الفهرس 
Introduction and RationaleOnly 14 pages are availabe for public view
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Abstract
Understanding speech in noise is one of the most complex activities encountered in everyday life, it is an important task for successful participation in educational, social and vocational environments, and it poses particular demands on subjects with hearing impairment. Successful perception of speech in noise is dependent on cognitive factors as well as sound processing at peripheral, subcortical and cortical level. Both behavioral and physiological measures have been used to understand the important factors that contribute to perception-in-noise abilities. Physiological measures may help determine whether deficits are due to abnormal neural encoding or difficulties with higher order cognitive processes needed for speech perception in noise. Subcortical and cortical evoked responses originate from different regions in the auditory pathway, representing acoustic information via distinct neural codes. Subcortical auditory responses represent the acoustics of the evoking stimulus with high fidelity, while cortical evoked responses provide a more abstract representation of sound. Consequently, each of these responses provides a unique neural framework within which to objectively assess the biological processes underlying speech-in-noise perception.
The aim of this work was to study the effect of background noise on subcortical and cortical speech encoding in both normal subjects and those with sensorineural hearing loss and correlate these neurophysiological results with subjective measures. Ninety subjects were included in this study, divided into two groups, control group consists of fifty normal-hearing subjects and study group consists of fourty subjects with mild to moderate sensorineural hearing loss. All were subjected to basic audiological evaluation, SSQ questionnaire, SPIN test, S-ABR and CAEPs using speech syllable /da/ in quiet and at three different signal to noise ratios(+10, 0 and -10).
Our study showed that in quiet, SNHL group demonstrated delayed neural timing in the region corresponding to the CV formant transition (onset and offset, VA slope), but timing in the steady-state region remains unchanged (FFR).Also robustness of CV frequency representation decreases in SNHL, with decline of amplitude of the transient and sustained regions of CV(onset, FFR, offset, VA complex amplitude and area) With addition of noise the brainstem encoding of /da/ in SNHL showed further affection of neural timing of sustained region of stimulus which become delayed together with onset wave, VA complex and wave C. Also robustness of syllables encoding decrease in SNHL than NH. In NH, addition of noise at different SNR caused delayed latencies of both transients (waves V,A,C and O) and FFR (waves D,E and F) with reduction of amplitudes of onset (V and A) and F wave only
In SNHL, addition of noise at different SNR caused delayed latencies and decreased amplitudes of both transients (waves V, A, C and O) and FFR (waves D, E and F)
In the current study latency of cortical onset wave N1 showed statistically significant differences between SNHL and NH in quiet and at different SNR, also amplitude of N1 is reduced in SNHL compared to NH but did not reach statistically significant differences.
Also in our study latency of P1showed a statistically significant delay in SNHL than NH in quiet only, while P1amplitudes are significantly different at +10, 0 and -10 SN. P1 amplitude was also reduced in SNHL in quiet condition although did not reach a statistically significant difference
In this study effect of noise can be seen in the overall waves of CAEPs; that is response latency increased and response amplitude decreased with decreasing SNR in both SNHL and NH.
Our study showed that there were no statistical significant correlations between SSQ and both S-ABR and CAEPs waves latencies and amplitudes in NH and SNHL groups.
In the current study in SNHL group better SPIN performance correlated with earlier peak response timing of S-ABR onset at all SNR. Also SPIN correlated with earlier peak response timing of wave C at 0SNR, offset and FFR at -10 SNR. SPIN correlated with larger peak response amplitude of FFR and wave C at all SNR. While it correlated with onset and offset at +10&0 SNR and wave D at +10 &-10 SNR. Also better SPIN performance in SNHL correlated with earlier peak response timing of waves P2 and N2 at all SNR, and correlated with larger peak response amplitude of waves P1at +10 &-10 SNR, N1at +10 &0 SNR and N2 at 0 & -10 SNR.