No abstract

45Age-related hearing loss leads to poorer speech comprehension, particularly in noise. Speech-in-noise 46 (SIN) deficits among the elderly could result from weaker neural activity within, or poorer signal 47 transmission between brainstem and auditory cortices. By recording neuroelectric responses from 48 brainstem (BS) and primary auditory cortex (PAC), we show that beyond simply attenuating neural 49 activity, hearing loss in older adults compromises the transmission of speech information between 50 subcortical and cortical hubs of the auditory system. The strength of afferent BS→PAC neural signaling 51 (but not the reverse efferent flow; PAC→BS) varied with mild declines in hearing acuity and this 52 "bottom-up" functional connectivity robustly predicted older adults' SIN perception. Our neuroimaging 53 findings underscore the importance of brain connectivity, particularly afferent neural communication, in 54 understanding the biological basis of age-related hearing deficits in real-world listening environments. 55 56 57 58 59 Keywords: Aging; auditory evoked potentials; auditory cortex; frequency-following response (FFR); 60 functional connectivity; source waveform analysis; neural speech processing 61 62 63 Importantly, besides hearing, the groups were otherwise matched in age (NH: 66.2±6.1 years, HL: 131 70.4±4.9 years; t 2.22 =-2.05, p = 0.052) and gender balance (NH: 5/8 male/female; HL: 11/8; Fisher's exact 132 test, p=0.47). Age and hearing loss were not correlated in our sample (Pearson's r=0.29, p=0.10). 133 Participants were compensated for their time and gave written informed consent in compliance with a 134 protocol approved by the Baycrest Centre research ethics committee. 135 Stimuli and task 136Three tokens from the standardized UCLA version of the Nonsense Syllable Test were used in 137 this study (Dubno and Schaefer, 1992). These tokens were naturally produced English consonant-vowel 138 phonemes (/ba/, /pa/, and /ta/), spoken by a female talker. Each phoneme was 100-ms in duration and 139 matched in terms of average root mean square sound pressure level (SPL). Each had a common voice 140 fundamental frequency (F0=150 Hz) and first and second formants (F1= 885, F2=1389 Hz). This 141

Four experiments were conducted to determine whether or not the presence and placement of distractors in a rapid serial auditory stream has any influence on the emergence of the auditory attentional blink (AB). Experiment 1 revealed that the presence of distractors is necessary to produce the auditory AB. In Experiments 2 and 3, the auditory AB was reduced when the distractor immediately following the probe was replaced by silence but not when the distractor following the target was replaced by silence. Finally, in Experiment 4, only a very small auditory AB was found to remain when all distractors following the probe were replaced by silence. These results suggest that the auditory AB is affected both by the overwriting of the probe by the distractors following it and by a reduction in discriminability generated by all of the distractors presented in the sequence.

Speech comprehension difficulties are ubiquitous to aging and hearing loss, particularly in noisy environments. Older adults' poorer speech-in-noise (SIN) comprehension has been related to abnormal neural representations within various nodes (regions) of the speech network, but how senescent changes in hearing alter the transmission of brain signals remains unspecified. We measured electroencephalograms in older adults with and without mild hearing loss during a SIN identification task. Using functional connectivity and graph-theoretic analyses, we show that hearing-impaired (HI) listeners have more extended (less integrated) communication pathways and less efficient information exchange among widespread brain regions (larger network eccentricity) than their normal-hearing (NH) peers. Parameter optimized support vector machine classifiers applied to EEG connectivity data showed hearing status could be decoded (> 85% accuracy) solely using network-level descriptions of brain activity, but classification was particularly robust using left hemisphere connections. Notably, we found a reversal in directed neural signaling in left hemisphere dependent on hearing status among specific connections within the dorsalventral speech pathways. NH listeners showed an overall net "bottom-up" signaling directed from auditory cortex (A1) to inferior frontal gyrus (IFG; Broca's area), whereas the HI group showed the reverse signal (i.e., "top-down" Broca's → A1). A similar flow reversal was noted between

Attentional blink (AB) describes a phenomenon whereby correct identification of a first target impairs the processing of a second target (i.e., probe) nearby in time. Evidence suggests that explicit attention orienting in the time domain can attenuate the AB. Here, we used scalp-recorded, event-related potentials to examine whether auditory AB is also sensitive to implicit temporal attention orienting. Expectations were set up implicitly by varying the probability (i.e., 80% or 20%) that the probe would occur at the +2 or +8 position following target presentation. Participants showed a significant AB, which was reduced with the increased probe probability at the +2 position. The probe probability effect was paralleled by an increase in P3b amplitude elicited by the probe. The results suggest that implicit temporal attention orienting can facilitate short-term consolidation of the probe and attenuate auditory AB.