Training to Improve Spatial Hearing and Situation Awareness when Wearing Hearing Protection.

INTRODUCTION: Hearing protection devices (HPDs) are standard personal protective equipment in military settings, but many service members may choose to not use HPDs because they impair spatial hearing and situation awareness. In an effort to reduce barriers to compliance by improving situation awareness while wearing HPDs, this study investigated whether brief training could counteract spatial hearing deficits when wearing HPDs. Participant's ability to correctly apply the HPDs across days was also examined. MATERIALS AND METHODS: Young adults were randomly assigned to one of two groups: training or control (n = 25/group). Participants in each group performed a spatial hearing task while wearing HPDs and in an open ear condition without HPDs. Individual targets were battlefield sounds or white noise presented from a speaker array that surrounded the participant in the horizontal plane. After presentation of each target sound, the participant then controlled a white noise "auditory pointer," which they moved to the perceived location of the target. The two primary measures were the percent of trials with very large errors (> 45°), which were usually due to confusing front and back locations, and absolute localization, which is the difference between the pointer location and the true sound location. Both groups were tested on Days 1 (baseline) and 5 (post-test). On Days 2 to 4, the training group wore HPDs while receiving auditory and visual feedback after each trial. RESULTS: Across all participants on Day 1, wearing HPDs increased the frequency of very large errors by about 3× and impaired localization by about 40%, relative to the open ear condition. When comparing performance at baseline (Day 1) and post-training Day 5, the training group with HPDs had significant reductions in very large errors and improved absolute localization (P values < .001). The training group also had significant improvements from Days 1 to 5 in the open ear condition. When the control group wore HPDs, there were also significant improvements from Days 1 to 5 (fewer very large errors and better localization), with smaller effect sizes vs. the training group. Controls did not have significant improvement in the open ear condition, but had similar trends. Most participants consistently applied the HPDs, but a subset of ∼20% frequently failed to achieve the criterion attenuation of 15 dB (over 0.25-4.0 kHz) in both ears. CONCLUSIONS: These findings show that simple, relatively brief practice and training can substantially reduce HPD impairments on spatial hearing and situation awareness. The gains from training and practice can inform the development of relatively simple, brief methods to reduce HPD spatial hearing impairments, potentially leading to increased HPD compliance. Longitudinal data show that a subset of participants would not have received the full benefit of hearing protection because of improper application of the HPDs.

A novel non-word speech preparation task to increase stuttering frequency in experimental settings for longitudinal research.

PURPOSE: The variable and intermittent nature of stuttering makes it difficult to consistently elicit a sufficient number of stuttered trials for longitudinal experimental research. This study tests the efficacy of using non-word pairs that phonetically mimic English words with no associated meaning, to reliably elicit balanced numbers of stuttering and fluent trials over multiple sessions. The study also evaluated the effect of non-word length on stuttering frequency, the consistency of stuttering frequency across sessions, and potential carry-over effects of increased stuttering frequency in the experimental task to conversational and reading speech after the task. METHODS: Twelve adults who stutter completed multiple sessions (mean of 4.8 sessions) where they were video-recorded during pre-task reading and conversation, followed by an experimental task where they read 400 non-word pairs randomized for each session, and then a post-task reading and conversation sample. RESULTS: On average, across sessions and participants, non-word pairs consistently yielded a balanced distribution of fluent (60.7%) and stuttered (39.3%) trials over five sessions. Non-word length had a positive effect on stuttering frequency. No carryover effects from experimental to post-task conversation and reading were found. CONCLUSIONS: Non-word pairs effectively and consistently elicited balanced proportions of stuttered and fluent trials. This approach can be used to gather longitudinal data to better understand the neurophysiological and behavioral correlates of stuttering.

Auditory spatial attention gradients and cognitive control as a function of vigilance.

Selection and effort are central to attention, yet it is unclear whether they draw on a common pool of cognitive resources, and if so, whether there are differences for early versus later stages of cognitive processing. This study assessed effort by quantifying the vigilance decrement, and spatial processing at early and later stages as a function of time-on-task. Participants performed an auditory spatial attention task, with occasional "catch" trials requiring no response. Psychophysiological measures included bilateral cerebral blood flow (transcranial Doppler), pupil dilation, and blink rate. The shape of attention gradients using reaction time indexed early processing, and did not significantly vary over time. Later stimulus-response conflict was comparable over time, except for a reduction to left hemispace stimuli. Target and catch trial accuracy decreased with time, with a more abrupt decrease for catch versus target trials. Diffusion decision modeling found progressive decreases in information accumulation rate and non-decision time, and the adoption of more liberal response criteria. Cerebral blood flow increased from baseline and then decreased over time, particularly in the left hemisphere. Blink rate steadily increased over time, while pupil dilation increased only at the beginning and then returned towards baseline. The findings suggest dissociations between resources for selectivity and effort. Measures of high subjective effort and temporal declines in catch trial accuracy and cerebral blood flow velocity suggest a standard vigilance decrement was evident in parallel with preserved selection. Different attentional systems and classes of computations that may account for dissociations between selectivity versus effort are discussed.

Widespread theta coherence during spatial cognitive control.

Cognitive control allows humans to process relevant sensory information while minimizing distractions from irrelevant stimuli. The neural basis of cognitive control is known to involve frontal regions of the brain such as the medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC), but the temporal dynamics of larger scale networks is unclear. Here we used EEG with source localization to identify how the neural oscillations localized to the mPFC and ACC coordinate with parietal, sensory, and motor areas during spatial cognitive control. Theta coherence (3-8 Hz) between the mPFC and ACC increased with task difficulty and predicted individual differences in reaction time. Individual differences in accuracy were predicted by earlier activation of ACC-motor coherence, highlighting the relationship between processing speed and task performance. Our results provide evidence that successful cognitive control requires dynamic coordination between a widespread network of brain regions. Long range theta coherence may be a key mechanism for efficient cognitive control across the neocortex.

Numbers in short-term memory bias auditory spatial perception.

The cognitive penetration literature suggests that top-down knowledge influences perception, but whether such influences exist is controversial. We tested for top-down influences on perception by loading short-term memory with digits and then had participants make perceptual judgments to index spatial hearing. Memory of spatial number codes were predicted to bias spatial judgments to the left for small digits and rightward for larger digits. Participants encoded one or more digits and then made spatial judgments in either spatial hearing or dichotic listening tasks. Results across five experiments supported the predicted spatial biases. Digits had to be deliberately encoded, and at least two were needed to be memorized before a small number left-right bias in dichotic listening was evident. In dichotic listening, smaller numbers in memory also promoted more intrusions, and a mix of small and large numbers enhanced the right ear advantage. Results suggest that long-term knowledge about number magnitude imparts a top-down bias on auditory spatial perception. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Strategic encoding and retrieval processes in verbal recall among middle-aged and older adults.

The authors used an analysis of individual differences to examine the role of executive control in strategic encoding and retrieval in verbal recall. Participants enrolled in the Louisiana Healthy Aging Study completed measures of working memory (WM), cognitive status, vocabulary, and free recall of words. Indices of clustering in free recall were calculated to permit inferences on strategic encoding and retrieval processes. We hypothesized that WM would be more strongly associated with strategic encoding and retrieval metrics than vocabulary based on the assumption that successful remembering requires executive control in WM. Regression analyses, together with a variance portioning procedure, confirmed that WM had comparable levels of unique and shared variance with the strategic encoding and retrieval metrics, and both exceeded vocabulary. Theoretical and clinical implications of these data are considered, with the suggestion of future research in lifespan samples as opposed to exclusively young adult or older adult samples.

Neural correlates of auditory sensory memory dynamics in the aging brain.

The auditory system allows us to monitor background environmental sound patterns and recognize deviations that may indicate opportunities or threats. The mismatch negativity and P3a potentials have generators in the auditory and inferior frontal cortex and index expected sound patterns (standards) and any aberrations (deviants). The mismatch negativity and P3a waveforms show increased positivity for consecutive standards and deviants preceded by more standards. We hypothesized attenuated repetition effects in older participants, potentially because of differences in prefrontal functions. Young (23 ± 5 years) and older (75 ± 5 years) adults were tested in 2 oddball paradigms with pitch or location deviants. Significant repetition effects were observed in the young standard and deviant waveforms at multiple time windows. Except the earliest time window (30-100 ms), repetition effects were absent in the older group. Repetition effects were significant at frontal but not temporal lobe sites and did not differ among pitch and location deviants. However, P3a repetition was evident in both ages. Findings suggest age differences in the dynamic updating of sensory memory for background sound patterns.

Sensorimotor Integration Can Enhance Auditory Perception.

Whenever we move, speak, or play musical instruments, our actions generate auditory sensory input. The sensory consequences of our actions are thought to be predicted via sensorimotor integration, which involves anatomical and functional links between auditory and motor brain regions. The physiological connections are relatively well established, but less is known about how sensorimotor integration affects auditory perception. The sensory attenuation hypothesis suggests that the perceived loudness of self-generated sounds is attenuated to help distinguish self-generated sounds from ambient sounds. Sensory attenuation would work for louder ambient sounds, but could lead to less accurate perception if the ambient sounds were quieter. We hypothesize that a key function of sensorimotor integration is the facilitated processing of self-generated sounds, leading to more accurate perception under most conditions. The sensory attenuation hypothesis predicts better performance for higher but not lower intensity comparisons, whereas sensory facilitation predicts improved perception regardless of comparison sound intensity. A series of experiments tested these hypotheses, with results supporting the enhancement hypothesis. Overall, people were more accurate at comparing the loudness of two sounds when making one of the sounds themselves. We propose that the brain selectively modulates the perception of self-generated sounds to enhance representations of action consequences.

Dynamics of auditory spatial attention gradients.

Auditory spatial attention faces the conflicting demands of focusing on the current task while also rapidly shifting location to unexpected stimuli. We examined the interplay of sustained focus and intermittent shifts in an auditory spatial attention task. Most trials required a choice response from a standard location in virtual space (L-R: -90°, 0°, +90°), but occasionally the location shifted between 45°-180°. Reaction time curves for angular shifts had a quadratic shape, with slowing for small shifts but faster reaction times for larger shifts. The reaction time curves were maintained at faster stimulus rates and usually scaled to fit the range of stimulus locations. However, focus on the right had an attenuated curve, and did not scale to the range of locations. The findings suggest two mechanisms: a top-down bias centered on standard locations that decreases with distance, and a bottom-up bias that under these conditions increases with distance from the standard location.

Auditory spatial attention capture, disengagement, and response selection in normal aging.

Attention control is a core element of cognitive aging, but the specific mechanisms that differ with age are unclear. Here we used a novel auditory spatial attention task to evaluate stimulus processing at the level of early attention capture, later response selection, and the lingering effects of attention capture across trials in young and older adults. We found that the shapes of spatial attention capture gradients were remarkably similar in young and older adults, but only the older group had lingering effects of attention capture on the next trial. Response selection for stimulus-response incompatibilities took longer in older subjects, but primarily when attending to the midline location. The results suggest that the likelihood and spatial tuning of attention capture is comparable among groups, but once attention is captured, older subjects take longer to disengage. Age differences in response selection were supported, but may not be a general feature of cognitive aging.

Cognitive control and midline theta adjust across multiple timescales.

Cognitive control of attention in conflict situations is a basic skill that is vital for goal-oriented behavior. Behavioral evidence shows that conflict control occurs over successive trials as well as longer time scales of trial blocks, but the relation among time scales as well as their neural mechanisms are unclear. This study used measures of behavior, EEG, and a simple quantitative model to test the hypothesis that conflict control at the block level is not exclusively driven by control adjustments over successive trials. Young adults performed an auditory Simon task, and the base rate of compatible vs. incompatible trials was manipulated in separate blocks (25, 50, 75% compatible). EEG data were analyzed using independent component analysis (ICA) to define cortical mechanisms of any base rate and trial-by-trial sequence effects. Reaction time measures had both sequence and base rate effects. Two fronto-medial ICA components indexed sequence and base rate effects, with specific profiles for evoked potentials and oscillations in the theta and alpha frequency bands. Predictive modeling showed that sequence effects accounted for a minority of the variance on behavioral and ICA measures (all < 36%). The results strongly suggest that the base rate manipulation affected behavior and many neural measures beyond the influence of sequence effects.

Single-Trial Classification of Disfluent Brain States in Adults Who Stutter.

Normal human speech requires precise coordination between motor planning and sensory processing. Speech disfluencies are common when children learn to talk, but usually abate with time. About 5% of children experience stuttering. For most, this resolves within a year. However, for approximately 1% of the world population, stuttering continues into adulthood, which is termed 'persistent developmental stuttering'. Most stuttering events occur at the beginning of an utterance. So, in principle, brain activity before speaking should differ between fluent and stuttered speech. Here we present a method for classifying brain network states associated with fluent vs. stuttered speech on a single trial basis. Brain activity was recorded with EEG before people who stutter read aloud pseudo-word pairs. Offline independent component analysis (ICA) was used to identify the independent neural sources that underlie speech preparation. A time window selection algorithm extracted spectral power and coherence data from salient windows specific to each neural source. A stepwise linear discriminant analysis (sLDA) algorithm predicted fluent vs. stuttered speech for 81% of trials in two subjects. These results support the feasibility of developing a brain-computer interface (BCI) system to detect stuttering before it occurs, with potential for therapeutic application.

Spatial Integration and the Underlying Mechanisms of Cross-Modality Interference.

Researchers have often utilized the classic Stroop task as a measure of selective attention processes. While it is largely agreed upon that semantic interference plays a role in the classic task, the role of attentional processes is less clear. The picture is further muddied when variations on the classic task are used. For example, the cross-modal Stroop task, in which one names the color of visual items while ignoring distracting auditory color words, typically leads to smaller sized interference effects and little or no facilitation when compared to the classic task. Furthermore, relationship(s) with working memory capacity have only been found in the classic version. We examined whether these differences are due to a methodological factor; namely, spatial integration versus separation of the target and distractor locations. We conducted four experiments manipulating the location of auditory distractors within the cross-modal Stroop task, and found that the location of the distractors had little to no impact on the size of the effect. This lack of an effect of location implies that the mechanisms contributing to the cross-modal Stroop effect are not the same as those of the classic Stroop effect, and that the role of spatial attention in cross-modal Stroop is limited. The implications of a unique role for auditory distractors is considered as well, and supports the conclusion that interference in the cross-modal Stroop effect is the result of a combination of semantic interference and modality-specific interference.

Numerical value biases sound localization.

Speech recognition starts with representations of basic acoustic perceptual features and ends by categorizing the sound based on long-term memory for word meaning. However, little is known about whether the reverse pattern of lexical influences on basic perception can occur. We tested for a lexical influence on auditory spatial perception by having subjects make spatial judgments of number stimuli. Four experiments used pointing or left/right 2-alternative forced choice tasks to examine perceptual judgments of sound location as a function of digit magnitude (1-9). The main finding was that for stimuli presented near the median plane there was a linear left-to-right bias for localizing smaller-to-larger numbers. At lateral locations there was a central-eccentric location bias in the pointing task, and either a bias restricted to the smaller numbers (left side) or no significant number bias (right side). Prior number location also biased subsequent number judgments towards the opposite side. Findings support a lexical influence on auditory spatial perception, with a linear mapping near midline and more complex relations at lateral locations. Results may reflect coding of dedicated spatial channels, with two representing lateral positions in each hemispace, and the midline area represented by either their overlap or a separate third channel.

Impact of Spatial and Verbal Short-Term Memory Load on Auditory Spatial Attention Gradients.

Short-term memory load can impair attentional control, but prior work shows that the extent of the effect ranges from being very general to very specific. One factor for the mixed results may be reliance on point estimates of memory load effects on attention. Here we used auditory attention gradients as an analog measure to map-out the impact of short-term memory load over space. Verbal or spatial information was maintained during an auditory spatial attention task and compared to no-load. Stimuli were presented from five virtual locations in the frontal azimuth plane, and subjects focused on the midline. Reaction times progressively increased for lateral stimuli, indicating an attention gradient. Spatial load further slowed responses at lateral locations, particularly in the left hemispace, but had little effect at midline. Verbal memory load had no (Experiment 1), or a minimal (Experiment 2) influence on reaction times. Spatial and verbal load increased switch costs between memory encoding and attention tasks relative to the no load condition. The findings show that short-term memory influences the distribution of auditory attention over space; and that the specific pattern depends on the type of information in short-term memory.

Cortical activity during cued picture naming predicts individual differences in stuttering frequency.

OBJECTIVE: Developmental stuttering is characterized by fluent speech punctuated by stuttering events, the frequency of which varies among individuals and contexts. Most stuttering events occur at the beginning of an utterance, suggesting neural dynamics associated with stuttering may be evident during speech preparation. METHODS: This study used EEG to measure cortical activity during speech preparation in men who stutter, and compared the EEG measures to individual differences in stuttering rate as well as to a fluent control group. Each trial contained a cue followed by an acoustic probe at one of two onset times (early or late), and then a picture. There were two conditions: a speech condition where cues induced speech preparation of the picture's name and a control condition that minimized speech preparation. RESULTS: Across conditions stuttering frequency correlated to cue-related EEG beta power and auditory ERP slow waves from early onset acoustic probes. CONCLUSIONS: The findings reveal two new cortical markers of stuttering frequency that were present in both conditions, manifest at different times, are elicited by different stimuli (visual cue, auditory probe), and have different EEG responses (beta power, ERP slow wave). SIGNIFICANCE: The cue-target paradigm evoked brain responses that correlated to pre-experimental stuttering rate.

Focused and divided attention in a simulated cocktail-party situation: ERP evidence from younger and older adults.

Speech perception under complex listening conditions usually decreases in aging. This is especially true for listening conditions requiring divided attention among 2 and more relevant speakers. Using a speech perception task and event-related potential measures, we studied the ability of younger and older adults to attend to speech information from a single-target speaker (focused attention) or from 2 different (alternative) target speakers (divided attention). The focused and divided attention conditions were presented either in silence or in the presence of 3 concurrent speakers. In the presence of concurrent speakers, older participants showed worse performance with divided versus focused attention. In contrast, there was no effect of attention condition for the younger adults. Relative to the young, event-related potential analysis in older subjects indicated a decline in preparatory activity for the critical speech information (a delayed and smaller contingent negative variation), and delayed attentional control (indicated by a longer P2 latency). Standardized low-resolution brain electromagnetic tomography revealed that the age-related decline in preparatory activity was associated with reduced activation of medial and superior frontal gyrus and anterior cingulate gyrus. The results suggest that age-related differences in these prefrontal brain areas reflect declines in preparatory attention and gating of subsequent task-related speech information, especially under conditions of divided attention. These findings may reflect mechanisms relating to impaired speech perception by older people in "cocktail-party" listening situations.

Atypical sensory reactivity influences auditory attentional control in adults with autism spectrum disorders.

Frequent observations of atypical sensory reactivity in people with autism spectrum disorders (ASD) suggest that the perceptual experience of those on the Spectrum is dissimilar to neurotypicals. Moreover, variable attention abilities in people with ASD, ranging from good control to periods of high distractibility, may be related to atypical sensory reactivity. This study used auditory event-related potential (ERP) measures to evaluate top-down and bottom-up attentional processes as a function of perceptual load, and examined these factors with respect to sensory reactivity. Twenty-five age and IQ-matched participants (ASD: 22.5 year, SD = 4.1 year; Controls: 22.8 year, SD = 5.1 year) completed the Adolescent/Adult Sensory Profile prior to performing a modified 3-stimulus (target, non-target, and distractor) auditory oddball target detection task EEG was recorded during task completion. ERP analysis assessed early sensory processing (P50, ∼50 ms latency; N100, ∼100 ms latency), cognitive control (N200, ∼200 ms latency), and attentional processing (P3a and P3b, ∼300 ms latency). Behavioral data demonstrates participants with ASD and neurotypical performed similarly on auditory target detection, but diverged on sensory profiles. Target ERP measures associated with top-down control (P3b latency) significantly increased under greater load in controls, but not in participants with ASD. Early ERP responses associated with bottom-up attention (P50 amplitude) were positively correlated to increased sensory sensitivity. Findings suggest specific neural mechanisms for increased perceptual capacity and enhanced bottom-up processing of sensory stimuli in people with autism. Results from participants with ASD are consistent with load theory and enhanced perceptual functioning. Autism Res 2016, 9: 1079-1092. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Interaction of Number Magnitude and Auditory Localization.

The interplay of perception and memory is very evident when we perceive and then recognize familiar stimuli. Conversely, information in long-term memory may also influence how a stimulus is perceived. Prior work on number cognition in the visual modality has shown that in Western number systems long-term memory for the magnitude of smaller numbers can influence performance involving the left side of space, while larger numbers have an influence toward the right. Here, we investigated in the auditory modality whether a related effect may bias the perception of sound location. Subjects (n = 28) used a swivel pointer to localize noise bursts presented from various azimuth positions. The noise bursts were preceded by a spoken number (1-9) or, as a nonsemantic control condition, numbers that were played in reverse. The relative constant error in noise localization (forward minus reversed speech) indicated a systematic shift in localization toward more central locations when the number was smaller and toward more peripheral positions when the preceding number magnitude was larger. These findings do not support the traditional left-right number mapping. Instead, the results may reflect an overlap between codes for number magnitude and codes for sound location as implemented by two channel models of sound localization, or possibly a categorical mapping stage of small versus large magnitudes.