Biology subjects

Chait, M.

Publications and source records attributed to Chait, M..

At least 19 recordsLinked to original sources

bioRxiv2026

Physiological Markers of Auditory Situational Awareness in Complex Spatialised Scenes

Detecting changes in acoustic environments is essential for situational awareness. It remains unclear whether the spatial location of such changes modulates automatic orienting and arousal mechanisms. We measured pupil dilation, pupil dilation rate, and microsaccade rate while listeners (n=25) heard complex, spatialized auditory scenes rendered over headphones using individualized HRTFs. Participants were naive to the critical manipulation: the appearance of a new source from one of five locations: front, left, right, back, or above. A subsequent localization task assessed perceptual spatial uncertainty. Behaviorally-irrelevant source appearances elicited a cascade of ocular responses. Microsaccadic inhibition emerged from [~]85ms after change onset, and was broadly comparable across locations, suggesting a location-invariant early orienting response to auditory change. Pupil dilation rate increased from [~]200ms, followed by a phasic pupil dilation response from [~]400ms, indicating engagement of arousal-related systems. Pupil responses were modulated by source location: changes from front/left/right elicited larger dilation than changes from above, with back responses showing a similar but weaker reduction. Behavioral localization revealed substantial confusion for front/back/above locations. However, this did not mirror the physiological data, as front sources elicited pupil responses comparable to lateral sources. These findings demonstrate that complex auditory scene changes recruit oculomotor and autonomic systems even outside the focus of task relevance. They further suggest a dissociation between early, location-invariant attentional capture indexed by microsaccadic inhibition and later, location-sensitive arousal indexed by pupil dilation. Spatial biases in auditory situational awareness therefore appear to emerge after initial change detection, shaping arousal and behavioral performance rather than the earliest orienting response.

neuroscience↗

bioRxiv2026

Characterizing the effect of aging on resting and event-evoked ocular response dynamics

Ocular measures are increasingly used as non-invasive proxies of cognitive processes such as attention and listening effort. However, their interpretation in aging populations is complicated by concurrent changes in ocular physiology and oculomotor control, raising a critical question: to what extent do age-related differences in these measures reflect cognitive rather than other physiological factors? Here, we dissociate these contributions by characterizing ocular dynamics (resting and event-evoked) during passive fixation in younger (N = 98, 18-35 years) and older adults (N = 71, 60+ years). Aging is associated with pronounced alterations in pupil dynamics, including reduced baseline variability and slower, attenuated responses to both auditory and visual events. In contrast, microsaccade dynamics did not correlate with aging. Across measures, ocular responses showed moderate-to-high within-subject stability across blocks, and factor analysis in the older cohort revealed separable components reflecting instantaneous pupil responsivity, sustained pupil responsivity, and microsaccade dynamics, with additional variance associated with sensory decline and age-related changes in pupil dynamics. Together, these findings demonstrate a clear dissociation: pupil-based metrics are strongly influenced by aging, whereas microsaccades remain comparatively stable across age groups. This dissociation provides a principled basis for interpreting ocular indices in aging research and highlights the need to account for baseline physiological differences when inferring cognitive processes from eye-based measures.

neuroscience↗

bioRxiv2026

An adaptive gain model for predicting auditory brain activity in mice outperforms standard methods for predicting cortical speech tracking in human EEG

Human brain activity tracks slow fluctuations in continuous sound, including speech, and modelling this relationship provides insight into how the brain encodes naturalistic auditory input. Traditional approaches to modelling brain tracking of speech with linear regression often use the amplitude envelope of the stimulus as a regressor, implicitly assuming that neural responses scale linearly with sound intensity. However, previous studies of central auditory processing in both animals and humans have shown that adaptive mechanisms adjust auditory responses based on recent sound history. Here, we find that a simple nonlinear transformation of the stimulus envelope, derived from studies of mouse auditory thalamic responses to temporally varying sounds, significantly improves modelling of human cortical speech tracking. This Adaptive Gain transformation essentially normalizes sound level by its recent context. Improvements in modelling of cortical speech tracking using the Adaptive Gain stimulus representation are robust across experiments, participant groups, and languages, indicating that short-timescale adaptation to recent sound level is a general feature of auditory processing. We further show that the optimal adaptation time constant for human cortical responses to continuous speech is approximately 50-100 ms, longer than previously observed for auditory thalamic responses to temporally varying sounds in mice. In summary, the Adaptive Gain transformation is a mathematically simple alternative to the standard envelope representation that captures dynamic adaptation in auditory processing and reliably improves prediction of human cortical EEG signals during listening to continuous speech. Significance StatementStandard models of human brain responses to continuous speech use the raw stimulus envelope as a predictor of EEG responses, implicitly assuming stationary sensitivity to sound intensity. Here, we use instead a simple nonlinear transformation of the stimulus envelope, Adaptive Gain, which normalizes sound level based on recent sound history over tens to hundreds of milliseconds. Originally derived from studies of auditory processing in mice, the Adaptive Gain transformation robustly improves prediction of EEG responses to continuous speech in humans across experiments, participant groups, and languages. Results demonstrate that dynamic adaptation to sound level is a core feature of auditory processing, and can be approximated in a mathematically simple form to improve prediction of cortical speech tracking.

neuroscience↗

bioRxiv2026

Reduced Pupil-Linked Arousal Marks Implicit Memory for Complex Auditory Sequences

Observers rapidly form long-lasting implicit memories for recurring sensory patterns, supporting adaptive behaviour through learning of environmental contingencies. Here we tested how such memories interact with neuromodulatory systems that regulate arousal--whether implicit familiarity increases arousal through retrieval-related processes or instead decreases arousal via more efficient sensory processing. We examined these competing accounts using complex auditory tone-pip sequences in which a subset of patterns recurred approximately every three minutes. One group of participants (N=30) actively detected transitions from random to regular structure, whereas a second group (N=40) heard the same sequences while performing a decoy task. Consistent with prior work, recurring regular sequences elicited faster reaction times in the active group, confirming the formation of implicit memory. Subsequently, both groups listened to previously encountered regular patterns (REGr) and matched novel regular patterns (REGn) while pupil diameter was recorded. Across groups, REGr sequences evoked significantly smaller pupil dilations than REGn sequences, indicating attenuated arousal for familiar patterns. This reduction was sustained until sequence offset in the active group but was transient in the exposure group, suggesting that task demands during exposure shape the stability of pupil-linked memory expression. Importantly, the REGr-REGn pupil difference did not correlate with explicit post-session recognition, demonstrating that the effect was not driven by conscious awareness. Together, these findings identify pupil dynamics as a robust physiological marker of learned auditory structure and show that implicit auditory sequence memory attenuates arousal. The results support predictive processing accounts in which familiarity reduces uncertainty and, consequently, neuromodulatory drive. Significance StatementHumans rapidly acquire implicit memories for recurring sounds, yet how such memories influence arousal during subsequent exposure remains poorly understood. Using pupillometry, we show that implicitly remembered auditory sequences evoke reduced pupil-linked arousal relative to matched novel sequences, even when listeners are unaware that the patterns have been previously experienced. This effect dissociates from explicit recognition, which typically yields the opposite "old/new" pattern of larger pupil responses to familiar items. Together, these findings establish pupil dynamics as a sensitive, non-invasive marker of implicit auditory memory and support predictive processing accounts in which familiarity reduces uncertainty and, consequently, neuromodulatory drive.

neuroscience↗

bioRxiv2026

Neural Signatures of Automatic Auditory Regularity Detection Reflect Individual Differences in Explicit Short-Term Memory

Perception is shaped by the statistical structure of the environment, reflecting the brains capacity to detect and exploit regularities in sensory input. This process requires the maintenance of contextual information over time, yet the nature of the memory mechanism supporting automatic structure learning remains unclear. Here, we ask whether auditory regularity processing relies on a dedicated sensory buffer or instead draws on domain-general mnemonic resources. We related neural indices of regularity processing measured with EEG during passive listening to behavioural performance on an explicit auditory short-term memory task. Human participants (N=30; both sexes) passively listened to regularly repeating (cycles of 5.5 seconds) or random tone sequences, while sustained and tone-locked neural responses were extracted as complementary markers of predictability tracking and prediction-error signalling. Individual differences in explicit memory performance, quantified using a delayed match to sample task, systematically predicted both neural measures: high performers showed enhanced sustained responses and attenuated tone-evoked responses (most pronounced in the N2 time window; 250-400 ms post-onset) to regular sequences, whereas low performers showed no reliable modulation by sequence structure. These findings demonstrate that the memory processes engaged automatically during auditory pattern analysis are not encapsulated, but instead draw on shared mnemonic resources, providing a link between predictive perception and individual variability in sensory memory capacity.

neuroscience↗

bioRxiv2025

Neural correlates of implicit memory for reoccurring sound patterns

The human brain exhibits remarkable sensitivity to auditory patterns. Previous research has shown that beyond the detection of such patterns, humans form memories for them that are implicit, robust to interference, and persistent over time. Here, we examine the mechanisms underlying implicit memory formation for reoccurring regular tone patterns using UHF fMRI. Prior to scanning, implicit memory was induced through a standard behavioral task where participants detected regular patterns embedded in random tone sequences. Unbeknownst to participants, five regular patterns reoccurred sporadically (every 1.5 min) across trials. Consistent with previous reports, behavioral performance indicated a reaction time advantage to reoccurring patterns, confirming the formation of implicit memory traces. During passive listening in the scanner, regularity engaged the superior temporal gyrus, inferior frontal gyrus, insula, putamen, and hippocampus, a result we interpret as reflecting the higher perceptual precision of regular patterns. Reoccurrence interacted with regularity in the superior temporal gyrus and a frontal cluster, showing higher activity for reoccurring compared to novel regular patterns. The hippocampus showed sensitivity to reoccurrence in both regular and random patterns. Together, these results indicate that the neocortex may selectively amplify reoccurring inputs in line with their enhanced (memory driven) perceptual precision.

neuroscience↗

bioRxiv2025

Spatial auditory change detection in listeners with hearing loss

Everyday listening relies on the auditory systems ability to automatically monitor the background soundscape and detect new or changing sources. Although change detection is a fundamental aspect of situational awareness, little is known about how hearing impairment affects this ability. This study examined how sensorineural hearing loss influences spatial auditory change detection. Older hearing-impaired listeners (N = 30) completed a spatial change detection task requiring them to identify the appearance of a new sound source within a complex spatialised acoustic scene. Hearing loss was characterised by three factors that were measured with standard clinical tests: audiometric hearing thresholds, sensitivity to small level changes, and sensitivity to spectrotemporal modulation. Simple and mixed-effects linear models were used to test how these factors predicted reaction time, hit rate, and false alarm rate. Listeners with poorer spectrotemporal sensitivity, higher audiometric hearing thresholds, and older age showed slower and less accurate detection, whereas sensitivity to small changes in level did not predict outcomes. Detection also varied with spatial location, where appearing sources from behind were detected more slowly and less accurately than those from the front or sides. Numerical analysis using head-related transfer functions confirmed that these rear-field effects were unlikely to be explained by overall or frequency-specific acoustic level differences. These findings reveal that hearing loss, age, and spatial factors jointly shape listeners ability to monitor dynamic auditory scenes. Additionally, testing spectrotemporal sensitivity offers a promising clinical measure of non-speech auditory processing with relevance for hearing-aid fitting and situational awareness.

neuroscience↗

bioRxiv2025

Auditory regularity detection in the ferret

Acoustic sequences that transition from random to regularly repeating tones are increasingly used to study how the auditory system detects structure. Humans can identify such regularities rapidly, often within a single cycle. To test whether this ability is unique to humans, we trained ferrets (n = 6) to detect transitions from random tone sequences to repeating patterns. All animals learned the task and showed high accuracy for short (3 tone) patterns. Performance remained above chance for longer patterns (5 or 7 tones), though accuracy declined with increased pattern length. In a control condition where both random and regular segments contained the same five frequencies, ferrets continued to detect regularity, indicating they relied on temporal patterning rather than spectral content. To further rule out spectral cues, we included transitions from random 20 tone sequences to random 3, 5 or 7 tone sequences without repetition. Although these stimuli elicited performance above the false alarm rate seen in fully random trials, detection accuracy remained substantially lower than that observed for regular sequences. This suggests ferrets were not solely detecting changes in spectral statistics, but true regularity. Together, our results indicate that sensitivity to regular patterns within sound is not unique to humans and may reflect a broader auditory computation shared across species.

animal behavior and cognition↗

bioRxiv2025

Dynamic remodeling of the pancreas immune landscape in obesity.

Obesity is a known risk factor for diseases of the pancreas, including diabetes, pancreatic cancer and pancreatitis, but mechanisms remain unclear. To elucidate how obesity impacts pancreatic immune homeostasis, we performed spatial, transcriptomic and functional profiling of human pancreatic immune cells from obese and non-obese organ donors. Obesity was associated with higher density of tissue resident memory T-cells (TRM) in the exocrine pancreas which display high cytotoxic functions and aggregated around macrophages. Single cell sequencing of pancreatic macrophages revealed two main subsets - FOLR2+ CD11c- fetal-derived macrophages with pro-repair and immunoregulatory function and a FOLR2- CD11c+ monocyte-derived macrophages with greater T-cell interactions and pro-inflammatory function. In obesity, the pancreatic macrophage landscape shifts to lower predominance of FOLR2+ CD11c- macrophages and higher FOLR2- CD11c+ macrophages which interact selectively with the TRM and inflamed exocrine epithelium. Together, these results identify macrophage-T cell circuits and immune epithelial interactions that fuel chronic pancreatic inflammation in obesity - a potential unifying mechanism for obesity-related pancreatic diseases.

immunology↗

bioRxiv2025

Pupil-linked arousal does not differ between white, pink and brown noises

Coloured noises, such as white, pink, and brown noise, have gained attention in popular media as potential tools for enhancing memory consolidation, sleep quality, attentional focus, and more. These terms refer to distinct spectral slopes, which give rise to perceptually different noise stimuli. Although empirical research on their effects remains limited, a prevailing hypothesis suggests that their influence may be mediated by differential effects on arousal. In this study, we investigated this hypothesis using pupillometry, a physiological marker closely linked to arousal. Participants (N = 31) listened to three types of noise (white, pink, and brown), each presented for 10 sec, while their pupil diameter was recorded. The results showed no significant modulation of pupil size across noise conditions. These findings suggest that, despite widespread claims about the distinct arousing or calming properties of coloured noises, they do not differentially affect sustained pupil-linked arousal.

physiology↗

bioRxiv2025

The Effect of Previously Encountered Sensory Information on Neural Representations of Predictability: Evidence from Human EEG

Accumulating evidence suggests that the brain continuously monitors the predictability of rapidly evolving sound sequences, even when they are not behaviorally relevant. An increasing body of empirical evidence links sustained tonic M/EEG activity to evidence accumulation and tracking the predictability, or inferred precision, of the auditory stimulus. However, it remains unclear whether, and how, this process depends on auditory contextual memory. In the present EEG study, we examined neural responses to sound sequences across two experiments, and compared them to predictions from ideal observer models with varying memory spans. Stimuli were sequences of 50 ms long tone-pips. In Experiment 1 (N=26; both sexes), a regularly repeating sequence of 10 tones (REG) transitioned directly to a different regular sequence (REGxREGy). In Experiment 2 (N=28; both sexes), the same regular sequence was repeated after an intervening random segment (REGxINTREGx). Results from Experiment 2 revealed that the inferred predictability of the resumed REGx pattern was influenced by the preceding INT tones, even several seconds after they ended, indicating that the brain retains contextual memory over time. In contrast, neural responses in Experiment 1 were best explained by models with minimal memory. This dissociation implies that the brain can dynamically adjust its strategy based on inferred environmental structure--resetting context when interruptions signal change, and preserving context when patterns are likely to resume.

neuroscience↗

bioRxiv2025

Dissociable Pupil and Oculomotor Markers of Attention Allocation and Distractor Suppression during listening

Emerging evidence suggests that ocular dynamics, pupil dilation, eye movements, and blinks, can serve as markers of task engagement. In this study, we examined whether these measures dissociate different perceptual states during an auditory attention task. Participants (Main and Control experiments; N = 34 and 27, both sexes) listened to tone sequences designated as Target, Distractor, and Probe, designed to isolate active attention from suppression of irrelevant input. We focused on four physiological signals: pupil diameter (PD), pupil dilation rate (PDR), blink rate, and microsaccades (MS). Compared to a control condition, both Target and Probe intervals elicited sustained PD increases, blink suppression, and prolonged MS inhibition indicating extended attentional engagement. Interestingly, the Distractor interval also showed prolonged blink suppression and elevated PDR, suggesting active arousal to suppress irrelevant input. However, MS dynamics during Distractors were indistinguishable from control, implying that attention was not allocated to the distractors despite the heightened arousal. This dissociation supports the interpretation that MS is specifically modulated by attentional allocation, while PD and blinks also reflect general arousal or suppressive mechanisms. Overall, these findings reveal that PD, MS, and blinking capture distinct aspects of cognitive control. Together, they offer a multidimensional framework for studying selective attention and distractor suppression in complex tasks. Significance statementUnderstanding an individuals moment-to-moment state during demanding attention tasks is crucial for identifying perceptual challenges, explaining inter-individual variability, and diagnosing difficulties in special populations. Ocular measures, such as pupil size, blinks, and microsaccades, are gaining traction as objective, non-invasive indicators of perceptual and cognitive states. In this study, we demonstrate that, during a challenging auditory task requiring selective attention and active ignoring, different eye-related signals capture distinct aspects of listener state. Specifically, the dynamics observed during active attention differ systematically from those during active distractor suppression. These findings highlight the value of ocular metrics for assessment of cognitive performance and for disentangling the contributions of arousal and attention during complex tasks.

neuroscience↗

bioRxiv2025

The Interplay of Bottom-Up Arousal and Attentional Capture during Auditory Scene Analysis: Evidence from Ocular Dynamics

The auditory system plays a crucial role as the brains early warning system. Previous work has shown that the brain automatically monitors unfolding auditory scenes and rapidly detects new events. Here, we focus on understanding how automatic change detection interfaces with the networks that regulate arousal and attention, measuring pupil diameter (PD) as an indicator of listener arousal and microsaccades (MS) as an index of attentional sampling. Naive participants (N=36; both sexes) were exposed to artificial scenes comprised of multiple concurrent streams of pure tones while their ocular activity was monitored. The scenes were categorized as REG or RND, featuring isochronous (regular) or random temporal structures in the tone streams, respectively. Previous work showed that listeners are sensitive to predictable scene structure and use this information to facilitate change processing. Scene changes were introduced by either adding or removing a single tone stream. Results revealed distinct patterns in the recruitment of arousal and attention during auditory scene analysis. PD was greater in REG scenes compared to RND, indicating heightened arousal in unpredictable contexts. However, no differences in overall MS activity were observed between scene types, suggesting no differences in attentional engagement. Scene changes--though unattended-- elicited both PD and MS suppression, consistent with automatic attentional capture and increased arousal. Notably, only MS responses were modulated by scene regularity. This suggests that changes within predictable environments more effectively recruit attentional resources. Together, these findings offer novel insights into how automatic auditory scene analysis interacts with neural systems governing arousal and attention. Significance StatementEven without active listening, our brains automatically respond to changes in complex sound environments--like noticing a new sound on a busy street. These responses involve shifts in arousal and attention, helping us decide how to react, often without conscious awareness. Understanding this process is key to studying how we perceive sound scenes and how it may be disrupted in individuals with attention or arousal difficulties. In this study, participants passively listened to artificial soundscapes while we tracked eye activity: pupil dilation (a sign of arousal) and microsaccades (tiny eye movements linked to attention). We found that sudden scene changes triggered both responses, but they were differently influenced by scene predictability--suggesting they reflect separate aspects of automatic auditory processing.

neuroscience↗

bioRxiv2025

Loudness and sound category: Their distinct roles in shaping perceptual and physiological responses to soundscapes

When compared to nature sounds, exposure to mechanical sounds evokes higher levels of perceptual and physiological arousal, prompting the recruitment of attentional and physiological resources to elicit adaptive responses. However, it is unclear whether these attributes are solely related to the sound intensity of mechanical sounds, since in most real-world scenarios, mechanical sounds are present at high intensities, or if other acoustic or semantic factors are also at play. We measured the Skin Conductance Response (SCR), reflecting sympathetic nervous system (SNS) activity as well as the pleasantness and eventfulness of the soundscape across two passive and active listening tasks in (N = 25) healthy subjects. The auditory stimuli were divided into two categories, nature, and mechanical sounds, and were manipulated to vary in three perceived loudness levels. As expected, we found that the sound category influenced perceived soundscape pleasantness and eventfulness. SCR was analysed by taking the mean level across the stimulus epoch, and also by quantifying its dynamic. We found that mean SCR was modulated by loudness only. SCR rise-time (a measure of speed of the skin response) correlated significantly with soundscape pleasantness and eventfulness for nature and mechanical sounds. This study highlights the importance of considering both loudness level and sound category in evaluating the perceptual soundscape, highlighting SCR as a valuable tool for such assessments. Impact statementLoud mechanical sounds are considered more unpleasant than nature sounds. This study examined whether loudness alone causes this effect or if the type of sound (e.g., mechanical vs. Nature) also plays a role. By measuring skin conductance reflecting the automatic and unconscious activation of the bodys autonomic system, we found that physical reactions are driven by loudness but also correlate with the listeners judgement of the pleasantness and eventfulness (describing the perceived level of activity or stimulation) of a soundscape.

neuroscience↗

bioRxiv2025

Discovery, Interruption, and Updating of Auditory Regularities in Memory: Evidence from Low-Frequency Brain Dynamics in Human MEG

During passive listening, the brain maintains a hierarchy of predictive models to monitor the statistics of its surroundings. The automatic discovery of regular patterns has been associated with a gradual increase in sustained tonic M/EEG activity, sourced in auditory, hippocampal, and frontal areas -- reflecting evidence accumulation and establishment of a regularity model. Conversely, when a regular pattern is interrupted, the sustained activity drops -- indicating disengagement from the model. However, how such models are established in and retrieved from memory as well as the conditions under which they are activated and interrupted remain underexplored. In this MEG experiment (N=26; both sexes), we examined how neural responses related to model establishment and interruption are influenced by (1) the rate of stimulus presentation (tone presentation rate 20 Hz vs. 40 Hz), and (2) the novelty of the experienced acoustic structure (novel vs resumed REG pattern). The results show that (1) the dynamics of model interruption and establishment are independent of stimulus presentation rate, and that (2) model establishment occurred much faster when an experienced vs novel pattern was presented after pattern interruption, suggesting re-activation of the stored original model facilitated by the hippocampus. (3) Finally, sustained response rises in response to pattern establishment and interruption were localized in auditory, hippocampal, and frontal sources, supporting top-down model information flow. These results unveil the temporal dynamics and neural network underlying the brains construction and selection of predictive models to monitor changes in sensory statistics. Significance statementSustained neural activity in response to statistical shifts in auditory sequences reflects how the brain integrates sensory information to build and update predictive models. The present magnetoencephalography (MEG) study aims to uncover the factors that affect this updating. Using tone-pip sequences as a controlled model system, we found that the brain tracks sequence information regardless of tempo and automatically retains a memory of previously encountered patterns, facilitating detection when they re-emerge. Source localization revealed activation in auditory, hippocampal, and frontal areas, highlighting a distributed network involved in top-down model updating and predictive processing. These findings provide new insights into the neural mechanisms of statistical learning and memory, revealing how the brain adapts perception in dynamic environments.

neuroscience↗

bioRxiv2025

Brain bases for navigating acoustic features

Whether physical navigation shares neural substrates with mental travel in other behaviourally relevant domains is debated. With respect to sound, pure-tone working memory in humans elicits hippocampal as well as auditory cortical and inferior frontal activity, and rodent work suggests that hippocampal cells that usually track an animals physical location can also map to tone frequency when task-relevant. We generated a sound dimension based on the density of random-frequency tones in a stack, resulting in a percept ranging from low- ("beepy") to high-density ("noisy"). We established that unlike tone frequency, which listeners automatically associate with vertical position, this density dimension elicited no consistent spatial mapping. During functional magnetic resonance imaging, human participants held in mind the density of a series of tone stacks and, after a short maintenance period, adjusted further stacks to match the target ("navigation"). Density of the currently heard sound was represented most strongly in bilateral non-primary auditory cortex, specifically bilateral planum polare, while density of the maintained target was represented in right anterior hippocampus and left inferior temporal gyrus. Encoding and maintenance activity in bilateral hippocampus, inferior frontal gyrus, planum polare and posterior cingulate was positively associated with subsequent navigation success. Bilateral inferior frontal gyrus and hippocampus were among regions with elevated activity during adjustment, compared to a parity-judgment condition with closely matched acoustics and motor demands. Bilateral orbitofrontal cortex was more active when navigation was toward a target density than when participants adjusted density in a control condition with no particular target. We find that self-initiated travel along a non-spatial auditory dimension engages a brain system overlapping with that supporting physical navigation. Key PointsO_LIWork in rodents suggests that navigation in physical space and the active analysis of sounds share a neural substrate in the hippocampus, supporting the use of common computational mechanisms. C_LIO_LIWe examined the human brain system for navigation through an acoustic environment to a remembered target. C_LIO_LIIn addition to high-level auditory cortex we demonstrate involvement of the hippocampus in acoustic navigation along with other sites in frontal and cingulate cortex that also support physical navigation. C_LI

neuroscience↗

bioRxiv2024

Assessing Behavioral and Neural Correlates of Change Detection in Spatialized Acoustic Scenes

The ability to detect changes in complex auditory scenes is crucial for human survival, yet the neural mechanisms underlying this process remain elusive. This study investigates how the presence and location of sound sources impacts active auditory change detection as well as neural correlates of passive change detection. We employed stimuli designed to minimize semantic associations while preserving naturalistic temporal envelopes and broadband spectra, presented in a spatial loudspeaker array. Behavioral change detection experiments tasked participants with detecting new sources added to spatialized and non-spatialized multi-source auditory scenes. In a passive listening experiment, participants were given a visual decoy task while neural data were collected via electroencephalography (EEG) during exposure to unattended spatialized scenes and added sources. Our behavioral experiments (N = 21 and 21) demonstrated that spatializing sounds facilitated change detection compared to non-spatialized presentation, but that performance declined with increasing number of sound sources and higher hearing thresholds at high frequencies, exclusively in spatialized conditions. Slower reaction times were also observed when changes occurred from above or behind the listener, exacerbated by a higher number of sources. EEG experiments (N = 32 and 30), using the same stimuli, showed robust change-evoked responses. However, no significant differences were detected in our analysis as a function of spatial location of the appearing source.

neuroscience↗

bioRxiv2024

Brain responses to predictable structure in auditory sequences: From complex regular patterns to tone repetition

In classical studies of auditory pattern learning, neuronal responses exhibit repetition suppression, where sequences of repeated tones show a reduced evoked response. This may be due in part to adaptation, but is also hypothesized to indicate suppression of expected stimuli. Repetition suppression is thought to form a building block of regularity learning, and is the paradigmatic example of predictive coding in humans and other animals. However, stimuli with more complex patterns appear to show the opposite effect. Predictable regular (REG) patterns distributed over a range of frequencies show a strongly enhanced sustained brain response compared to frequency-matched random (RAND) sequences, sitting at odds with the usual reduced evoked responses to predictable stimuli. A limiting factor in reconciling these findings is that they are obtained using different stimuli and analysis methods. This human EEG study (N=20) brings together auditory sequence predictability and repetition in a single paradigm, based on rapidly unfolding tone pip patterns, incorporating sequences consisting of exactly repeating tones at a single frequency, alongside REG and RAND of varying complexity. We demonstrate that regularity is associated with increased sustained responses, offset responses, tone locked responses and cycle-locked responses. We further show that both repetition suppression and repetition enhancement occur over different timescales, and that sustained brain responses to simple repetition show qualitatively different effects than to more complex regularities during automatic tracking of stimulus statistics. Our results indicate a system for automatic monitoring of predictability in the auditory environment, which is distinct from, but concurrent with, repetition suppression. NEW & NOTEWORTHYWe investigate how human brain response patterns evolve as auditory patterns become progressively simplified, focusing on the impact of sequence structure on various aspects of EEG responses, both evoked and induced. By contrasting EEG responses across different phases of the stimulus--onset, sustained, and offset--we uncover the interplay between repetition suppression and predictability. This approach allows us to discern how the brain processes and adapts to changing regularities in sensory input.

neuroscience↗