a test to measure subjective and objective speech intelligibility · 2019-12-19 · 48% de la...

J Am Acad Audiol 13 : 38-49 (2002)

A Test to Measure Subjective and Objective Speech Intelligibility Gabrielle H. Saunders* Kathleen M. Cienkowskit

Abstract

Measurement of hearing aid outcome is particularly difficult because there are numerous dimen-sions to consider (e .g ., performance, satisfaction, benefit) . Often there are discrepancies between scores in these dimensions . It is difficult to reconcile these discrepancies because the materials and formats used to measure each dimension are so very different . We report data obtained with an outcome measure that examines both objective and subjective dimensions with the same test format and materials and gives results in the same unit of measurement (signal-to-noise ratio) . Two variables are measured : a "performance" speech reception threshold and a "perceptual" speech reception threshold . The signal-to-noise ratio difference between these is computed to determine the perceptual-performance discrepancy (PPDIS) . The results showed that, on average, 48 per-cent of the variance in subjective ratings of a hearing aid could be explained by a combination of the performance speech reception threshold and the PPDIS.These findings suggest that the mea-sure is potentially a valuable clinical tool .

Key Words: Hearing aid satisfaction, objective, speech intelligibility, subjective

Abbreviations : 4F-PTA = four-frequency pure-tone average (mean of 0 .5, 1, 2, and 4 kHz), HINT = Hearing In Noise Test, NU-6 = Northwestern University Auditory Test No . 6, OAD = obscure audi-tory dysfunction, PPDIS = perceptual-performance discrepancy, PPT = Perceptual Performance Test, SNR = signal-to-noise ratio, SRT = speech reception threshold

Sumario

La medici6n de los resultados en el use de un audifono es particularmente dificil debido a las numerosas dimensiones a considerar (p.ej ., rendimiento, satisfacci6n, beneficio) . A menudo hay discrepancias en los puntajes de todas estas dimensiones . Es dificil reconciliar estas discrepan-cias porque los materiales y los formatos utilizados para medir cada dimension son muy diferentes . Estamos reportando informaci6n obtenida con una medida de resultado que examina tanto las dimensiones subjetivas como las objetivas, con los mismos materiales y formato de prueba, y que da los resultados en las mismas unidades de medida (S/N = sepal/ruido) . Se miden dos variables : un umbral de recepci6n del lenguaje de rendimiento (performance SRT) y un umbral de recep-cion del lenguaje perceptual (perceptual SRT) . La diferencia en la relaci6n sepal/ruido (SIN ratio) de estos dos parametros es registrada para determinar la discrepancia rendimiento/percepci6n (perceptual/performance discrepancy = PPDIS) . Los resultados muestran que, en promedio, el 48% de la variancia en puntajes subjetivos sobre un audifono, puede ser explicada por una com-binaci6n del umbral de recepcion de lenguaje de rendimiento (performance SRT) y de PPDIS . Estos hallazgos sugieren que tal medida puede ser una herramienta clinica potencialmente valiosa .

Palabras Clave: Inteligibilidad del lenguaje, objetivo, satisfaccion con el auxiliar auditivo, subjetivo

Abreviaturas : 4F-PTA = promedio tonal puro en 4 frecuencias (media de 0.5, 1 .0, 2 .0, y 4.0 kHz), HINT = Prueba de Audici6n en Ruido, OAD = disfunci6n auditiva obscura, PPDIS = discrepancia rendimiento/percepci6n, PPT = Prueba de Rendimiento/Percepci6n, SNR = tasa o relaci6n sepal/ruido, SRT = umbral de recepcion del lenguaje de rendimiento, UN-6 = Prueba Auditiva de la Universidad Northwestern No. 6

*National Center for Rehabilitative Auditory Research, Portland, Oregon ; tUniversity of Connecticut, Storrs, Connecticut Reprint requests : Gabrielle H . Saunders, National Center for Rehabilitative Auditory Research, 3710 S.W . Veterans

Hospital Road, Portland, OR 97207

Subjective and Objective Outcome Measure/Saunders and Cienkowski

H

earing aids are routinely provided to the hearing impaired . It is difficult, how-ever, to measure the efficacy of the fit-

ting in terms of outcome success because there are numerous dimensions to consider, such as user performance, measurable benefit, user sat-isfaction, residual reported disability and hand-icap, and reported benefit . These dimensions are broadly considered to be "objective"' or "sub-jective" in nature . Objective measures typically assess a listener's ability to correctly identify speech materials (e .g ., phonemes, syllables, words, or sentences) . These measures are used to compare aided and unaided performance or performance with two or more different hearing aids . Examples of objective performance tests are the Hearing In Noise Test (HINT; Nilsson et al, 1994), the Speech Perception in Noise Test (Kalikow et al, 1977), and the Connected Speech Test (Cox et al, 1987) . Subjective evaluations can be made in at least two ways . First, ratings of speech quality and intelligibility can be carried

out in the laboratory (e .g ., Speaks et a1,1972 ; Cox and McDaniel, 1989 ; Cienkowski and Speaks, 2000) . Second, questionnaires can be completed

following a period of hearing aid wear to evalu-ate patients' satisfaction with their hearing aids in specific situations or to rate aided and unaided auditory disability and handicap . Examples of

such questionnaires are the Satisfaction with Amplification in Daily Life questionnaire (Cox and Alexander, 1999), the Hearing Handicap

Inventory for the Elderly (Ventry and Wein-stein, 1982), and the Client-Oriented Scale of

Improvement (Dillon et al, 1997) . The aim of this study was to evaluate a test

measure that could reconcile differences between subjective and objective ratings of hearing loss and hearing aids using the same test format, materials, and unit of measurement for each .

Studies that have examined the relationship between speech intelligibility and subjective ratings of hearing handicap and/or hearing aid satisfaction often show discrepancies between the two types of measure. For instance, there are studies in which speech intelligibility scores do not differ between hearing aids/hearing aid set-tings, even though subjective evaluations show a listener preference (e.g ., Horwitz et al, 1991 ;

'The term objective." as used here, refers to an indi-vidual's psychoacoustic performance as opposed to a physiologic response .

Ricketts and Bentler, 1992 ; Valente et al, 1998 ; Preminger et al, 2000) . Conversely, audiologists regularly encounter individuals who show con-

siderable improvements in aided speech under-standing and yet are dissatisfied with their hearing aids . Currently, it is difficult to recon-

cile conflicting data such as these, in part because the materials and formats used for measuring speech performance are so different from those used for subjective evaluations .

The results of studies in which objective and subjective speech intelligibility have been directly compared also often show conflicting findings . Some have found significant positive relationships between performance on a speech test and subjective ratings of speech intelligi-bility (e .g ., Speaks et al, 1972 ; Punch and Parker, 1981; Cox et al, 1991; Larsby and Arlinger, 1994 ; Cienkowski and Speaks, 2000), whereas

others show little or no relationship between the two (e.g ., Gray and Speaks, 1977 ; Punch and Howard, 1978 ; Preminger et al, 2000) . A detailed

examination of these studies leads to the fol-lowing conclusions : (a) subjective intelligibility ratings correlate more highly with objective

intelligibility scores when the same test mate-rials are used for measuring both conditions, (b) the relationship between subjective and objec-tive speech intelligibility tends to be more pre-dictable for normal-hearing individuals than

for hearing-impaired individuals, (c) nonaudi-tory factors may explain differences between

subjective ratings and objective scores, and (d) presumably, the instructions given to subjects in the subjective condition explain some of the

variance between these studies . In this article, data are reported from a

study in which objective and subjective evalua-tions were made using the same test format, materials, and unit of measurement (signal-to-noise ratio [SNR]) using an outcome measure

called the Perceptual-Performance Test (PPT) . The HINT sentence lists were used to measure

a performance speech reception threshold (SRT)

and a perceptual SRT. The performance SRT is measured with the HINT protocol ; thus, the

SNR at which listeners can understand 50 per-cent of the material is determined . The percep-

tual SRT is also measured with the HINT

materials, but the SNR is determined by the lis-teners' perception of their ability to understand the speech . The result is the SNR at which lis-teners perceive that they can just understand all of the speech material . A third result is avail-able from this procedure : the difference between the performance SRT and the perceptual SRT.

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Journal of the American Academy of Audiology/Volume 13, Number 1, January 2002

This is called the perceptual-performance dis-crepancy (PPDIS). It is a measure of the extent to which the listener "misjudges" his or her hearing ability. If the SNR obtained during the perceptual condition is more adverse than that obtained during the performance condition, it suggests that the listener overestimated his or her hearing ability. If the SNR obtained during the perceptual condition is less adverse than that obtained during the performance condi-tion, it suggests that the listener underesti-mated his or her hearing ability. To date, the HINT has been found to be a clinically practi-cal and useful tool . It has been employed in a number of research studies that generally show it to be sensitive, valid, and reliable (e .g., Valente et al, 1995; Humes et al, 1996; Preves et al, 1999 ; Ricketts and Mueller, 2000). Thus, it was considered to be a good starting tool for the above procedure.

Saunders and colleagues used methodology very similar to that described above to evaluate patients with obscure auditory dysfunction (OAD) (Saunders and Haggard, 1992 ; Saunders et al, 1992). Individuals with OAD complain of hearing difficulties, especially in noisy envi-ronments, and yet have clinically normal hear-ing. The study revealed that individuals with OAD selected significantly less adverse SNRs during the perceptual condition of the test than they required for performance; that is, they underestimated their hearing ability. On the other hand, age- and gender-matched normal-hearing controls obtained SNRs on the percep-tual condition that were within 1 dB of those obtained on the performance condition; that is, they accurately gauged their hearing ability. It was thus concluded that, as a group, individu-als with OAD underestimate their hearing abil-ity and thus perceive greater disability and handicap than their performance suggests they should. It was also found that provision of coun-seling regarding the PPDIS score successfully altered the OAD patients' perception of their hearing difficulties . These data provide evidence that individuals with normal hearing who do not perceive hearing difficulty can gauge their abil-ity to hear speech in noise accurately using this procedure. Data from Cienkowski and Speaks (2000) show that it is likely that these relations will also hold for hearing-impaired individuals who experience handicap that is commensurate with their degree of hearing loss. It is also likely that this test procedure will be able to differ-entiate between individuals who are experi-encing greater disability and handicap than

would be expected from their performance abil-ity from those who are not and that PPDIS scores could be used effectively to counsel such individuals.

Presented below are data from a study in which the PPT was used to examine the hand-icap, disability, and hearing aid satisfaction of individuals who wore a number of different hearing aids . It is believed that the PPT removes some of the uncertainties that arise from using different materials for the objective and sub-jective measurements . Furthermore, it provides an additional dimension when measuring hear-ing aid outcome. It is proposed that the PPDIS variable, in conjunction with the performance condition of the test, will be able to differenti-ate between contented and discontented hear-ing aid users .

METHOD

T he data described below originate from a field study of three programmable hearing

aids (Matthes et al, 1995). During that study, subjects underwent a large battery of tests. Only those experimental details directly relevant to this article will be described here .

Subjects

Forty-eight male veterans with mild-to-moderate sensorineural hearing loss took part. At the start of the study, subjects ranged in age from 55 to 75 years. Twenty-five subjects were experienced hearing aid users; 23 had no previ-ous hearing aid experience . Table 1 provides fur-ther biographic and audiometric information about the subjects . All were enrolled in the Audiology Clinic at the East Orange VA Medical Center.

Experimental Design

Subjects were fitted with hearing aids bin-aurally. They wore three different hearing aids with a total of six different configurations (com-bination of frequency response, method of out-put limiting, and number of memories available) . Each configuration was worn for 3 months . At the end of each 3-month period, the subjects came to the laboratory for post-use testing with that configuration of hearing aid followed by fitting and testing with the next aid. Speech recognition testing was included at the start and end of each 3-month wearing period . In addition, subjects rated residual aided auditory disability and handicap and their satisfaction

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Table 1 Means and SDs of Audiometric and Demographic Data (n = 45)

Mean (SD) Range

Age (yr) 69 .8 (5 .3) 56.3-76 .3 4F-PTA (mean of 0 . 5, 1 .0, 2.0, and 4.0 kHz) 46 .7 (5 .1) 37.5-59 .4

SRT-Q (dB HL) 32 .7 (7 .5) 12.0-47 .0 PBMAX (%) 76 .2 (10 .8) 46.0-94.0

4F-PTA = four-frequency pure-tone average ; SRT Q =

speech reception threshold in quiet, PBMAX = phonetically

balanced word list maximum score .

with each hearing aid configuration once a month for the duration of the study. Thus, each subject took part in the study for 18 months and visited the laboratory seven times for testing during the study. Prior to the study, subjects received a complete audiologic evaluation and completed a number of questionnaires (see below) .

Test Battery

Audiologic Measures

1. Pure-tone thresholds were measured using the American Speech-Language-Hearing Association's (1978) recommended proce-dure . A four-frequency pure-tone average (4F-PTA) was computed using thresholds at 0.5, 1, 2, and 4 kHz .

2 . Speech reception threshold in quiet was measured with Central Institute for the Deaf (CID) W-1 spondees using a 2-dB step size .

3 . PBMAX (the maximum score for phonetically balanced word list) was mea-sured using Northwestern University Audi-tory Test No . 6 (NU-6) half-lists . Masking was played to the nontest ear at a level 20 dB below that of the speech in the test ear.

All above testing was carried out monaurally through TDH-50P headphones in an Acoustic Systems double-walled test booth. Pure-tone signals came from a GSI-16 two-channel audiometer. Recordings of the CID W-1 spondees and the NU-6 word lists were played from the Speech Recognition and Identification Materials, Disc 1.1 compact disc produced by the Depart-ment of Veterans Affairs (1991) via the two-channel audiometer. All subjects had symmetric hearing impairment; therefore, the values obtained for both ears were averaged for the analyses . Measures were made at the start of the study only. There were no indications that the thresholds of any individual changed signifi-cantly during the study.

Perceptual-Performance Test

Performance Speech Reception Threshold. A performance SRT was measured both aided and unaided at the start and end of each 3-month wearing period with the HINT materi-als recorded on digital audiotape. The HINT consists of 250 simple sentences, 6 to 8 syllables in length, and accompanying HINT speech spec-trum-shaped noise . The HINT protocol uses an adaptive procedure to obtain the SNR at which the subject correctly identifies 50 percent of the material . On each test occasion, two repli-cations were averaged to obtain a result. Twelve-sentence HINT lists were used . The level of the speech was fixed, and the level of the noise was adjusted . The step size for the initial four sen-tences was 4 dB, and 2 dB thereafter. When a sentence was repeated correctly, the speech noise was increased to make the SNR more adverse; if one or more words were repeated incorrectly, the noise level was decreased to make the SNR less adverse . The final SNR was computed by averaging the SNR of the final six sentences, plus the SNR at which the thir-teenth sentence would have been presented had it existed.

Perceptual Speech Reception Threshold. A perceptual SRT was measured both aided and unaided at the start and end of each 3-month wearing period . A perceptual SRT is defined as the SNR at which the subject believes he or she

can just understand everything that is being said . Subjects were told to nod their head if they could just understand a sentence or to shake their head if they could not . Following this response from the subject, the SNR was adjusted .

The SNR was made more adverse if they could understand everything that was being said and

made less adverse if they could not. Subjects

were encouraged to respond at least once every two to three sentences . As described in the intro-

duction, a previous study (Saunders and Hag-gard, 1992) showed that these instructions yielded perceptual SRTs that were within 1 dB

of performance SRTs with normal-hearing sub-jects (mean = -0.71 dB, SD = 3 .7) . To measure a perceptual SRT, the digital audiotape record-

ing of the HINT materials was re-recorded with the silent intervals between sentences removed

to create the effect of running speech . In this way,

two original lists of 12 sentences were combined

into a single list of 24 sentences . Once again, on

each test occasion, two replications were aver-aged to obtain a result . The same adaptive

41


procedure as for the performance SRT was used, except that the SNR was changed only when the subject indicated that he needed it changed. The final perceptual SRT was calculated by averaging the SNR during the final 10 sen-tences in a list .

Aided Advantage. The aided advantage was computed by subtracting the aided performance SRT from the unaided performance SRT. A pos-itive aided advantage means that the subjects performed better with their hearing aids than without them .

All performance and perceptual SRT mea-surements were carried out in the sound field in an Acoustic Systems double-walled test booth. Sentences were played from a digital audiotape recorder via the GSI-16 audiometer to soundfield speakers . The subject was seated 3 feet away from the speaker, which was located at 0 degrees azimuth. Both speech and noise were presented through this speaker. The level of the speech remained fixed at the subject's aided most com-fortable listening level for HINT materials in quiet. The level of the noise was adjusted as required by the adaptive procedure. Most com-fortable listening levels ranged from 50 to 70 dB SPL with a mean of 62.1 dB and a standard deviation of 3 .7 dB.

Perceptual-Performance Discrepancy. This is the difference between a perceptual SRT and its associated performance SRT. It provides a comparison between the SNR at which a subject perceives he or she can understand all of the HINT sentences and the SNR at which he or she can actually understand the sentences. PPDIS values were calculated by subtracting the per-formance SRT from the perceptual SRT. There-fore, a positive PPDIS means that an individual underestimated his or her hearing ability, whereas a negative PPDIS means that the indi-vidual overestimated his or her ability.

Subjective Ratings of Auditory Difficulties

Three questions were used to assess resid-ual auditory disability for speech, one question was used to evaluate the subjects' impressions of their hearing ability relative to that of normal-hearing individuals, three questions were used to assess residual auditory handicap, and four questions were used to assess hearing aid sat-isfaction (Appendix) .

All questions originated from questionnaires used by the Medical Research Council Institute

of Hearing Research during the National Study of Hearing in the United Kingdom (Davis, 1995). Factor analysis on data from 84 subjects revealed these four scales ; reliability analyses showed the scales to be statistically robust ; that is, alpha values of each scales were greater than .85. These scales are very similar to those obtained by Lutman et al (1987) .

Each of the above ratings was made once per month for aided listening with each of the six hearing aid configurations, resulting in 18 rat-ings in total.

ANALYSES AND RESULTS

T he purpose of this study was to learn whether PPT scores can provide insights into ratings of residual auditory disability and handicap and of hearing aid satisfaction that are not available from other test measures . Thus, only aided PPT scores and aided advantages were analyzed. Performance SRTs were averaged to obtain an average performance SRT, and all PPDIS values were averaged to obtain an aver-age PPDIS. Similarly, all administrations of the rating scales were averaged to obtain an aver-age disability for speech rating, an average handicap rating, an average rating of hearing ability, and an average hearing aid satisfaction rating. In addition to ensuring that the results are not confounded by order of wear versus con-figuration effects, averaging the data also decreases within-subject variability.

Table 2 shows means, standard deviations, maximum and minimum scores, and possible ranges of scores on all variables measured . The subjective ratings encompassed almost the entire range of possible values, and the two 9-point scales each had a similar standard deviation. The standard deviation of the performance SRT and the perceptual SRT are similar to each other and to those of other HINT data from hearing-impaired individuals (e.g ., Valente et al, 1995, 1998). This confirms that the individuals can carry out the perceptual condition as consis-tently as they can the performance condition. It is interesting to note that the group mean PPDIS is almost zero, showing that, as a group, subjects accurately assessed their hearing ability. A group mean PPDIS of zero is not necessary for obtain-ing meaningful data, but it is convenient in that it makes the data easier to interpret: a positive PPDIS value indicates that the subject under-estimated his or her hearing ability; a negative PPDIS indicates that the subject overestimated his or her hearing ability. This is because (a) bet-

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Table 2 Means, SDs, and Ranges

Variable

of Disability,

Mean (SD)

Handicap, and Satisfaction

Maximum and Minimum

Ratings (n = 45)

Possible Range

Performance SRT (SNR) 7 .6 (1 .8) 4.0-12 .4 No limit Perceptual SRT (SNR) 7 .6 (1 .9) 5.1-14 .6 No limit Performance SRT aided advantage (dB) 1 .3 (1 .8) -1 .3-6 .9 No limit PPDIS (dB) 0 .015(l .5) -3.9-3 .7 No limit Aided handicap 5 .7 (1 .7) 3.1-8 .6 0-9 Aided disability for speech 4 .5 (1 .0) 3.0-7 .1 0-9 Aided rating of hearing ability 74 .1 (12 .6) 41-98 0-100 Hearing aid satisfaction 10 .9 (1 .6) 6.7-14 .6 5-15

SRT = speech reception threshold, SNR = signal-to-noise ratio ; PPDIS = perceptual-performance discrepancy.

ter performance is reflected in a more adverse, that is more negative, SNR and (b) the PPDIS is computed by subtracting the performance SRT from the perceptual SRT. The standard deviation of the PPDIS is 1.5 dB, which is sim-ilar to the test-retest reliability of the HINT itself. This indicates that the HINT adaptive pro-cedure and the instruction "hear everything that is being said" yield equivalent SNRs. This is not surprising since the HINT adaptive rules require subjects to repeat all words in a sentence correctly if the SNR is to be made more adverse ; if any word or words are repeated incorrectly, the SNR is made less adverse . Essentially, this becomes an "all or nothing" rule for change .

To evaluate the extent to which routine audiologic test measures and the PPT underlie subjective ratings of auditory difficulties, step-wise multiple regression analyses were carried out. Multiple regression analysis ascertains the combination of independent variables that best explain the variance in a dependent variable . Here the regression analyses were used to deter-mine which test measures best combine to explain scores on the ratings of disability for speech, handicap, rating of hearing, and hear-ing aid satisfaction . Multiple regression analy-sis relies on correlations between variables. The

more highly correlated the independent vari-able is with a dependent variable, the more variance the independent variable will explain . Single outlying points in a data set can cause spuriously high correlation coefficients ; therefore, prior to carrying out the regression analyses, his-tograms of all dependent and independent vari-ables were plotted . Three subjects had outlying data points on one or more variables so their data were omitted from all further analyses . There-fore, data from 45 subjects were analyzed . To

understand the results of the regression analy-ses, it is helpful to see the raw correlations among the independent variables . These corre-

lations are shown in Table 3 . There are very few significant correlations, indicating that the infor-mation provided by each variable is unique to that variable .

Four sets of stepwise multiple regression analyses were carried out to predict scores on the four subjective rating scales . The independent variables used in each regression were age, hearing aid user status (new or experienced), 4F-PTA, SRT, PBMAX, performance SRT, aided advantage, and PPDIS. The results of the regres-sion analyses are shown in Tables 4 to 7. Only those variables that entered the regression equa-tion with a p < .05 are shown. The performance

Table 3

Age

Raw Correlations

4F-PTA

between

SRT-Q

Measured Variables

PBMAX

(n = 45)

PSRT Aided Advantage

4F-PTA -0.07 SRT-Q -0.07 0.64" PBMAX -0.08 -0.02 0.24

Performance SRT 0.10 0.15 -0.07 -0.24 Aided advantage -0.44` 0.39' 0 .07 -0.29 0.18 PPDIS -0.11 -0.10 -0.03 0.24 0.38" -0.08

Correlation significant at *p < .01 ; **p < .001 . 4F-PTA = four-frequency pure-tone average; SRT Q = speech reception threshold in quiet ; PBMAX = phonetically balanced word list

maximum score; SRT = speech reception threshold ; PPDIS = perceptual-performance discrepancy

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Table 4 Results of Multiple Regression Analyses to Predict Handicap (n = 45)

Variable Entering Equation (p < .05) Variance Explained by Variable (Rz Change) (3-Value in Final Equation

PPDIS 17 .6 0.646 Performance SRT 30.3 0.596 Total variance explained 47 .9

PPDIS = perceptual-performance discrepancy; SRT = speech reception threshold .

SRT and the PPDIS entered each of the regres-sion equations, together explaining between 42 .6 and 54.0 percent of the total variance . In addition, user status entered the equation for dis-ability for speech . The direction of the (3-value, combined with the coding of user status, shows that experienced hearing aid users tended to report more residual aided disability for speech than new hearing aid users. The reason for this is not immediately obvious since new and expe-rienced hearing aid users show the same per-formance and hearing acuity. The performance SRT explained more of the variance in handicap scores than did the PPDIS, whereas the oppo-site was true for hearing aid satisfaction . The performance SRT and the PPDIS explain simi-lar degrees of variance in the disability for speech and rating of hearing scales .

To interpret the regression analyses, 0-val-ues (direction of the correlation) and the impli-cations of a high and low score on each variable must be understood . Table 8 provides an inter-pretation of what high and low scores on each variable imply, and the (3-values are provided in Tables 4 to 7. Combining these, it is seen that more reported difficulties and less hearing aid satisfaction are primarily associated with poorer understanding of speech in noise and underes-timation of hearing ability.

Data were next examined on a case-by-case basis to determine whether the combination of PPDIS and performance SRT scores would cor-rectly classify subjects into being "discontent" and "content" hearing aid users. Discontent and

content hearing aid users were defined as follows. For the disability for speech and handicap scales, an individual was defined as being content if his score was below the 25th percentile and was considered to be discontent if his rating was above the 75th percentile since a low score on these scales is a positive finding. Conversely, for the rating of hearing and the hearing aid satis-faction scales, an individual was considered to be content if his rating was above the 75th per-centile and was considered discontent if his score was less than the 25th percentile since low scores on these scales are negative findings . Subjects were also grouped into those with poor versus not poor performance SRT scores and as underestimating or not underestimating their hearing ability based on their PPDIS scores . Poor performance SRT scores were defined as being worse than the mean performance SRT score by more than two standard errors . All other performance SRT scores were considered to be not poor. A subject was classified as under-estimating his hearing ability if his PPDIS score was positive by more than two standard errors ; if not, he was not considered to have underes-timated his hearing ability. Discriminant func-tion analysis was carried out to determine the percentage of subjects correctly and incorrectly classified as being discontent or content when the performance SRT and PPDIS score group-ings were used as the independent variables. Table 9 shows the results in terms of the per-centage of content and discontent subjects who were correctly and incorrectly classified as con-

Table 5 Results of Multiple Regression Analyses to Predict Disability for Speech (n = 45)

Variable Entering Equation (p < .05) % Variance Explained by Variable (Rz Change) ,6-Value in Final Equation

PPDIS 18 .5 0.474 Performance SRT 21 .0 0.511 User 6.3 -0.294 Total variance explained 45.8



Table 6 Results of Multiple Regression Analyses to Predict Aided Rating of Hearing Ability (n = 45)

Variable Entering Equation (p < .05) Variance Explained by Variable (R2 Change) [3-Value in Final Equation

PPDIS Performance SRT

Total variance explained

29 .4 -0.746 24 .6 -0.536

54.0

PPDIS = perceptual-performance discrepancy, SRT = speech reception threshold .

tent and discontent by their PPDIS and perfor-

mance SRT groupings . Together the two vari-

ables correctly classified between 73 and 82

percent of subjects .

DISCUSSION

T he purpose of this study was to determine

whether the PPT provides information about

residual aided disability and handicap and hear-ing aid satisfaction that is not provided by rou-tine audiologic test measures . To this end, data collected from subjects who were taking part in an evaluation of programmable hearing aids were analyzed . Multiple regression analysis was

used to determine which combination of the test measures explained subjects' residual hearing difficulties and their hearing aid satisfaction. The

analyses showed that both understanding of speech in noise and the accuracy with which an

individual estimates his or her ability to under-stand speech in noise underlie reported residual disability for speech, handicap, and hearing aid satisfaction . In other words, both actual hear-ing ability and the perception of that ability are major determinants .

Multiple regression analyses showed that

the combination of ability to understand speech

in noise (performance SRT) and accuracy of esti-

mation of hearing ability (PPDIS) explained up

to 54 percent of the variance in the subjective rat-

ings of residual hearing difficulties and hearing

aid satisfaction . A more positive PPDIS score

(underestimation of hearing ability) and a more

positive performance SRT score (poorer ability

Table 7 Results of Multiple Regression Analyses to Predict Hearing Aid Satisfaction (n = 45)

Variable Entering Equation (p < .05) Variance Explained (RZ) ,B-Value in Final Equation

PPDIS 31 .6 -0.699

Performance SRT 11 .0 -0.358

Total variance explained 42 .6

Pp IS = perceptual-performance discrepancy: SRT = speech reception threshold .

to understand speech in noise) were associated

with greater reported disability and handicap, lower ratings of hearing ability, and less hear-ing aid satisfaction . The percentage of the vari-

ance explained by the PPDIS relative to that explained by the performance SRT varied across

the rating scales . Whether examined in terms

of the percentage of the variance explained or as

a ratio of the total variance explained, the role

played by the PPDIS was greatest in explaining hearing aid satisfaction and second greatest in

explaining rating of hearing ability, whereas the role played by the performance SRT was

greatest in explaining handicap, followed by

disability for speech . Note, however, that both

variables explained variance in each scale . This is presumably because subjective ratings com-

bine actual reality (performance SRT) with an

individual's interpretation of that reality (PPDIS) . An individual's performance SRT score

presumably reflects his or her ability to hear in

a particular test condition, whereas an individ-ual's PPDIS score is likely to be strongly in-

fluenced by nonauditory factors as well, such as

expectations, personality traits, and self-

confidence . This issue is further discussed in

Saunders and Cienkowski (1996) . Other studies that have investigated objective and subjective

(nonauditory) factors in reported handicap, dis-

ability, and hearing aid benefit show that both

dimensions play a role (e .g., Gatehouse, 1990,

1991a, 1994 ; Saunders and Cienkowski, 1996 ;

Cox et al, 1999) . The PPDIS was most effective in explaining

hearing aid satisfaction. This is probably because

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Table 8 Interpretation of Variables

Variable High Score Low Score

Disability for speech Handicap

Hearing rating

Hearing aid satisfaction Performance SRT

PPDIS

Hearing aid user status

Considerable perceived hearing difficulty Hearing loss impacts subject socially and emotionally

The closer the rating is to 100, the closer to "normal" the subject considers his/her hearing to be

More satisfied with hearing aids Unit is SNR ; therefore, a higher value means poorer performance

Positive value means underestimation of hearing ability 2=new

Little perceived hearing difficulty

Hearing loss has little impact on subject The closer the rating is to 0, the further from "normal" the individual considers his/her hearing to be

Less satisfied with hearing aids

Lower value means better performance Negative value means overestimation of hearing ability

1 = experienced SRT = speech reception threshold ; SNR = signal-to-noise ratio ; PPDIS = perceptual-performance discrepancy

the hearing aid satisfaction rating requires the subject to consider not only how well he or she can hear with the hearing aids but also to judge how satisfied he or she is with that improvement. Subjects who do not "like" their hearing aids, for whatever reason, whether this is related to degree of measurable benefit, physical discom-fort, and/or psychosocial issues such as stigma and denial, underestimate how well they can hear with those hearing aids . Gatehouse (1991b) reported a similar but lesser effect . He found that a PPDIS type of measure explained 8.3 percent of the variance in reported benefit from ampli-fication.

Routine audiologic test measures did not enter any regression equation . This is not because another variable preempted their enter-ing since, as is seen in Table 3, the audiologic test measures do not correlate with either the per-

formance SRT or the PPDIS. The fact that the performance SRT and not the audiologic test measures explained variance in subjective audi-tory difficulties illustrates the importance of using real-world test measures that involve suprathreshold test levels in the presence of noise to evaluate aided hearing. As is frequently found, threshold-based measures, such as pure tones and SRT in quiet, are not useful predic-tors of hearing aid benefit, satisfaction, or use (e.g., Kapteyn, 1977 ; Surr et al, 1978; Hickson et al, 1986; Cox et al, 1999).

Discriminant function analysis correctly classified between 73 .3 and 82 .2 percent of sub-jects based on the PPDIS and performance SRT groups (i .e ., underestimated versus not under-estimated hearing ability and poor versus not poor performance SRT score) into contented and discontented hearing aid users. In other words,

Table 9 Classification of "Contented" and "Discontented" Subjects (%) by PPDIS and Performance SRT Scores

Predicted Group

Actual Group Discontent Content Total Correctly Classified (%)

Hearing aid satisfaction Discontent 72 .7 27.3 75 .6 Content 23 .5 76 .5 Handicap Discontent 66.7 33.3 82 .2 Content 12 .1 87 .9

Rating of hearing ability Discontent 81 .8 18.2 73.3 Content 29.4 70.6

Disability for speech Discontent 83.3 16.7 75.6 Content 27 .3 72 .7



by examining a subject's score on just two vari-ables, it was possible to correctly determine whether he was a contented or discontented hearing aid user about 75 percent of the time . This degree of accuracy, from just two variables, seems remarkable, especially because other studies attempting to understand reported hear-ing aid benefit and/or satisfaction explain less variance (Cox et al, 1999) or find that the vari-ance is explained by numerous variables that are relatively complex to measure (e.g ., Gatehouse, 1991b) .

Clinicians are constantly looking for ways to predict whether an individual will be a con-tented or discontented hearing aid user . Such information would help them counsel patients prior to provision of a hearing aid and perhaps also help in the selection of one hearing aid model over another, and ultimately prevent later distress on the part of the user . The data here suggest that the PPT is a valuable tool for under-standing hearing aid satisfaction and reported residual hearing difficulties . It is realized, how-ever, that the data presented were obtained fol-lowing hearing aid wear. Future studies to determine whether the PPT has predictive power, that is, whether PPT results obtained prior to a hearing aid fitting also correlate with hearing aid satisfaction following hearing aid wear, must be carried out .

Further, the PPT may be a useful counsel-ing tool . Saunders et al (1992) found that coun-seling geared toward making OAD patients aware of their PPDIS and thus toward increas-ing confidence in their hearing ability helped patients become less distressed . The majority of studies investigating the effect of counseling on hearing aid use have shown that counseling at the time of hearing aid fitting is effective at increasing hearing aid use and/or decreasing perceived handicap (Surr et al, 1978 ; Brooks, 1979 ; Abrams et al, 1992 ; Kapteyn et al, 1997) . It must therefore be determined whether simi-lar counseling will be effective for increasing hearing aid use among individuals with hearing impairment .

measurement of the PPDIS. Test scores from these two variables alone explained up to 54 percent of the variance in hearing aid satisfac-tion and reported residual auditory difficulties . In addition, the perceptual condition of the PPT is easier for listeners to carry out than other sub-jective intelligibility measures, such as the Speech Intelligibility Rating, because listeners simply have to decide whether they can under-stand everything that is being said . Other tests tend to require more complex ratings, such as the percentage of speech understood. Finally, the test materials used are those of the HINT. The psychometric properties of the HINT materials have been well documented, as has the sensi-

tivity of the test . Thus, it appears that the PPT described here potentially has considerable clin-ical use .

Acknowledgment This work was supported by the Department of Veterans Affairs, Veterans Health Administration, Rehabilitation Research and Development Service and Department of Veterans Affairs Rehabilitation Research and Development Grant #C664-RA and the National Center for Rehabilitative Auditory Research . We thank Arelene Neuman for helpful comments on earlier drafts of this article .

REFERENCES

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Brooks DN . (1979) . Counseling and its effect on hearing aid use. Scand Audiol 8:101-107 .

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Cox RM, Alexander GC, Gilmore C . (1987). Development of the Connected Sentence Test (CST) . Ear Hear 8(Suppl 5): 1195-1265 .

CONCLUSIONS

T he PPT is an efficient test of speech under-standing, with several advantages over

other outcome measures currently available . As described here, it takes approximately 15 min-utes to administer. It provides outcome infor-mation in two dimensions : the objective measurement of performance and the subjective

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Cox RM, McDaniel MD . (1989) . Development of the Speech Intelligibility Rating (SIR) test for hearing aid comparisons. J Speech Hear Res 33:347-352 .

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Davis AC . (1995) Hearing in Adults . UK: Whurr.

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APPENDIX

Residual Auditory Disability for Speech

1. When you are wearing your hearing aids, can you follow what is being said on the radio news when the volume is turned up only enough to suit other people?

(a) not at all (b) great difficulty (c) some diffi-culty (d) easily

48


2 . When you are wearing your hearing aids, can you follow what is being said on the television news when the volume is turned up only enough to suit other people?

might have restrict your enjoyment of your social and personal life compared with oth-

ers around you?

(a) very often (b) quite often (c) rarely (d) never


3. When you are wearing your hearing aids, how much difficulty do you usually have following someone's conversation when other people are talking close by?


Rating of Aided Hearing Ability

Imagine that a young adult has a hearing

ability of 100 and someone who is totally deaf has a hearing ability of 0 . We want you to cir-cle the number that best describes your own

hearing, for each ear separately, when you are wearing your hearing aids :

(a) LEFT EAR 100 90 80 70 60 50 40 30 20 10 0

Young adult Totally deaf person 3.

(b) RIGHT EAR 100 90 80 70 60 50 40 30 20 10 0

Young adult Totally deaf person 4 .

Residual Auditory Handicap (a)

1 . When you are wearing your hearing aids, how often does any hearing problem you

2. When you are wearing your hearing aids, do you get a feeling of being cut off from things because of your difficulty hearing?


3 . When you are wearing your hearing aids, do any hearing difficulties you may have lead to embarrassment?


Rating of Hearing Aid Satisfaction

1 . How satisfied are you with the overall per-formance of your hearing aids?

(a) totally (b) moderately (c) slightly (c) not at all

2. To what extent do the hearing aids fulfill your specific needs?

well (c) moderately well (b) ver y letel y (a) com p (d) slightly (e) not at all Do you consider that you get as much ben-efit from you hearing aid as most other users?

yes no

For talking in a group, I find my hearing aids : very helpful (b) slightly helpful (c) not at all helpful (d) I do not use my aids when talk-ing in a group

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