Biology subjects

Shinn-Cunningham, B. G.

Publications and source records attributed to Shinn-Cunningham, B. G..

4 recordsLinked to original sources

bioRxiv2019

Weak neural signatures of spatial selective auditory attention in hearing-impaired listeners

Spatial attention may be used to select target speech in one location while suppressing irrelevant speech in another. However, if perceptual resolution of spatial cues is weak, spatially focused attention may work poorly, leading to difficulty communicating in noisy settings. In electroencephalography (EEG), the distribution of alpha (8-14 Hz) power over parietal sensors reflects the spatial focus of attention (Banerjee et al., 2011; Foxe and Snyder, 2011). If spatial attention is degraded, however, alpha may not be modulated across parietal sensors. A previously published behavioral and EEG study found that, compared to normal-hearing (NH) listeners, hearing-impaired (HI) listeners often had higher interaural time difference (ITD) thresholds, worse performance when asked to report the content of an acoustic stream from a particular location, and weaker attentional modulation of neural responses evoked by sounds in a mixture (Dai et al., 2018). This study explored whether these same HI listeners also showed weaker alpha lateralization during the previously reported task. In NH listeners, hemispheric parietal alpha power was greater when the ipsilateral location was attended; this lateralization was stronger when competing melodies were separated by a larger spatial difference. In HI listeners, however, alpha was not lateralized across parietal sensors, consistent with a degraded ability to use spatial features to selectively attend.

neuroscience↗

bioRxiv2019

Non-spatial features reduce the reliance on sustained spatial auditory attention

Top-down spatial attention is effective at selecting a target sound from a mixture. However, non-spatial features often distinguish sources in addition to location. This study explores whether redundant non-spatial features are used to maintain selective auditory attention for a spatially defined target. We recorded electroencephalography (EEG) while subjects focused attention on one of three simultaneous melodies. In one experiment, subjects (n = 17) were given an auditory cue indicating both the location and pitch of the target melody. In a second experiment (n = 17 subjects), the cue only indicated target location, and we compared two conditions: one in which the pitch separation of competing melodies was large, and one in which this separation was small. In both experiments, responses evoked by onsets of events in sound streams were modulated equally as strong by attention, suggesting that the target stimuli were correctly selected regardless of the cue or pitch information available. In all cases, parietal alpha was lateralized following the cue, but prior to melody onset, indicating that subjects always initially focused attention in space. During the stimulus presentation, however, this lateralization weakened when pitch cues were strong, suggesting that strong pitch cues reduced reliance on sustained spatial attention. These results demonstrate that once a well-defined target stream at a known location is selected, top-down spatial attention is unnecessary to filter out a segregated competing stream.

neuroscience↗

bioRxiv2019

Non-Invasive Assays of Cochlear Synaptopathy -- Candidates and Considerations

Studies in multiple species, including in post-mortem human tissue, have shown that normal aging and/or acoustic overexposure can lead to a significant loss of afferent synapses innervating the cochlea. Hypothetically, this cochlear synaptopathy can lead to perceptual deficits in challenging environments and can contribute to central neural effects such as tinnitus. However, because cochlear synaptopathy can occur without any measurable changes in audiometric thresholds, synaptopathy can remain hidden from standard clinical diagnostics. To understand the perceptual sequelae of synaptopathy and to evaluate the efficacy of emerging therapies, sensitive and specific non-invasive measures at the individual patient level need to be established. Pioneering experiments in specific mice strains have helped identify many candidate assays. These include auditory brainstem responses, the middle-ear muscle reflex, envelope-following responses, and extended high-frequency audiograms. Unfortunately, because these non-invasive measures can be also affected by extraneous factors other than synaptopathy, their application and interpretation in humans is not straightforward. Here, we systematically examine six extraneous factors through a series of interrelated human experiments aimed at understanding their effects. Using strategies that may help mitigate the effects of such extraneous factors, we then show that these suprathreshold physiological assays exhibit across-individual correlations with each other indicative of contributions from a common physiological source consistent with cochlear synaptopathy. Finally, we discuss the application of these assays to two key outstanding questions, and discuss some barriers that still remain.

neuroscience↗

bioRxiv2019

Impoverished auditory cues fail to engage brain networks controlling spatial selective attention

Spatial selective attention enables listeners to process a signal of interest in natural settings. However, most past studies on auditory spatial attention used impoverished spatial cues: presenting competing sounds to different ears, using only interaural differences in time (ITDs) and/or intensity (IIDs), or using non-individualized head-related transfer functions (HRTFs). Here we tested the hypothesis that impoverished spatial cues impair spatial auditory attention by only weakly engaging relevant cortical networks. Eighteen normal-hearing listeners reported the content of one of two competing syllable streams simulated at roughly +30 {degrees} and -30{degrees} azimuth. The competing streams consisted of syllables from two different-sex talkers. Spatialization was based on natural spatial cues (individualized HRTFs), individualized IIDs, or generic ITDs. We measured behavioral performance as well as electroencephalographic markers of selective attention. Behaviorally, subjects recalled target streams most accurately with natural cues. Neurally, spatial attention significantly modulated early evoked sensory response magnitudes only for natural cues, not in conditions using only ITDs or IIDs. Consistent with this, parietal oscillatory power in the alpha band (8-14 Hz; associated with filtering out distracting events from unattended directions) showed significantly less attentional modulation with isolated spatial cues than with natural cues. Our findings support the hypothesis that spatial selective attention networks are only partially engaged by impoverished spatial auditory cues. These results not only suggest that studies using unnatural spatial cues underestimate the neural effects of spatial auditory attention, they also illustrate the importance of preserving natural spatial cues in assistive listening devices to support robust attentional control.

neuroscience↗