination test difficulty. Journal of Speech and Hearing Research, 12(2): 281-287. Labuschagne, D.A. (1990). The application of the PPVT-R to an urban group of North-Sotho speaking children. Unpublished undergraduate research report, Department of Communication Pathology, University of Pretoria. Lehiste, 1. & Peterson, G.E. (1959). Linguistic considerations in the study of speech intelligibility. Journal of the Acoustic Society of America, 31: 280-286. Lyregaard, P. (1987). Towards a theory of speech audiometry tests. In M. Martin (Ed.), Speech Audiometry. London: Taylor and Francis Ltd. Markides, A (1987). Speech tests of hearing for children. In M. Martin (Ed.), Speech Audiometry. London: Taylor and Francis Ltd. Martin, F.N. & Forbis, N.K. (1978). The present status of audiometric practice: A follow-up study. ASHA, 20: 531-541. Mehl, T. (1992). Speech audiometry testing for pre-school first language English speaking South African children: Compari- son of the WIPI and NU-CHIPS speech discrimination tests. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwaters- rand. Mendel, L.L. & Danhauer, J.L. (1997). Audiological Eualuation and Management and Speech Perception Assessment. San Diego: Singular Publishing Group Inc. Modi, N. (1995). Use of the SA-SSW and the SA-Willeford battery with South African Indian speakers of English. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersrand. Northern, J.L. & Hattler, K.w. (1974). Evaluation of four speech discrimination test procedures on hearing impaired patients. Journal of Auditory Research, (Supp!): 1-37. Ostergard, C.A. (1983). Factors influencing the validity and reliability of speech audiometry. Seminars in Hearing, 4: 221- 240. Pakendorf, C. & Alant, E. (1997). Culturally valid assessment tools: Northern Sotho translation of the Peabody Picture Vocabulary Test-Revised. South African Journal of Communication Disorders, 44: 3-13. Ross, M. & Huntington, D.A. (1962). Concerning the reliability and equivalency of the C.LD. W-22 auditory tests. Journal of Auditory Research, 2: 220-228. Stevens, P. (1991). The effect of linguistic background on the Staggered Spondaic Word (SSW) test performance. Unpublished undergraduate research report, Department of Speech Pathology and Audiology, University of the Witwatersrand. Studebaker, G.A. & Sherbecoe, RL. (1991). Frequency-importance and transfer functions for recorded C.LD. W-22 word lists. Journal of Speech and Hearing Research, 34: 427-438. Taylor, O.L. (1986). Treatment of communication disorders in linguistically diuerse populations. Boston: College-Hill. Thorton, AR & Raffin, M.J. (1978). Speech discrimination scores modelled as a binomial variable. Journal of Speech and Hearing Research, 21(3): 507-518. Tillman, T.W., Cahart, R & Wilber, L. (1963). A test for speech discrimination composed of CNC monosyllabic words. Northwestern University Auditory Test No.4. Technical Documentary Report No. SAM-TDR-62-135, USAF School of Aerospace Medicine, Brooks Airforce Base, Texas. Tobias, J.v. (1964). On phonemic analysis of speech discrimination, Journal of Speech and Hearing Research, 7: 98-100. Travers, A (1990). AB Word Lists: NAL Protocols. Australian Hearing Services, Victoria, Australia. Die Suid-AfrikaanseTydskrifvir Kommunikasieafwykings, Vol. 45,1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 ) 86 Wayne J. Wilson, Beverley Jones and Peter Fridjhon APPENDIX 1 National Acoustics Laboratories Arthur Boothroyd Wordlists one to fifteen. List 1 List 2 List 3 List 4 List 5 List 6 List 7 List 8 List 9 List 10 fan fun thug hush Jug bath have hug math wish rug will witch gas latch hum wig dish hip dutch ship vat teak thin wick dig buff ban gun jam cheek shape rap fake faith five mIce rage ride heath haze wreath VIce chime sign ways teeth chief siege laze dice hide jail weave beep reach jays pIes veil bike both guess hen jet hem joke poach wet chose rove well comb shows rob rod noose rule cove shoot pet jot choose food dope vote pot den loose web fog move job bomb lose shoes shell shock moth cough soon List 11 List 12 List 13 List 14 List 15 badge fish fib fill kiss hutch duck thatch catch buzz kill path sum thumb hash thighs cheese heel heap thieve wave race wide wise gate reap hive rake rave wife foam bone goes got pole goose wedge shop shown wretch not log vet bed dodge shed tomb june juice moon The South African Journal of Communication Disorders, Vol. 45, 1998 R ep ro du ce d b y Sa bi ne t G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r ( da te d 20 12 )