Cognitive function in relation to hearing aid use

Review International Journal of Audiology 2003; 42:S49–S58

Thomas Lunner Oticon A/S, Research Centre Eriksholm, Snekkersten, Denmark, and Department of Technical Audiology, Linköping University, Linköping, Sweden

Key Words Hearing aids Hearing aid use Ageing Hearing loss Assessment Speech processing Noise processing Speech recognition in noise Cognitive Working memory Reading span Verbal information-processing speed

Cognitive function in relation to hearing aid use Abstract Two experiments were conducted to investigate possible relationships between cognitive function and hearing aid use. In Experiment 1, 72 first-time hearing aid users were tested for speech recognition in noise (Hagerman sentence test) with and without hearing aids. Cognitive function was assessed by tests of working memory (reading span test) and verbal information-processing speed. The results indicate that, after controlling for age and hearing loss, significant correlations exist between the measures of cognitive performance and speech recognition in noise, both with and without hearing aids. High cognitive performance was associated with high performance in the speech recognition task. In Experiment 2, 17 first-time hearing aid users with either high or low working-memory capacity tested an experimental hearing aid which processed the sound differently depending on whether or not speech was detected. The results revealed that those with high working-memory capacity were better than those with low capacity at identifying and reporting the specific processing effects of the aid. This may have implications for how reported results should be interpreted in a research context, how a person’s rehabilitation needs are formulated, and how hearing aid controls should be supervised. In conclusion, careful attention should be paid to the cognitive status of listeners, as it can have a significant influence on their ability to utilize their hearing aids.

Introduction Will the hearing-impaired wear cognitive aids in the future? The question arises because hearing aids are becoming increasingly complex, and we actually do not know whether the increased complexity is equally beneficial for all subjects. Complexity in the signal processing carried out by a hearing aid may be cognitively demanding to differing degrees for different persons. If so, the hearing aid fitting may need to be tailored to the individual user’s cognitive ability. In line with technical progress, signal processing in hearing aids is becoming increasingly complex. For instance, multichannel wide-dynamic-range compression with various sets of time constants has entered the scene during the last decade, as well as greater flexibility in tailoring the frequency response to individual requirements, different kinds of noise reduction schemes, and directional microphones. Many of the new signalprocessing systems are intended to compensate for the perceptual consequences of cochlear hearing loss, such as reduced sensitivity, abnormal growth of loudness, and reduced frequency selectivity (e.g. Moore, 1996). However, the development of such sound-processing schemes tends to ignore the fact that processing of sound information includes both perceptual and cognitive processing. Thus, differences in individual listeners’ cognitive function may lead to differing abilities to perform with (and benefit from) any given signal-processing scheme. Incoming auditory or visual stimuli are processed through a

cognitive system that allows us, for a brief period of time, to both store and process limited amounts of information, e.g. in the case of comprehension of sentences presented either auditorily or visually. This system is often referred to as working memory (e.g. Baddeley, 1986). Working memory is involved in resource allocation in complex tasks. Some of the best evidence that working memory plays a role in higher-level cognition is the substantial correlation between verbal working-memory capacity on a reading span task and performance on languageunderstanding tasks (Daneman & Carpenter, 1980; Just & Carpenter, 1992). Correlations have also been found between measures of working-memory capacity and performance on reasoning tasks (e.g. Carpenter, Just & Shell, 1990). Verbal information-processing speed is the speed with which lexical information can be accessed from long-term memory (Hunt, 1985). It correlates, for example, with general verbal ability (Hunt, 1985), reading comprehension (Baddeley, Logie, Nimmo-Smith & Brereton, 1985), age (Salthouse, 1982), and sentence-based speech reading (Rönnberg, Arlinger, Lyxell & Kinnefors, 1989; Rönnberg, 1990; Lyxell & Rönnberg, 1992). The aim of this paper is not to delve into the modelling of cognitive functions, but rather to investigate whether any aspects of cognitive function correlate with aspects of hearing aid use. Nevertheless, the characteristics of cognitive function that would be included in any such modelling would certainly include working-memory performance and verbal information-processThomas Lunner Oticon A/S, Research Centre Eriksholm, Kongevejen 243, DK-3070 Snekkersten, Denmark E-mail: [email protected]

effective use of linguistic context by the elderly. Pichora-Fuller et al (1995) also showed compensatory effects of context. Thus, cognitive factors can both enhance and limit auditory performance in elderly listeners. Fourth, processing in the hearing aid itself may be cognitively demanding. Different non-linear signal-processing schemes may make differing cognitive demands on the listener. For example, in multichannel compression, different speech (and noise) cues may be emphasized and distorted differently, depending on the time constants used in the compression regulation system (see Gatehouse et al, this supplement). The individual’s ability to benefit from such cues may be dependent on cognitive function. Fifth, the hearing aid dispensing process may be dependent on the hearing aid user’s cognitive function. When hearing aids are fitted, the users identify and report their experiences with the new hearing aids. Their statements are used to fine-tune the hearing aid. The ability to identify and report specific effects of hearing aid signal processing may be seen as a kind of reasoning task. Thus, cognitive function may be important for the person’s ability to report on the effects of, for example, different kinds of noise-processing schemes and/or effects of directional microphones. The above listing is by no means comprehensive, but is rather a sample of possible issues regarding interactions between cognitive function and hearing aid use. Here, we will look more closely at two hypotheses:

ing speed performance. For a recent review of cognitive models, see Miyake & Shah (1999). In order to better understand how auditory function and hearing aid use might interact with cognitive function, several issues have to be considered, including the consequences of cochlear damage, ageing, working-memory capacity, verbal information-processing speed, and signal processing in hearing aids. First, it seems that a cochlear hearing loss makes listening in adverse conditions more cognitively demanding (information degradation hypothesis, according to Schneider & PichoraFuller (2000)). For example, Pichora-Fuller (this supplement) argues that presbyacusic auditory systems are slower and more asynchronous than intact auditory systems. According to Pichora-Fuller, Schneider & Daneman (1995), cochlear damage and possibly other age-related differences in auditory processing affect speech understanding not only by reducing the amount of information coming through the perceptual channel, but also indirectly because effortful listening consumes cognitive resources that could otherwise be allocated to the storage of information in working memory (see also Schneider, Daneman & Pichora-Fuller (2002), Wingfield & Tun (2001), and Wingfield & Stine-Morrow (2000)). This reduces the ability to remember what has been said, at least in adverse listening conditions, by providing a ‘noisier’ signal for the brain to interpret. Thus, sentence performance under difficult listening conditions may be correlated with cognitive function. Furthermore, there is evidence that hearing impairment per se may contribute to cognitive dysfunction in older adults (deprivation hypothesis); see, for example, Appollonio, Carabellese, Magni, Frattola & Trabucci (1995), Appollonio, Carabellese, Frattola & Trabucci (1996), and Uhlmann, Larson, Rees, Koepsell & Duckert (1989). Second, individual differences in working-memory capacity and/or verbal information-processing speed may correlate with auditory performance as they correlate with language-processing performance. Hearing-impaired listeners miss information in acoustically demanding everyday life situations even when using hearing aids. They have to guess and fill in words to get the message. This processing is cognitively demanding, and therefore its effectiveness may be dependent on working-memory capacity and/or verbal information-processing speed. If cochlear damage indirectly draws resources from working memory in effortful listening situations, as discussed above, then the listener’s overall working-memory capacity may also influence auditory performance indirectly. Third, ageing may influence both perceptual and cognitive functions (common cause hypothesis). For instance, Tun and Wingfield (1999) showed that listening performance was predicted not only by individual differences in hearing ability but also by speed of processing, which underscores the combined role of age-related auditory and cognitive changes in spoken language. Baltes & Lindenberger (1997) investigated 687 individuals from 25 to 103 years of age, and found strong ageassociated links between cognitive and sensory functioning, which they interpreted as reflecting brain ageing. Furthermore, Wingfield (1996) argued that two cognitive factors, cognitive slowing and age-related memory constraints, are of especial importance for auditory performance in elderly adults. For instance, elderly listeners show special vulnerability to timecompressed speech, but this decline is mitigated by more

Figure 1. Mean thresholds and threshold ranges for the subjects participating in Experiment 1 (n = 72). Average of left and right ears.

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1. Sentence performance in noise may be correlated with cognitive function. 2. The ability to identify and report specific effects of complex signal processing in the hearing aid may depend on cognitive function. In order to test these hypotheses, two experiments were performed.

Hearing threshold (dB HL)

Average HTL including min./max. range

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0.5 1 2 Frequency (kHz)

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Experiment 1 was an investigation of the possible link between cognitive function and speech recognition threshold in noise (with and without hearing aids). In Experiment 2, we studied the relationship between working-memory capacity and the ability to identify and report specific effects of complex signal processing. This was tested with hearing aids that process signals differently in situations dominated by noise. The local ethics committee approved the two experiments.

Experiment 1: Sentences in noise and cognitive function Working memory is believed to be a general information-processing system. Thus, testing of cognitive function may be performed by either visual or auditory presentation. By using a visual presentation, we may avoid cognitive performance being affected by possible extra-cognitive loading caused by the individual hearing impairment. If significant correlations are found between the visual cognitive tests and the speech test in noise, then it seems reasonable to surmise that cognitive function is important for speech recognition in noise.

Methods COGNITIVE FUNCTION TESTS

The cognitive tests were performed with an application developed for a PC (Rönnberg et al, 1989; Hällgren, Larsby, Lyxell & Arlinger, 2001). Stimuli were presented on the screen. The test words were presented in Swedish. WORKING-MEMORY TEST

Reading span is a working-memory test designed to tax memory storage and processing simultaneously (Daneman & Carpenter, 1980). The subjects’ task was to comprehend sentences and to recall either the first or the final words of a presented sequence of sentences (Baddeley et al, 1985). The words were presented in a word-by-word fashion, at a rate of one word per 0.80 s. Half of the sentences were absurd (e.g. ‘The train sang a song’), and half were normal (e.g. ‘The girl brushed her teeth’). The subjects’ task was to respond ‘yes’ verbally (for a normal sentence) and ‘no’ verbally (for an absurd sentence) during a 1.75-s interval after each sentence. After a sequence of sentences (three, four, five or six sentences in ascending order), one of the words ‘First’ or ‘Final’ was displayed on the screen, indicating that the subjects should start to recall either the first or the final words of all the three, four, five or six sentences in the sequence. The order (‘First’ or ‘Final’) was randomized. The performance measure was the percentage of the number of totally presented words correctly recalled. TEST OF VERBAL INFORMATION-PROCESSING SPEED

The subjects were given a rhyme judgment test, in which they had to decide whether two simultaneously presented words rhymed. The two rhyming words were orthographically dissimilar in spelling (e.g. DAGS–LAX (Lyxell, Rönnberg & Samuelsson (1994)). The subjects were to respond by pressing predefined buttons for ‘yes’ and ‘no’ answers. Half of the pairs rhymed, and half did not. The performance measure was the response time in milliseconds.

Cognitive function in relation to hearing aid use

SPEECH RECOGNITION IN NOISE TEST

Aided and unaided speech recognition in noise was measured by determining the signal-to-noise ratio (SNR) that yielded 40% correct recognition of test words using lists of 10 lowredundancy five-word sentences in an adaptive test procedure (The Hagerman Sentences (Hagerman & Kinnefors (1995)). Since the sentences had low redundancy, subjects could not make use of context to guess the sentences. The speech material, as well as the competing speech-shaped noise, was recorded on CD (see Hagerman (1982) for details on the speech material and the speech-shaped noise) and presented through a single frontally located loudspeaker in an audiometric test room. The noise level was variable, and aided and unaided performance were tested at a speech level of 70 dB SPL (C-weighted equivalent level). The outcome measure from this test is the SNR yielding 40% correct recognition. The lower the SNR for 40% correct, the better the performance.

Subjects and hearing aids Seventy-two first-time hearing aid users, 32 females and 40 males, with a mean age of 67 years (range 33–89 years), were chosen from the patient population at the University Hospital of Linköping. The subjects fulfilled the following criteria: they were all bilaterally fitted with the same type of non-linear signalprocessing hearing aids (Oticon Digifocus), and had used the aids for about 1 year at the time of testing. Figure 1 shows the mean hearing threshold levels (HTLs) and ranges. All subjects had normal vision, or normal vision with eyeglasses.

Results Table 1 shows the average results and standard deviations of the speech-in-noise test, as well as the cognitive test results. Furthermore, data are shown for two variables that can be expected to covary with the other variables, age and average hearing threshold. Age should be expected to correlate with the cognitive tests (e.g. Salthouse, 1982). Pure-tone average hearing threshold (average 250 Hz to 6 kHz) should be expected to correlate with speech recognition in noise (e.g. Hagerman, 1984; Humes et al, 1994; Moore, 1996). The average values for speech recognition in noise correspond well with previously presented data (e.g. Arlinger, Billermark, Öberg, Lunner & Hellgren, 1997). The cognitive results are in reasonable agreement with previous studies (Lyxell et al, 1996). The age and pure-tone average values are as expected for the chosen population (firsttime users at a Swedish hearing clinic). A correlation matrix was calculated for the variables listed in Table 1, and is shown in Table 2. As can be seen from Table 2, substantial correlations were found. The expected correlations between age and the cognitive variables were found. As subjects get older, cognitive performance becomes worse (higher age corresponds with longer reaction time and lower workingmemory capacity). Also, the expected correlation between speech recognition in noise and hearing thresholds was found. Larger HTLs correspond to worse speech recognition in noise (higher SNR is needed to recall 40% correct). The correlation between age and average HTL indicates that hearing loss increases with age, which was also an expected result. Verbal information-processing speed (rhyme) and reading span were correlated, indicating that a longer reaction time is associated with lower working-memory capacity. Lunner

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Table 1. Mean and standard deviations for the speech recognition in noise, cognitive function variables, and subject description variables Mean SNR in noise WO (dB) 2.0 SNR in noise HA (dB) 2.9 Rhyme (ms) 1723 Reading span (no. of items correct) 24 Age (years) 67 HTL average (dB HL) 47

Table 2. Correlation matrix using Pearson correlations SNR in noise WO

SD 3.1 2.3 550 9 12 8.9

SNR in noise, HA Rhyme Reading span Age HTL average

0.78a 0.39a 0.53a 0.55a 0.49a

SNR Rhyme Reading Age in noise span HA 0.45a 0.61a 0.54a 0.47a

0.48a 0.35a 0.64a 0.26a 0.33a 0.43a

WO, without hearing aid; HA, with hearing aid; SD, standard deviation

a

However, we also found the hypothesized correlations between speech recognition in noise variables and the cognitive variables. The correlation between reading span and SNR in noise indicates that large working-memory capacity is associated with low SNR in noise, both aided and unaided. Furthermore, short reaction time in the rhyme test also corresponds to low SNR in noise. Figure 2 shows scatter plots of the speech recognition in noise variables versus the cognitive variables. Figure 2 also shows the Pearson correlations with 95% confidence limits. The difference between aided and unaided SNR in noise (i.e. hearing aid benefit, not shown in Table 2) did not show a significant correlation with cognitive performance. This may indicate that hearing aid benefit is not dependent on cognitive function (for this particular choice of hearing aid, speech-innoise test, presentation level, and noise type). Multiple regression analysis was performed to control for the correlations of age and HTL average. Table 3 shows the correlations between the variables for speech recognition in noise and the cognitive function variables when age and HTL average were partialled out. As can be seen from the table, correlations between the cognitive function variables and the speech-in-noise variables are still significant after controlling for age and average HTL. This constitutes the main result of Experiment 1: the results indicate that good cognitive function is important for good performance in demanding listening situations, both with and without hearing aids. In connection with another study, a further 30 subjects fulfilling the same criteria as above were tested only with the reading span test and in the aided condition with the SNR in noise test. The correlation between reading span and the SNR in noise test was –0.60, i.e. about the same as the correlation found above.

were recruited from the patient population at the University Hospital of Linköping. Forty-nine subjects were pre-tested with the reading span test. The result of the test is shown in Figure 3. To maximize differences in working-memory capacity, only those with especially high or especially low results were invited to participate in the field test. The limits for high and low performance were arbitrarily set to ≤ 16 and ≥ 26, respectively. Thus, about 25% of the subjects were assigned as high cognitive performers (High-Cog), about 50% as normal performers, and about 25% as low performers (Low-Cog). Nine subjects with high working-memory performance and eight subjects with low performance participated in the field test, nine females and eight males. Their average age was 66 years (range 48–78 years). Figure 4 shows the mean HTLs and ranges.

Experiment 2: Hearing aids which process signals differently in situations dominated by noise: cognitive function and sensitivity to processing effects In Experiment 2, we studied the relationship between workingmemory capacity and the ability to identify and report specific effects of an experimental hearing aid in a field test. The experimental aid processed the sound differently depending on whether or not speech was detected as being present in the input signal.

Subjects and methods

Statistically significant (p < 0.05) WO, without hearing aid; HA, with hearing aid.

Experimental aids The experimental aid processed the sound differently depending on whether or not speech was detected as being present in the input signal. The idea behind the signal processing was to increase the audibility of speech sounds (both in quiet and in noisy backgrounds) and to reduce background sound if no speech was present. If no speech was present, the signal processing entered ‘comfort mode’, with lower amplification, and with compression characteristics that reduced the dynamic range of the output. On the other hand, if speech was present, the signal processing entered ‘speech mode’, with higher amplification and compression characteristics that provided a larger dynamic range of the output than in the ‘comfort mode’. The experimental hearing aid had a program switch with two settings, A and B, programmed as follows: (A) Speech-dependent setting: process sounds with the speechdependent signal processing as described above (‘speech mode’ in the presence of speech, and ‘comfort mode’ in the absence of speech). (B) Reference setting: always process sounds in ‘speech mode’.

Table 3. Multiple regression analysis to control for age and average HTL Partial correlations SNR in noise WO SNR in noise HA

Reading span

Rhyme

0.27 0.40a

0.24a 0.30a

a

a

Subjects who had no previous experience of hearing aid use

Statistically significant (p0.05) WO, without hearing aid; HA, with hearing aid.

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(a)

(b)

(c)

(d)

Figure 2. Correlation between cognitive variables and speech recognition in noise variables (n = 72). Pearsson correlations with 95% confidence limits for the correlation coefficient. Low (negative) SNR means high performance in noise. (a) Reading span versus SNR in noise with hearing aid. (b) Reading span versus SNR in noise without hearing aid. (c) Rhyme versus SNR in noise with hearing aid. (d) Rhyme versus SNR in noise without hearing aid.

The reference setting was included to allow for direct comparisons between A and B. The only difference between A and B was the inclusion of the ‘comfort mode’ in setting A. Therefore, the differences that were expected to be reported in the field test were differences in the way that sounds were processed in the absence of speech.

Field test procedure All subjects were bilaterally equipped with experimental in-theear devices. They were fitted with the reference setting (i.e. only reference setting active and the A/B switch inactivated) and wore this for 2 months to become acclimatized. After this period, the A/B switch was activated, and the subjects were asked to compare the speech-dependent setting and the reference setting over a 1-month period. The subjects were not informed of which Cognitive function in relation to hearing aid use

setting represented the reference setting and which the speechdependent setting.

Questionnaire To evaluate the differences, we used a questionnaire in which the subjects reported the performance of the two settings in different listening situations. The situations are listed in Table 4. The author classified the questions into situations that probably are dominated by speech (S), noise (N), or both speech and noise (SN). (The classifications were not known to the subjects.) The subjects rated each listening situation for both the experimental setting and the reference setting by placing two separate marks on a visual analogue scale graded from 0 to 10, as shown in Figure 5. The outcome measure was the difference between the two ratings. Lunner

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Reading span test

Total score (max=54)

Figure 3. Histogram of reading span pre-test results. Number of words correctly recalled (maximum 54 words). Only subjects with results 16 or results 26 were invited to participate in Experiment 2.

Table 5 lists all specific situations in which the average difference was rated significantly different from zero (±95% confidence interval does not span zero), for at least one of the subject

groups. No significant differences were found in situations where speech was present. This is in accordance with expectations, since signal processing in the speech-dependent setting and that in the reference setting were identical for situations with speech present. All specific situations listed in Table 5 were situations that included significant amounts of noise but with no speech present, i.e. situations where we would expect differences between the speech-dependent setting and the reference setting. All situations had averages greater than zero, indicating that the speechdependent setting was rated higher than the reference setting. However, note that the significant differences were found only among listeners in the group with high cognitive performance, indicating that only those listeners were able to identify the situations where the speech-dependent processing was effective. Figure 6 shows, for each situation, the average difference in rating between the two settings. The situations were ranked and plotted according to the results of the group with high cognitive performance. Thus, situations to the left were those situations where the difference between the speech-dependent setting and the reference setting was greatest in the group with high cognitive performance. As can be seen from Figure 6, the group with high cognitive performance rated the speech-dependent setting as better in all but one of the situations with noise but no speech (N), but rated both settings equal in situations containing speech: (S) and (SN). The group with low cognitive performance did not report such a setting-dependent difference for different situations; rather, they tended to rate the speechdependent setting slightly higher in all situations. This may indicate that A was better for both groups, but that the listeners with low cognitive performance were merely not able to report details of how, or it may indicate that they obtained little or no extra benefit with A in the specific situations. Nevertheless, across all situations, A was rated significantly higher for both subject groups. This may mean that both subject groups had more benefit from A, but the ability to report details was different between the two subject groups. It

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Figure 4. Mean thresholds and threshold ranges for the subjects participating in Experiment 2 (n = 17). Average of left and right ears.

Results AVERAGE RATINGS ACROSS LISTENING SITUATIONS Ratings different from zero may indicate identified differences between settings A and B. The results are summarized in Table 5. The ±95% confidence intervals for the average differences A–B across all listening situations were positive and significantly different from zero for subjects with both high and low workingmemory performance. This indicates that both subject groups overall rated the speech-dependent setting higher than the reference setting. SITUATION-SPECIFIC RATINGS

Table 4. Questions in questionnaire. Question numbers and corresponding classifications into situations which are probably dominated by speech (S), noise (N), or both speech and noise (SN) How good are the hearing aids at: No. (class) q1 (S) q2 (S) q3 (SN) q4 (N) q5 (SN) q6 (N) q7 (S) q8 (S) q9 (S) q10 (N) q11 (SN) q12 (SN) q13 (SN) q14 (S) q15 (SN) q16 (SN) q17 (S) q18 (SN) q19 (S) q20 (S) q21 (N) q22 (N) q23 (N) q24 (N)

Making speech as understandable as possible Making speech as comfortable as possible Suppress loud sounds Making sure that continuous noise does not annoy or disturb you Allowing you to detect sounds that change in level Keeping background noise to a minimum Allowing your own voice to sound natural Allowing your own raised voice to sound natural (own raised voice natural) Helping you to catch the beginnings of sentences Allowing comfortable listening when in a motor car Helping you to understand speech when in a motor car Allowing you to hear alerting sounds such as door or telephone bells Making quiet sounds loud enough so that you can hear them Helping you to understand a dialogue in quiet Helping you to understand a dialogue in a car Helping you to understand a dialogue in the street Helping you to understand a dialogue in general Helping you to understand a dialogue in a crowd Helping you to understand when listening to the television Providing pleasant loudness of the own voice Providing pleasant loudness of sounds in the street Minimize disturbance of a vacuum cleaner Minimize disturbance of pouring water Minimize disturbance of noise in a car

seems that the group with high cognitive performance had exceptional ability to grasp the details in the signal processing, and to understand how they should report their experiences in the questionnaire. This was not the case for the group with low cognitive performance. One explanation for the differences

Very poor

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Figure 5. Rating scales used in the questionnaire. Subjects made separate marks for the speech-dependent setting and the reference setting.

could be that the group with low cognitive performance had poorer ability to grasp details in the signal processing, and therefore did not report the details, but only their general (positive) experience distributed across all questions. Another explanation could be that they had benefit from A in the same situations as those with high cognitive performance, but they simply did not understand how to report their experiences in the questionnaire. To summarize, the main result of Experiment 2 was that listeners with high cognitive performance were better than those with low cognitive performance at identifying and/or reporting the specific effects of the speech-dependent signal processing.

Discussion The results from Experiment 1 indicate that cognitive function is correlated with performance in demanding listening situations, both with and without hearing aids, even when age and hearing loss are accounted for. The results differ somewhat from those of Humes et al (1994) and van Rooij and Plomp (1992), who concluded that measures of hearing loss alone explained most of their results, and that cognitive function accounted for little or no additional variance. However, differences in assessment measures may explain some of the differences between the studies. Humes et al (1994) used the well-established Wechsler Scales, WAIS-R and WMS-R (Wechsler, 1981, 1987), to assess cognitive function. The memory testing (e.g. digit span) in the Wechsler tests does not include measures that tax working-memory storage and processing simultaneously as extensively as, for example, the reading span test. It is also known that simple span measures such as digit span only show small or non-significant correlations with age

Table 5. Differences in ratings between the speech-dependent setting (A) and the reference setting (B). A–B Ratings

High–Cog. Mean difference

Low–Cog. Mean difference

q1-q24

Situation Average rating across situations

0.21a

0.25a

q4 (N) q22 (N) q23 (N) q6 (N) q24 (N) q10 (N)

Specific situations Making sure that continuous noise does not annoy or disturb you Minimize disturbance of a vacuum cleaner Minimize disturbance of pouring water Keeping background noise to a minimum Minimize disturbance of noise in a car Allowing comfortable listening when in a motor car

1.0a 1.0a 0.8a 0.8a 0.6a 0.5a

0.4 0.2 0.3 0.3 0.2 0.4

Average rating across situations and situation-specific average ratings where the average difference was rated significantly different from zero for at least one of the cognitive performance groups. a ± 95% confidence interval did not span zero.

Cognitive function in relation to hearing aid use

Lunner

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Plot of means 1.2 1.0

(*)

(*) (*)

(*)

0.6

(*) (*)

0.4 0.2 0.0 –0.2 –0.4

q4 (N) q22 (N) q23 (N) q6 (N) q24 (N) q10 (N) q2 (S) q20 (S) q16 (S N) q21 (N) q3 (S N) q7 (S) q15 (S N) q18 (S N) q5 (S N) q8 (S) q14 (S) q19 (S) q11 (S N) q12 (S N) q13 (S N) q9 (S) q1 (S) q17 (S)

Difference in rating (A–B)

0.8

Low Cogs High Cogs

Question no.

Figure 6. Average differences in rating between the speech-dependent setting (A) and the reference setting (B). The specific situations were ranked and plotted according to the cognitive high performers’ results. An asterisk (*) denotes a difference in average rating where the ±95% confidence interval was greater than or less than zero.

(e.g. Craik, 1977; Wingfield & Tun, 2001), but reading span tests do show age effects, as in the present study (e.g. Gick, Craik & Morris, 1988; Light & Anderson, 1985; Verhaegen, Marcoen & Goosens, 1993). Among others, Daneman and Merikle (1996) argue that measures that tax the combined processing and storage capacity of working memory (e.g. reading span, listening span) are more sensitive measures of cognitive function than are measures that tax only the storage capacity (e.g. word span, digit span). Thus, the lack of correlation between cognitive and speech recognition performance in the Humes et al (1994) study may be attributed to their cognitive tests not being sensitive enough. Also, speech testing using sentences as in the current study may tax memory performance more than single-word testing as used in the Humes et al (1994) study. Thus, the differences in results between the previous study and the current study could possibly be explained by the more demanding test conditions used in the latter. Mackersie, Prida & Stiles (2001) presented another recent study that supports a correlation between speech perception and cognitive factors. They suggested that the abilities to perceptually separate pitch patterns and to separate sentences spoken simultaneously by different talkers were mediated by the same underlying perceptual and/or cognitive factors. Their data do not support the conclusion that competing sentence perception is affected by reduced frequency selectivity, as would be the case if hearing loss were the only factor that affected speech performance. Furthermore, Alain, McDonald, Ostroff & Schneider (2001) found age-related changes in detecting a mistuned harmonic. These results are consistent with an agerelated decline in parsing simultaneous auditory events, which may contribute to the speech perception difficulties in the elderly. The test conditions in which testing is performed are probably of the utmost importance to the results obtained. For example, the effects of the particular choice of hearing aid

signal-processing scheme, speech-in-noise test, presentation level, noise type and SNR may be differently influenced by cognitive function. We were not able to show that hearing aid benefit was correlated with cognitive function in Experiment 1. However, this may be because the test conditions used in the current study were too insensitive to reveal any correlations. However, Gatehouse et al (this supplement) found relationships between benefit and cognitive function under various test conditions. For example, they found that cognitive high performers improved more than cognitive low performers on speech-innoise benefit scores when comparing modulated noise to steadystate noise. This indicates that the cognitively high-performing subjects were better than the low-performing subjects at utilizing the modulations in the noise when using hearing aids. So far, we have discussed only direct relationships between cognitive function and speech recognition under various test conditions. However, cognitive function may also have indirect relationships with the use of hearing aids. The results from Experiment 2 revealed that listeners with high cognitive performance were better than those with low cognitive performance at identifying and/or reporting specific effects of a certain hearing aid processing scheme. This may have implications for how results should be interpreted when evaluating hearing aids in a research context. A sample of subjects with low cognitive function may not reveal relationships that would have been found with another sample with higher cognitive skills. However, the preferential use of test subjects who previously have shown exceptional ability to discern differences might also lead to unrepresentative results. Furthermore, the different abilities to identify and/or to report processing effects may have implications for dispensing of hearing aids. The hearing aid users’ ability to express aspects of their experience with hearing aids may influence the fitting and fine-tuning of the hearing aid. Individuals with high cognitive performance may be better at identifying and expressing their

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specific listening preferences, but, on the other hand, they may also be difficult to satisfy if their preferences are difficult to fulfil with the hearing aids at hand. This implies that those with high cognitive performance may be more able to clearly formulate and express their needs. On the other hand, individuals with low cognitive performance may be difficult to satisfy if they cannot express how their needs are not being met. Therefore, they may need more help to formulate their needs. Different abilities to formulate needs because of different cognitive skills may therefore have consequences for individual counselling in relation to hearing aid fitting and fine-tuning. Cognitive function may also affect the ability to adjust or supervise controls on the hearing aids. For example, use of volume control, choice of microphone or telecoil input, use of multi-program controls and selection of directional microphones may include aspects of identifying changing listening circumstances and reacting to those by applying appropriate action via the controls. Those with low cognitive performance may have problems in taking appropriate action under changing listening circumstances. The use of systems that automatically identify and react to changing listening circumstances may be beneficial, but automatic action may also induce effects that are confusing, surprising or distracting, if not properly understood by the user.

Summary Differences in individual listeners’ cognitive function may lead to differing abilities to perform with (and benefit from) hearing aids. Experiments 1 and 2 were designed to investigate some possible relationships between cognitive function and hearing aid use. The results from Experiment 1 indicate that measures of working-memory capacity and verbal information-processing speed correlate with speech recognition in noise. The pattern of results was consistent with the idea that when auditory processing becomes very difficult, because of an adverse listening situation and a damaged cochlea, the individual’s cognitive function influences performance to a high degree (PichoraFuller et al, 1995). In other words, it is not only the peripheral hearing loss that limits performance under demanding listening conditions. However, the results did not indicate that the hearing aid benefit (i.e. the difference between aided and unaided performance) was correlated with cognitive function under the chosen test conditions (for this particular choice of hearing aid, speech-in-noise test, presentation level, and noise type). Nevertheless, other recent studies (Gatehouse et al, this supplement) indicate that hearing aid benefit is correlated with cognitive function under slightly different test conditions (e.g. when modulated noise is used instead of unmodulated noise). The results from Experiment 2 revealed that those with high cognitive performance were better than those with low cognitive performance at identifying and/or reporting the specific effects of a certain hearing aid processing scheme. The results are in line with the notion that the person’s reasoning ability, in this case to identify, analyse and give details of their experiences of a certain type of signal processing, is dependent on cognitive function. This may have implications for how reported results should be interpreted in a research context, how a person’s Cognitive function in relation to hearing aid use

rehabilitation needs are formulated, and how hearing aid controls should be adjusted/supervised. All in all, it seems that careful attention should be paid to the cognitive status of the listeners, as it can, in a broad sense, have a significant influence on their ability to utilize their hearing aids.

Acknowledgments We wish to thank all subjects who participated in the experiments. We also wish to thank Marie Öberg, Gunilla Wänström and Erica Billermark for their assistance during the project. The project involved cooperation between the Department of Neuroscience and Locomotion, Linköping University, Sweden, and Oticon Research Centre, Eriksholm, Snekkersten, Denmark.

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