Evaluation of a Frequency-Lowering Algorithm for Adults With High-Frequency Hearing Loss

Abstract

The objective was to determine the effects of a frequency-lowering algorithm (frequency composition, Fcomp) on consonant identification, word-final /s, z/ detection, the intelligibility of sentences in noise, and subjective benefit, for people with high-frequency hearing loss, including people with dead regions (DRs) in the cochlea. A single-blind randomized crossover design was used. Performance with Bernafon Acriva 9 hearing aids was compared with Fcomp off and Fcomp on. Participants wore the hearing aids in each condition in a counterbalanced order. Data were collected after at least 8 weeks of experience with a condition. Outcome measures were audibility, scores from the speech perception tests, and scores from a questionnaire comparing self-perceived hearing ability with Fcomp off and Fcomp on. Ten adults with mild to severe high-frequency hearing loss (seven with extensive DRs, one with patchy or restricted DRs, and two with no DR) were tested. Fcomp improved the audibility of high-frequency sounds for 6 out of 10 participants. There was no overall effect of Fcomp on consonant identification, but the pattern of consonant confusions varied across conditions and participants. For word-final /s, z/ detection, performance was significantly better with Fcomp on than with Fcomp off. Questionnaire scores showed no differences between conditions. In summary, Fcomp improved word-final /s, z/ detection. No benefit was found for the other measures.

Keywords: dead regions; frequency lowering; frequency transposition; hearing aids.

Figures

Figure 1.

Schematic illustration of three forms of frequency lowering: frequency compression (FC, top right), frequency transposition (FT, bottom left), and frequency composition (Fcomp, bottom right). U = unprocessed (top left), SB = source band, DB = destination band. For FC, the SB (gray cross hatching) is wider than the DB (green cross hatching), and these bands have the same low-frequency edge. For FT, the SB (gray cross hatching) and the DB (green cross hatching) have the same width. For Fcomp, the SB is divided into three subbands, shown in different colors, and all subbands are transposed to the same DB. For FT and Fcomp, the frequency-lowered components are added to the unprocessed components.

Figure 2.

Example of the SB (right panel) and DB (left panel) for the medium setting of Fcomp. Each of the three subbands in the SB (termed “Shift1,” “Shift2,” and “Shift3” here) is transposed to the same DB. Therefore, the DB is narrower than the SB. Based on information provided by Bernafon AG. SB = source band; DB = destination band; Fcomp = frequency composition.

Figure 3.

Audiograms of the participants. The shaded areas show the outcomes of the TEN(HL) test.

Figure 4.

Fast PTCs obtained for the participants for whom the TEN(HL) test outcome was inconclusive or positive. The open symbols indicate the level and frequency of the signal. The jagged line shows the masker levels visited. The continuous line shows the combination of an upward sweep and a downward sweep in masker center frequency (except for P05R, fs = 1 kHz and P09L, for whom only upward sweeps were available) after smoothing each of them. All fast PTCs show a significantly shifted tip, which indicates a DR, except for P04R, P05Rfs = 1 and 2 kHz, and P09L. The MMF is given only when it is shifted by more than 10% from fs. MMF = minimum masker frequency; fs = frequency signal; DR = dead region.

Figure 5.

Average and individual scores for the VCV test expressed in RAU, plotted for all vowel contexts combined (“all”) and separately for each vowel context (/i/, /a/, /u/). Error bars show ± 1 standard error. Fcomp = frequency composition.

Figure 6.

Consonant-confusion matrix showing the difference in responses for Fcomp-on and Fcomp-off. All numbers represent percentage points. Positive numbers on the diagonal mean that Fcomp improved the identification score for that consonant, while negative numbers mean that Fcomp worsened the score. Positive numbers off the diagonal mean that confusions between the two consonants determining the cell were increased when Fcomp was used, while negative numbers mean that confusions decreased. /θ/, /ʃ/, /tʃ/, and /tʒ/ are labeled using their orthographic representations, th, sh, ch, and j, respectively.

Figure 7.

Outcomes of SINFA for the sum of responses of the participants. Correct responses are shown in the left panels, and the percentage of information transmitted for each feature is shown in the right panels. Analyses were made for the features voicing and manner of articulation (top panels) and for the feature of place of articulation (bottom panels). The label used for each feature is specified in Table 3. Fcomp = frequency composition.

Figure 8.

Average and individual scores for the S-test. Error bars show ± 1 standard error. The star denotes a significant difference.

Figure 9.

Mean and individual outcomes for the speech-in-noise test. Results in RAU are plotted separately for the colocated (“col”) and the spatially separated (“sep”) configurations. Error bars show ± 1 standard error.

Figure 10.

Outcomes of the SSQ-C questionnaire. Positive values indicate better scores for Fcomp-on, and negative values indicate better scores for Fcomp-off. Values close to zero indicate no difference. Average group outcomes are plotted in red, and individual outcomes are plotted in black. Fcomp = frequency composition.