Factors Associated With Individual Differences in Clinical Measures of Speech Recognition Among the Elderly

Transcription

1 Jurnal f Speech and Hearing Research, Vlume 37, , April 994 Factrs Assciated With ndividual Differences in Clinical Measures f Speech Recgnitin Amng the Elderly Larry E. Humes Betty U. Watsn Laurel A. Christensen Carl G. Ckely Dan C. Hailing Lidia Lee Audilgy Research Labratry Department f Speech and Hearing Sciences ndiana University, Blmingtn -- r rllgli n the present study, the speech-recgnitin perfrmance f 5 subjects aged 63 t 83 years was measured fr a wide range f materials (nnsense syllables, mnsyllabic wrds, sentences) and listening cnditins (presentatin levels f 7 and 9 db SPL, bth in quiet and in a nise backgrund). n additin t cmplete audilgic evaluatins, measures f auditry prcessing (the Test f Basic Auditry Capabilities [TBAC], Watsn, 987) and cgnitive functin (Wechsler Adult ntelligence Scale-Revised [WAS-R], and the Wechsler Memry Scale-Revised [WMS-R], Wechsler, 98, 987) were btained frm all subjects. Principal cmpnent analyses were applied t each f the three sets f measures (speech-recgnitin, auditry, and cgnitive) prir t examining assciatins amng the sets using cannical analyses. Tw principal cmpnents captured mst f the systematic variatin in perfrmance sampled by the set f speech-recgnitin measures. Hearing lss emerged as the single largest factr assciated with individual differences in speech-recgnitin perfrmance amng the elderly, accunting fr 7-75% f the ttal variance in speech-recgnitin perfrmance, with the measures f auditry prcessing and cgnitive functin accunting fr little r n additinal variance. KEY WORDS: speech recgnitin, elderly, aging, presbyacusis, auditry prcessing t is generally acknwledged that there are large individual differences in speechrecgnitin ability amng individuals ver 6 years f age. Several recent studies have suggested that the primary factr underlying these differences has been individual variatin in peripheral hearing lss. n tw recent studies examining the speech-recgnitin perfrmance f elderly persns in a wide range f listening cnditins (Humes & Christphersn, 99; Humes & Rberts, 99), fr example, we have nted strng crrelatins (.7 < r <.9) between speech recgnitin and the degree f high-frequency hearing lss. Clsed-set identificatin f nnsense syllables (the CUNY Nnsense Syllable Test [NST], Resnick, Dubn, Hffnung, & Levitt, 975) was used t measure speech recgnitin in these studies. Similar findings using the same nnsense-syllable identificatin task have been reprted recently by Helfer and Wilber (99). Perfrmance n the CUNY NST, mre than n the ther clinical measures f speech recgnitin available, is likely t be heavily influenced by peripheral factrs, such as sensrineural hearing lss, in that semantic and syntactic infrmatin makes n cntributin t perfrmance. t is quite pssible that the strng crrelatins with hearing lss bserved in the previus studies may be attributed, in part, t the use f these materials. Other investigatrs, hwever, have als bserved strng assciatins between the degree f hearing lss and speech-recgnitin perfrmance when the latter was assessed using pen-set recgnitin f mnsyllables (Jerger, Jerger, C 994, American Speech-Language-Hearing Assciatin /94/ $. /

2 466 Jurnal f Speech and Hearing Research & Pirl, 99) and either clsed-set identificatin r pen-set recgnitin f sentences (Jerger et al., 99; van Rij & Plmp, 99, 99; van Rij, Plmp, & Orlebeke, 989). Many previus studies f individual differences in speechrecgnitin ability amng the elderly have suffered frm tw primary shrtcmings. First, speech-recgnitin ability has ften been narrwly defined by sampling speech-recgnitin perfrmance fr nly ne r tw types f speech materials and in a very restricted set f listening cnditins. Secnd, the number f ther abilities measured in the elderly subjects and crrelated with speech recgnitin has ften been restricted t their age and hearing lss. This study attempted t remedy bth f these shrtcmings. n the present study, speech-recgnitin ability was bradly defined using a wide range f clinical speechrecgnitin tests ranging frm clsed-set identificatin f nnsense syllables (CUNY NST) t pen-set recgnitin f mnsyllabic wrds (CD W-, Hirsh, Davis, Silverman, Reynlds, Eldert, & Bensn, 95), t recgnitin f the final wrd in lw-predictability (PL) and high-predictability (PH) sentences (Speech Perceptin in Nise [SPN] test, Bilger, Nuetel, Rabinwit, & Reckwski, 984; Kalikw, Stevens, & Ellitt, 977). n additin t bradly defining speech-recgnitin perfrmance acrss a range f materials and respnse tasks, we als assessed a wide range f listening cnditins. All materials were presented at bth mderate and high intensities and in bth quiet and nise. Finally, the mnsyllabic wrds were als presented fllwing spectral shaping f the materials t mimic the shaping prduced by a hearing aid. Spectrally shaped materials were used because when they were presented at high levels the cntributins f audibility t speech-recgnitin perfrmance wuld be reduced. This, in turn, culd result in the emergence f factrs ther than audibility as cntributrs t individual differences in speech recgnitin. The amunt f spectral shaping was cnstant fr all subjects and was determined by applying the revised NAL gain-prescriptin methd (Byrne & Dilln, 986) t the estimated average audigram fr the study participants (audilgic infrmatin was available fr mst f the subjects in this study prir t their participatin). t is acknwledged that this apprach t spectral shaping did nt result in relative gain that clsely matched the NAL prescriptin fr all subjects, but nly fr thse with audigrams near the grup average. Nnetheless, the speech spectrum was mre audible fr all subjects fr the spectrally shaped speech materials than fr the unshaped materials. n ttal, measures f speech-recgnitin were btained frm each f the subjects in this study. These measures resulted frm factrial cmbinatins f five types f material (NST, SPN-PL, SPN-PH, W--unshaped, W--spectrally shaped) with tw presentatin levels (7 and 9 db SPL) and tw backgrund cnditins (quiet, nise). Given the relatively wide range f ages (63-83 years) and f hearing lss amng the elderly subjects in this study, it was anticipated that there wuld be sieable individual differences in perfrmance. The tw basic questins addressed in this study relate t the anticipated variability in perfrmance. First, hw strng is the assciatin amng these measures f speech recgnitin? s the individual wh perfrms the best r the wrst in ne cnditin and fr ne set f materials likely t be the best r wrst perfrmer fr mst r all f the speech-recgnitin measures? Secndly, what factrs r characteristics f the subjects are assciated with individual differences in speech-recgnitin perfrmance? Are the best perfrmers simply the yungest f the elderly subjects, the nes with the least amunt f hearing lss, the nes with the best cgnitive functin, the subjects with the best suprathreshld auditry prcessing, r sme cmbinatin f these factrs? The secnd fundamental questin listed abve was addressed in this study by btaining measures f hearing lss, suprathreshld auditry prcessing, and cgnitive functin frm all subjects. The measure f suprathreshld auditry prcessing used in this study was the Test f Basic Auditry Capabilities ([TBAC], Watsn, Jhnsn, Lehman, Kelly, & Jensen, 98). Perfrmance n this battery f auditrydiscriminatin tasks has been demnstrated t be reliable and minimally affected by hearing lss in elderly subjects (Christphersn & Humes, 99). n additin, perfrmance n the TBAC can accunt fr sme f the variability in nnsense-syllable recgnitin amng the elderly beynd that explained by hearing lss (Humes & Christphersn, 99). Measures f cgnitive functin btained frm all subjects were the Wechsler Adult ntelligence Scale-Revised (WAS-R, Wechsler, 98) and the Wechsler Memry Scale- Revised (WMS-R, Wechsler, 987). Subtest and cmpsite scres derived frm bth f these cgnitive measures resulted in the generatin f a ttal f 7 measures f cgnitive functin. The basic strategy pursued in the present study was the fllwing. The redundancy in each f the 3 large sets f variables ( speech-recgnitin measures, 9 auditry measures [ pure-tne averages and 7 auditry-discriminatin measures frm the TBAC], and 7 cgnitive measures) was minimied by perfrming principal cmpnents analyses (Kim & Mueller, 978a, 978b) n each set. This yielded uncrrelated principal cmpnents fr each set that were likely t be fewer in number than the variables they represented, yet captured the systematic variance in perfrmance. Next, the assciatin between the set f speech-recgnitin principal cmpnents and the ther tw sets f principal cmpnents (auditry and cgnitive) was evaluated. The statistical tl used in this study t examine the strength f assciatin between the sets f variables was cannical analysis (Thmpsn, 984). Methds Subjects April 994 A ttal f 5 subjects, ranging in age frm 63 t 83 years (M = 7.3 years; SD = 5. years), participated in this study. All subjects had nrmal middle-ear functin in the test ear as determined by tympangrams f nrmal shape, amplitude, and peak-pressure pint and the presence f an acustic reflex at db HL (ANS, 989) at H. The mean

3 Humes et al.: Speech Recgnitin in the Elderly 467 TABLE. Means (M) and standard deviatins (SD) f aircnductin pure-tne threshlds, n db HL (ANS, 989), fr the 5 elderly subjects in this study. Frequency (kh) = M SD air-cnductin threshlds f the test ear are shwn in Table, tgether with the crrespnding standard deviatins. Materials/Apparatus Three sets f cmmercially available speech materials were used in this study: (a) the CUNY NST (Resnick et al., 975); (b) the CD W- wrd lists (Hirsh et al., 95); and (c) the revised SPN test (Bilger et al., 984). All materials, including the supplied calibratin tne, were dubbed nt separate Digital Audi Tapes (DATs) fr playback in this study. The -subtest versin f the CUNY NST, which cnsists f items administered in a clsed-set frmat, was used in this experiment. Different randmiatins f the NST were used, ne fr each f the fur listening cnditins. Fr the SPN test, materials were generated such that each scre was based n a ttal f 5 lw-predictability (SPN-PL) r 5 high-predictability (SPN-PH) sentences. Fur lists f 5 sentences were generated fr each f these materials by arbitrarily pairing the eight sets f 5 equivalent PH and PL sentences established by Bilger et al. (984). n this way, nne f the PH r PL sentences was repeated, and the reliability f individual scres was imprved by dubling the number f sentences typically used t derive a scre. Previus wrk has suggested that SPN-PH and SPN-PL scres derived frm 5 sentences may nt yield reliable results in elderly listeners with hearing lss (Ckely & Humes, 99). Tw versins f the CD W- materials were presented t all subjects in this prject: (a) unshaped (W-U); and (b) spectrally shaped (W-S). The unshaped materials were standard recrdings f the W-s. The spectrally shaped materials were prepared specifically fr this investigatin. These materials were amplified (Crwn, D-75) and passed thrugh a /3-ctave spectrum shaper (ndustrial Research Prducts, TEQ DG-43) prir t being recrded by the DAT. The frequency respnse f the spectrum shaper was adjusted t shape a white-nise input s that the gain prvided wuld match that prescribed by the NAL-R prescriptive methd (Byrne & Dilln, 986) fr a hearing lss crrespnding t that f the average audigram (Table ). This was cnfirmed by measuring the utput f the spectrum shaper with a spectrum analyer (Spectral Dynamics, SD38) and cmparing the utput t an identical analysis f the input. Each W- scre was again based n 5 items t imprve the reliability f the measurements. Lists were nt repeated acrss the fur listening cnditins. The Test f Basic Auditry Capabilities (TBAC) has been described previusly in cnsiderable detail and recently in this jurnal by Humes and Christphersn (99) and Christphersn and Humes (99). Briefly, the TBAC measures frequency discriminatin, intensity discriminatin, and duratin discriminatin fr a -H pure tne, tempral-rder discriminatin fr pure tnes differing in frequency, and fr sequences f cnsnant-vwel nnsense syllables, rhythm r jitter discriminatin fr a sequence f brief -H tne pulses, and intensity discriminatin fr a pure-tne signal embedded in the middle f a sequence f tnes differing in frequency. All perfrmance measurements are expressed as the percentage f crrect respnses btained with a standard-tw-alternative frced-chice (AFC) paradigm. n this paradigm, three stimuli are presented n each trial: the standard stimulus fllwed by tw alternatives. The subject must select the alternative that differs frm the standard. The difficulty f the discriminatin is changed frm trial t trial and is designed t yield scres f 75-9% in yung adults with nrmal hearing. This tape-recrded test was als dubbed t DAT fr use in this study. The TBAC was presented at a level f 7 db SPL as specified in an NBS-9A cupler using the supplied calibratin signal. Speech materials were presented at 7 and 9 db SPL, as specified in an NBS-9A cupler using the apprpriate calibratin signal supplied with each speech material. The backgrund nise was a speech-shaped nise generated by a Grasn-Stadler 6 audimeter. Nise level was als specified in the NBS-9A cupler. Fr all cnditins invlving backgrund nise, the signal-t-nise rati was +7 db, which apprximates a typical signal-t-nise rati acrss a wide range f everyday listening envirnments (Pearsns, Bennett, & Fidell, 977). All acustic stimuli were presented t the subjects thrugh TDH-39 headphnes munted in supra-aural cushins (MX-4/AR). Subjects were seated in a quiet test envirnment having ambient nise levels within 5 db f thse specified in ANS (987) fr headphne measurement f hearing threshlds frm 5-8 H. Prcedures All subjects had cmplete audilgic evaluatins within 6 mnths f testing and received tympanmetric screening prir t each test sessin. A ttal f fur test sessins, each 9-5 minutes in length, were required fr cmpletin f all tasks in this study. Speech-recgnitin testing was divided acrss tw such sessins with the W-U, SPN-PL and SPN-PH materials presented in ne sessin, and the CUNY NST and W-S materials presented in the ther. The TBAC was administered in a separate sessin, as were bth f the cgnitive measures (WAS-R and WMS-R). The latter tests were administered by r under the supervisin f a licensed clinical psychlgist wh had been instructed in the use f a hard-wired assistive listening device (ALD). The ALD was available fr use with any subjects expressing difficulty in perfrming any f the cgnitive tasks due t difficulty hearing the stimuli r instructins. Written respnses were used fr the TBAC and all speechrecgnitin measures. All subjects were paid fr their participatin.

4 468 Jurnal f Speech and Hearing Research April 994 TABLE. Means and standard deviatins (in parentheses) f percent-crrect scres btained frm the 5 subjects in this study n each f the measures f speech recgnitin. Level = 7 db SPL Level = 9 db SPL Material Quiet Nise Quiet Nise SPN-PL 67. (3.8) 44. (3.4) 8.9 (.) 4.5 (7.5) SPN-PH 86.6 (4.3) 8.4 (8.6) 95.5 (8.7) 87.4 (5.4) W-S 85.5 (.6) 7. (4.) 9. (9.) 7. (5.7) W-U 8.5 (6.) 65.6 (6.) 86. (4.4) 64.3 (6.7) NST 7.4 (.6) 55.3 (7.6) 78.9 (.9) 6. (.6) Results ---and Discussin Descriptive Statistics and Crrelatins Table shws the means and standard deviatins fr the 5 subjects n each f the measures f speech recgnitin. Of primary interest fr the present study was the crrelatin amng these varius measures. Fr all crrelatins reprted in this paper, the assciated scattergrams were visually inspected t ensure that the crrelatins were nt due t utliers r clusters f extreme values. A histgram f the distributin f the 9 crrelatin cefficients representing all unique pairwise cmbinatins f the scres is shwn in Figure. Nte that all crrelatins are psitive in directin and f mderate strength with a mdal value f.775. Mrever, apprximately tw thirds f the crrelatins (63%) are greater than.7 in magnitude and 99% are statistically significant at the. level f significance; all are significant at the. level f significance. The directin and strength f assciatin between pairs f speech-recgnitin scres frm these listeners indicate a cnsiderable degree f Li ry D U O O, i DSTRBUTON OF CORRELATONS N=5 AMONG THE MEASURES OF - SPEECH RECOGNTON (Ttal= 9) _ 7, n up.ja" Z/,,,...,... y Y -_--... n n - U) n LO r-n N ) c CORRELATON COEFFCENT FGURE. Distributin f crrelatins amng the measures f speech recgnitin fr 5 subjects. Ttal number f crrelatins calculated, and the maximum pssible, s redundancy amng the measures. That is, there is a strng indicatin in these data that a subject wh btained a high scre n ne f the measurement cnditins was likely t d s n mst f the ther cnditins. Principal Cmpnents Analyses All the percent-crrect scres were arcsine-transfrmed t stabilie the errr variance and then subjected t a principal cmpnents analysis (PCA) using the Statistical Package fr the Scial Sciences (SPSS/PC+). Tw principal cmpnents were extracted with the PCA. (Unless nted therwise, the criterin fr cmpnent extractin fr all PCAs was an eigenvalue >..) These tw principal cmpnents accunted fr a ttal f 8.4% f the variance, with 74.% f the ttal variance accunted fr by the first cmpnent alne. The weightings f each variable n the tw principal cmpnents after cmpnent rtatin (varimax criterin) are shwn in Figure. Each f the speech-recgnitin measures is rdered alng the x-axis accrding t their weight n the first cmpnent. Mst f the speech-recgnitin measures are weighted heavily (>.6) n principal cmpnent N. and less s n principal cmpnent N. (<.6), the primary exceptins being the cnditins invlving the 9-dB presentatin level in nise (thse labeled "N9" alng the x-axis). Based n examinatin f the crrelatins f the speechrecgnitin measures with hearing lss (pure-tne averages at 5,, H, and at,, 4 H), we interpret the first principal cmpnent t represent, r be strngly assciated with, the audibility f the speech signal. The greater the hearing lss, the lwer the speech-recgnitin scre and the higher the weighting n principal cmpnent N.. This same examinatin f crrelatins f speechrecgnitin measures with hearing lss revealed that the measures btained at high presentatin levels in nise (thse labeled "N9" alng x-axis) were generally less strngly crrelated with pure-tne average (.4 < r <.69) than the ther 5 measures btained at the lwer presentatin level and/r in quiet (.59 < r <.87). The secnd principal cmpnent, therefre, appears t be assciated with perfrmance at high levels in nise with the scres frm these five cnditins being amng the seven mst heavily weighted n cmpnent N.. The secnd principal cmpnent appears t represent a factr less strngly assciated with audibility that is especially imprtant t the recgnitin f speech in nise at high intensities.

5 Humes et al.: Speech Recgnitin in the Elderly 469. a_ LUi : LiJ - : & : COMPONENT NUMBER N = 5 (8.4% Var).3 N N N 6 : 6 N:i N N Z N L a- a Uv) U ( a r, a- LO ) rn N N a a a N N L N N l 3: 3: Z Un U) O3 - J v) N a U) a a M N V) N Z N Z N 6: 6 : SPEECH-RECOGNTON MEASURE FGURE. Results f the principal cmpnents analysis n the speech-recgnitin measures. Each f the measures f speech recgnitin is rdered alng the x-axis accrding t its weight n principal cmpnent N.. Cmpnent weights are shwn fr each variable with "" representing the weighting fr cmpnent N. and "" representing the weighting f that variable n cmpnent N.. Only cmpnent weights greater than r equal t.4 are pltted. The labels fr the x-axis are cded as fllws: WU = W- mnsyllabic wrds, unshaped; Ws = W- wrds, spectrally shaped; SPN-PH = high-predictability sentences frm the SPN test; SPN-PL = lw-predictability sentences frm the SPN test; NST = CUNY Nnsense Syllable Test; 7 = quiet, 7 db SPL; 9 = quiet, 9 db SPL; N7 = nise, 7 db SPL; and N9 = nise, 9 db SPL. Hereafter, the principal cmpnents N. and N. will be referred t as SPCH and SPCH, respectively. Next, the nine auditry measures (seven auditry-discriminatin measures frm the TBAC and tw pure-tne averages) were subjected t the same type f principal cmpnents analysis. The cmpnent structure that emerged is shwn in Figure 3. A ttal f fur principal cmpnents were extracted and accunted fr 78.3% f the variance in the data. These cmpnents will be referred t here as AUD, AUD, AUD3 and AUD4. These cmpnents separately accunted fr 34.,.9, 3.6, and 9.7% f the ttal variance, respectively. (The minimum eigenvalue criterin f. used in the ther PCAs was relaxed t.85 fr this analysis, which resulted in a cmpnent structure clser t thse previusly reprted fr the TBAC.) f ne assumes that frequency discriminatin f a midfrequency pure tne is mediated by tempral r peridicity infrmatin, rather than place infrmatin (Mre, 989), then AUD can be interpreted as representing a tempralprcessing dimensin r factr. AUD, n the ther hand, is clearly an audibility factr, with the tw pure-tne averages being the nly tw variables weighted heavily n this cmpnent. AUD3 is interpreted as an energy-discriminatin factr with duratin discriminatin and intensity discriminatin representing tw ways in which subjects can make use f energy differences between tw stimuli. Finally, AUD4 is a unique cmpnent assciated with the lne speech-based measure f auditry discriminatin, the syllable-sequence task. The results f this principal cmpnents analysis are in general agreement with previus factr analyses f the TBAC, which have identified three factrs cmparable t AUD, AUD3 and AUD4 in Figure 3 (Espina-Varas & Watsn, 986; Watsn, 987). n sme f these prir PCAs and factr analyses, hwever, perfrmance in the -tne pattern discriminatin task assciated with AUD in this study has been assciated with the measures gruped with AUD3. (Measures f hearing lss [AUD] were nt included in these previus analyses.) Reliability cefficients f.8 t.9 reprted fr the TBAC when administered t elderly hearing-impaired subjects (Christphersn & Humes, 99) suggest that the systematic variance in the data (the squared reliability cefficient) amunts t 64-8% f the ttal variance, with the rest attributed t randm errr variance. Given that the fur principal cmpnents in Figure 3 can accunt fr 78.3% f the ttal variance, this amunts t accunting fr almst all f the systematic variance in these data. The 7 measures f cgnitive perfrmance derived frm perfrmance n the WAS-R and the WMS-R were als subjected t a principal cmpnents analysis. This analysis resulted in the extractin f seven cgnitive cmpnents accunting fr 79.8% f the ttal variance, as shwn in Figure 4. All 7 cgnitive measures are shwn alng the

6 47 Jurnal f Speech and Hearing Research April N = 5 (78.3% Var) 3 4 t- 3: LO.6.5 thrugh 4: COMPONENT NUMBER.4 a E c E -c C ) M Cq 4 U 4-4 U a) a- C,) (A AUDTORY MEASURE FGURE 3. Results f the principal cmpnents analysis fr the seven measures f auditry discriminatin frm the TBAC and tw average measures f hearing lss (pure tne average at 5, and H, PTA5, and at,, and 4 H, PTA4). Fur cmpnents were extracted in this analysis with each f the auditry measures' weighting n these factrs being represented by a number frm t 4. Only cmpnent weights greater than r equal t.4 are pltted here. X-axis in this figure with the prefix "M" (fr Memry) identifying thse measures derived frm the WMS and the prefix "" (fr intelligence ) identifying thse frm the WAS-R. Cmpnent weights are pltted in this figure with numbers frm ne t seven, each number representing a unique principal cmpnent that was extracted frm the analysis. These cgnitive principal cmpnents will be referred t hereafter as COG thrugh COG7. The percentages f variance accunted fr by COG thrugh COG7 were 37., 3., 9.4, 6.8, 5.3, 4., and 4.%, respectively. t is interesting t nte that there is very little verlap f the measures frm the WMS-R and WAS-R fr a given principal cmpnent. That is, all but tw f the 5 cgnitive measures that were weighted very heavily n COG, COG3 r COG4 are subtest scres r derived scres frm the WMS-R. On the ther hand, fur principal cmpnents are predminantly r exclusively assciated with measures frm the WAS-R (COG, COG5, COG6, COG7). We knw f n previus studies in the cgnitive literature that have perfrmed a factr analysis r principal cmpnents analysis n a cmbined set f WAS-R and WMS-R measures. There have been several such analyses, hwever, n the WAS-R itself, with many f these having been reviewed by Leckliter, Matara and Silverstein (986). When we perfrmed a separate principal cmpnents analysis n just the subtest scres f the WAS-R, three cmpnents emerged that were nearly identical t mst previus such analyses, with the tw primary factrs interpreted as Cmprehensin and Perceptual Organiatin. The third factr has emerged incnsistently and varied in interpretatin acrss several studies (Leckliter et al., 986), with "freedm frm distractability" being the mst cmmn interpretatin attached t the third cmpnent when it was extracted frm the analyses. n this study, hwever, the third cmpnent was extracted frm perfrmance n the Cmprehensin and Picture Cmpletin subtests f the WAS-R. The preceding principal cmpnents analyses n the measures f speech-recgnitin, auditry perfrmance, and cgnitive functin greatly reduced the redundancy in each f these sets f variables while still prviding an accurate descriptin f perfrmance as revealed by the percentage f ttal variance accunted fr by each grup f principal cmpnents. The measures f speech recgnitin were reduced t tw principal cmpnents (SPCH, SPCH), the nine auditry measures were reduced t fur cmpnents (AUD thrugh AUD4), and perfrmance n 7 measures f cgnitive functin was captured by seven factrs (COG thrugh COG7).

7 Humes et al.: Speech Recgnitin in the Elderly 47 C) Q,- L i i i i i i i i i N= , 4 O a > e Da M _ 4. 4) thru 7: FACTOR NUMBER ac a) - 4) i E - C - O C D a C M - v) c m > 3 5 i i i i i i i i E - E= gn -4) 4) - a 4)4) 5.8W >>, 636 ' a c a E - COGNTVE MEASURE FGURE 4. Results f the principal cmpnents analysis fr the 7 measures f cgnitive functin. Each label alng the x-axis describes a particular subtest f the WMS-R (label prefix f "M") r the WAS-R (label prefix f ""). The symbls, numbered thrugh 7, represent each f the seven cmpnents extracted frm the analysis and depict the weighting f each measure n these factrs. Only cmpnent weights greater than r equal t.4 are pltted here. Cannical Analyses Ultimately, we wished t examine the relatin amng these sets f principal cmpnents. n particular, the primary questin was hw individual differences in speech-recgnitin abilities were assciated with individual differences in auditry perfrmance, cgnitive functin, and age. Cannical analyses represent a cmmn tl used in examining the strength f assciatin between tw sets f variables and determining the measures in each set that are primarily respnsible fr this assciatin (Thmpsn, 984). Usually the tw sets f variables are referred t as the predictr set and the criterial set (the latter is the set t be predicted). A ptentially cnfunding factr in cannical analyses is cllinearity, which is the existence f a strng assciatin amng the variables within the predictr set f variables. Recall that the preceding factr analyses made use f principal cmpnents analysis. The bjective f this type f factr analysis is t extract rthgnal r uncrrelated factrs frm the set f measures. That is, the crrelatin amng the cmpnents in a given PCA is. Althugh cllinearity has been eliminated fr each f the principal cmpnents in the predictr set within their respective subset f measures (i.e., crrelatin matrix fr the fur AUD cmpnents is and fr the seven COG cmpnents is ), it is nt necessarily true fr the entire predictr set resulting frm the cmbinatin f these tw subsets. The tp prtin f Figure 5, hwever, depicts the multiple r-squared values btained fr the entire set f predictr variables (COG-COG7, AUD-AUD4, and age). Each vertical bar in the tp prtin f this figure represents the crrelatin f each variable in the predictr set with all ther variables in that same set. n general, all the squared multiple crrelatins are less than.4 and indicate that cllinearity amng the set f predictr variables has been minimied. Examinatin f the matrix f 56 crrelatin cefficients fr the predictr variables revealed nly ne crrelatin that was statistically significant (p <.). AUD4 was fund t be psitively crrelated with COG6 (r =.39). n summary, cllinearity within the set f predictr variables was nt a cnfunding factr in these analyses. The lwer prtin f Figure 5 depicts the squared multiple crrelatins fr each variable in the predictr set with each variable in the criterial set (SPCH and SPCH). Nte that the squared multiple crrelatin f AUD with the criterial set is much greater than any f the thers in the set f predictr variables. n fact, this was the nly statistically significant multiple crrelatin in the predictr set [F (, 47) = 63.4, p <.], althugh the multiple crrelatins fr COG4 and COG5 apprached statistical significance (p =.6 and.3, respectively). (Given the large number f multiple cmparisns in these analyses, an alpha level f. had been adpted fr determinatin f significant effects.) The results f the cannical analyses are summaried in Figure 6. Only the first cannical functin between the criterial and predictr variable sets was significant (p <.) and the crrespnding cannical crrelatin was.89. This crrelatin indicates that there is a strng assciatin between the set f predictr variables (AUD-AUD4, COG- COG7, and age) and the set f criterial variables (SPCH,

8 47 Jurnal f Speech and Hearing Research Apri 994 Ld D Cr) U) w EL Predictr with all ther N=5 predictr variables V7 7" F- L U LL LL C) F- F L CRTERAL _ PREDCTOR..8 Predictr with criterial set. N N N W O D D < an n~ ~ L~ CY Lr.6 tn-.4 p-.. M 7'7J N77 N FA VA % -4. " (N rc O L O N b r d b D D D D < U c) ( )O OO) < < < < PREDCTOR VARABLE FGURE 5. Multiple r-squared values frm multiple crrelatins calculated amng all variables in the predictr set (tp) r between these variables and bth variables n the criterlal set (bttm). SPCH). The structure cefficients pltted in Figure 6 graphically depict the factrs in each set that underlie this strng assciatin. The higher the structure cefficient, the greater the cntributin f that variable t the verall assciatin between the tw sets f variables. t is clear frm this figure that AUD, r hearing lss, is the majr cmpnent amng the set f predictr variables respnsible fr the strng assciatin with speech-recgnitin perfrmance. n additin, f the tw variables in the criterial set, SPCH is primarily respnsible fr the strng between-set assciatin. Recall that SPCH was a cmpnent assciated with the recgnitin f speech in high levels f backgrund nise and, as such, may nt be expected t be t strngly assciated with hearing lss (AUD). VARABLE FGURE 6. Magnitudes f structure cefficients fr each f the variables in the criterial (pen bars) and predictr sets (filled bars) f variables resulting frm the cannical analyses. The cannical crrelatin, Rc, describing the strength f assciatin between these tw sets f variables was.89. Relatin t Previus Studies Our measures f auditry functin did nt include measures f auditry tempral r spectral reslutin, such as gap detectin r auditry-filter shape. t is quite pssible that individual differences in either r bth f these auditry capabilities culd underlie the bserved systematic individual differences in speech recgnitin in nise at high intensities (SPCH). The recent wrk f Klein, Mills, and Adkins (99) ffers sme supprt fr the ptentially significant rle f individual differences in spectral reslutin n speech recgnitin by elderly persns with hearing impairment, at least fr high levels f lw-frequency nise. SPCH, hwever, was the predminant principal cmpnent that emerged frm the measures f speech recgnitin, accunting fr 74% f the ttal variance in speechrecgnitin perfrmance. This factr, in turn, was strngly assciated with hearing lss (AUD) in the cannical analyses. Thus, amng this grup f 5 elderly listeners, individual differences in hearing lss were the primary determinants f individual differences in speech-recgnitin ability acrss a wide range f materials and cnditins. This general finding is cnsistent with several recent studies cnducted with similar subject samples. n a series f studies by van Rij and clleagues, fr example, hearing lss has emerged cnsistently as the primary factr assciated with individual differences in speech recgnitin and has accunted fr 67-95% f the systematic variance in speechrecgnitin perfrmance (van Rij & Plmp, 99, 99;

9 Humes et al.: Speech Recgnitin in the Elderly 473 van Rij et al., 989). n a recent study invlving five measures f speech recgnitin in subjects between the ages f 5 and 9 years, Jerger et al. (99) als fund that hearing lss alne accunted fr apprximately 6% f the ttal variance in perfrmance n three f the five speechrecgnitin measures that made use f mnsyllabic wrds (PAL PB wrds, SPN-PL, SPN-PH). Fr these three measures, all ther predictr variables emplyed, including age and a variety f cgnitive measures, nly accunted fr an additinal 3-6% f the ttal variance in speech-recgnitin perfrmance. Hearing lss was als the mst imprtant predictr f perfrmance n the tw ther measures f speech recgnitin included in the study by Jerger et al. (99), the Synthetic Sentence dentificatin (SS) task (Speaks & Jerger, 965), and the Dichtic Sentence dentificatin (DS) task (Fifer, Jerger, Berlin, Tbey, & Campbell, 983). Fr each f these measures, hwever, additinal variables accunted fr significant prtins f the ttal variance in perfrmance. Fr the SS, age accunted fr an additinal % f the variance in perfrmance (vs. 4% fr hearing lss), whereas perfrmance n the digit-symbl subtest f the WAS-R accunted fr an additinal 3% f the variance in DS scres (vs. 3% accunted fr by hearing lss). The significant cntributins f factrs ther than hearing lss t the perfrmance f subjects n the SS and DS and nt n ther measures f speech recgnitin may be due t the unique aspects f the SS and DS. Bth the DS and the SS, fr example, use clsed-set identificatin f synthetic third-rder apprximatins t real sentences administered with cmpeting speech. n the case f the SS, the cmpeting speech is cntinuus discurse presented in the same ear as the target sentences, while similar synthetic sentences presented simultaneusly t the ppsite ear represent the cmpetitin fr the DS. Unfrtunately, neither the DS nr the SS appear t have adequate reliability fr use with elderly persns having hearing impairment (Ckely & Humes, 99; Humes, Christphersn & Ckely, 99), which makes interpretatin f the findings f Jerger et al. (99) fr these materials mre difficult. This study has cnfirmed the previus findings frm this labratry that have emphasied the primary imprtance f audibility t the understanding f speech in the elderly (Humes & Christphersn, 99; Humes & Rberts, 99), but fr a much wider range f speech materials and listening cnditins. As nted previusly, several recent studies with the elderly have reached similar cnclusins (Heifer, 99; Heifer & Wilber, 99; Jerger et al., 99; van Rij & Plmp, 99, 99; van Rij et al., 989). This finding is encuraging regarding the prspects fr rehabilitatin f elderly persns with hearing impairment via use f amplificatin. The majr imprtance f hearing lss as a factr underlying individual differences in speech-recgnitin perfrmance amng the elderly implies that effrts t imprve the audibility f speech thrugh amplificatin shuld be largely successful. nterestingly, the results f this study als suggest that limitatins t the successful use f amplificatin may exist fr listening cnditins invlving a backgrund f nise. Recall that SPCH represented a unique aspect f speech-recgnitin ability that was related t perfrmance in nise at high intensities and that this speech-recgnitin factr was nt related t audibility (r any ther factr measured in this study). Thus, cmpensating fr the lss f audibility thrugh well-fit amplificatin may nt imprve the speech-recgnitin f elderly listeners in nise. Hwever, the findings f this study als indicate that hearing lss, which can be treated r cmpensated fr with well-fit amplificatin, is the majr determinant f speech recgnitin in quiet, whereas cgnitive and suprathreshld auditry-discriminatin abilities, which are largely untreatable, make minimal cntributins t speech recgnitin. Finally, it is imprtant t nte that this study was nt a study f the general effects f aging n speech recgnitin. Subjects were nt selected t span the entire age range f adulthd. Rather, the fcus in this study was placed n the identificatin f thse factrs, including age, hearing lss, cgnitive functin and auditry-prcessing ability, that were related t individual differences in speech-recgnitin perfrmance amng the elderly. Acknwledgment This wrk was supprted, in part, by a grant t the first authr frm the Natinal nstitute n Aging. References American Natinal Standards nstitute (987). Criteria fr permissible ambient nise during audimetric testing, ANS S New Yrk: ANS. American Natinal Standards nstitute (989). Specificatins fr audimeters, ANS S New Yrk: ANS. Blger, R. C., Nuetel, J. M., Rabinwlt, W. M., & Reckwskl, C. (984). Standardiatin f a test f speech perceptin in nise. Jurnal f Speech and Hearing Research, 7, Byrne, D., & Dilln, J. (986). The Natinal Acustics Labratries (NAL) new prcedure fr selecting the gain and frequency respnse f a hearing aid. Ear Hear, 7, Christphersn, L. A., & Humes, L. E. (99). Sme psychmetric prperties f the Test f Basic Auditry Capabilities (TBAC). Jurnal f Speech and Hearing Research, 35, Ckely, C. G., & Humes, L E. (99). Reliability f tw measures f speech recgnitin in elderly peple. Jurnal f Speech and Hearing Research, 35, Esplna-Varas, B., & Watsn, C. S. (986). Tempral prcessing abilities f hearing-impaired listeners. Jurnal f the Acustical Sciety f America, 8, S. Fifer, R., Jerger, J., Berlin, C., Tbey, E., & Campbell, J. (983). Develpment f a dichtic sentence identificatin test fr hearingimpaired adults. 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10 . 474 Jurnal f Speech and Hearing Research Central auditry prcessing disrders in the elderly: Fact r fictin? n J. Kat, N. Stecker, & D. Hendersn (Eds.), Central Auditry Prcessing: A Transdisciplinary View (pp. 4-49). Philadelphia: B. C. Decker. Humes, L. E., & Rberts, L. (99). Speech-recgnitin difficulties f the hearing-impaired elderly: The cntributins f audibility. Jurnal f Speech and Hearing Research, 33, Jerger, J., Jerger, S., & Plrl, F. (99). Crrelatinal analysis f speech audimetric scres, hearing lss, age and cgnitive abilities in the elderly. Ear and Hearing,, 3-9. Kallkw, D. N., Stevens, K. N., & Ellit, L. L. (977). Develpment f a test f speech intelligibility in nise using sentence materials with cntrlled wrd predictability. Jurnal f the Acustical Sciety f America, 6, Kim, J.-O., & Mueller, C. W. (978a). ntrductin t factr analysis. Lndn: Sage Publicatins. Kim, J.-O., & Mueller, C.W. (978b). Factr analysis. Lndn: Sage Publicatins. Klein, A. J., Mills, J. H., & Adkins, W. Y. (99). Upward spread f masking, hearing lss and speech recgnitin in yung and elderly listeners. Jurnal f the Acustical Sciety f America, 87, Leckliter,. R., Matara, J. D., & Silverstein, A. B. (986). A literature review f factr analytic studies f the WAS-R. Jurnal f Clinical Psychlgy, 4, Mre, B. C. J. (989). An ntrductin t the Psychlgy f Hearing. Lndn: Academic. Pearsns, K. S., Bennett, R. L., & Fidell, S. (977). Speech Levels in Varius Nise Envirnments. EPA Reprt N. 6/ Resnick, S., Dubn, J. R., Hffnung, S., & Levitt, H. (975). Phneme errrs n a nnsense syllable test. Jurnal f the Acustical Sciety f America, 58(suppl), 4. Speaks, C., & Jerger, J. (965). Methd fr measurement f speech identificatin. Jurnal f Speech and Hearing Research, 8, Thmpsn, B. (984). Cannical crrelatin analysis. Lndn: Sage Publicatins. van Rll, J.C.G.M., & Plmp, R. (99). Auditive and cgnitive factrs in speech perceptin by elderly listeners.. Mutivariate analyses. Jurnal f the Acustical Sciety f America, 88, van Rll, J. C. G. M., & Plmp, R. (99). Auditive and cgnitive factrs in speech perceptin by elderly listeners. ll. Additinal data and final discussin. Jurnal f the Acustical Sciety f America, 9, van Rij, J. C. G. M., Plmp, R., & Orlebeke, J. F. (989). Auditive and cgnitive factrs in speech perceptin by elderly listeners..: Develpment f test battery. Jurnal f the Acustical Sciety f America, 86, Watsn, C. S. (987). Uncertainty, infrmatinal masking, and the capacity f immediate auditry memry. n W. A. Yst, & C. S. Watsn (Eds.), Auditry prcessing f cmplex sunds (pp ). Hillsdale, New Jersey: Lawrence Erlbaum. Watsn, C. S., Jhnsn, D. M., Lehman, J. R., Kelly, W. J., & Jensen, J. K. (98). An auditry discriminatin test battery. Jurnal f the Acustical Sciety f America, 7, S73. Wechsler, D. (98). The Wechsler Adult ntelligence Scale-Revised. New Yrk: The Psychlgical Crpratin. Wechsler, D. (987). Wechsler Memry Scale-Revised. New Yrk: The Psychlgical Crpratin. Received February 5, 993 Accepted Nvember 4, April 994 Cntact authr: Larry E. Humes, PhD, Department f Speech and Hearing, ndiana University, Blmingtn, N 4745.