Research On Speech-ABR And Its Correlation With Speech-In-Noise Ability

Speech-in-noise perception is a complex auditory processing task affected by the brain sensory and perceptual interaction. Currently, the evaluation of speech and hearing functions in daily clinical works are mainly dependent on the subjective tests, such as pure tone test. However, the results of subjective tests are sometimes not that sentitive. And the objective methods used in clinical work, such as ABR, ASSR, electrocochleogram (ECochG) and so on sometimes fail to reflect or predict the speech intelligence of patients. While auditory brainstem responses to speech sounds(s-ABR) can objectively reflect the features of acoustic signal, such as frequency information and timing information which is important to understanding speech.This study mainly recorded auditory brainstem responses to speech sounds (s-ABR) from normal hearing adults in different age groups and evaluated whether neural encoding of speech features at the brain stem level is altered by aging auditory system,gender and pure-tone thresholds. We also investigated a neural basis of speech-in-noise perception in older adults and the possibility of objective method to assess speech intelligence.In this paper,40ms/da/syllable was used as acoustic stimulation. The s-ABR were collected from 100 normal hearing native Mandarin adults, aged from 20 to 70 years (50 males,50 females). The Chinese speech audiometry software named "Xin ai fei yang" was used to test each subject’s noise speech recognition threshold. Analysising of each subject’s s-ABR, including latencies, amplitudes, V-A slopes (V-Apeak to peak and V-A wave interval ratio), were conducted to evaluate whether there are significant relationships among pure-tone thresholds, noise speech recognition ability, age and gender.This study found that (1) in different groups subjects’ pure-tone average thresholds were different, especially at the frequency higher than 2000Hz; the speech-in-noise recognition threshold increased with the aging; and the latency of s-ABR turned longer with the age growth, while amplitude turned lower, V-A slope decreased. (2) besides the latency and amplitude of the s-ABR wave V, A and O, V-A slope, noise speech recognition threshold.age and pure-tone average thresholds has showed a significant correlations. S-ABR’s sustained response also had correlations with noise speech recognition threshold and age. This study also found that (3) female’s high frequency audibility threshold is smaller than that in male, the female’s pure tone thresholds with age growth trend was smaller than that in male. Female’s latency of wave V, A and O is shorter than male’s and V-A slope of female was sharper than man, while the latency of frequency following response has small gender differences influence.(4) the wave latencies and amplitudes do not have statistically significant difference between the left and right ear.Analysis mechanism of s-ABR, indicated that with growth of aging, subjects’ pure tone hearing thresholds decreased significantly. S-ABR reflects the brainstem response to transient information coding by onset responses, and with the offset responses weakened, brainstem response phase locking ability of FO amplitude decreased, which prompted us to draw the following conclusions:(1) the sound processing ability of brainstem and pure-tone threshold decreased gradually with aging, which increase the difficulty to discriminate speech information in noise background and induce the listening ability decrease in noisy environment. (2) different gender’s pure-tone threshold was affected differently by age. Different neural responses to the different components of the speech information, speech information with rapid time variation and high frequency was more sensitive to gender effect,while that with slow time avariation, and low-frequency was less sensitive to gender effects. (3) The auditory of brain stem showed no hemisphere asymetery for speech processing.