Inyong Choi

Quantifying attentional modulation of auditory-evoked cortical responses from single-trial electroencephalography

Selective auditory attention is essential for human listeners to be able to communicate in multi-source environments. Selective attention is known to modulate the neural representation of the auditory scene, boosting the representation of a target sound relative to the background, but the strength of this modulation, and the mechanisms contributing to it, are not well understood. Here, listeners performed a behavioral experiment demanding sustained, focused spatial auditory attention while we measured cortical responses using electroencephalography (EEG). We presented three concurrent melodic streams; listeners were asked to attend and analyze the melodic contour of one of the streams, randomly selected from trial to trial. In a control task, listeners heard the same sound mixtures, but performed the contour judgment task on a series of visual arrows, ignoring all auditory streams. We found that the cortical responses could be fit as weighted sum of event-related potentials evoked by the stimulus onsets in the competing streams. The weighting to a given stream was roughly 10 dB higher when it was attended compared to when another auditory stream was attended; during the visual task, the auditory gains were intermediate. We then used a template-matching classification scheme to classify single-trial EEG results. We found that in all subjects, we could determine which stream the subject was attending significantly better than by chance. By directly quantifying the effect of selective attention on auditory cortical responses, these results reveal that focused auditory attention both suppresses the response to an unattended stream and enhances the response to an attended stream. The single-trial classification results add to the growing body of literature suggesting that auditory attentional modulation is sufficiently robust that it could be used as a control mechanism in brain–computer interfaces (BCIs).

Transmastoid reshaping of the sigmoid sinus: preliminary study of a novel surgical method to quiet pulsatile tinnitus of an unrecognized vascular origin

OBJECTIVE A dominant sigmoid sinus with focal dehiscence or thinning (DSSD/T) of the overlying bony wall is a commonly encountered, but frequently overlooked, cause of vascular pulsatile tinnitus (VPT). Also, the pathophysiological mechanism of sound perception in patients with VPT remains poorly understood. In the present study, a novel surgical method, termed transmastoid SS-reshaping surgery, was introduced to ameliorate VPT in patients with DSSD/T. The authors reviewed a case series, analyzed the surgical outcomes, and suggested the pathophysiological mechanism of sound perception. The theoretical background underlying VPT improvement after transmastoid SS-reshaping surgery was also explored. METHODS Eight patients with VPT that was considered attributable to DSSD/T underwent transmastoid SS-reshaping surgery between February 2010 and February 2015. The mean postoperative follow-up period was 9.5 months (range 4-13 months). Transmastoid SS-reshaping surgery featured simple mastoidectomy, partial compression of the SS using harvested cortical bone chips, and reinforcement of the bony SS wall with bone cement. Perioperative medical records, imaging results, and audiological findings were comprehensively reviewed. RESULTS In 7 of the 8 patients (87.5%), the VPT abated immediately after surgery. Statistically significant improvements in tinnitus loudness and distress were evident on numeric rating scales. Three patients with preoperative ipsilesional low-frequency hearing loss exhibited postoperative improvements in their low-frequency hearing thresholds. No major postoperative complications were encountered except in the first subject, who experienced increased intracranial pressure postoperatively. This subsided after a revision operation for partial decompression of the SS. CONCLUSIONS Transmastoid SS-reshaping surgery may be a good surgical option in patients with DSSD/T, a previously unrecognized cause of VPT. Redistribution of severely asymmetrical blood flow, reinforcement of the bony SS wall with bone cement to reconstruct a soundproof barrier, and disconnection of a problematic sound conduction route via simple mastoidectomy silence VPT.

Objectification and Differential Diagnosis of Vascular Pulsatile Tinnitus by Transcanal Sound Recording and Spectrotemporal Analysis: A Preliminary Study.

Objective: Although frequently classified as “objective tinnitus,” in most cases vascular pulsatile tinnitus (VPT) is not equal to objective tinnitus because it is not easy to objectively document VPT. The present study was conducted to develop a novel transcanal sound recording and spectrotemporal analysis method for the objective and differential diagnosis of VPT. Study Design: A case series with a control group. Setting: Tertiary referral center. Patients: Six VPT subjects with radiological abnormalities and six normal controls. Interventions and Main Outcome Measure: The method was tested based on recordings obtained from the ipsilateral external auditory canal (EAC) using an insert microphone with the subjects head in four different positions. The recorded signals were first analyzed in the time domain, and short-time Fourier transform was performed to analyze the data in the time–frequency domain. Results: From the temporal analysis, the ear canal signals recorded from the VPT subjects exhibited large peak amplitudes and periodic structures, whereas the signals recorded from the control subjects had smaller peak amplitudes and weaker periodicity. From the STA represented by two-dimensional spectrograms and three-dimensional waterfall diagrams, all of the VPT subjects demonstrated pulse-synchronous acoustic characteristics that were representative of their respective presumptive vascular pathologies, whereas the control subjects did not display such characteristics. Conclusion: The present diagnostic approach may provide additional information regarding the origins of VPT cases as well as an efficient and objective diagnostic method. Furthermore, this approach may aid in the determination of appropriate imaging modalities, treatment planning, and evaluation of treatment outcomes.

Pre-Treatment Objective Diagnosis and Post-Treatment Outcome Evaluation in Patients with Vascular Pulsatile Tinnitus Using Transcanal Recording and Spectro-Temporal Analysis

Objective Although vascular pulsatile tinnitus (VPT) has been classified as “objective”, VPT is not easily recognizable or documentable in most cases. In response to this, we have developed transcanal sound recording (TSR) and spectro-temporal analysis (STA) for the objective diagnosis of VPT. By refining our initial method, we were able to apply TSR/STA to post-treatment outcome evaluation, as well as pre-treatment objective diagnosis. Methods TSR was performed on seven VPT patients and five normal controls before and after surgical or interventional treatment. VPT was recorded using an inserted microphone with the subjects placed in both upright and supine positions with 1) a neutral head position, 2) head rotated to the tinnitus side, 3) head rotated to the non-tinnitus side, and 4) a neutral position with ipsi-lesional manual cervical compression. The recorded signals were analyzed in both time and time-frequency domains by performing a short-time Fourier transformation. Results The pre-treatment ear canal signals of all VPT patients demonstrated pulse-synchronous periodic structures and acoustic characteristics that were representative of their presumptive vascular pathologies, whereas those the controls exhibited smaller peaks and weak periodicities. Compared with the pre-treatment signals, the post-treatment signals exhibited significantly reduced peak- and root mean square amplitudes upon time domain analysis. Additionally, further sub-band analysis confirmed that the pulse-synchronous signal of all subjects was not identifiable after treatment and, in particular, that the signal decrement was statistically significant at low frequencies. Moreover, the post-treatment signals of the VPT subjects revealed no significant differences when compared to those of the control group. Conclusion We reconfirmed that the TSR/STA method is an effective modality to objectify VPT. In addition, the potential role of the TSR/STA method in the objective evaluation of treatment outcomes in patients with VPT was proven. Further studies incorporating a larger sample size and more refined recording techniques are warranted.

Automatic processing of abstract musical tonality

Music perception builds on expectancy in harmony, melody, and rhythm. Neural responses to the violations of such expectations are observed in event-related potentials (ERPs) measured using electroencephalography. Most previous ERP studies demonstrating sensitivity to musical violations used stimuli that were temporally regular and musically structured, with less-frequent deviant events that differed from a specific expectation in some feature such as pitch, harmony, or rhythm. Here, we asked whether expectancies about Western musical scale are strong enough to elicit ERP deviance components. Specifically, we explored whether pitches inconsistent with an established scale context elicit deviant components even though equally rare pitches that fit into the established context do not, and even when their timing is unpredictable. We used Markov chains to create temporally irregular pseudo-random sequences of notes chosen from one of two diatonic scales. The Markov pitch-transition probabilities resulted in sequences that favored notes within the scale, but that lacked clear melodic, harmonic, or rhythmic structure. At the random positions, the sequence contained probe tones that were either within the established scale or were out of key. Our subjects ignored the note sequences, watching a self-selected silent movie with subtitles. Compared to the in-key probes, the out-of-key probes elicited a significantly larger P2 ERP component. Results show that random note sequences establish expectations of the “first-order” statistical property of musical key, even in listeners not actively monitoring the sequences.

Quantifying supra-threshold sensory deficits in listeners with normal hearing thresholds

There is growing suspicion that some listeners with normal-hearing thresholds may be suffering from a specific form of sensory deficit—a loss of afferent auditory nerve fibers. We believe such deficits manifest behaviorally in conditions where perception depends upon precise spectro-temporal coding of supra-threshold sound. In our lab, we find striking inter-subject differences in perceptual ability even among listeners with normal hearing thresholds who have no complaints of hearing difficulty and have never sought clinical intervention. Among such ordinary listeners, those who perform relatively poorly on selective attention tasks (requiring the listener to focus on one sound stream presented amidst competing sound streams) also exhibit relatively weak temporal coding in subcortical responses and have poor thresholds for detecting fine temporal cues in supra-threshold sound. Here, we review the evidence for supra-threshold hearing deficits and describe measures that reveal this sensory loss. Given our f...

How individual differences in sensory coding and attentional control impact understanding speech in noise

Historically, the majority of psychoacoustic studies of hearing ability have viewed individual differences as noise: a nuisance that makes it difficult to see the effects that different acoustic conditions have on auditory perception. This talk reviews how we have begun to use individual differences to tease apart the processes that affect perception, with a particular focus on how listeners understand speech when there are competing sound sources. We find that individual subjects show consistent differences in their ability to understand speech in noise. These consistent differences can come both from differences in the fidelity of sensory coding and from differences in the ability to focus selectively on important sound and suppress unimportant sound. Importantly, which of these factors predicts performance depends greatly on the details of the stimuli used in a given task, and what stage of processing is the resulting bottleneck, determining performance. When fine differences in the sound content, such...

Cortical oscillatory signatures of active listening complement brainstem coding measures in predicting listening performance

Following the finding of cochlear deafferentation (“synaptopathy”) in noise exposure and aging in animal models (Kujawa and Liberman, J. Neurosci. 2009; Sergeyenko et al., J. Neurosci. 2013), there is considerable interest among hearing scientists and clinicians to investigate the presence and consequences of synaptopathy in humans. In the laboratory, human subjects with clinically normal hearing (NH) listeners from the general population exhibit large individual differences in suprathreshold perceptual ability. Through a recent series of experiments using otoacoustic emissions and electrophysiology, we studied these individual differences and showed that they partly arise from differences in subcortical coding of temporal information consistent with synaptopathy (Bharadwaj et al., J. Neurosci. 2015). In the current study, we examined cortical oscillations accompanying cued preparation to selectively attend to a target spatial location as a correlate of top-down active listening. We find that both brainst...

Cortical dynamics of spatial and non-spatial auditory selective attention

Auditory selective attention suppresses processing of task-irrelevant stimuli, and it is crucial for effective communication in social settings. Previous studies showed that space- and pitch-based auditory attention engages different neural networks. However, the cortical dynamics underlying spatial and non-spatial auditory attention are unclear. Since accumulating evidence suggests that selective suppression is related to alpha band oscillation (8–14 Hz), we examine the spatial and non-spatial attentional modulation of alpha oscillation power as well as event-related potential (ERP) and behavioral performance. Using Electroencephalography (EEG) in humans, we compare behavior and physiological measures during focused attention (where listeners maintain focus on one “target” stream) and broad attention (where listeners are prepared to switch attention to a “super-target” stream which may or may not appear after the “target” stream) in spatial and non-spatial settings. We find that spatial attention shows o...

Auditory attention in a dynamic scene: Behavioral and electrophysiological correlates

The ability to direct and redirect selective auditory attention varies substantially across individuals with normal hearing thresholds, even when sounds are clearly audible. We hypothesized that these differences can come from both differences in the spectrotemporal fidelity of subcortical sound representations and in the efficacy of cortical attentional networks that modulate neural representations of the auditory scene. Here, subjects were presented with an initial stream from straight ahead and a second stream (from either left or right), each comprised of four monotonized consonant-vowel syllables. Listeners were instructed to report the contents of either the first stream (holding attentional focus) or the second stream (switching attentional focus). Critically, the direction of the second stream informed subjects whether to hold or to switch attention. Pilot results suggest that when the lateral angle of the second stream is small, task performance is linked to subcortical encoding fidelity of supra...