dB Sound Pressure Level Research Articles

Sonic restoration: acoustic stimulation enhances plant growth-promoting fungi activity.

Ecosystem restoration interventions often utilize visible elements to restore an ecosystem (e.g. replanting native plant communities and reintroducing lost species). However, using acoustic stimulation to help restore ecosystems and promote plant growth has received little attention. Our study aimed to assess the effect of acoustic stimulation on the growth rate and sporulation of the plant growth-promoting fungus Trichoderma harzianum Rifai, 1969. We played a monotone acoustic stimulus (80 dB sound pressure level (SPL) at a peak frequency of 8 kHz and a bandwidth at -10 dB from the peak of 6819 Hz-parameters determined via review and pilot research) over 5 days to T. harzianum to assess whether acoustic stimulation affected the growth rate and sporulation of this fungus (control samples received only ambient sound stimulation less than 30 dB). We show that the acoustic stimulation treatments resulted in increased fungal biomass and enhanced T. harzianum conidia (spore) activity compared to controls. These results indicate that acoustic stimulation influences plant growth-promoting fungal growth and potentially facilitates their functioning (e.g. stimulating sporulation). The mechanism responsible for this phenomenon may be fungal mechanoreceptor stimulation and/or potentially a piezoelectric effect; however, further research is required to confirm this hypothesis. Our novel study highlights the potential of acoustic stimulation to alter important fungal attributes, which could, with further development, be harnessed to aid ecosystem restoration and sustainable agriculture.

Frequency dependence and harmonic distortion of stapes displacement and intracochlear pressure in response to very high level sounds

Previous reports have suggested that intracochlear pressures (PIC) measured at the base of the cochlea increase directly proportionally with stapes displacement (DStap) in response to moderately high (<130 dB SPL) level sounds. Consistent with this assumption, we have reported that for low frequency sounds (<1 kHz), stapes displacement and intracochlear pressures increase linearly with sound pressure level (SPL) for moderately high levels (<130 dB SPL), but saturate at higher exposure levels (>130 dB SPL). However, the magnitudes of each response were found to be frequency dependent, thus the relationship between DStap and PIC may vary at higher frequencies or higher levels.In order to further examine this frequency and level dependence, measurements of DStap and PIC were made in cadaveric human temporal bones prepared with a mastoidectomy and extended facial recess to expose the ossicular chain. PIC was measured in scala vestibuli (PSV) and scala tympani (PST) simultaneously with SPL in the external auditory canal (PEAC) and laser Doppler vibrometry (LDV) measurements of stapes velocity (VStap). Consistent with prior reports, DStap and PSV increased proportionally with sound pressure level in the ear canal up to a frequency-dependent saturation point, above which both DStap and PSV showed a distinct deviation from proportionality with PEAC, suggesting that their relationship may remain constant at these high frequencies. Likewise, while the asymptotic value, and SPL at which saturation occurred were frequency dependent in both DStap and PSV, the reduction in gain with increasing SPL above this level was constant above this level at all frequencies, and the magnitude of responses at harmonics of the driving frequency increased with increasing level, consistent with harmonic distortion via peak clipping. Importantly, this nonlinear distortion shifts the energy arriving at the inner ear to higher frequencies than are present in incident stimulus, thus exposing the high frequency sensitive components of the auditory system to more noise than would be expected from measurement of that stimulus on its own. Overall, responses suggest that the cochlear representation of very high-level air conducted stimuli is limited by nonlinearities in the middle ear, and that this peak limiting leads to increased high frequency cochlear exposures than are present in the driving stimulus.

Bandwidth enhancement of piezoelectric MEMS microspeaker via central diaphragm actuation and filter integration

Abstract This study presents the piezoelectric microspeaker design consisted of the central-diaphragm, connecting-spring, and cantilever-plate actuators to create two resonances in the desired frequency range. In addition to the cantilever-plate actuator, the electrical routing and piezoelectric film are designed to drive the central-diaphragm independently. According to the stress distributions on the microspeaker structure for both lower and higher modes, the all-pass filter circuit is designed and implemented to manage the phase of input signals to the central-diaphragm, thereby changing the motion of the proposed design. Thus, the sound pressure level (SPL) beyond 1 kHz is improved and the SPL zero at specific frequency range is avoided. As a result, the bandwidth enhancement is achieved by the proposed microspeaker. Measurements are conducted under 0.707 Vrms with 9 VDC driving voltage in standard ear simulator to evaluate the performances of the proposed design. A reference design without a piezoelectric film on the central-diaphragm is also implemented for comparison. Measurements indicate, in the low frequency range (before 4 kHz), the proposed designs have over 3 dB SPL enhancement due to the excitation of central-diaphragm. Moreover, compared to the reference design, proposed designs prevent the occurrence of an SPL zero near 10 kHz (between lower and higher modes) and achieve over 15 dB SPL enhancement. When the driving frequency exceeds the higher mode (14 kHz), the proposed design with the all-pass filter eliminates the SPL zero (at 16.8 kHz) with nearly 8 dB enhancement in the 15–18 kHz frequency range. Thus, this study demonstrates the bandwidth enhancement by the proposed microspeaker design with central-diaphragm actuation and all-pass filter integration.

Audiological outcome of bimodal CI users over time and depending on different influencing factors

Hearing-impaired persons with asymmetric hearing loss and aunilateral indication for acochlear implant (CI) generally benefit from abimodal hearing solution. The influence of bimodal fitting on speech comprehension (SC) over time has not yet been sufficiently investigated. The present study examines the influence of bimodal fitting on SC in bimodally fitted CI users with postlingual deafness at least 36months after implantation and analyzes possible influencing factors. Included in this retrospective longitudinal study were 54bimodally fitted speech-competent CI users with at least 36months of CI experience. Audiometric data of these CI users at predefined timepoints were compared. The change in the results of the Freiburg monosyllabic test (FT) over 36months was significant (p < 5%) for the deafness group at <10years for both the 65 dB sound pressure level (SPL) and at 80 dB SPL and also significant for the deafness group ≥10years for 65 dB SPL. In the Oldenburg sentence test (OlSa) there was ahighly significant change (p < 0.1%) for S0, S0N0, and S0NCI configurations and avery significant change (p < 1%) for S0NHA (HA: hearing aid). Age at implantation as apossible influencing factor could not be confirmed in the FT. In contrast, the duration of deafness was anegative influencing factor for SC with CI in the FT, whereas alonger duration of deafness was associated with worse results in the FT. The degree of hearing loss in the ear fitted with an HA did not influence SC. The median bimodal benefit (here: difference in SC with bimodal fitting compared to unilateral HA fitting for FT at 65 dB SPL) was 10% over the total study period. For amedian of 79% of the test subjects, the bimodal benefit was found over the entire period of 36months. Over time, SC improves significantly with aCI for the bimodal test subjects. The investigated influencing factors (age, duration of deafness, and degree of hearing loss in the contralateral ear) support the indication for bimodal provision in accordance with the guideline in Germany for cochlear implantation-regardless of age, duration of deafness, and hearing ability of the contralateral ear.

Comparison between the international outcome inventory for hearing aids questionnaire and real-ear measurement.

The international outcome inventory for hearing aids (IOI-HA) is a questionnaire widely used to assess the subjective benefits of hearing aids. This study aimed to evaluate the relationship between IOI-HA outcomes and target mismatch in real-ear measurement (REM). Thirty-four ears of 25 patients who had worn hearing aids were evaluated using the Korean version of the IOI-HA and REM after fitting for 2 months. Real-ear insertion gain (REIG) was measured at three different levels of input intensity-50, 65, and 80 dB sound pressure level (SPL)-and a frequency range of 0.25 to 6 kHz. Factors 1 and 2 and total IOI-HA scores were compared with the mismatches of REIGs and target gains of REM. Factor 1, Factor 2, and total IOI-HA scores were 14.6 ± 3.5, 11.4 ± 2.2, and 25.9 ± 5.1, respectively. The averages of the difference of REIGs and target gains in REM at 50, 65, and 80 dB SPL input levels were -3.1 ± 6.7, -2.3 ± 7.2, and -3.0 ± 8.2, respectively. Factors 1 and 2 scores of the IOI-HA showed significant correlations with target mismatch in REM at 1 kHz and 0.75 kHz frequencies, respectively. Total IOI-HA scores had significant correlations with target mismatches in REM at 0.75 and 1 kHz frequencies. IOI-HA scores correlated with target mismatch in REM at mid frequencies. The IOI-HA can be a useful screening measure for evaluating the necessity of further adjustments in hearing aids through REM at mid frequencies.

Earmuff performance in the presence of high-level impulse from a recoilless weapon firing in a confined space.

A noise attenuation performance test was conducted on earmuffs using a recoilless weapon launch platform in a confined space, along with two acoustic test fixtures (ATFs). The overpressure at the ATF's effective tympanic membrane comprised direct sound at 185 dB sound pressure level (SPL) and reflected sound at 179 dB SPL. Wearing earmuffs reduced these peaks to 162 dB SPL and 169 dB SPL, respectively. The reflected sound from walls was defined as delayed sound. An analytical model for earmuff noise attenuation simulated their effectiveness. The simulation revealed that when the earmuffs attenuated delayed sound, the acoustic impedance of acoustic leakage and the acoustic impedance of the earmuff material decreased by 96% and 50%, respectively. The negative overpressure zone between direct and delayed sound decreased the earmuffs' fit against the ATF. Additionally, the enclosed volume between the earmuff and the ear canal decreased by 12%. After the installation of bandages on the earmuffs, the overpressure peak of delayed sound was reduced by 5 dB. Furthermore, the acoustic impedance of the earmuff's sound leakage path and the acoustic impedance of the earmuff material deformation path increased by 100% and 809%, respectively.

Evaluation of a super powerful bone-anchored hearing system and its users: A retrospective study.

Although the Baha 5SP has been commercially available for six years, very few studies have been performed on the device's efficacy. The current study aims to evaluate the characteristics and audiological results in patients with severe-to-profound mixed hearing loss fitted with this superpower sound processor. This retrospective evaluation was conducted at a tertiary referral centre where a series of 82 adult patients with severe-to-profound mixed hearing loss were implanted with a percutaneous bone-anchored hearing system and fitted with a superpower sound processor between 2016 and 2019. Patients with incomplete or unreliable audiological data (n = 24) were excluded, resulting in 58 data sets for analysis. The main outcome measures were unaided and aided pure-tone thresholds and aided free-field speech perception in quiet. The median unaided air conduction (AC) threshold averaged across 0.5, 1 and 2 kHz (PTA0.5-2kHz) of all patients was 75 dB hearing loss (HL); the median unaided AC averaged across 1, 2 and 4 kHz (PTA1-4kHz) was 84 dB HL. For bone conduction and direct bone conduction, the median PTA0.5-2kHz was 52 and 47 dB HL, respectively. With the superpower device, the median free-field speech reception threshold was 54 dB sound pressure level (SPL), and the median speech perception score at 65 dB SPL was 80%. At least 75% of the patients reached a maximum phoneme score of 70%. For patients with lower scores, the superpower device still provides a substantial hearing benefit. This makes the superpower device particularly suitable for patients with severe-to-profound mixed hearing loss with a contraindication for conventional hearing aids and/or cochlear implants.

Impact of low-frequency noise on a residential zone due to commercial HVAC systems

Low frequency noise (LFN) is a serious growing global challenge for the urban environment where noise itself is an undervalued pollutant. The commercial establishments are equipped with multiple HVAC (Heating Ventilation and Air Conditioning) units responsible for the generation of LFN. To assess the impact of LFN, the noise was monitored using A and C-weighting sound level meters at HVAC outlets as well as in and around the residential premises. The noise due to HVAC units is found to be highly intensive in the lower frequency zones (<250Hz), affecting psychological and physiological health of living beings in the residential zones. A substantial 39.4 dB sound pressure level discrepancy between A and C-weighting inside the residential premises underscores the pronounced predominance of low-frequency noise. Noise monitoring using A-weighting failed to highlight the significant impact of lower frequency octave bands. The C-weighting noise monitoring revealed a substantial contribution of lower frequency octave bands (8Hz–250Hz) with 48.2 dB(C), in the overall equivalent noise level of 48.6(C), primarily attributed to HVAC units. The study suggests monitoring and assessment of the LFN, its mitigation and control strategies and its impact on the noise environment, especially on a residential zone.

Sound Exposure Promotes Intratympanic Drug Delivery to the Inner Ear.

To investigate the impact of sound exposure, with the resultant windows vibration on perilymphatic concentrations following intratympanic (IT) dexamethasone and gentamicin in an animal model. Animal model blinded study. Animal facility of a tertiary medical center. Bilateral IT dexamethasone or gentamicin was applied to 15 tested rats. Following injections, each rat was exposed for 3minutes to free field 30 dB sound pressure level (SPL), 512 vHz noise, with 1external auditory canal plugged (contralateral control). Following noise exposure, perilymph was obtained from both ears. Drug concentrations were measured using ultrahigh-performance liquid chromatography-mass spectrometer. For dexamethasone, the average (±SD) perilymphatic steroidal concentration was 0.417 µg/mL (±0.549) in the control ears versus 0.487 µg/mL (±0.636) in the sound-exposed ears (P = .008). The average (±SD) gentamicin perilymphatic concentration was 8.628 µg/mL (±2.549) in the sound-exposed ears, compared to 4.930 µg/mL (±0.668) in the contralateral control (nonsound exposed) ears. Sound exposure promoted steroidal and gentamicin diffusion to the inner ear by an averaged (±SD) factor of 1.431 and 1.730 (±0.291 and 0.339), respectively. Low-intensity noise (30 dB SPL) was found to enhance dexamethasone phosphate and gentamicin diffusion to the inner ear (by an averaged factor of ∼1.4 and 1.7, respectively) in a murine model.

Mechanism of noise induced hidden hearing loss based on proteomics

Objective: To explore the mechanism of noise-induced hidden hearing loss by proteomics. Methods: In October 2022, 64 SPF male C57BL/6J mice were divided into control group and noise exposure group with 32 mice in each group according to random sampling method. The noise exposure group was exposed to 100 dB sound pressure level, 2000-16000 Hz broadband noise for 2 h, and the mouse hidden hearing loss model was established. Auditory brainstem response (ABR) was used to test the change of hearing threshold of mice on the 7th day after noise exposure, the damage of basal membrane hair cells was observed by immunofluorescence, and the differentially expressed proteins in the inner ear of mice in each group were identified and analyzed by 4D-Label-free quantitative proteomics, and verified by Western blotting. The results were statistically analyzed by ANOVA and t test. Results: On the 7th day after noise exposure, there was no significant difference in hearing threshold between the control group and the noise exposure group at click and 8000 Hz acoustic stimulation (P>0.05) . The hearing threshold in the noise exposure group was significantly higher than that in the control group under 16000 Hz acoustic stimulation (P<0.05) . Confocal immunofluorescence showed that the basal membrane hair cells of cochlear tissue in noise exposure group were arranged neatly, but the relative expression of C-terminal binding protein 2 antibody of presynaptic membrane in middle gyrus and basal gyrus was significantly lower than that in control group (P<0.05) . GO enrichment analysis showed that the functions of differentially expressed proteins were mainly concentrated in membrane potential regulation, ligand-gated channel activity, and ligand-gated ion channel activity. KEGG pathway enrichment analysis showed that differentially expressed proteins were significantly enriched in phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt) signaling pathway, NOD-like receptor signaling pathway, calcium signaling pathway, etc. Western blotting showed that the expression of inositol 1, 4, 5-trisphosphate receptor 3 (Itpr3) was increased and the expression of solute carrier family 38 member 2 (Slc38a2) was decreased in the noise exposure group (P<0.05) . Conclusion: Through proteomic analysis, screening and verification of the differential expression proteins Itpr3 and Slc38a2 in the constructed mouse noise-induced hidden hearing loss model, the glutaminergic synaptic related pathways represented by Itpr3 and Slc38a2 may be involved in the occurrence of hidden hearing loss.

Andrographolide Attenuates Noise-Induced Hearing Loss by Ameliorating Cochlear Inflammation

Abstract Objective: This study aimed to explore andrographolide’s mechanism of action and its protective effect on noise-induced hearing loss (NIHL). Materials and Methods: A mice animal model for NIHL was established through exposure to broadband noise at 120 dB sound pressure level for 4 h. Transcriptomics analysis and pharmacodynamic experiments were carried out. Results: Andrographolide enters the inner ear and effectively prevents hearing damage following noise exposure in the mice model for permanent hearing loss. Moreover, treatment with andrographolide inhibited the excessive activation of inflammatory factors in the cochleae of noise-exposed mice. Conclusion: Andrographolide might be a promising candidate for auditory protective drug investigation.

Intensive Voice Treatment following Botulinum Neurotoxin Injection for a Speaker with Abductor Laryngeal Dystonia: An Exploratory Case Study.

Abductor laryngeal dystonia (ABLD) is a rare neurological voice disorder which results in sporadic opening of the vocal folds during speech. Etiology is unknown, and to date there is no identified effective behavioral treatment for it. It is hypothesized that LSVT LOUD®, which was developed to treat dysphonia secondary to Parkinson's disease, may have application to speakers with ABLD to improve outcomes beyond that with botulinum neurotoxin (BoNT) treatment alone. The participant received one injection of BoNT in each vocal fold 2 to 3 months prior to initiating intensive voice therapy via teletherapy. Objective measures of vocal loudness (dB sound pressure level), maximum phonation time, and high/low pitch frequency (Hz) were recorded in all treatment sessions and follow-up sessions. Over the course of treatment, the participant showed steady gains in phonation time, volume, pitch range, and vocal quality with a substantial reduction in aphonic voice breaks by the end of the treatment program. Perceptual symptoms of ABLD were nearly undetectable by the participant and the clinicians up to 12 months posttreatment, with no additional BoNT injections. The results suggest that LSVT LOUD® following BoNT was effective, with long-lasting improvement in vocal function, for this speaker with ABLD.

Pros and cons of a bone-conduction device implanted in the worse hearing ear of patients with asymmetric hearing loss

PurposeBone-conduction devices can be considered a viable treatment option for patients experiencing asymmetric hearing loss (AHL), especially those with severe to profound hearing loss (HL) present in one ear. However, there are only a few reports on the effects of bone-anchored hearing aids (BAHAs) on patients with AHL. This retrospective study analyzed in detail the effects of BAHA on softer sounds than other hearing aids and identified situations in which BAHA had a negative effect.MethodsPatients with AHL, characterized by severe to profound hearing loss in one ear with a difference of ≥45 dB from that of the contralateral ear, underwent BAHA implantation in the ear with worse hearing. The BAHA effects were evaluated by assessing the word recognition score (WRS) and speech reception threshold (SRT) using the Japanese Oldenburg Sentence Test for various signal settings and noise directions. For a subjective analysis, the Speech, Spatial and Qualities of Hearing Scale (SSQ12) score was determined.ResultsThirteen patients who underwent BAHA implantation at the Miyazaki University Hospital between 2007 and 2021 were included. The BAHA demonstrated a significant improvement in the WRS from 40 to 70 dB sound pressure levels. Although the SRT showed significant improvement in noisy environments when speech was presented to the BAHA-wearing side, it worsened significantly when noise was presented to this side. In the survey of subjective hearing ability, both the total and subscale SSQ12 scores improved significantly after wearing the BAHA.ConclusionThis study identified scenarios in which BAHAs were beneficial and detrimental to individuals with AHL. Generally used audiological tests, such as the WRS with fixed sound pressure, may underestimate the effectiveness of BAHAs for softer sounds. In addition, depending on the direction of the noise, BAHAs may have adverse effects. These results could help patients comprehend the potential benefits and limitations of bone-conduction devices for their hearing.

Transcriptomic analysis reveals prolonged neurodegeneration in the hippocampus of adult C57BL/6N mouse deafened by noise.

Several studies have reported a significant correlation between noise-induced hearing loss and cognitive decline. However, comprehensive analyses of this relationship are rare. This study aimed to assess the influence of hearing impairment on cognitive functions by analyzing organ samples in the afferent auditory pathway of deafened mice using mRNA sequencing. We prepared 10 female 12-week-old C57BL/6N mice as the experimental and control groups in equal numbers. Mice in the experimental group were deafened with 120 dB sound pressure level (SPL) wideband noise for 2 h. Cochlea, auditory cortex, and hippocampus were obtained from all mice. After constructing cDNA libraries for the extracted RNA from the samples, we performed next-generation sequencing. Subsequently, we analyzed the results using gene ontologies (GOs) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway databases for differentially expressed genes (DEGs) of each organ. Our results revealed 102, 89, and 176 DEGs for cochlea, auditory cortex, and hippocampus, respectively. We identified 294, 203, and 211 GOs; 10, 7, and 17 KEGG pathways in the cochlea, auditory cortex, and hippocampus, respectively. In the long term (12 weeks) from noise-induced hearing loss, GOs and KEGG pathways related to apoptosis or inflammation persisted more actively in the order of hippocampus, auditory cortex, and cochlea. This implies that the neurodegenerative effects of noise exposure persist more longer time in the central regions.

ART and AutoART ECAP measurements and cochlear nerve anatomy as predictors in adult cochlear implant recipients

PurposeThe purpose of this retrospective study is to compare the results of electrically evoked compound action potential (ECAP) measurements using automatic auditory response telemetry (AutoART) with those obtained by ART in adults. The study also aimed to evaluate the predictive value of intraoperative ART and AutoART ECAPs for speech intelligibility (SI) and hearing success (HS), and to determine if cochlear nerve (CN) cross-sectional area (CSA) obtained preoperatively by magnetic resonance imaging (MRI) scans could predict ART and AutoART ECAPs and SI and HS outcome.MethodsThe study analyzed and correlated ART and AutoART ECAP thresholds at electrodes E2, E6, and E10, as well as averaged ECAP thresholds over electrodes E1–E12, using data from 32 implants. Correlations were also examined for ART and AutoART ECAP slopes. In addition, averaged ART and AutoART ECAP thresholds and slopes over all 12 electrodes for each participant were correlated with CN CSA measured from MRI sequences. SI of the monosyllabic Freiburg Speech Test at 65 dB sound pressure level was examined along with averaged ART and AutoART thresholds and slopes over all 12 electrodes. A parallel analysis was performed for HS, derived from the difference between baseline and 6-month SI. Finally, correlations between CN CSA and SI, as well as CN CSA and HS were examined.ResultsThe results of the study showed a significant positive correlation between ART and AutoART ECAP thresholds and as well as slopes for E2, E6, E10 and averaged thresholds and slopes of E1–E12. However, no significant correlation was observed between ART and AutoART averaged ECAP thresholds and slopes and either SI and HS or CN CSA. Furthermore, no significant correlation was found between CN CSA and SI and HS.ConclusionWhile AutoART is a reliable and safe program for measuring ECAPs in adults, the study found no preoperative prognostic information on intraoperative ECAP results using parameters extracted from current MRI sequences or pre-/intraoperative information on subsequent hearing outcome using ECAP and CN CSA.

Ultra-broadband and nonlinear robust sound absorption based on ultra-microperforated panel

An ultra-broadband sound absorber with excellent nonlinear robustness is proposed. The absorber consists of an ultra-microperforated panel (UMPP) with the orifice diameter of less than 0.1 mm and three back cavities. The UMPP has a stable impedance matching the air characteristics impedance, thus being selected as the acoustic resistance component. Three back cavities with a height-doubling recursive relationship are designed as the acoustic reactance component, which greatly expands the near-zero acoustic reactance frequency bandwidth. After space optimization, the proposed 71-mm high UMPP sound absorber achieves a mean absorption coefficient α of 0.965 in the quasi-perfect band ranging from 540–3800 Hz. Moreover, the UMPP absorber shows excellent robust sound absorption at extremely high sound intensities. Experimental results suggest the absorption coefficient is still greater than 0.8 in the range of 600–4000 Hz with a 155 dB sound pressure level. Based on the theoretical analysis, small orifice diameter, large percent open area, and large aspect ratio are the key geometric features for achieving good nonlinear robustness. The proposed UMPP absorber has potential in aerospace noise-control engineering owing to its ultra-broadband absorption performance, simple structure, excellent nonlinear robustness, and good aerodynamic performance.

Shouting affects temporal properties of the speech amplitude envelope.

Distinguishing shouted from non-shouted speech is crucial in communication. We examined how shouting affects temporal properties of the amplitude envelope (ENV) in a total of 720 sentences read by 18 Swiss German speakers in normal and shouted modes; shouting was characterised by maintaining sound pressure levels of ≥80 dB sound pressure level (dB-SPL) (C-weighted) at a 1-meter distance from the mouth. Generalized additive models revealed significant temporal alterations of ENV in shouted speech, marked by steeper ascent, delayed peak, and extended high levels. These findings offer potential cues for identifying shouting, particularly useful when fine-structure and dynamic range cues are absent, for example, in cochlear implant users.

Modified Fear Conditioning for Inducing Flight Behaviors in Mice.

The appropriate manifestation of defensive behavior in a threatening situation is critical for survival. The prevailing theory suggests that an active defensive behavior, such as jumping or rapid darting, is expressed under high threat imminence or actual threat, whereas passive defensive behavior, such as freezing, is expressed when the threat is predicted, but the threat imminence is relatively low. In classical fear conditioning, subjects typically exhibit freezing as a conditioned defensive response, with little expression of active defensive behavior in most cases. Here, we introduce a modified fear conditioning procedure for mice to observe the transition from freezing to flight and vice versa, involving five repetitive pairings of conditioned stimuli (CS; continuous tone, 8 kHz, 95 dB SPL (sound pressure levels)) and unconditioned stimuli (US; foot shock, 0.9 mA, 1.0 s) over two days. This modified fear conditioning procedure requires a relatively large number of conditioning sessions and conditioning days but does not necessitate a high-intensity foot shock for modest expression of flight behavior. Using the same context for conditioning and salient CS presentations is essential to elicit flight behaviors. This modified fear conditioning procedure is a reliable method for observing active defensive behaviors in mice, providing an opportunity to elucidate the fine mechanisms and characteristics of such behaviors in a fearful context.

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.

Temporal coherence of harmonic frequencies affects echo detection in the big brown bat, Eptesicus fuscus.

Echolocating big brown bats (Eptesicus fuscus) broadcast frequency modulated (FM) ultrasonic pulses containing two prominent harmonic sweeps (FM1, FM2). Both harmonics typically return as echoes at the same absolute time delay following the broadcast, making them coherent. Electronically splitting FM1 and FM2 allows their time delays to be controlled separately, making them non-coherent. Earlier work shows that big brown bats discriminate coherent from split harmonic, non-coherent echoes and that disruptions of harmonic coherence produce blurry acoustic images. A psychophysical experiment on two trained big brown bats tested the hypothesis that detection thresholds for split harmonic, non-coherent echoes are higher than those for coherent echoes. Thresholds of the two bats for detecting 1-glint echoes with coherent harmonics were around 35 and 36 dB sound pressure level, respectively, while thresholds for split harmonic echoes were about 10 dB higher. When the delay of FM2 in split harmonic echoes is shortened by 75 μs to offset neural amplitude-latency trading and restore coherence in the auditory representation, thresholds decreased back down to those estimated for coherent echoes. These results show that echo detection is affected by loss of harmonic coherence, consistent with the proposed broader role of coherence across frequencies for auditory perception.