Today’s high-end hearing instruments offer a wide range of features which provide substantial benefits to the hearing-impaired listener in daily life. Prior to the launch of these advanced products, thorough testing under realistic conditions is essential to ensure that the hearing instrument and the fitting software meet the demands of the hearing impaired and the hearing care professional.

Prior to the launch of Perseo, an extensive beta-trial was conducted in 6 countries with 104 hearing-impaired subjects. The aim of this trial was to extensively assess the new hearing instrument in terms of initial acceptance, speech understanding in realistic environments, customer satisfaction after every-day experience, and satisfaction of the hearing care professional with the hearing instrument and the fitting software.

Test Instrument
Perseo is a 20-channel digital hearing instrument. The default base-program is optimized for speech understanding in quiet environments. A second base-program with different frequency response settings and optional adaptive directional microphones provides additional support in noisy situations. The acoustic environment is continuously monitored and the appropriate base-program is automatically selected. This dual-base automatic function allows for independent fine tuning in one listening situation without compromising performance in the other. The automatic performance is designed to be easily personalized for the individual needs and preferences of the user.

The sound signal processing, called DPP2, is designed to enhance audibility and intelligibility due to new TK settings, an increased use of the available dynamic range, and optimized temporal processing. Depending on the model, an optional adaptive directional AudioZoom enhances speech understanding in more difficult listening environments.

Figure 1. Subjects’ own hearing instruments (ie, reference hearing aids).

Subjects and Methods
In total, 104 hearing-impaired subjects (29% female; 61% male) with mild to severe sensorineural hearing loss (Pure Tone Average: 43 dB) participated in the trial. The subjects’ own hearing instruments served as a reference (Figure 1). The largest sub-group of subjects had digital hearing instruments as a reference (43%). If first-time users had at least 2 weeks of experience with another (test) hearing instrument prior to the trial, this was taken as reference.

The trial involved a minimum of 2 sessions in addition to a session at which the ear impressions were taken, if needed. At the initial fitting session, the subjects were asked to answer questionnaires concerning the performance of their own instruments. Afterwards, the test instruments (Perseo) were fit and the subjects were asked about their spontaneous reaction. If necessary, an extra fine tuning session was conducted after the fitting session. The follow-up was conducted at least 10 days after the fitting. In the follow-up session, the subjects were asked to report on their experiences with the test instruments in daily life. At the end of the trial, the dispensing professionals were asked about their impression of the test instruments and the fitting process.

The trial was conducted in parallel at 26 sites in 6 countries (United States, New Zealand, Germany, Switzerland, Belgium and Austria). Apart from telling the subjects that they were given a new hearing instrument that was to be tested, no specific information was given to avoid bias. All available test instrument models, from CIC to power BTE, were deployed in the study. The gain settings were pre-calculated using the proprietary fitting rule (Phonak Digital).

A range of subjective and objective outcome measures was used to assess the fittings. Various questionnaires were administered to examine initial fitting, experience after using the instruments in daily life, and the impression of the hearing care professionals, respectively. One of the questionnaires used was the International Outcome Inventory for Hearing Aids (IOI-HA).¹ The IOI-HA is available in many languages and covers a minimal set of 7 core outcome items which are sufficiently general to apply to investigations carried out in different countries.

Formal speech tests and real-ear measures were conducted if they were routinely used by the respective fitting sites.

Initial Impression
Spontaneous acceptance: An important factor which influences fitting success is the spontaneous acceptance of the hearing instrument directly after pre-calculation. Subjects were asked about their impression regarding sound quality and loudness. In addition, the subjects rated their own hearing instruments in these categories.

Figure 2. Sound quality rating of test aids (after pre-calculation) compared to the reference hearing instruments.

In general, the sound quality ratings for the test instruments directly after pre-calculation were positive and exceeded the ratings for the reference hearing instruments (Figure 2).

This is significant when considering the general sound quality ratings for own hearing instruments tend to increase over time, as the users acclimatize to their instruments.² Nevertheless, the test subjects on average spontaneously preferred the test instruments in terms of sound quality, without any acclimatization. Relative to loudness, the average rating for both the reference instruments and test instruments was “comfortable.”

Accuracy of pre-calculation and fine tuning: In 38% of the test instruments fittings, no fine tuning was required. When fine tuning was needed, it solved the reported problems almost in every case (96%). In most cases, the necessary fine tuning was quite limited. The relative gain adjustment from pre-calculation for all frequency channels was less than ±1 dB (ie, the pre-calculation is balanced and generally does not tend to over- or under-estimate necessary gain across frequency).

Feedback: Directly after pre-calculation, feedback occurred in 29% of all test instrument fittings. The extent of feedback varied across subjects and increased with hearing loss. When feedback occurred, the feedback manager was used. It eliminated feedback in almost all cases (92%).

Follow-up Results
After using the test instruments for at least 10 days, the subjects attended a follow-up session.

Figure 3. Self-reported general sound quality at follow-up.

General sound quality: Compared to the initial impression directly after fitting, the self-reported general sound quality of the test instruments further increased after the short acclimatization period in daily life (Figure 3).

The percentage of subjects which used the best rating category for the sound quality (ie, “very pleasant”) increased from 26% to 36%, compared to the initial session. This confirms the trend of increased general sound quality ratings for hearing instruments along with acclimatization as reported by Ovegård et al.² The self-reported general sound quality of the reference hearing instruments (which were not worn in the trial period) was re-assessed at the follow-up session to check whether there was a retrospective change of judgement. Subject judgement appeared to be remarkably stable over time.

Figure 4a-b. Self-reported speech understanding in quiet (top) and in noise (bottom).

Self-reported speech understanding: In quiet situations, the majority of subjects indicated that they understood at least “most” utterances with both the reference instruments and the test instruments (Figure 4). However, while the highest rating (“understand everything”) was chosen in about half (49%) of all test instrument fittings, it was chosen less often (29%) for the reference hearing instruments.

In noisy situations (Figure 4b), the overall self-reported speech understanding was slightly worse, as expected. But again, positive ratings were more frequent with the test instruments. The “understand most” response was selected about half (48%) the time with the test instruments, compared to 23% for the reference instruments.

Figure 5. Objective speech test results with the test instrument compared to the reference hearing instruments: ratings given by dispensing professionals.

Objective speech tests: Formal speech tests with the test instruments and the reference hearing instruments were conducted if they were routinely used at the respective fitting site (n=27 subjects). However, pooling of the data is difficult due to the large differences in test conditions across different sites and countries. Instead, the dispensing professionals were asked to rate the speech test results according to their experience with the respective speech test, taking into account the individual hearing loss. They scaled the speech test results with Perseo, compared to the reference hearing instruments, in 5 categories ranging from “much worse” to “much better” (Figure 5).

On average, objective tests revealed an improvement in speech understanding with the test instruments. Thus, the results from the objective speech tests correspond with the self-reported speech understanding in daily life.

Figure 6. Change in total IOI-HA score test instruments compared to reference instruments. Positive numbers indicate improvement, while negative numbers indicate worsened situation.

IOI-HA: The International Outcome Inventory for Hearing Aids (IOI-HA)¹ covers a minimal set of 7 core outcome items, including topics such as daily wearing time or benefit from hearing aids in difficult situations. The ratings for each item are given on a 5-point scale, where higher categories are associated with better performance. The total score differences between the own instruments and the test instruments are illustrated in Figure 6.

A majority of subjects (74%) reached an increased total IOI-HA score with the test instruments compared to their own hearing instruments. Twenty percent showed no difference and only 6% did better with their own instruments.

Figure 7. Overall direct comparison by subjects between test and reference instruments (ie, “Compared to your own hearing instrument, Perseo is...”)

Overall direct comparison: When asked to directly compare the reference hearing instruments and the test instruments, a clear preference for the test instruments could be seen (Figure 7; page 42). In total, 72% of all subjects rated the test instruments as “better” or “much better,” and only 16% preferred their own hearing instruments.

The hearing care professionals: It is essential that hearing instruments are easy to fit and do not require excessive fine tuning. In addition, the fitting software must be intuitive and easy to use, as the software is the interface between the client’s needs and the intervention of the professional. Thus, the dispensing professionals who participated in the study were asked about their impression of the test instruments and the fitting process at the end of the trial.

Figure 8. Judgement of the hearing care professionals on fitting the hearing instrument after trial.

When asked to compare the fine-tuning effort for the test instruments to that of other comparable instruments, most dispensing professionals stated that they need the same or less effort (Figure 8; page 42). Accordingly, the majority of hearing care professionals (80%) said it is easy to fit the test instruments. This result is noteworthy, as none of the fitters had experience with fitting the test instruments prior to the trial. They were only given a short introduction to the product prior to commencing with the study.

With respect to feedback, the majority of fitters stated that the test instruments produce the same (42%) or less (42%) feedback than other advanced digital instruments. Overall, a large majority of hearing care professionals (87%) were satisfied or very satisfied with the test device.

Conclusion
Prior to its launch, the Perseo hearing instrument was assessed in an extensive multinational study in which 104 hearing-impaired subjects participated. The study covered three areas: initial acceptance, experience in daily life, and the impression of the hearing care professional.

The results from these areas correlate well with each other and provide a coherent picture of the new hearing aid. A high level of initial satisfaction, speech understanding, and sound quality ratings is confirmed by the clients after experience in daily life. The subjects expressed a clear preference for the device compared to their own hearing instruments. Additionally, dispensing professionals rated the hearing instrument as easy to fit and were satisfied with the aid.

References
1. Cox RM, Stephens D, Kramer SE. Translations of the International Outcome Inventory for Hearing Aids (IOI-HA). Intl Jour Audiol. 2002;41(1):3-26.
2. Ovegård A, Lundberg G, Hagerman B, Gabrielsson A, Bengtsson M, Brändström U. Sound quality judgement during acclimatization of hearing aid. Scand Audiol. 1997;26:43-51.