Auditory Enhancement Research Articles

Auditory enhancement in younger and older listeners with normal and impaired hearinga).

Auditory enhancement is a spectral contrast aftereffect that can facilitate the detection of novel events in an ongoing background. A single-interval paradigm combined with roved frequency content between trials can yield as much as 20 dB enhancement in young normal-hearing listeners. This study compared such enhancement in 15 listeners with sensorineural hearing loss with that in 15 age-matched adults and 15 young adults with normal audiograms. All groups were presented with stimulus levels of 70 dB sound pressure level (SPL) per component. The two groups with normal hearing were also tested at 45 dB SPL per component. The hearing-impaired listeners showed very little enhancement overall. However, when tested at the same high (70-dB) level, both young and age-matched normal-hearing listeners also showed substantially reduced enhancement, relative to that found at 45 dB SPL. Some differences in enhancement emerged between young and older normal-hearing listeners at the lower sound level. The results suggest that enhancement is highly level-dependent and may also decrease somewhat with age or slight hearing loss. Implications for hearing-impaired listeners may include a poorer ability to adapt to real-world acoustic variability, due in part to the higher levels at which sound must be presented to be audible.

Effects of obstruent voicing on vowel fundamental frequency in Dutch.

It has been known for a long time and a wide variety of languages that vowel fundamental frequency (F0) following voiceless obstruents tends to be significantly higher than F0 following voiced obstruents. There has been a long-standing debate about the cause of this phenomenon. Some evidence in previous work is more compatible with an articulatory account of this effect, while others support the auditory enhancement account. This paper investigates these consonant-related F0 perturbations in Dutch after initial fricatives (/v, f/) and stops (/b, p/), as compared to after the nasal /m/. Dutch is particularly interesting because it is a "true voicing" language, and because fricatives are currently undergoing a process of devoicing. Results show that F0 was raised after voiceless, but largely unaffected after voiced obstruents. Fricative voicing in /v/ and F0 level tend to covary: the less voicing in /v/, the higher F0 at onset. There was no trace of an active gesture to explicitly lower pitch after highly devoiced fricatives, as would be predicted by an auditory account. In conclusion, F0 perturbations after Dutch obstruents and their covariation patterns are taken as additional evidence to support an articulatory cause of consonant-related F0 effects.

Efficacy of digital picture book enhancements grounded in multimedia learning principles: Dependent on age?

We designed an experiment with stratified randomization to investigate the effects of visual and auditory enhancements in digital picture books on comprehension and incidental word learning. Participants were 183 children aged 3, 4, and 5 years (81 girls and 102 boys) from childcare centers and schools in the Southwest USA. We contrasted the still-image condition (an onscreen picture book with a voice-over reading the narrative aloud) with three enhanced conditions: a digital book that included auditory and visual enhancements, only auditory enhancement, or only visual enhancement. All participants watched and listened thrice to the researcher-assigned digital picture book version within three weeks. The posttests assessed children's story comprehension and book-based vocabulary. The visual and auditory enhancements benefited children's story comprehension and book-based vocabulary. However, a version with auditory and visual enhancements was less beneficial for comprehension than versions with single (auditory or visual) enhancements, particularly in the youngest group.

Auditory enhancement of visual searches for event scenes.

Increasing research has revealed that uninformative spatial sounds facilitate the early processing of visual stimuli. This study examined the crossmodal interactions of semantically congruent stimuli by assessing whether the presentation of event-related characteristic sounds facilitated or interfered with the visual search for corresponding event scenes in pictures. The search array consisted of four images: one target and three non-target pictures. Auditory stimuli were presented to participants in synchronization with picture onset using three types of sounds: a sound congruent with a target, a sound congruent with a distractor, or a control sound. The control sound varied across six experiments, alternating between a sound unrelated to the search stimuli, white noise, and no sound. Participants were required to swiftly localize a target position while ignoring the sound presentation. Visual localization resulted in rapid responses when a sound that was semantically related to the target was played. Furthermore, when a sound was semantically related to a distractor picture, the response times were longer. When the distractor-congruent sound was used, participants incorrectly localized the distractor position more often than at the chance level. These findings were replicated when the experiments ruled out the possibility that participants would learn picture-sound pairs during the visual tasks (i.e., the possibility of brief training during the experiments). Overall, event-related crossmodal interactions occur based on semantic representations, and audiovisual associations may develop as a result of long-term experiences rather than brief training in a laboratory.

A Systematic Review of Auditory Loss and Its Management

Auditory loss is a highly under recognised undermined issue which needs to be studied in extensive detail, as according to World Health Organisation, more than 45% of the global population has loss of auditory. The high percentage can be lowered if auditory enhancement techniques such as auditory aids or implants of cochlea were not underused. In order to increase the usage of these devices we must first understand the inner workings of the ear and the pathologies that may cause it to malfunction and then move on to proper management. Auditory loss as defined by WHO as the inability to hear as well as someone with normal auditory, these are persons having auditory thresholds of 20 dB or better than 20 dB in both ears. Auditory loss is often classified into two types, conductive auditory loss and sensorineural auditory loss which is a broad classification into which we can separate the various pathologies which bring about same outcomes. In conductive auditory loss, there is often involvement of external or middle ear where there is obstruction in relay of sound waves, hence, quite literally a problem with the conduction. Conductive auditory loss can be both congenital or acquired but most often can be resolved in a manner which will result in recovery of auditory. Sensorineural auditory loss occurs when there is dysfunction in the inner ear which often leads to progressive and permanent auditory loss. Though it can be congenital, it is most often acquired, especially when it is age related more commonly known as presbycusis which affects a large amount of the aging population. The management can be done through various processes including oral medications, surgical interventions and other manual procedures. Various assistive technologies like auditory aids and cochlear implants are also vital in preservation of auditory.

Neural auditory contrast enhancement in humans

The perception of sensory events can be enhanced or suppressed by the surrounding spatial and temporal context in ways that facilitate the detection of novel objects and contribute to the perceptual constancy of those objects under variable conditions. In the auditory system, the phenomenon known as auditory enhancement reflects a general principle of contrast enhancement, in which a target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This effect is highly robust, producing an effective enhancement of the target of up to 25 dB (more than two orders of magnitude in intensity), depending on the task. Despite the importance of the effect, neural correlates of auditory contrast enhancement have yet to be identified in humans. Here, we used the auditory steady-state response to probe the neural representation of a target sound under conditions of enhancement. The probe was simultaneously modulated in amplitude with two modulation frequencies to distinguish cortical from subcortical responses. We found robust correlates for neural enhancement in the auditory cortical, but not subcortical, responses. Our findings provide empirical support for a previously unverified theory of auditory enhancement based on neural adaptation of inhibition and point to approaches for improving sensory prostheses for hearing loss, such as hearing aids and cochlear implants.

The Modulation of Exogenous Attention on Emotional Audiovisual Integration.

Although emotional audiovisual integration has been investigated previously, whether emotional audiovisual integration is affected by the spatial allocation of visual attention is currently unknown. To examine this question, a variant of the exogenous spatial cueing paradigm was adopted, in which stimuli varying by facial expressions and nonverbal affective prosody were used to express six basic emotions (happiness, anger, disgust, sadness, fear, surprise) via a visual, an auditory, or an audiovisual modality. The emotional stimuli were preceded by an unpredictive cue that was used to attract participants’ visual attention. The results showed significantly higher accuracy and quicker response times in response to bimodal audiovisual stimuli than to unimodal visual or auditory stimuli for emotional perception under both valid and invalid cue conditions. The auditory facilitation effect was stronger than the visual facilitation effect under exogenous attention for the six emotions tested. Larger auditory enhancement was induced when the target was presented at the expected location than at the unexpected location. For emotional perception, happiness shared the biggest auditory enhancement among all six emotions. However, the influence of exogenous cueing effect on emotional perception seemed to be absent.

Face and voice perception: Monkey see, monkey hear

Primate brains contain specialized areas for perceiving social cues. New research shows that only some of these areas integrate visual faces with auditory voices.

Perceptual Weighting of Binaural Lateralization Cues across Frequency Bands

The auditory system uses interaural time and level differences (ITD and ILD) as cues to localize and lateralize sounds. The availability of ITDs and ILDs in the auditory system is limited by neural phase-locking and by the head size, respectively. Although the frequency-specific limitations are well known, the relative contribution of ITDs and ILDs in individual frequency bands in broadband stimuli is unknown. To determine these relative contributions, or spectral weights, listeners were asked to lateralize stimuli consisting of eleven simultaneously presented 1-ERB-wide noise bands centered between 442 and 5544 Hz and separated by 1-ERB-wide gaps. Either ITDs or ILDs were varied independently across each noise band, while fixing the other interaural disparity to either 0 dB or 0 μs. The weights were obtained using a multiple linear regression analysis. In a second experiment, the effect of auditory enhancement on the spectral weights was investigated. The enhancement of single noise bands was realized by presenting ten of the noise bands as preceding and following sounds (pre- and post-cursors, respectively). Listeners were asked to lateralize the stimuli as in the first experiment. Results show that in the absence of pre- and post-cursors, only the lowest or highest frequency band received highest weight for ITD and ILD, respectively. Auditory enhancement led to significantly enhanced weights given to the band without the pre- and post-cursor. The weight enhancement could only be observed at low frequencies, when determined with ITD cues and for low and high frequencies for ILDs. Hence, the auditory system seems to be able to change the spectral weighting of binaural information depending on the information content.

Auditory Enhancement of Illusory Contour Perception.

Illusory contours (ICs) are borders that are perceived in the absence of contrast gradients. Until recently, IC processes were considered exclusively visual in nature and presumed to be unaffected by information from other senses. Electrophysiological data in humans indicates that sounds can enhance IC processes. Despite cross-modal enhancement being observed at the neurophysiological level, to date there is no evidence of direct amplification of behavioural performance in IC processing by sounds. We addressed this knowledge gap. Healthy adults ( n = 15) discriminated instances when inducers were arranged to form an IC from instances when no IC was formed (NC). Inducers were low-constrast and masked, and there was continuous background acoustic noise throughout a block of trials. On half of the trials, i.e., independently of IC vs NC, a 1000-Hz tone was presented synchronously with the inducer stimuli. Sound presence improved the accuracy of indicating when an IC was presented, but had no impact on performance with NC stimuli (significant IC presence/absence× Sound presence/absence interaction). There was no evidence that this was due to general alerting or to a speed-accuracy trade-off (no main effect of sound presence on accuracy rates and no comparable significant interaction on reaction times). Moreover, sound presence increased sensitivity and reduced bias on the IC vs NC discrimination task. These results demonstrate that multisensory processes augment mid-level visual functions, exemplified by IC processes. Aside from the impact on neurobiological and computational models of vision, our findings may prove clinically beneficial for low-vision or sight-restored patients.

Evaluating peripheral versus central contributions to spectral context effects in speech perception

Perception of a sound is influenced by spectral properties of surrounding sounds. When frequencies are absent in a preceding acoustic context before being introduced in a subsequent target sound, detection of those frequencies is facilitated via an auditory enhancement effect (EE). When spectral composition differs across a preceding context and subsequent target sound, those differences are perceptually magnified and perception shifts via a spectral contrast effect (SCE). Each effect is thought to receive contributions from peripheral and central neural processing, but the relative contributions are unclear. The present experiments manipulated ear of presentation to elucidate the degrees to which peripheral and central processes contributed to each effect in speech perception. In Experiment 1, EE and SCE magnitudes in consonant categorization were substantially diminished through contralateral presentation of contexts and targets compared to ipsilateral or bilateral presentations. In Experiment 2, spectrally complementary contexts were presented dichotically followed by the target in only one ear. This arrangement was predicted to produce context effects peripherally and cancel them centrally, but the competing contralateral context minimally decreased effect magnitudes. Results confirm peripheral and central contributions to EEs and SCEs in speech perception, but both effects appear to be primarily due to peripheral processing.

Spectral contrast effects and auditory enhancement under normal and impaired hearing.

We are generally able to identify sounds and understand speech with ease, despite the large variations in the acoustics of each sound, which occur due to factors such as different talkers, background noise, and room acoustics. This form of perceptual constancy is likely to be mediated in part by the auditory system's ability to adapt to the ongoing environment or context in which sounds are presented. Auditory context effects have been studied under different names, such as spectral contrast effects in speech and auditory enhancement effects in psychoacoustics, but they share some important properties and may be mediated by similar underlying neural mechanisms. This review provides a survey of recent studies from our laboratory that investigate the mechanisms of speech spectral contrast effects and auditory enhancement in people with normal hearing, hearing loss, and cochlear implants. We argue that a better understanding of such context effects in people with normal hearing may allow us to restore some of these important effects for people with hearing loss via signal processing in hearing aids and cochlear implants, thereby potentially improving auditory and speech perception in the complex and variable everyday acoustic backgrounds that surround us.

Visual Reliance During Speech Recognition in Cochlear Implant Users and Candidates.

Adults with cochlear implants (CIs) are believed to rely more heavily on visual cues during speech recognition tasks than their normal-hearing peers. However, the relationship between auditory and visual reliance during audiovisual (AV) speech recognition is unclear and may depend on an individual's auditory proficiency, duration of hearing loss (HL), age, and other factors. The primary purpose of this study was to examine whether visual reliance during AV speech recognition depends on auditory function for adult CI candidates (CICs) and adult experienced CI users (ECIs). Participants included 44 ECIs and 23 CICs. All participants were postlingually deafened and had met clinical candidacy requirements for cochlear implantation. Participants completed City University of New York sentence recognition testing. Three separate lists of twelve sentences each were presented: the first in the auditory-only (A-only) condition, the second in the visual-only (V-only) condition, and the third in combined AV fashion. Each participant's amount of "visual enhancement" (VE) and "auditory enhancement" (AE) were computed (i.e., the benefit to AV speech recognition of adding visual or auditory information, respectively, relative to what could potentially be gained). The relative reliance of VE versus AE was also computed as a VE/AE ratio. VE/AE ratio was predicted inversely by A-only performance. Visual reliance was not significantly different between ECIs and CICs. Duration of HL and age did not account for additional variance in the VE/AE ratio. A shift toward visual reliance may be driven by poor auditory performance in ECIs and CICs. The restoration of auditory input through a CI does not necessarily facilitate a shift back toward auditory reliance. Findings suggest that individual listeners with HL may rely on both auditory and visual information during AV speech recognition, to varying degrees based on their own performance and experience, to optimize communication performance in real-world listening situations.

Auditory enhancement under forward masking in normal-hearing and hearing-impaired listeners.

A target within a spectrally notched masker can be enhanced by a preceding copy of the masker. Enhancement can also increase the effectiveness of the target as a forward masker. Enhancement has been reported in hearing-impaired listeners under simultaneous but not forward masking. However, previous studies of enhancement under forward masking did not fully assess the potential effect of differences in sensation level or spectral resolution between the normal-hearing and hearing-impaired listeners. This study measured enhancement via forward masking in hearing-impaired and age-matched normal-hearing listeners with different spectral notches in the masker, to account for potential differences in frequency selectivity, and with levels equated by adding a background masking noise to equate both sensation level and sound pressure level or by reducing the sound pressure level of the stimuli to equate sensation level. Hearing-impaired listeners showed no significant enhancement, regardless of spectral notch width. Normal-hearing listeners showed enhancement at high levels, but showed less enhancement when sensation levels were reduced to match those of the hearing-impaired group, either by reducing sound levels or by adding a masking noise. The results confirm a lack of forward-masked enhancement in hearing-impaired listeners but suggest this may be partly due to reduced sensation level.

Auditory enhancement and spectral contrast effects in speech perception.

The auditory system is remarkably sensitive to changes in the acoustic environment. This is exemplified by two classic effects of preceding spectral context on perception. In auditory enhancement effects (EEs), the absence and subsequent insertion of a frequency component increases its salience. In spectral contrast effects (SCEs), spectral differences between earlier and later (target) sounds are perceptually magnified, biasing target sound categorization. These effects have been suggested to be related, but have largely been studied separately. Here, EEs and SCEs are demonstrated using the same speech materials. In Experiment 1, listeners categorized vowels (/ɪ/-/ɛ/) or consonants (/d/-/g/) following a sentence processed by a bandpass or bandstop filter (vowel tasks: 100-400 or 550-850 Hz; consonant tasks: 1700-2700 or 2700-3700 Hz). Bandpass filtering produced SCEs and bandstop filtering produced EEs, with effect magnitudes significantly correlated at the individual differences level. In Experiment 2, context sentences were processed by variable-depth notch filters in these frequency regions (-5 to -20 dB). EE magnitudes increased at larger notch depths, growing linearly in consonant categorization. This parallels previous research where SCEs increased linearly for larger spectral peaks in the context sentence. These results link EEs and SCEs, as both shape speech categorization in orderly ways.

Cue-shifting between acoustic cues: Evidence for directional asymmetry

Previous research shows that experience with co-varying cues is neither sufficient nor necessary for listeners to integrate them perceptually. Auditory Enhancement theorists explain this by positing that listeners integrate two cues more readily if the cues enhance each other’s percept. To isolate the role of enhancement from that of experience, we forced English adult listeners to shift attention between two enhancing cues that they do not use phonemically, pitch and breathiness, by reversing the informativeness of the two cues in a cue weighting experiment. Listeners were able to shift attention from pitch to breathiness and vice versa if the two cues were in an enhancing relation. When this relationship was reversed, listeners could shift attention from pitch to breathiness but not in the opposite direction. Clearly, both the change in informativeness and the enhancing properties of the cues influenced the listeners’ re-weighting of these cues. However, the directional asymmetry was not predicted. Moreover, the same asymmetry was observed in two new groups of listeners who have native language experience with either pitch or breathiness. We discuss the consequences of such asymmetric enhancement effects, rising from either processing limitations or articulatory contingencies, for language change.

Neural correlates of auditory enhancement

Auditory enhancement is the increase in salience of a target embedded in a simultaneous masker that occurs when a copy of the masker, termed the precursor, is presented first. The effect reflects the general principle of contrast enhancement and may help in the perceptual constancy of speech under varying acoustic conditions. The physiological mechanisms underlying auditory enhancement remain unknown. This study investigated EEG responses under conditions that elicited perceptual enhancement. The target tone was amplitude-modulated at two modulation frequencies to target cortical (~40 Hz) and subcortical (100–200 Hz) responses. Measurements were made in either passive conditions or under active tasks to examine the potential effects of attention on the neural correlates of enhancement. Robust effects of enhancement were observed at the cortical level, replicating our earlier findings. Preliminary data under passive conditions also suggest a trend towards increased neural response to the enhanced target tone at frequencies exceeding 200 Hz, suggesting a subcortical contribution. The results suggest that this paradigm can be used to tap into the neural correlates of auditory enhancement at both cortical and subcortical levels simultaneously and show the potential for tapping into attentional modulation of auditory enhancement. [Work supported by NIH grant R01DC012262.]

Post-sauna recovery enhances brain neural network relaxation and improves cognitive economy in oddball tasks

Objective: The aim of this study was to investigate the post-sauna residual consequences on brain neural network arousal, information processing and cognitive performance.Methods: Sixteen male subjects (24 ± 1 yr.) participated in the study. Whole-body hyperthermia was induced with Finnish sauna bathing. Before and 90 min after the sauna, resting electroencephalography (EEG) for spectral analysis and EEG event-related potentials (ERPs) during oddball tasks by two modalities (auditory and visual) were recorded.Results: Sauna bathing increased rectal temperature (Tre, 37.11 ± 0.33 °C to 38.84 ± 0.32 °C) and heart rate (HR, 65.63 ± 9.39 bpm to 151.0 ± 21.8 bpm). At 90 min after the sauna, Tre (37.00 ± 0.29 °C) and HR (72.1 ± 2.80 bpm) recovered to baseline levels. An increase was found in alpha power following sauna recovery. In the visual task modality, post-sauna recovery led to enhancement in the N2 amplitude with centroparietal distribution and decreases in P3 amplitude with distribution along the frontoparietal axis for executive motor–cognitive processing. In the auditory task modality, post-sauna recovery led to a decrease in P3 amplitude with a frontoparietal distribution and this change was accompanied by auditory N2 amplitude enhancement along the centroparietal distribution for non-target cognitive processing. No significant differences in task performance were found.Conclusion: Post-sauna recovery to normothermia led to enhanced resting neural network relaxation followed by increases in cognitive processing economy for the given oddball tasks. The auditory processing was not affected more by post-sauna recovery than was visual processing. Post-sauna recovery modifications in ERP components (stimulus processing) were insufficient to affect cognitive performance in both visual and auditory task modalities.

Loudness Context Effects and Auditory Enhancement in Normal, Impaired, and Electric Hearing

Loudness Context Effects and Auditory Enhancement in Normal, Impaired, and Electric Hearing

Auditory enhancement and the role of spectral resolution in normal-hearing listeners and cochlear-implant users.

Detection of a target tone in a simultaneous multi-tone masker can be improved by preceding the stimulus with the masker alone. The mechanisms underlying this auditory enhancement effect may enable the efficient detection of new acoustic events and may help to produce perceptual constancy under varying acoustic conditions. Previous work in cochlear-implant (CI) users has suggested reduced or absent enhancement, due perhaps to poor spatial resolution in the cochlea. This study used a supra-threshold enhancement paradigm that in normal-hearing listeners results in large enhancement effects, exceeding 20 dB. Results from vocoder simulations using normal-hearing listeners showed that near-normal enhancement was observed if the simulated spread of excitation was limited to spectral slopes no shallower than 24 dB/oct. No significant enhancement was observed on average in CI users with their clinical monopolar stimulation strategy. The variability in enhancement between CI users, and between electrodes in a single CI user, could not be explained by the spread of excitation, as estimated from auditory nerve evoked potentials. Enhancement remained small, but did reach statistical significance, under the narrower partial-tripolar stimulation strategy. The results suggest that enhancement may be at least partially restored by improvements in the spatial resolution of current CIs.