Effects of Adaptive Non-linear Frequency Compression in Hearing Aids on Mandarin Speech and Sound-Quality Perception

Abstract

Objective: This study was aimed at examining the effects of an adaptive non-linear frequency compression algorithm implemented in hearing aids (i.e., SoundRecover2, or SR2) at different parameter settings and auditory acclimatization on speech and sound-quality perception in native Mandarin-speaking adult listeners with sensorineural hearing loss.

Design: Data consisted of participants' unaided and aided hearing thresholds, Mandarin consonant and vowel recognition in quiet, and sentence recognition in noise, as well as sound-quality ratings through five sessions in a 12-week period with three SR2 settings (i.e., SR2 off, SR2 default, and SR2 strong).

Study sample: Twenty-nine native Mandarin-speaking adults aged 37-76 years old with symmetric sloping moderate-to-profound sensorineural hearing loss were recruited. They were all fitted bilaterally with Phonak Naida V90-SP BTE hearing aids with hard ear-molds.

Results: The participants demonstrated a significant improvement of aided hearing in detecting high frequency sounds at 8 kHz. For consonant recognition and overall sound-quality rating, the participants performed significantly better with the SR2 default setting than the other two settings. No significant differences were found in vowel and sentence recognition among the three SR2 settings. Test session was a significant factor that contributed to the participants' performance in all speech and sound-quality perception tests. Specifically, the participants benefited from a longer duration of hearing aid use.

Conclusion: Findings from this study suggested possible perceptual benefit from the adaptive non-linear frequency compression algorithm for native Mandarin-speaking adults with moderate-to-profound hearing loss. Periods of acclimatization should be taken for better performance in novel technologies in hearing aids.

Keywords: Mandarin Chinese; acclimatization; adult; hearing aids; non-linear frequency compression; sound quality; speech recognition.

FIGURE 1

Unaided pure-tone thresholds of left and right ears in the 29 subjects. The thin gray lines represent individual thresholds and the thick black line represents the group mean threshold (n = 29). The shaded area represents ±1 S.D. of the mean.

FIGURE 2

The waveform and spectrogram of the bird chirps. The spectrogram shows that the chirps are rapid downward frequency sweeps from 4000 to 2,000 Hz approximately.

FIGURE 3

Diagram of test procedures and group assignments. There were 5 sessions equally distributed in the 12-week period. Participants were randomly assigned into two groups. Group A (n = 14) used SR2 default as the home trial setting for the first 6 weeks and switched to SR2 strong for the home trial in the second 6 weeks. Group B (n = 15) used SR2 strong for the first 6 weeks and SR2 default for the second 6 weeks in their home trial.

FIGURE 4

Mean group unaided and aided hearing thresholds. The black line represents the unaided thresholds. The dashed line, the solid line, and the dotted lines represent free-field thresholds for the aided thresholds with SR2 off, SR2 default, and SR2 strong settings, respectively. The shaded area represents ±1 S.D. of the mean.

FIGURE 5

Individual and group mean speech-recognition performance. Consonant and vowel recognition in quiet, and sentence recognition in noise (+5 dB SNR) are represented in the three columns whereas performance for the three SR2 settings is represented in the three rows of panels. In each panel, performance scores (% correct) are plotted as a function of test sessions. Each thin line represents one participant. Those in Group A are plotted with triangles in blue whereas those in Group B are plotted with circles in orange. The thick black line represents the overall group mean performance.

FIGURE 6

Group mean performance of speech-recognition performance. The three panels are for consonant and vowel recognition in quiet, and sentence recognition in noise (+5 dB SNR), respectively. The three different lines represent the group mean results for the three SR2 settings.

FIGURE 7

Consonant confusion matrices. Consonant recognition data were collapsed from all 5 sessions. The three panels show the confusion matrices for SR2 off, SR2 default, and SR2 strong settings. In each panel, the stimulus is represented by the ordinate and the response by the abscissa. The color of each cell in a matrix represents the percent of a stimulus being identified as a particular consonant (see color bar on the right).

FIGURE 8

The average sound-quality ratings from the 29 participants. The three columns represent SR2 off, SR2 default, and SR2 strong setting, respectively. From top to down, the 5 rows indicate the 5 sessions. In each panel, the five types of stimuli (i.e., own voice, male voice, female voice, bird chirps, and music) are represented in rows whereas the category of percepts (i.e., loudness, clearness, naturalness, and overall quality) are represented in columns. The color in each cell represents the rating score as indicated by the color bar on the right.