Introduction: Subjects with unilateral hearing loss (UHL) report difficulties in speech understanding in noise. Speech-evoked auditory brainstem response (S-ABR) provides cues for temporal and spectral encoding of speech in the brainstem. S-ABR recording in noise increases its sensitivity in evaluating the auditory processing and related disorders.
Objectives: Study speech encoding at the level of brainstem when the auditory system relies on one ear and to study the effect of noise on this encoding.
Subjects and method: This study included two groups: control group consisted of 15 adults with normal hearing sensitivity and study group consisted of 30 adults with UHL. The study group was further subdivided into two subgroups: study subgroup A (SG A) consisted of 15 adults with right functioning ears and study subgroup B (SG B) consisted of 15 adults with left functioning ears. S-ABR in quiet and with ipsilateral noise was recorded in both the groups using complex ABR advanced auditory research module.
Results: In UHL, there was a statistically significant delay in the S-ABR onset and offset in noise compared to quiet. Moreover, quiet-noise (+5 SNR) correlation was significantly low compared to NH. Furthermore, pitch representation (F0 amplitude) was significantly degraded with noise. In addition, there was a statistically significant noise-induced phase shift in the transition region of speech syllable in these subjects.
Conclusion: In monaural processing, pitch representation (F0 amplitude) and cross-phaseogram were the main affected domains. Speech phonemes of transient origin can be confused in subjects with UHL.
Keywords: F0 amplitude; S-ABR in noise; Speech-evoked auditory brainstem response; phase shift; pitch representation; unilateral hearing loss.