Comparison of Frequency Transposition and Frequency Compression for People With Extensive Dead Regions in the Cochlea

Marina Salorio-Corbetto, Thomas Baer, Brian C J Moore, Marina Salorio-Corbetto, Thomas Baer, Brian C J Moore

Abstract

The objective was to determine the effects of two frequency-lowering algorithms (frequency transposition, FT, and frequency compression, FC) on audibility, speech identification, and subjective benefit, for people with high-frequency hearing loss and extensive dead regions (DRs) in the cochlea. A single-blind randomized crossover design was used. FT and FC were compared with each other and with a control condition (denoted 'Control') without frequency lowering, using hearing aids that were otherwise identical. Data were collected after at least 6 weeks of experience with a condition. Outcome measures were audibility, scores for consonant identification, scores for word-final /s, z/ detection ( S test), sentence-in-noise intelligibility, and a questionnaire assessing self-perceived benefit (Spatial and Qualities of Hearing Scale). Ten adults with steeply sloping high-frequency hearing loss and extensive DRs were tested. FT and FC improved the audibility of some high-frequency sounds for 7 and 9 participants out of 10, respectively. At the group level, performance for FT and FC did not differ significantly from that for Control for any of the outcome measures. However, the pattern of consonant confusions varied across conditions. Bayesian analysis of the confusion matrices revealed a trend for FT to lead to more consistent error patterns than FC and Control. Thus, FT may have the potential to give greater benefit than Control or FC following extended experience or training.

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

Figures

Figure 1.
Figure 1.
Schematic representation of frequency transposition (FT, bottom left) and frequency compression (FC, bottom right). For FT, the source band (SB) and the destination band (DB) have the same width. For FC, the destination band is narrower than the source band. FT = frequency transposition; FC = frequency compression.
Figure 2.
Figure 2.
Fast PTCs for each ear. Participants are identified by P followed by a number and a subscript indicating the ear, right (R) or left (L).The signal frequency (fs)and level in each case are indicated by a star. The minimum masker frequency (MMF) is shown. The jagged line indicates the masker level as a function of masker center frequency. Two PTCs are plotted, one for an upward frequency sweep and one for a downward frequency sweep, except for P15R, as described in the text. The green line shows the smoothed curve derived from the two PTCs. fs=signal frequency; MMF = minimum masker frequency.
Figure 3.
Figure 3.
Mean ratings for the ‘Difference test.’
Figure 4.
Figure 4.
Consonant-identification scores for the group (average) and for each participant. Outcomes are shown for each vowel context (/i/, /a/, /u/) and across vowel contexts (‘all’). Error bars show ±1 standard deviation for the individual results and ±1 standard error of the mean for the group results. FT = frequency transposition; FC = frequency compression; RAU = rationalized arcsine unit.
Figure 5.
Figure 5.
S-test results for the group (top panel, ‘Average’) and for each participant. Error bars show ±1 standard deviation for the individual results and ±1 standard error of the mean for the group results. FT = frequency transposition; FC = frequency compression.
Figure 6.
Figure 6.
SRTs for speech in noise. Cross-hatched, dark gray, and light gray bars show the results for Control, FT, and FC, respectively. Lower SRTs indicate better performance. Error bars show ±1 standard deviation for the individual results and ±1 standard error of the mean for the group results. SRT = Speech reception threshold.
Figure 7.
Figure 7.
SSQ outcomes for the group (‘Average,’ top-left) and for each participant. Cross-hatched, dark gray, and light gray bars show results for Control, FT, and FC, respectively. Error bars show ±1 standard deviation for the individual results and ±1 standard error of the mean for the group results. FT = frequency transposition; FC = frequency compression.

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