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Outer Hair Cell and Auditory Nerve Function in Speech Recognition in Quiet and in Background Noise

View Article: PubMed Central - PubMed

ABSTRACT

The goal of this study was to describe the contribution of outer hair cells (OHCs) and the auditory nerve (AN) to speech understanding in quiet and in the presence of background noise. Fifty-three human subjects with hearing ranging from normal to moderate sensorineural hearing loss were assayed for both speech in quiet (Word Recognition) and speech in noise (QuickSIN test) performance. Their scores were correlated with OHC function as assessed via distortion product otoacoustic emissions, and AN function as measured by amplitude, latency, and threshold of the VIIIth cranial nerve Compound Action Potential (CAP) recorded during electrocochleography (ECochG). Speech and ECochG stimuli were presented at equivalent sensation levels in order to control for the degree of hearing sensitivity across patients. The results indicated that (1) OHC dysfunction was evident in the lower range of normal audiometric thresholds, which demonstrates that OHC damage can produce “Hidden Hearing Loss,” (2) AN dysfunction was evident beginning at mild levels of hearing loss, (3) when controlled for normal OHC function, persons exhibiting either high or low ECochG amplitudes exhibited no statistically significant differences in neither speech in quiet nor speech in noise performance, (4) speech in noise performance was correlated with OHC function, (5) hearing impaired subjects with OHC dysfunction exhibited better speech in quiet performance at or near threshold when stimuli were presented at equivalent sensation levels. These results show that OHC dysfunction contributes to hidden hearing loss, OHC function is required for optimum speech in noise performance, and those persons with sensorineural hearing loss exhibit better word discrimination in quiet at or near their audiometric thresholds than normal listeners.

No MeSH data available.


Subjects with larger CAP amplitudes exhibited no significant improvement in SIQ or SIN when OHC function is normal. (A) Persons exhibiting normal OHC function (Normal Group) were subdivided into two groups (Low and High) based on whether their CAP amplitudes were either higher or lower than the group mean ± 1 s.e.m. Persons exhibiting normal OHC function and high CAP amplitudes exhibited statistically significant shorter CAP latencies at high presentation levels (B), but failed to exhibit statistically significant differences in DPOAE SNRs (C) or DPOAE thresholds (D) at most frequencies. Speech testing showed no clinically significant differences in word recognition in quiet (E) or speech recognition ion the presence of background noise (F) between these groups. Panels (A–E) represent mean data +/1 1 s.e.m. Panel (F) is a box and whisker plot showing the median data (line within the box). Open circle represents suspected outliers, and numbers indicate the subject identification of the suspected outlier. *Statistically significant difference between groups.
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Figure 7: Subjects with larger CAP amplitudes exhibited no significant improvement in SIQ or SIN when OHC function is normal. (A) Persons exhibiting normal OHC function (Normal Group) were subdivided into two groups (Low and High) based on whether their CAP amplitudes were either higher or lower than the group mean ± 1 s.e.m. Persons exhibiting normal OHC function and high CAP amplitudes exhibited statistically significant shorter CAP latencies at high presentation levels (B), but failed to exhibit statistically significant differences in DPOAE SNRs (C) or DPOAE thresholds (D) at most frequencies. Speech testing showed no clinically significant differences in word recognition in quiet (E) or speech recognition ion the presence of background noise (F) between these groups. Panels (A–E) represent mean data +/1 1 s.e.m. Panel (F) is a box and whisker plot showing the median data (line within the box). Open circle represents suspected outliers, and numbers indicate the subject identification of the suspected outlier. *Statistically significant difference between groups.

Mentions: Next, the data was analyzed to determine whether AN density, measured by CAP amplitude (Kujawa and Liberman, 2009), contributed to SIN performance. Since diminished DPOAE SNRs and increased DPOAE thresholds existed in the Minimal-Moderate SNHL groups (Figure 5B) only the Normal group (n = 29) was used in this analysis in order to control for OHC loss. The Normal group was ranked by CAP amplitudes at the 40 dB SL presentation level, and divided into high and low CAP amplitude groups based on whether their CAP amplitudes were either 1 s.e.m higher or 1 s.e.m lower than the Normal SNHL group mean of 156 μV (Low CAP < 156 μV < High CAP; Figure 7A). J–T testing indicated that persons with normal hfPTAs and normal OHC function who also exhibited higher CAP amplitudes exhibited statistically significantly shorter CAP latencies at higher presentation levels (maximum difference of −0.206 ms, p = 0.002; Figure 7B). This data suggest a general trend of an inverse relationship between CAP amplitude and latency at both low and high presentation levels when OHC function is normal. The data further showed there was no statistically significant differences in DPOAE SNRs between these two groups at most frequencies, however there was a statistically insignificant difference in DPOAE SNR at 4 k Hz (−5.1 dB SPL difference at 40 dB SL, p = 0.048; Figure 7C), while there were no statistically significant differences in DPOAE threshold between these groups (Figure 7D). Next, SIN and SIQ scores between these groups were analyzed to determine whether AN function played a solitary role in speech recognition. There were no significant differences in either SIQ (Figure 7E) or SIN (Figure 7F) performance in persons with diminished CAP amplitudes and normal OHC function. This data suggests that AN function by itself does not play a significant role in speech recognition in quiet or in the presence of background noise.


Outer Hair Cell and Auditory Nerve Function in Speech Recognition in Quiet and in Background Noise
Subjects with larger CAP amplitudes exhibited no significant improvement in SIQ or SIN when OHC function is normal. (A) Persons exhibiting normal OHC function (Normal Group) were subdivided into two groups (Low and High) based on whether their CAP amplitudes were either higher or lower than the group mean ± 1 s.e.m. Persons exhibiting normal OHC function and high CAP amplitudes exhibited statistically significant shorter CAP latencies at high presentation levels (B), but failed to exhibit statistically significant differences in DPOAE SNRs (C) or DPOAE thresholds (D) at most frequencies. Speech testing showed no clinically significant differences in word recognition in quiet (E) or speech recognition ion the presence of background noise (F) between these groups. Panels (A–E) represent mean data +/1 1 s.e.m. Panel (F) is a box and whisker plot showing the median data (line within the box). Open circle represents suspected outliers, and numbers indicate the subject identification of the suspected outlier. *Statistically significant difference between groups.
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Figure 7: Subjects with larger CAP amplitudes exhibited no significant improvement in SIQ or SIN when OHC function is normal. (A) Persons exhibiting normal OHC function (Normal Group) were subdivided into two groups (Low and High) based on whether their CAP amplitudes were either higher or lower than the group mean ± 1 s.e.m. Persons exhibiting normal OHC function and high CAP amplitudes exhibited statistically significant shorter CAP latencies at high presentation levels (B), but failed to exhibit statistically significant differences in DPOAE SNRs (C) or DPOAE thresholds (D) at most frequencies. Speech testing showed no clinically significant differences in word recognition in quiet (E) or speech recognition ion the presence of background noise (F) between these groups. Panels (A–E) represent mean data +/1 1 s.e.m. Panel (F) is a box and whisker plot showing the median data (line within the box). Open circle represents suspected outliers, and numbers indicate the subject identification of the suspected outlier. *Statistically significant difference between groups.
Mentions: Next, the data was analyzed to determine whether AN density, measured by CAP amplitude (Kujawa and Liberman, 2009), contributed to SIN performance. Since diminished DPOAE SNRs and increased DPOAE thresholds existed in the Minimal-Moderate SNHL groups (Figure 5B) only the Normal group (n = 29) was used in this analysis in order to control for OHC loss. The Normal group was ranked by CAP amplitudes at the 40 dB SL presentation level, and divided into high and low CAP amplitude groups based on whether their CAP amplitudes were either 1 s.e.m higher or 1 s.e.m lower than the Normal SNHL group mean of 156 μV (Low CAP < 156 μV < High CAP; Figure 7A). J–T testing indicated that persons with normal hfPTAs and normal OHC function who also exhibited higher CAP amplitudes exhibited statistically significantly shorter CAP latencies at higher presentation levels (maximum difference of −0.206 ms, p = 0.002; Figure 7B). This data suggest a general trend of an inverse relationship between CAP amplitude and latency at both low and high presentation levels when OHC function is normal. The data further showed there was no statistically significant differences in DPOAE SNRs between these two groups at most frequencies, however there was a statistically insignificant difference in DPOAE SNR at 4 k Hz (−5.1 dB SPL difference at 40 dB SL, p = 0.048; Figure 7C), while there were no statistically significant differences in DPOAE threshold between these groups (Figure 7D). Next, SIN and SIQ scores between these groups were analyzed to determine whether AN function played a solitary role in speech recognition. There were no significant differences in either SIQ (Figure 7E) or SIN (Figure 7F) performance in persons with diminished CAP amplitudes and normal OHC function. This data suggests that AN function by itself does not play a significant role in speech recognition in quiet or in the presence of background noise.

View Article: PubMed Central - PubMed

ABSTRACT

The goal of this study was to describe the contribution of outer hair cells (OHCs) and the auditory nerve (AN) to speech understanding in quiet and in the presence of background noise. Fifty-three human subjects with hearing ranging from normal to moderate sensorineural hearing loss were assayed for both speech in quiet (Word Recognition) and speech in noise (QuickSIN test) performance. Their scores were correlated with OHC function as assessed via distortion product otoacoustic emissions, and AN function as measured by amplitude, latency, and threshold of the VIIIth cranial nerve Compound Action Potential (CAP) recorded during electrocochleography (ECochG). Speech and ECochG stimuli were presented at equivalent sensation levels in order to control for the degree of hearing sensitivity across patients. The results indicated that (1) OHC dysfunction was evident in the lower range of normal audiometric thresholds, which demonstrates that OHC damage can produce &ldquo;Hidden Hearing Loss,&rdquo; (2) AN dysfunction was evident beginning at mild levels of hearing loss, (3) when controlled for normal OHC function, persons exhibiting either high or low ECochG amplitudes exhibited no statistically significant differences in neither speech in quiet nor speech in noise performance, (4) speech in noise performance was correlated with OHC function, (5) hearing impaired subjects with OHC dysfunction exhibited better speech in quiet performance at or near threshold when stimuli were presented at equivalent sensation levels. These results show that OHC dysfunction contributes to hidden hearing loss, OHC function is required for optimum speech in noise performance, and those persons with sensorineural hearing loss exhibit better word discrimination in quiet at or near their audiometric thresholds than normal listeners.

No MeSH data available.