Degradation in Binaural and Spatial Hearing and Auditory Temporal Processing Abilities as a Function of Aging.

Objectives: Sensorineural hearing loss is common with advancing age, but even when hearing is normal or near normal in older persons, performance deficits are often seen for suprathreshold listening tasks such as understanding speech in background noise or localizing the direction sounds are coming from. This suggests there is also a more central source of the problem. Objectives of this study were to examine as a function of age (young adult to septuagenarian) performance on: 1) a spatial acuity task examining lateralization ability, and a spatial speech-in-noise (SSIN) recognition task, both measured in a hemi-anechoic sound field using a circular horizontal-plane loudspeaker array, and 2) a suprathreshold auditory temporal processing task and a spectro-temporal processing task, both measured under headphones. Further, we examined any correlations between the measures. Design: Subjects were 48 adults, aged 21 to 78, with either normal hearing or only a mild sensorineural hearing loss through 4000 Hz. The lateralization task measured minimum audible angle (MAA) for 500 and 4000 Hz narrowband noise (NBN) bursts in diffuse background noise for both an on-axis (subject facing 0°) and off-axis (facing 45°) listening condition at signal-to-noise ratios (SNRs) of -3, -6, -9, and -12 dB. For 42 of the subjects, SSIN testing was also completed for key word recognition in sentences in multi-talker babble noise; specifically, the separation between speech and noise loudspeakers was adaptively varied to determine the difference needed for 40% and 80% correct performance levels. Finally, auditory temporal processing ability was examined using the Temporal Fine Structure test (44 subjects), and the Spectro-Temporal Modulation test (46 subjects). Results: Mean lateralization performances were poorer (larger MAAs) in older compared to younger subjects, particularly in the more adverse listening conditions (i.e., for 4000 Hz, off-axis, and at poorer SNRs). Performance variability was notably higher for older subjects than for young adults. The 4000 Hz NBN bursts produced larger MAAs than did 500 Hz NBN bursts. The SSIN data also showed declining mean performance with age at both criterion levels, with greater variability again found for older subjects. Spearman rho analyses revealed some low to moderate, but significant correlation coefficients for age versus MAA and for age versus SSIN results. Results from both the TFS and STM showed decreased mean performance with aging, and revealed moderate, significant correlations, with the strongest relationship shown with the TFS test. Finally, of note, extended-high-frequency (EHF) hearing loss (measured between 9000 and 16,000 Hz) was found to increase with aging, but was not seen in the young adult subjects. Conclusions: Particularly for more adverse listening conditions, age-related deficits were found on both of the spatial hearing tasks and in temporal and spectro-temporal processing abilities. It may be that deficits in temporal processing ability contribute to poorer spatial hearing performance in older subjects due to inaccurate coding of binaural/interaural timing information sent from the periphery to the brainstem. In addition, EHF hearing loss may be a coexisting factor that impacts performance in older subjects.

Working memory limitations constrain visual episodic long-term memory at both specific and gist levels of representation.

Limitations in one's capacity to encode information in working memory (WM) constrain later access to that information in long-term memory (LTM). The present study examined whether these WM constraints on episodic LTM are limited to specific representations of past episodes or also extend to gist representations. Across three experiments, young adult participants (n = 40 per experiment) studied objects in set sizes of two or six items, either sequentially (Experiments 1a and 1b) or simultaneously (Experiment 2). They then completed old/new recognition tests immediately after each sequence (WM tests). After a long study phase, participants completed LTM conjoint recognition tests, featuring old but untested items from the WM phase, lures that were similar to studied items at gist but not specific levels of representation, and new items unrelated to studied items at both specific and gist levels of representation. Results showed that LTM estimates of specific and gist memory representations from a multinomial-processing-tree model were reduced for items encoded under supra-capacity set sizes (six items) relative to within-capacity set sizes (two items). These results suggest that WM encoding capacity limitations constrain episodic LTM at both specific and gist levels of representation, at least for visual objects. The ability to retrieve from LTM each type of representation for a visual item is contingent on the degree to which the item could be encoded in WM.

Postnatal Brain Trajectories and Maternal Intelligence Predict Childhood Outcomes in Complex CHD.

Objective: To determine whether early structural brain trajectories predict early childhood neurodevelopmental deficits in complex CHD patients and to assess relative cumulative risk profiles of clinical, genetic, and demographic risk factors across early development. Study Design: Term neonates with complex CHDs were recruited at Texas Children's Hospital from 2005-2011. Ninety-five participants underwent three structural MRI scans and three neurodevelopmental assessments. Brain region volumes and white matter tract fractional anisotropy and radial diffusivity were used to calculate trajectories: perioperative, postsurgical, and overall. Gross cognitive, language, and visuo-motor outcomes were assessed with the Bayley Scales of Infant and Toddler Development and with the Wechsler Preschool and Primary Scale of Intelligence and Beery-Buktenica Developmental Test of Visual-Motor Integration. Multi-variable models incorporated risk factors. Results: Reduced overall period volumetric trajectories predicted poor language outcomes: brainstem ((ß, 95% CI) 0.0977, 0.0382-0.1571; p = 0.0022) and white matter (0.0023, 0.0001-0.0046; p = 0.0397) at 5 years; brainstem (0.0711, 0.0157-0.1265; p = 0.0134) and deep grey matter (0.0085, 0.0011-0.0160; p = 0.0258) at 3 years. Maternal IQ was the strongest contributor to language variance, increasing from 37% at 1 year, 62% at 3 years, and 81% at 5 years. Genetic abnormality's contribution to variance decreased from 41% at 1 year to 25% at 3 years and was insignificant at 5 years. Conclusion: Reduced postnatal subcortical-cerebral white matter trajectories predicted poor early childhood neurodevelopmental outcomes, despite high contribution of maternal IQ. Maternal IQ was cumulative over time, exceeding the influence of known cardiac and genetic factors in complex CHD, underscoring the importance of heritable and parent-based environmental factors.

The time course of encoding specific and gist episodic memory representations among young and older adults.

How rapidly can we encode the specifics versus the gist of episodic memories? Competing theories have opposing answers, but empirical tests are based primarily on tasks of item memory. Few studies have addressed this question with tasks measuring the binding of event components (e.g., a person and a location), which forms the core of episodic memory. None of these prior studies included older adults, whose episodic memories are less specific in nature. We addressed this critical gap by presenting face-scene pairs (e.g., an old man with a park) at various encoding presentation rates to 80 young (M = 21.83 years) and 86 older (M = 68.62 years) adults. Participants completed associative recognition tests featuring old/intact (e.g., the old man with the same park), similar (e.g., the old man with a different park), and unrelated (e.g., the old man with a kitchen) pairs. Multinomial-processing-tree model analyses revealed that young and older adults encoded each pair's gist representation more rapidly than its specific representation, supporting fuzzy-trace theory. No age-related differences in gist representations were obtained at any presentation rate, but older adults required more time to encode specific representations commensurate with those of younger adults. However, older adults' abilities to retrieve these representations were cue-dependent, as they were more susceptible than younger adults to experiencing vivid false memories of similar lures. These phantom recollections were remediated with further increases in encoding time. Thus, slower speed of encoding partially underlies age-related declines in episodic memory specificity, but retrieval mechanisms also play a role. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A lifespan study of the confidence-accuracy relation in working memory and episodic long-term memory.

The relation between an individual's memory accuracy and reported confidence in their memories can indicate self-awareness of memory strengths and weaknesses. We provide a lifespan perspective on this confidence-accuracy relation, based on two previously published experiments with 320 participants, including children aged 6-13, young adults aged 18-27, and older adults aged 65-77, across tests of working memory (WM) and long-term memory (LTM). Participants studied visual items in arrays of varying set sizes and completed item recognition tests featuring 6-point confidence ratings either immediately after studying each array (WM tests) or following a long period of study events (LTM tests). Confidence-accuracy characteristic analyses showed that accuracy improved with increasing confidence for all age groups and in both WM and LTM tests. These findings reflect a universal ability across the lifespan to use awareness of the strengths and limitations of one's memories to adjust reported confidence. Despite this age invariance in the confidence-accuracy relation, however, young children were more prone to high-confidence memory errors than other groups in tests of WM, whereas older adults were more susceptible to high-confidence false alarms in tests of LTM. Thus, although participants of all ages can assess when their memories are weaker or stronger, individuals with generally weaker memories are less adept at this confidence-accuracy calibration. Findings also speak to potential different sources of high-confidence memory errors for young children and older adults, relative to young adults. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Hearing ability of prairie voles (Microtus ochrogaster).

The hearing abilities of mammals are impacted by factors such as social cues, habitat, and physical characteristics. Despite being used commonly to study social behaviors, hearing of the monogamous prairie vole (Microtus ochrogaster) has never been characterized. In this study, anatomical features are measured and auditory brainstem responses (ABRs) are used to measure auditory capabilities of prairie voles, characterizing monaural and binaural hearing and hearing range. Sexually naive male and female voles were measured to characterize differences due to sex. It was found that prairie voles show a hearing range with greatest sensitivity between 8 and 32 kHz, binaural hearing across interaural time difference ranges appropriate for their head sizes. No differences are shown between the sexes in binaural hearing or hearing range (except at 1 kHz), however, female voles have increased amplitude of peripheral ABR waves I and II and longer latency of waves III and IV compared to males. The results confirm that prairie voles have a broad hearing range, binaural hearing consistent with rodents of similar size, and differences in amplitudes and thresholds of monaural physiological measures between the sexes. These data further highlight the necessity to understand sex-specific differences in neural processing that may underly variability in responses between sexes.

The Relation Between Attention and Memory.

The relation between attention and memory has long been deemed important for understanding cognition, and it was heavily researched even in the first experimental psychology laboratory by Wilhelm Wundt and his colleagues. Since then, the importance of the relation between attention and memory has been explored in myriad subdisciplines of psychology, and we incorporate a wide range of these diverse fields. Here, we examine some of the practical consequences of this relation and summarize work with various methodologies relating attention to memory in the fields of working memory, long-term memory, individual differences, life-span development, typical brain function, and neuropsychological conditions. We point out strengths and unanswered questions for our own embedded processes view of information processing, which is used to organize a large body of evidence. Last, we briefly consider the relation of the evidence to a range of other theoretical views before drawing conclusions about the state of the field.

Sex Differences and Similarities in Relations Between Mathematics Achievement, Attitudes, and Anxiety: A Seventh-to-Ninth Grade Longitudinal Study.

There are consistent correlations between mathematics achievement, attitudes, and anxiety, but the longitudinal relations among these constructs are not well understood nor are sex differences in these relations. To address this gap, mathematics achievement, attitudes, and anxiety were longitudinally assessed for 342 (169 boys) adolescents from 7th to 9th grade, inclusive, and Latent Growth Curve Models were used to assess the relations among these traits and developmental change in them. Spatial abilities (7th, 8th grade) and trait anxiety (8th, 9th grade) were also assessed and used for control for sex differences in these traits. Overall, boys had stronger spatial abilities and more positive mathematics attitudes and were less anxious than girls, but there were no sex differences in mathematics achievement. Across grades, mathematics achievement improved, attitudes became less positive, and anxiety increased for both boys and girls. Higher than average cross-grade growth in mathematics achievement mitigated boys' developmental declines in mathematics attitudes and increases in anxiety. Girls with strong spatial abilities had lower mathematics anxiety, but girls overall maintained higher mathematics anxiety and less positive mathematics attitudes relative to boys, even when they showed strong cross-grade gains in mathematics achievement. The study demonstrated that longitudinal gains in mathematics are associated with cross-grade changes in attitudes and anxiety but with several different developmental patterns for boys and girls.

Differential attentional costs of encoding specific and gist episodic memory representations.

Theories of episodic memory posit that more attentional resources are needed for encoding specific compared to gist representations. This position has been challenged by recent findings of similar divided attention (DA) at encoding costs on both specific and gist representations. However, the disrupting effects of DA on specific representations may emerge under less difficult DA conditions than those under which effects on gist representations emerge. The present study addressed this possibility by manipulating the difficulty of a concurrent DA task (low, intermediate, or high difficulty) during encoding among 176 young adult participants, who encoded face-scene pairs under either full attention or one of the three levels of DA. During retrieval, participants discriminated intact pairs from recombined pairs that varied in how similar they were to studied pairs. Results, interpreted using a multinomial-processing-tree model of specific and gist memory, showed that the disrupting effects of DA on specific representations emerged under less difficult attentional loads (intermediate-demanding condition) compared to those under which gist representations were disrupted (high-demanding condition). These findings reinforce the suggestion of differential attentional demands for specific and gist representations and also provide insights into attentional resource theories of adult age-related cognitive decline. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Interaural frequency mismatch jointly modulates neural brainstem binaural interaction and behavioral interaural time difference sensitivity in humans.

The binaural interaction component (BIC) of the auditory brainstem response (ABR) is the difference obtained after subtracting the sum of right and left ear ABRs from binaurally evoked ABRs. The BIC has attracted interest as a biomarker of binaural processing abilities. Best binaural processing is presumed to require spectrally-matched inputs at the two ears, but peripheral pathology and/or impacts of hearing devices can lead to mismatched inputs. Such mismatching can degrade behavioral sensitivity to interaural time difference (ITD) cues, but might be detected using the BIC. Here, we examine the effect of interaural frequency mismatch (IFM) on BIC and behavioral ITD sensitivity in audiometrically normal adult human subjects (both sexes). Binaural and monaural ABRs were recorded and BICs computed from subjects in response to narrowband tones. Left ear stimuli were fixed at 4000 Hz while right ear stimuli varied over a ∼2-octave range (re: 4000 Hz). Separately, subjects performed psychophysical lateralization tasks using the same stimuli to determine ITD discrimination thresholds jointly as a function of IFM and sound level. Results demonstrated significant effects of IFM on BIC amplitudes, with lower amplitudes in mismatched conditions than frequency-matched. Behavioral ITD discrimination thresholds were elevated at mismatched frequencies and lower sound levels, but also more sharply modulated by IFM at lower sound levels. Combinations of ITD, IFM and overall sound level that resulted in fused and lateralized percepts were bound by the empirically-measured BIC, and also by model predictions simulated using an established computational model of the brainstem circuit thought to generate the BIC.

Forgetting of specific and gist visual associative episodic memory representations across time.

Associative binding between components of an episode is vulnerable to forgetting across time. We investigated whether these forgetting effects on inter-item associative memory occur only at specific or also at gist levels of representation. In two experiments, young adult participants (n = 90, and 86, respectively) encoded face-scene pairs and were then tested either immediately after encoding or following a 24-hour delay. Tests featured conjoint recognition judgments, in which participants were tasked with discriminating intact pairs from highly similar foils, less similar foils, and completely dissimilar foils. In both experiments, the 24-hour delay resulted in deficits in specific memory for face-scene pairs, as measured using multinomial-processing-tree analyses. In Experiment 1, gist memory was not affected by the 24-hour delay, but when associative memory was strengthened through pair repetition (Experiment 2), deficits in gist memory following a 24-hour delay were observed. Results suggest that specific representations of associations in episodic memory, and under some conditions gist representations, as well, are susceptible to forgetting across time.

Adult age-related changes in the specificity of episodic memory representations: A review and theoretical framework.

We provide a comprehensive review describing research on the qualitative representational nature of older adults' episodic memories. Our review considers several broad theoretical frameworks and decades of research converging on a universal principle of adult aging: Episodic memory in older adulthood is characterized as being less specific in nature than in younger adulthood. Going beyond earlier specific reviews on related topics in the false memory, neuroscience, and reading comprehension literatures, our review synthesizes findings from these fields with more recent research from the precision literature, along with several new studies on age differences in the specificity of associative aspects of episodic memory, where age deficits have long been reported. We also sketch a new theoretical framework as inspiration for future research that can better elucidate the mechanisms underpinning age differences in the specificity of memory representations, including reduced attentional resources and slower speed of processing. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Effects of Varying Laser Parameters During Laser Stapedotomy on Intracochlear Pressures.

OBJECTIVE: Sensorineural hearing loss is a known complication of stapes surgery. We previously showed that laser stapedotomy can result in intracochlear pressures that are comparable to high sound pressure levels. Optimizing laser settings to those that correspond with the lowest pressure changes may mitigate risk for postoperative hearing loss. Here we quantify the effects of various laser parameters on intracochlear pressures and test the hypothesis that intracochlear pressure changes are proportional to the laser energy delivered. STUDY DESIGN: Basic and translational science. SETTING: Cadaveric dissection and basic science laboratory. METHODS: Cadaveric human heads underwent mastoidectomies. Intracochlear pressures were measured via fiber-optic pressure probes placed in scala vestibuli and tympani. Pulses of varied stimulus power and duration from a 980-nm diode laser were applied to the stapes footplate. RESULTS: Sustained high-intensity pressures were observed in the cochlea during all laser applications. Observed pressure magnitudes increased monotonically with laser energy and rose linearly for lower stimulus durations and powers, but there was increased variability for laser applications of longer duration (200-300 ms) and/or higher power (8 W). CONCLUSIONS: Results confirm that significant pressure changes occur during laser stapedotomy, which we hypothesize may cause injury. Overall energy delivered depends predictably on duration and power, but surgeons should use caution at the highest stimulus levels and longest pulse durations due to the increasing variability in intracochlear pressure under these stimulus conditions. While the risk to hearing from increased intracochlear pressures from laser stapedotomy remains unclear, these results affirm the need to optimize laser settings to avoid unintended injury.

Occluded insertion loss from intracochlear pressure measurements during acoustic shock wave exposure.

INTRODUCTION: Injuries to the peripheral auditory system are among the most common results of high intensity impulsive noise exposure. Hearing protection can mitigate this injury, but careful assessment of the insertion loss they provide is necessary. Insertion loss is typically measured using microphone-based acoustic manikins to measure the decrease in sound pressure level transmitted into the ear canal, which precisely measure the change in air conducted sound, but neglect alternate pathways to the inner ear such as bone conduction. In a previous study we reported intracochlear pressures in cadaveric human specimens to acoustic shock waves, which revealed a substantial bone conducted component (Greene, et al., 2018). Here we evaluate insertion loss to several hearing protection devices (HPDs) in those same specimens using intracochlear pressure measurements. METHODS: Human cadaver heads were exposed to impulsive acoustic pressure waves with peak overpressures of 7 and 28 kPa (171 & 183 dB SPL). Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured bilaterally with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. Responses were measured with specimen ears unoccluded, as reported previously, as well as fitted with four types of HPDs. Impulse peak insertion loss (IPIL) and impulse spectrum insertion loss (ISIL) were calculated for each HPD. RESULTS: For all HPDs, IPIL generally increases with exposure level, though ISIL tended to be more consistent, and the spectral characteristics across frequency appear to be highly dependent on exposure level. ISIL measured in the ear canal tended to overestimate insertion loss measured in the cochlea, particularly at frequencies > 1 kHz; however, low signal-to-noise in intracochlear pressures limited comparisons. As a proof of concept, 36 low-level unoccluded exposures, were averaged together, and the resulting signal-to-noise ratio was improved by up to 15 dB. CONCLUSIONS: Insertion loss measured in the cochlea was lower than in the ear canal, suggesting substantial contributions from transmission pathways in parallel with air conduction (e.g., bone conduction) were present, which will require novel strategies to mitigate. However, high variance was observed, and noise reduction strategies should be utilized in future studies to facilitate more precise insertion loss estimates.

The formation of specific and gist associative episodic memory representations during encoding: Effects of rate of presentation.

Assessing the time course under which underlying memory representations can be formed is an important question for understanding memory. Several studies assessing item memory have shown that gist representations of items are laid out more rapidly than verbatim representations. However, for associations among items/components, which form the core of episodic memory, it is unclear whether gist representations form more quickly than, or at least in parallel with, verbatim representations, as fuzzy-trace theory predicts, or whether gist is extracted more slowly from inferring the meaning of verbatim representations, as in gist macroprocessor theories. To test these contrasting possibilities, we used a novel associative recognition task in which participants studied face-scene pairs for .75, 1.5, or 4 seconds each, and were later tested on their ability to discriminate intact pairs from foils which varied in how similar they were to originally studied pairs. Across 2 experiments, we found that verbatim memory for associations, measured using a multinomial-processing-tree model, improved from .75 to 1.5 to 4 seconds of presentation time. Paralleling these effects of encoding time on verbatim memory, for gist memory, there were improvements from .75 seconds to 1.5 seconds in both experiment 1 and 2, while improvements from 1.5 seconds to 4 seconds were only evident when the retention interval between study and test was increased (experiment 2). These results provide strong support for the parallel processing framework of fuzzy-trace theory over the slow gist extraction framework of an alternative gist macroprocessor theory. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Opioid and non-opioid analgesic prescribing practices for pediatric adenotonsillectomy in a tertiary care center.

IMPORTANCE: The U.S. is in an opioid epidemic with greater than 40,000 deaths annually. Pediatric adenotonsillectomy is one of the most common and painful otolaryngology surgeries performed, often associated with opioid prescriptions. OBJECTIVE: To understand postoperative prescribing practices of adenotonsillectomy in a tertiary care institution and associated postoperative emergency department (ED) visits. DESIGN: Descriptive analysis of retrospective cohort data. SETTING: Tertiary academic healthcare institution. PARTICIPANTS: Pediatric patients <18yo undergoing adenotonsillectomy between 2013 and 2016. INTERVENTIONS/EXPOSURES: Postoperative analgesic regimens assessed including opioid and non-opioid analgesic prescriptions upon discharge from tonsillectomy surgery. MAIN OUTCOMES AND MEASURES: Main outcomes included ED presentation within 30-days of surgery and reoperation. Secondary outcomes included reason for ED presentation and relation to prescribed analgesics. Data was analyzed between November 2021-February 2022. RESULTS: 200 patients were included in the study with 69% prescribed opioids, and 51% prescribed non-opioid analgesics. Number of opioid doses ranged widely with a median of 37 (Q1, Q3: 0, 62). There were no demographic differences in patients prescribed opioids from those who were not. Of those patients who presented to the ED, 81% were not specifically prescribed acetaminophen (p < 0.001). Regression analysis models were not predictive of postoperative analgesic regimen or 30-day ED presentation (p > 0.05) CONCLUSIONS: Wide ranges of post tonsillectomy prescribing practices currently exist in our institution. Prescribing acetaminophen may help to reduce 30-day ED presentation rate. Larger prospective studies are needed to optimize pain control regimens and reduce variability of opioid prescribing practices. Standardization of postoperative pain medication doses may also reduce postoperative ED presentations.

The proportion of working memory items recoverable from long-term memory remains fixed despite adult aging.

We explored whether long-term memory (LTM) retrieval is constrained by working memory (WM) limitations, in 80 younger and 80 older adults. Participants performed a WM task with images of unique everyday items, presented at varying set sizes. Subsequently, we tested participants' LTM for items from the WM task and examined the ratio of LTM/WM retention. While older adults' WM and LTM were generally poorer than that of younger adults, their LTM deficit was no greater than what was predicted from their WM performance. The ability to encode WM information into LTM appeared immune to age-related cognitive decline. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The acoustical effect of the neck frill of the frill-necked lizard (Chlamydosaurus kingii).

Animals localise sound by making use of acoustical cues resulting from space and frequency dependent filtering of sound by the head and body. Sound arrives at each ear at different times, with different intensities, and with varying spectral content, all of which are affected by the animal's head and the relative sound source position. Location cues in mammals benefit from structures (pinnae) that modify these cues and provide information that helps resolve the cone of confusion and provide cues to sound source elevation. Animals without pinnae must rely on other mechanisms to solve localisation problems. Most non-mammals lack pinna-like structures, but some possess other anatomical features that could influence hearing. One such animal is the frill-necked lizard (Chlamydosaurus kingii). The species' elaborate neck frill has been speculated to act as an aid to hearing, but no acoustical measurements have been reported. In this study, we characterise the frill's influence on the acoustical information available to the animal. Results suggest that the change in binaural cues is not sufficiently large to impact localisation behavior within the species' likely audiometric range; however, the frill does increase gain for sounds directly in front of the animal similar to a directional microphone.

Effects of unilateral eye closure on middle ear muscle contractions.

Middle ear muscle contractions (MEMCs) are most commonly considered a response to high-level acoustic stimuli. However, MEMCs have also been observed in the absence of sound, either as a response to somatosensory stimulation or in concert with other motor activity. The relationship between MEMCs and non-acoustic sources is unclear. This study examined associations between measures of voluntary unilateral eye closure and impedance-based measures indicative of middle ear muscle activity while controlling for demographic and clinical factors in a large group of participants (N=190) with present clinical acoustic reflexes and no evidence of auditory dysfunction. Participants were instructed to voluntarily close the eye ipsilateral to the ear canal containing a detection probe at three levels of effort. Orbicularis oculi muscle activity was measured using surface electromyography. Middle ear muscle activity was inferred from changes in total energy reflected in the ear canal using a filtered (0.2 to 8 kHz) click train. Results revealed that middle ear muscle activity was positively associated with eye muscle activity. MEMC occurrence rates for eye closure observed in this study were generally higher than previously published rates for high-level brief acoustic stimuli in the same participant pool suggesting that motor activity may be a more reliable elicitor of MEMCs than acoustic stimuli. These results suggest motor activity can serve as a confounding factor for auditory exposure studies as well as complicate the interpretation of any impulsive noise damage risk criteria that assume MEMCs serve as a consistent, uniform protective factor. The mechanism linking eye and middle ear muscle activity is not understood and is an avenue for future research.

Auditory brainstem development of naked mole-rats (Heterocephalus glaber).

Life underground often leads to animals having specialized auditory systems to accommodate the constraints of acoustic transmission in tunnels. Despite living underground, naked mole-rats use a highly vocal communication system, implying that they rely on central auditory processing. However, little is known about these animals' central auditory system, and whether it follows a similar developmental time course as other rodents. Naked mole-rats show slowed development in the hippocampus suggesting they have altered brain development compared to other rodents. Here, we measured morphological characteristics and voltage-gated potassium channel Kv3.3 expression and protein levels at different key developmental time points (postnatal days 9, 14, 21 and adulthood) to determine whether the auditory brainstem (lateral superior olive and medial nucleus of the trapezoid body) develops similarly to two common auditory rodent model species: gerbils and mice. Additionally, we measured the hearing onset of naked mole-rats using auditory brainstem response recordings at the same developmental timepoints. In contrast with other work in naked mole-rats showing that they are highly divergent in many aspects of their physiology, we show that naked mole-rats have a similar hearing onset, between postnatal day (P) 9 and P14, to many other rodents. On the other hand, we show some developmental differences, such as a unique morphology and Kv3.3 protein levels in the brainstem.