Does Tinnitus Fill in the Gap Using Electrophysiology? A Scoping Review.

The results showed a trend of increased post-gap amplitudes and reduced gap salience; however, the small number of articles yield and limited consensus prohibit any conclusions for clinical use. Nevertheless, gap-induced EPs may be further explored as a potential tool for tinnitus detection.

A Cortico-Collicular Amplification Mechanism for Gap Detection.

Auditory cortex (AC) is necessary for the detection of brief gaps in ongoing sounds, but not for the detection of longer gaps or other stimuli such as tones or noise. It remains unclear why this is so, and what is special about brief gaps in particular. Here, we used both optogenetic suppression and conventional lesions to show that the cortical dependence of brief gap detection hinges specifically on gap termination. We then identified a cortico-collicular gap detection circuit that amplifies cortical gap termination responses before projecting to inferior colliculus (IC) to impact behavior. We found that gaps evoked off-responses and on-responses in cortical neurons, which temporally overlapped for brief gaps, but not long gaps. This overlap specifically enhanced cortical responses to brief gaps, whereas IC neurons preferred longer gaps. Optogenetic suppression of AC reduced collicular responses specifically to brief gaps, indicating that under normal conditions, the enhanced cortical representation of brief gaps amplifies collicular gap responses. Together these mechanisms explain how and why AC contributes to the behavioral detection of brief gaps, which are critical cues for speech perception, perceptual grouping, and auditory scene analysis.

Utilizing High-Density Electroencephalography and Motion Capture Technology to Characterize Sensorimotor Integration While Performing Complex Actions.

Studies of sensorimotor integration often use sensory stimuli that require a simple motor response, such as a reach or a grasp. Recent advances in neural recording techniques, motion capture technologies, and time-synchronization methods enable studying sensorimotor integration using more complex sensory stimuli and performed actions. Here, we demonstrate that prehensile actions that require using complex sensory instructions for manipulating different objects can be characterized using high-density electroencephalography and motion capture systems. In 20 participants, we presented stimuli in different sensory modalities (visual, auditory) containing different contextual information about the object with which to interact. Neural signals recorded near motor cortex and posterior parietal cortex discharged based on both the instruction delivered and object manipulated. Additionally, kinematics of the wrist movements could be discriminated between participants. These findings demonstrate a proof-of-concept behavioral paradigm for studying sensorimotor integration of multidimensional sensory stimuli to perform complex movements. The designed framework will prove vital for studying neural control of movements in clinical populations in which sensorimotor integration is impaired due to information no longer being communicated correctly between brain regions (e.g. stroke). Such a framework is the first step towards developing a neural rehabilitative system for restoring function more effectively.

Change detection in complex auditory scenes is predicted by auditory memory, pitch perception, and years of musical training.

Our world is a sonically busy place and we use both acoustic information and experience-based knowledge to make sense of the sounds arriving at our ears. The knowledge we gain through experience has the potential to shape what sounds are prioritized in a complex scene. There are many examples of how visual expertise influences how we perceive objects in visual scenes, but few studies examine how auditory expertise is associated with attentional biases toward familiar real-world sounds in complex scenes. In the current study, we investigated whether musical expertise is associated with the ability to detect changes to real-world sounds in complex auditory scenes, and whether any such benefit is specific to musical instrument sounds. We also examined whether change detection is better for human-generated sounds in general or only communicative human sounds. We found that musicians had less change deafness overall. All listeners were better at detecting human communicative sounds compared to human non-communicative sounds, but this benefit was driven by speech sounds and sounds that were vocally generated. Musical listening skill, speech-in-noise, and executive function abilities were used to predict rates of change deafness. Auditory memory, musical training, fine-grained pitch processing, and an interaction between training and pitch processing accounted for 45.8% of the variance in change deafness. To better understand perceptual and cognitive expertise, it may be more important to measure various auditory skills and relate them to each other, as opposed to comparing experts to non-experts.

Comparison of Standard and Enhanced Pulse Oximeter Auditory Displays of Oxygen Saturation: A Laboratory Study With Clinician and Nonclinician Participants.

BACKGROUND: When engaged in visually demanding tasks, anesthesiologists depend on the auditory display of the pulse oximeter (PO) to provide information about patients' oxygen saturation (SpO2). Current auditory displays are not always effective at providing SpO2 information. In this laboratory study, clinician and nonclinician participants identified SpO2 parameters using either a standard auditory display or an auditory display enhanced with additional acoustic properties while performing distractor tasks and in the presence of background noise. METHODS: In a counterbalanced crossover design, specialist or trainee anesthesiologists (n = 25) and nonclinician participants (n = 28) identified SpO2 parameters using standard and enhanced PO auditory displays. Participants performed 2 distractor tasks: (1) arithmetic verification and (2) keyword detection. Simulated background operating room noise played throughout the experiment. Primary outcomes were accuracies to (1) detect transitions to and from an SpO2 target range and (2) identify SpO2 range (target, low, or critical). Secondary outcomes included participants' latency to detect target transitions, accuracy to identify absolute SpO2 values, accuracy and latency of distractor tasks, and subjective judgments about tasks. RESULTS: Participants were more accurate at detecting target transitions using the enhanced display (87%) than the standard display (57%; odds ratio, 7.3 [95% confidence interval {CI}, 4.4-12.3]; P < .001). Participants were also more accurate at identifying SpO2 range using the enhanced display (86%) than the standard display (76%; odds ratio, 2.7 [95% CI, 1.6-4.6]; P < .001). Secondary outcome analyses indicated that there were no differences in performance between clinicians and nonclinicians for target transition detection accuracy and latency, SpO2 range identification accuracy, or absolute SpO2 value identification. CONCLUSIONS: The enhanced auditory display supports more accurate detection of target transitions and identification of SpO2 range for both clinicians and nonclinicians. Despite their previous experience using PO auditory displays, clinicians in this laboratory study were no more accurate in any SpO2 outcomes than nonclinician participants.

Prefrontal Cortex Regulates Sensory Filtering through a Basal Ganglia-to-Thalamus Pathway.

To make adaptive decisions, organisms must appropriately filter sensory inputs, augmenting relevant signals and suppressing noise. The prefrontal cortex (PFC) partly implements this process by regulating thalamic activity through modality-specific thalamic reticular nucleus (TRN) subnetworks. However, because the PFC does not directly project to sensory TRN subnetworks, the circuitry underlying this process had been unknown. Here, using anatomical tracing, functional manipulations, and optical identification of PFC projection neurons, we find that the PFC regulates sensory thalamic activity through a basal ganglia (BG) pathway. Engagement of this PFC-BG-thalamus pathway enables selection between vision and audition by primarily suppressing the distracting modality. This pathway also enhances sensory discrimination and is used for goal-directed background noise suppression. Overall, our results identify a new pathway for attentional filtering and reveal its multiple roles in sensory processing on the basis of internal goals.

A time-efficient multi-deviant paradigm to determine the effects of gap duration on the mismatch negativity.

The insertion of a silent period (or gap) in a frequently occurring standard stimulus elicits a negative-going event-related potential (ERP), called the Deviant-Related Negativity (DRN). This is often studied using a single-deviant paradigm. To study the effects of gaps with multiple durations, a different sequence would be required for each gap. A more time-efficient multi-deviant paradigm has been developed in which stimuli of various gap widths are included in a single sequence. In the present study, 14 young adults watched a silent video while ignoring an auditory sequence. A single run of a multi-deviant sequence was presented in which 6 different rare deviants alternated with a standard stimulus. The standard was a 200-ms white noise burst. The deviants were constructed by inserting a gap in the standard. The duration of the 6 gaps ranged from 2 to 40 ms. Participants were also presented with multiple runs of single-deviant sequences. Each of the 3 deviants was run in a separate sequence. The amplitude of the DRN elicited by the deviant increased as gap duration became longer, although it did plateau for the longer duration gaps. The amplitudes of the DRNs were larger in the single-deviant paradigm than in the multi-deviant paradigm. However, the difference was only significant when the mastoid reference was used. Behavioural data showed a mean d' of 2.1 for the 5-ms gap. None of the participants were able to detect the 2-ms gap. There was no correlation between d' and the DRN amplitude. Still, the effects of gap duration on the amplitude of the DRN were similar between the single and multi-deviant sequences. This makes the multi-deviant paradigm a possible time-saving alternative to the single-deviant paradigm.

Electro-cortical correlates of multisensory integration using ecologically valid emotional stimuli: Differential effects for fear and disgust.

Multisensory integration (MSI) is crucial for human communication and social interaction and has been investigated in healthy populations and neurodevelopmental disorders. However, the use of stimuli with high ecological validity is sparse, especially in event-related potential (ERP) studies. The present study examined the ERP correlates of MSI in healthy adults using short (500 ms) ecologically valid professional actor-produced emotions of fear or disgust as vocal exclamation or facial expression (unimodal conditions) or both (bimodal condition). Behaviourally, our results show a general visual dominance effect (similarly fast responses following bimodal and visual stimuli) and an MSI-related speedup of responses only for fear. Electrophysiologically, both P100 and N170 showed MSI-related amplitude increases only following fear, but not disgust stimuli. Our results show for the first time that the known differential neural processing of fear and disgust also holds for the integration of dynamic auditory and visual information.

Differential coactivation in a redundant signals task with weak and strong go/no-go stimuli.

When participants respond to stimuli of two sources, response times (RTs) are often faster when both stimuli are presented together relative to the RTs obtained when presented separately (redundant signals effect [RSE]). Race models and coactivation models can explain the RSE. In race models, separate channels process the two stimulus components, and the faster processing time determines the overall RT. In audiovisual experiments, the RSE is often higher than predicted by race models, and coactivation models have been proposed that assume integrated processing of the two stimuli. Where does coactivation occur? We implemented a go/no-go task with randomly intermixed weak and strong auditory, visual, and audiovisual stimuli. In one experimental session, participants had to respond to strong stimuli and withhold their response to weak stimuli. In the other session, these roles were reversed. Interestingly, coactivation was only observed in the experimental session in which participants had to respond to strong stimuli. If weak stimuli served as targets, results were widely consistent with the race model prediction. The pattern of results contradicts the inverse effectiveness law. We present two models that explain the result in terms of absolute and relative thresholds.

Contralateral suppression of human hearing sensitivity in single-sided deaf cochlear implant users.

Cochlear implants (CIs) are being implanted in people with unilateral hearing loss because they can improve speech intelligibility and sound source localization. Though designed to restore the afferent auditory stimulation, the CI possibly restores some efferent effects. The present study aimed at investigating this possibility. Five single-sided deaf CI users with less than 30 dB hearing loss up to 4 kHz in their acoustic ear participated in the study. Absolute thresholds for their acoustic ears were measured for pure tones of 500 and 4000 Hz with durations of 10 and 200 ms in the presence and in the absence of contralateral broadband electrical stimulation (CBES) delivered with the CI. The electrical stimulus consisted of pulse trains (symmetric biphasic pulses with phase duration 36 µs) on all 16 electrodes sequentially stimulated at a rate of 843 Hz. Its intensity was set to sound as loud as broadband noise at 50 or 60 dB SPL in the acoustic ear. Thresholds were measured using a three-interval, three-alternative, forced-choice procedure with a two-down, one-up adaptive rule to estimate the level for 71% correct in the psychometric function. Thresholds measured without the CBES were lower for the longer than for the shorter tones, and the difference was larger at 500 than at 4000 Hz. CBES equivalent to 50 or 60 dB SPL caused significant threshold elevation only for short (10 ms) and low frequency (500 Hz) acoustic tones of 1.2 and 2.2 dB. These increases appear smaller than previously reported for normal hearing listeners in related experiments. These results support the notion that for single-sided deaf CI users, the CI modulates hearing in the acoustic ear. The possible mechanisms that may be contributing this effect are discussed.

Masking Release for Speech in Modulated Maskers: Electrophysiological and Behavioral Measures.

OBJECTIVES: The purpose of this study was to obtain an electrophysiological analog of masking release using speech-evoked cortical potentials in steady and modulated maskers and to relate this masking release to behavioral measures for the same stimuli. The hypothesis was that the evoked potentials can be tracked to a lower stimulus level in a modulated masker than in a steady masker and that the magnitude of this electrophysiological masking release is of the same order as that of the behavioral masking release for the same stimuli. DESIGN: Cortical potentials evoked by an 80-ms /ba/ stimulus were measured in two steady maskers (30 and 65 dB SPL), and in a masker that modulated between these two levels at a rate of 25 Hz. In each masker, a level series was undertaken to determine electrophysiological threshold. Behavioral detection thresholds were determined in the same maskers using an adaptive tracking procedure. Masking release was defined as the difference between signal thresholds measured in the steady 65-dB SPL masker and the modulated masker. A total of 23 normal-hearing adults participated. RESULTS: Electrophysiological thresholds were uniformly elevated relative to behavioral thresholds by about 6.5 dB. However, the magnitude of masking release was about 13.5 dB for both measurement domains. CONCLUSIONS: Electrophysiological measures of masking release using speech-evoked cortical auditory evoked potentials correspond closely to behavioral estimates for the same stimuli. This suggests that objective measures based on electrophysiological techniques can be used to reliably gauge aspects of temporal processing ability.

Effectiveness of Implantable DEfibrillators Alert Systems: comparison between audible and vibratory alert: IDEAS study.

INTRODUCTION: Implantable cardioverter-defibrillator (ICD) alarm systems are an important means of monitoring device functioning. The aim of this study was to compare the ability of patients with sense two types of device alert systems: an audible alert and a vibratory alarm. METHODS: The ability to recognize the alarms was assessed in three alarm tests performed in a series of consecutive ICD patients enrolled during routine outpatient device follow-up. To avoid overestimating the rate of patients able to sense the alarm, the first test was performed without forewarning. Subsequently, the second test was performed after the patients had been forewarned. Finally, to assess the learning effect of a demonstration test, a third test was performed, again without forewarning. RESULTS: A total of 528 patients (65.4 ±â€Š14.4 years, 74.6% male) were enrolled: 347 (65.7%) with an audible alert-endowed device and 181 (34.3%) with a vibratory alarm-endowed device. When emitted without warning, the alarms were sensed by 72.4% of patients. When patients were forewarned, the probability of sensing the alarms rose to 92.5% (P < 0.001). In both cases, the vibratory alarm was more likely to be sensed than the audible alert (77.3 vs. 67.7% in the first case; 96.1 vs. 87.9% in the second case; all P < 0.05). CONCLUSION: ICD alarms emitted in an outpatient setting are sensed by a large proportion of patients, but not by all. Training patients by means of demonstration tests significantly increases the rate of patients who recognize the alarm. Vibratory alarm seems to be more effective than audible alert.

Effects of signal bandwidth and noise on individual speaker identification.

Two experiments were conducted to evaluate the effects of increasing spectral bandwidth from 3 to 10 kHz on individual speaker recognition in noisy conditions (+5, 0, and -5 dB signal-to-noise ratio). Experiment 1 utilized h(Vowel)d (hVd) signals, while experiment 2 utilized sentences from the Rainbow Passage. Both experiments showed significant improvements in individual speaker identification in the 10 kHz bandwidth condition (6% for hVds; 10% for sentences). These results coincide with the extant machine recognition literature demonstrating significant amounts of individual speaker information present in the speech signal above approximately 3-4 kHz. Cues from the high-frequency region for speaker identity warrant further study.

Partial loudness at masker onset indicates temporal effects at supra-threshold levels.

This study examines temporal effects both at threshold and at supra-threshold levels. The level needed to detect a short-duration 4.0-kHz signal was measured for signals presented with different onset delays relative to a 300-ms broadband noise masker: 100 ms and 5 ms before the onset of the masker and 5 ms and 100 ms after the onset of the masker. Loudness matches between the signal in quiet and the signal at the same four onset delays were obtained for five presentation levels of the short-duration signal and for three masker levels. The temporal effect was defined as the level difference between the signals near masker onset and the signals well before or well after masker onset, needed to reach threshold and/or achieve equal loudness. Both at threshold and at supra-threshold levels temporal effects were observed consistent with a decrease in gain at the masker frequency during the course of the masker. The temporal effect was not restricted to simultaneous masking, but was also found for backward masking. In both cases the temporal effects were stronger at supra-threshold levels than at threshold. This may be caused by a transient effect at masker onset. The almost simultaneous onset of the signal and the masker makes it difficult for subjects to separate signal from the masker, especially when the signal level is close to masked threshold.

Assessing the background decomposition of a complex auditory scene with event-related brain potentials.

A listener who focusses on a sound source of interest must continuously integrate the sounds emitted by the attended source and ignore the sounds emitted by the remaining sources in the auditory scene. Little is known about how the ignored sound sources in the background are mentally represented after the source of interest has formed the perceptual foreground. This is due to a key methodological challenge: the background representation is by definition not overtly reportable. Here we developed a paradigm based on event-related brain potentials (ERPs) to assess the mental representation of background sounds. Participants listened to sequences of three repeatedly presented tones arranged in an ascending order (low, middle, high frequency). They were instructed to detect intensity deviants in one of the tones, creating the perceptual foreground. The remaining two background tones contained timing and location deviants. Those deviants were set up such that mismatch negativity (MMN) components would be elicited in distinct ways if the background was decomposed into two separate sound streams (background segregation) or if it was not further decomposed (background integration). Results provide MMN-based evidence for background segregation and integration in parallel. This suggests that mental representations of background integration and segregation can be concurrently available, and that collecting empirical evidence for only one of these background organization alternatives might lead to erroneous conclusions.

Auditory gap detection: psychometric functions and insights into the underlying neural activity.

The detection of a silent interval or gap provides important insight into temporal processing by the auditory system. Previous research has uncovered a multitude of empirical findings leaving the mechanism of gap detection poorly understood and key issues unresolved. Here, we expand the findings by measuring psychometric functions for a number of conditions including both across-frequency and across-intensity gap detection as a first study of its kind. A model is presented which not only accounts for our findings in a quantitative manner, but also helps frame the body of work on auditory gap research. The model is based on the peripheral response and postulates that the identification of gap requires the detection of activity associated with silence.

Perceived Weight Is Affected by Auditory Pitch Not Loudness.

This study examined whether auditory pitch and loudness affect the perception of object's weight. Two series experiments showed that the object with High-Pitch sound was perceived as being lighter than the object with Low-Pitch sound and that the perceived weight was not affected by loudness. Because auditory pitch has a relationship to the weight of an object while loudness has a relationship to the distance of a placed object, the perceived weight was affected by auditory pitch not loudness. Given these results, perhaps sound effects may make it easier to carry heavy luggage?

Spatial variation in signal and sensory precision both constrain auditory acuity at high frequencies.

Sensory performance is constrained by the information in the stimulus and the precision of the involved sensory system(s). Auditory spatial acuity is robust across a broad range of sound frequencies and source locations, but declines at eccentric lateral angles. The basis of such variation is not fully understood. Low-frequency auditory spatial acuity is mediated by sensitivity to interaural time difference (ITD) cues. While low-frequency spatial acuity varies across azimuth and some physiological models predict strong medial bias in the precision of ITD sensitivity, human psychophysical ITD sensitivity appears to vary only slightly with reference ITD magnitude. Correspondingly, recent analyses suggest that spatial variation in human low-frequency acuity is well-accounted for by acoustic factors alone. Here we examine the matter of high-frequency auditory acuity, which is mediated by sensitivity to interaural level difference (ILD) cues. Using two different psychophysical tasks in human subjects, we demonstrate decreasing ILD acuity with increasing ILD magnitude. We then demonstrate that the multiplicative combination of spatially variant sensory precision and physical cue information (local slope of the ILD cue) provides improved prediction of classic high-frequency spatial acuity data. Finally, we consider correlates of magnitude dependent acuity in neurons that are sensitive to ILDs.

Assessing auditory nerve condition by tone decay in deaf subjects with a cochlear implant.

The condition of the auditory nerve is a factor determining hearing performance of cochlear implant (CI) recipients. Abnormal loudness adaptation is associated with poor auditory nerve survival. We examined which stimulus conditions are suitable for tone decay measurements to differentiate between CI recipients with respect to their speech perception. Tone decay was defined here as occurring when the percept disappears before the stimulus stops. We measured the duration of the percept of a 60-s pulse train. Current levels ranged from below threshold up to maximum acceptable loudness, pulse rates from 250 to 5000 pulses/s, and duty cycles (percentages of time the burst of pulses is on) from 10% to 100%. Ten adult CI recipients were included: seven with good and three with poor speech perception. Largest differences among the subjects were found at 5000 pulses/s and 100% duty cycle. The well performing subjects had a continuous percept of the 60-s stimulus within 3 dB above threshold. Two poorly performing subjects showed abnormal loudness adaptation, that is, no continuous percept even at levels greater than 6 dB above threshold. We conclude that abnormal loudness adaptation can be detected via an electric tone decay test using a high pulse rate and 100% duty cycle.

Adversarial relationship between combined medial olivocochlear (MOC) and middle-ear-muscle (MEM) reflexes and alarm-in-noise detection thresholds under negative signal-to-noise ratios (SNRs).

The role of auditory efferent feedback from the medial olivocochlear system (MOCS) and the middle-ear-muscle (MEM) reflex in tonal detection tasks for humans in the presence of noise is not clearly understood. Past studies have yielded inconsistent results on the relationship between efferent feedback and tonal detection thresholds. This study attempts to address this inconsistency. Fifteen human subjects with normal hearing participated in an experiment where they were asked to identify an alarm signal in the presence of 80 dBA background (pink) noise. Masked detection thresholds were estimated using the method of two-interval forced choice (2IFC). Contralateral suppression of transient-evoked otoacoustic emissions (TEOAEs) was measured to estimate the strength of auditory efferent feedback. Subsequent correlation analysis revealed that the contralateral suppression of TEOAEs was significantly negatively correlated (r = -0.526, n = 15, p = 0.0438) with alarm-in-noise (AIN) detection thresholds under negative signal-to-noise conditions. The result implies that the stronger the auditory efferent feedback, the worse the detection thresholds and thus the poorer the tonal detection performance in the presence of loud noise.