1In social settings, speech waveforms from nearby speakers mix together in our ear canals. The brain 2 unmixes the attended speech stream from the chorus of background speakers using a combination of fast 3 temporal processing and cognitive active listening mechanisms. Multi-talker speech perception is 4 vulnerable to aging or auditory abuse. We found that ~10% of adult visitors to our clinic have no 5 measurable hearing loss, yet offer a primary complaint of poor hearing. Multi-talker speech intelligibility 6 in these adults was strongly correlated with neural phase locking to frequency modulation (FM) cues, as 7 determined from ear canal EEG recordings. Combining neural temporal fine structure (TFS) processing 8 with pupil-indexed measures of cognitive listening effort could predict most of the individual variance in 9 speech intelligibility thresholds. These findings identify a confluence of disordered bottom-up and top-10 down processes that predict poor multi-talker speech perception and could be useful in next-generation 11 tests of hidden hearing disorders. 12 13 2015). Here, we apply parallel psychophysical and neurophysiological tests of sTFS processing in 1 combination with physiological measures of effortful listening to converge on a set of neural biomarkers 2 that identify poor multi-talker speech intelligibility in adults with clinically normal hearing. 3 4
Results
5Many individuals seek medical care for poor hearing but have no evidence of hearing loss 6We identified the first visit records of English-speaking adult patients from the Mass. Eye and Ear 7 audiology database over a 16-year period, with complete bilateral audiometric records at six octave 8 frequencies from 250 Hz to 8000 Hz according to the inclusion criteria in Figure 1A. Of the 106,787 patient 9 records that met these criteria, we found that approximately one out of every five individuals had no 10 clinical evidence of hearing loss, defined as thresholds > 20 dB HL at test frequencies up to 8 KHz (19,952, 11 19%, Figure 1B). The majority of these individuals were between 20-50 years old ( Figure 1C) and had no 12 conductive hearing impairment, nor focal threshold shifts or "notches" in their audiograms greater than 13 10 dB ( Fig. 1 -Fig. supplement 1A). The thresholds between their left and right ears were also symmetrical 14 within 10 dB for >95% of these patients ( Fig. 1 -Fig. supplement 1B). Despite these clinically normal 15measures of hearing, 45% of these individuals presented to the clinic reporting a primary complaint of 16 decreased hearing or hearing loss (Figure 1D). Absent any objective measure of hearing difficulty, these 17 patients are typically informed that their hearing is "normal" and that they are not expected to experience 18 communication problems. 19 20 Speech-in-noise intelligibility varies widely in individuals with clinically normal hearing 21