Starkey Research & Clinical Blog

The DSL 5.0a is a successful fitting formula for adults

Fit to Targets, Preferred Listening Levels, and Self-Reported Outcomes for the DSL v5.0a Hearing Aid Prescription for Adults

Polonenko, M.J., Scollie, S.D., Moodie, S., Seewald, R.C., Laurnagaray, D., Shantz, J. & Richards, A. (2010) Fit to targets, preferred listening levels and self-reported outcomes for the DSL v5.0a hearing aid prescription for adults. International Journal of Audiology 49, 550-560.

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

The importance of perceived benefit for successful hearing aid fittings is well established. According to two MarkeTrak studies by Sergei Kochkin (2005, 2007), perceived benefit was the number one factor contributing to hearing aid user satisfaction.  Similarly, the lack of benefit was the most commonly cited reason for hearing aid returns.  Perceived benefit from hearing aids may be determined by a number of factors, but the appropriateness of the individually fitted gain is one of the main contributors (Cox & Alexander, 1994).

The Desired Sensation Level (DSL) prescriptive method was originally developed for children and prescribes targets that are generally very close to children’s preferred listening levels. However, DSL v4.1 targets have been found to prescribe gain that is 9 to 11 dB greater than adult preferred listening levels (Scollie et al., 2005).  Therefore, DSL v5.0a was developed with lower perceived loudness levels, ones that more closely approximate the needs of adult hearing aid users.

The success of a hearing aid prescription can be measured in terms of clinical efficacy, or how closely the hearing aid settings achieve a desired clinical result or test outcome. One such measure is the Preferred Listening Level (PLL). The PLL is defined as “the sound pressure level at the eardrum that the person chooses or prefers for listening to hearing aid amplified speech”(Cox & Alexander, 1994) and represents a compromise between comfort, intelligibility, background noise and distortion (Cox, 1982).  One method of measuring the PPL is by instructing listeners to adjust the volume setting of their hearing instruments to the level that sounds best to them, as they listen to speech presented at a conversational level.

A related but different way to determine the success of a hearing aid fitting strategy is measure effectiveness, or how well hearing aid settings help the user function in real-world situations.  One commonly used measure of hearing aid effectiveness is the Client Oriented Scale of Improvement or COSI (Dillon et al., 1997).  On the COSI questionnaire, the hearing aid user lists up to 5 typical listening situations in which he struggles to hear or would like to hear better.  Following a period of acclimatization, they rate the degree of perceived change in these situations as well as their final ability to function in each situation.

Although the DSL v5.0a prescriptive method was specifically developed for adults with acquired hearing loss, there have been relatively few studies evaluating it. Therefore the current authors sought to determine the electroacoustic feasibility, clinical efficacy, and effectiveness with adult hearing aid users. They had three primary goals:

1.  To measure final fit versus targets in a clinical environment

2.  To evaluate the preferred listening levels (PLLs) of adults versus the DSL v5.0a targets

3.  To measure the effectiveness of the DSL v5.0a prescription as reported on the COSI

Thirty subjects with predominantly sensorineural hearing loss participated in the study. Nineteen were new hearing aid users and eleven were experienced hearing aid users. Twenty-four were fitted binaurally, six were monaural users. Subjects were fitted in private clinics and the audiologists were specifically instructed to program and adjust the instruments to meet the patients’ needs, rather than to meet prescriptive targets.

Hearing aid fittings were matched to DSL 5.0 prescribed targets and verified with simulated real ear measurements, to ensure consistency between test sites and to promote replicable measures. Hearing aids were set to their primary programs and were measured in 2cc couplers, after individual Real Ear to Coupler Differences (RECD) were measured.  Following electroacoustic measures, the aids were fitted to the patients’ ears and adjustments were made based on patients’ subjective satisfaction. These procedures were not carried out according to any protocol established by the authors; the audiologists conducted fine tuning adjustments as needed for each individual. After an approximately 30-day period, subjects returned to the clinics for fine tuning.  After a total acclimatization period of 90 days, preferred listening levels (PLLs) and COSI outcome evaluations were conducted.

Electroacoustic analyses revealed that the clinical fittings were significantly correlated with the DSL v5.0a targets.  Sixty-eight percent of initial fittings were within 2.9 to 4.2 dB of target and 95% were within 5.8 to 8.4 dB of target across frequencies. These results contrast with previous research using NAL-R and NAL-NL1 targets, in which initial fittings differed from targets by 10-15dB. (Sammeth, 1993; Aazh and Moore, 2007).

Preferred listening levels (PLLs) were compared to targets and initial fittings and differed by only about 2dB.  The DSL v5.0a targets were on average 2.6dB lower than PLLs and 1.95dB lower than initial fittings.  Furthermore, DSL v5.0a targets were significantly correlated with PLLs at all frequencies and the targets and PLLs did not differ significantly as a function of degree of hearing loss.  The authors noted a trend for higher PLLs than targets at 250Hz, indicating that some users preferred more low-frequency output than prescribed.

COSI ratings of real-world performance were obtained at the 90-day appointment. The top five situations in which subjects hoped to hear better were similar to those chosen by subjects in the COSI normative study (Dillon et al, 1999):

1.  conversation with a group in noise

2.  conversation with a group in quiet

3.  conversation with one or two partners in noise

4.  listening to the television or radio

5.  conversation with one or two partners in quiet

Subjects were asked to rate the degree of change in their hearing with amplification as well as the final hearing ability (or hearing aid performance) in these situations. Results indicated that they judged their hearing to be “better” or “much better” for 83% of the fittings, which compares well to the normative results obtained by Dillon et al. (1999) of 80%. For final hearing ability, 93% of the current respondents reported hearing 75% of the time (a COSI rating of 4 or better) as compared to 90% of the normative study participants.

The purpose of the current study was to determine if DSLv5.0a prescriptive targets, developed for adults, provided electroacoustically appropriate fittings and subjectively favorable real-world results.  Indeed, clinician-adjusted fittings were within 10 dB of prescriptive targets for 92% of the subjects.  Targets also closely approximated preferred listening levels, which is particularly important because prior studies showed DSL v4.1 targets were generally higher than adults’ preferred levels.  COSI measurements indicated positive ratings for benefit and communication performance which were similar or slightly better than those obtained for the normative population.

An incidental finding of the current study was that instruments with more than six channels of processing may meet prescriptive targets more accurately than those with only six channels.  This was not specifically studied in the current paper, but the authors provided a matrix of number of channels versus errors in matching to target, showing that instruments with more than six channels yielded fewer and smaller errors than those with only six channels of processing. This result is probably consistent with clinical observations, in which sophisticated hearing aid circuits with more channels of processing often provide better fittings than instruments with fewer channels.  The importance of this factor may depend on the client’s hearing loss.  Gently sloping audiometric configurations may generally require fewer channels to meet targets.

The current results show that in a group of adults preferred listening levels and positive real-world outcomes were achieved with programs matched to DSL v5.0a targets, at least in quiet situations. In noisy listening situations, participants may have accessed alternate memories with directionality and noise reduction, causing amplification characteristics to differ from DSL settings.  Even if this is the case, the current study shows that the DSL v5.0a prescriptive measure for adults yields a close approximation to patient preferred settings for a wide range of hearing losses.

References

Aazh, H. &Moore, B.C.J. (2007). The value of routine real ear measurement of the gain of digital hearing aids. Journal of the American Academy of Audiology 18, 653-664.

Cox, R.M. (1982). Functional correlates of electroacoustic performance data. In: G.A. Studebaker & F.H. Bess (eds.) The Vanderbilt Hearing Aid Report. Parkton, MD: York Press, pp. 78-84.

Cox, R.M. & Alexander, G.C. (1994). Prediction of hearing aid benefit: the role of preferred listening levels. Ear and Hearing 15(1), 22-29.

Dillon, H., James, A. & Ginis, J. (1997). Client Oriented Scale of Improvement (COSI) and its relationship to several other measures of benefit and satisfaction provided by hearing aids. Journal of the American Academy of Audiology 8, 27-43.

Dillon, H., Birtles, G. & Lovegrove, R. (1999). Measuring the outcomes of a National Rehabilitation Program: normative data for the Client Oriented Scale of Improvement (COSI) and the Hearing Aid User’s Questionnaire (HAUQ). Journal of the American Academy of Audiology 10, 67-79.

Kochkin, S. (2005). MarkeTrak VII: Customer satisfaction with hearing instruments in the digital age. Hearing Journal 58(9), 30-43.

Kochkin, S. (2008). MarkeTrak VII:  Obstacles to adult non-user adoption of hearing aids. Hearing Journal 60(4), 24-51.

Polonenko, M.J., Scollie, S.D., Moodie, S., Seewald, R.C., Laurnagaray, D., Shantz, J. & Richards, A. (2010) Fit to targets, preferred listening levels and self-reported outcomes for the DSL v5.0a hearing aid prescription for adults. International Journal of Audiology 49, 550-560.

Sammeth, C., Peek, B., Bratt, G., Bess, F. & Amberg, S. (1993). Ability to achieve gain/frequency response and SSPL-90 under three prescription formulas with in-the-ear hearing aids. Journal of the American Academy of Audiology 4, 33-41.

Scollie, S., Seewald, R., Cornelisse, L., Moodie, S., Bagatto, M., et al. (2005). The Desired Sensation Level Multistage Input/Output Algorithm. Trends in Amplification 4(9), 159-197.