Hearing aid fitting for visual and hearing impaired patients with Usher syndrome type IIa

Abstract

Objectives: Usher syndrome is the leading cause of hereditary deaf-blindness. Most patients with Usher syndrome type IIa start using hearing aids from a young age. A serious complaint refers to interference between sound localisation abilities and adaptive sound processing (compression), as present in today's hearing aids. The aim of this study was to investigate the effect of advanced signal processing on binaural hearing, including sound localisation.

Design and participants: In this prospective study, patients were fitted with hearing aids with a nonlinear (compression) and linear amplification programs. Data logging was used to objectively evaluate the use of either program. Performance was evaluated with a speech-in-noise test, a sound localisation test and two questionnaires focussing on self-reported benefit.

Results: Data logging confirmed that the reported use of hearing aids was high. The linear program was used significantly more often (average use: 77%) than the nonlinear program (average use: 17%). The results for speech intelligibility in noise and sound localisation did not show a significant difference between type of amplification. However, the self-reported outcomes showed higher scores on 'ease of communication' and overall benefit, and significant lower scores on disability for the new hearing aids when compared to their previous hearing aids with compression amplification.

Conclusions: Patients with Usher syndrome type IIa prefer a linear amplification over nonlinear amplification when fitted with novel hearing aids. Apart from a significantly higher logged use, no difference in speech in noise and sound localisation was observed between linear and nonlinear amplification with the currently used tests. Further research is needed to evaluate the reasons behind the preference for the linear settings.

Figure 1

Compression ratios for the linear and nonlinear program. (a) The mean compression ratios in the nonlinear program are represented by squares and continuous line with the standard deviation on either side of the squares. The mean compression ratios in the linear program are represented by the triangles and continuous line with the standard deviation on either side of the triangles. (b) Compression ratios for the linear program between 50–65 dB SPL and 65–80 dB SPL. The mean compression ratios in the linear program are represented by black triangles and continuous black line with the standard deviation on either side of the triangles. The average compression ratios in the linear program between 50 and 65 dB SPL are represented by the grey downward triangles and continuous grey line. The average compression ratios in the linear program between 65 and 80 dB SPL are represented by grey upward triangles and continuous grey line.

Figure 2

Average thresholds and Loudness Discomfort Levels of the best ear. Average thresholds are represented by black squares and continuous line. Per frequency, the standard deviations are represented by thick black lines on either sides of the squares. The loudness discomfort levels are represented by the grey squares and continuous line. Per frequency, the standard deviations are represented by thick grey lines on either side of the squares. Abbreviations: LDL, Loudness Discomfort Levels; HL, hearing level.

Figure 3

Sound localisation in azimuth in three conditions for two patients. Graph representing the results of two individual patients (#6 and #16) for sound localisation in azimuth (horizontal plane) in three conditions: with their own hearing aids, with the new hearing aids with the nonlinear amplification program and with the new hearing aids with the linear amplification program. Each dot represents one of the 36 broadband stimuli. The dotted line represents the best linear fit (least squares criterion) of the stimulus–response relationship. The parameters of the fit are shown in the panel: g = response gain, b = response bias, and r ² = coefficient of determination (see ‘Patients and methods’). Abbreviations: deg, degrees.

Figure 4

Individual sound localisation parameters. Graphs representing individual gain, bias, coefficient of determination and Mean Absolute Error (MAE) values for broadband stimuli in three conditions: with the patient's own (dots) and new hearing aids in nonlinear (squares) and linear (triangles) program. The values for patients #6 and #16 are highlighted for they were represented in Fig. 3.

Figure 5

Comparison of normalised average gains. Graph representing the mean gain‐error (G _E) for the differences between the own and new hearing aids in the nonlinear amplification program (nlin), between the own and new hearing aids in the linear amplification program (lin) and between the nonlinear amplification program of the new hearing aids. Per mean G _E, the standard deviations are represented by black lines on either sides of the squares.

Figure 6

Abbreviated Profile of Hearing Aid Benefit (APHAB). Mean scores for the AHPAB subscales for the own (black squares −sd) and new (black triangles +sd) hearing aids. For comparison, the norm percentiles as defined by Johnson et al. in 2010 for successful hearing aid users were added.28