Biology subjects

Veillette, J. P.

Publications and source records attributed to Veillette, J. P..

6 recordsLinked to original sources

bioRxiv2024

Cortical Representation of the Glottal Events during Speech Production

To learn complex motor skills, an organism must be able to assign sensory feedback events to the actions that caused them. This matching problem would be simple if motor neuron output led sensory feedback with a fixed, predictable lag. However, nonlinear dynamics in the brain and the bodys periphery can decouple the timing of critical events from that of the motor output which caused them. During human speech production, for example, phonation from the glottis (a sound source for speech) begins suddenly when subglottal pressure and laryngeal tension cross a sharp threshold (i.e. a bifurcation). Only if the brain can predict the timing of these discrete peripheral events resulting from motor output, then, would it be possible to match sensory feedback to movements based on temporal coherence. We show that event onsets in the human glottal waveform, as measured using electroglottography, are reflected in the human electroencephalogram during speech production, leading up to the time of the event itself. Conversely, glottal event times can be decoded from the electroencephalogram. After prolonged exposure to delayed auditory feedback, subjects recalibrate their behavioral threshold for detecting temporal auditory-motor mismatches, and decoded event times decouple from actual movements. This suggests decoding performance is driven by plastic predictions of peripheral timing, providing a missing component for hindsight credit assignment in motor control, in which specific feedback events are associated with the neural activity that gave rise to movements. We discuss parallel findings from the birdsong system suggesting that results may generalize across vocal learning species. Significance StatementTo learn complex motor skills such as speech, the brain must pair actions with sensory feedback. However, feedback is delayed in time relative to actual movement, rendering this "hindsight credit assignment" problem a nontrivial task. We present evidence that events in the glottis, the articulatory organ that generates sound for human speech, are predictively encoded in the human brain during speech production. Given that corresponding events in auditory feedback are known to be prominently encoded in cortex, this highlights a common temporal marker by which articulatory gestures and sensory feedback could be aligned. Findings suggest activity in the human vocomotor system is shaped by biophysical dynamics in the vocal periphery, aligning with corresponding results in the birdsong system.

neuroscience↗

bioRxiv2024

What the Average Really Means: Dissociating Effect Size and Effect Prevalence using p-curve Mixtures

Much research in the behavioral sciences aims to characterize the "typical" person. A statistically significant group-averaged effect size is often interpreted as evidence that the typical person shows an effect, but that is only true under certain distributional assumptions for which explicit evidence is rarely presented. Mean effect size varies with both within-participant effect size and population prevalence (proportion of population showing effect). Few studies consider how prevalence affects mean effect size estimates and existing estimators of prevalence are, conversely, confounded by uncertainty about effect size. We introduce a widely applicable Bayesian method, the p-curve mixture model, that jointly estimates prevalence and effect size by probabilistically clustering participant-level data based on their likelihood under a null distribution. Our approach, for which we provide a software tool, outperforms existing prevalence estimation methods when effect size is uncertain and is sensitive to differences in prevalence or effect size across groups or conditions.

neuroscience↗

bioRxiv2024

Overlapping Cortical Substrate of Biomechanical Control and Subjective Agency

Every movement requires the nervous system to solve a complex biomechanical control problem, but this process is mostly veiled from ones conscious awareness. Simultaneously, we also have conscious experience of controlling our movements--our sense of agency (SoA). Whether SoA corresponds to those neural representations that implement actual neuromuscular control is an open question with ethical, medical, and legal implications. If SoA is the conscious experience of control, this predicts that SoA can be decoded from the same brain structures that implement the so-called "inverse dynamics" computations for planning movement. We correlated human (male and female) fMRI measurements during hand movements with the internal representations of a deep neural network (DNN) performing the same hand control task in a biomechanical simulation- revealing detailed cortical encodings of sensorimotor states, idiosyncratic to each subject. We then manipulated SoA by usurping control of participants muscles via electrical stimulation, and found that the same voxels which were best explained by modeled inverse dynamics representations-- which, strikingly, were located in canonically visual areas--also predicted SoA. Importantly, model-brain correspondences and robust SoA decoding could both be achieved within single subjects, enabling relationships between motor representations and awareness to be studied at the level of the individual. Significance StatementThe inherent complexity of biomechanical control problems is belied by the seeming simplicity of directing movements in our subjective experience. This aspect of our experience suggests we have limited conscious access to the neural and mental representations involved in controlling the body - but of which of the many possible representations are we, in fact, aware? Understanding which motor control representations percolate into awareness has taken on increasing importance as emerging neural interface technologies push the boundaries of human autonomy. In our study, we leverage machine learning models that have learned to control simulated bodies to localize biomechanical control representations in the brain. Then, we show that these brain regions predict perceived agency over the musculature during functional electrical stimulation.

neuroscience↗

bioRxiv2023

Cardiac afferent signals can facilitate visual dominance in binocular rivalry

Sensory signals from the bodys visceral organs (e.g. the heart) can robustly influence the perception of exteroceptive sensations. This interoceptive-exteroceptive interaction has been argued to underlie self-awareness by situating ones perceptual awareness of exteroceptive stimuli in the context of ones internal state, but studies probing cardiac influences on visual awareness have yielded conflicting findings. In this study, we presented separate grating stimuli to each of subjects eyes as in a classic binocular rivalry paradigm - measuring the duration for which each stimulus dominates in perception. However, we caused the gratings to "pulse" at specific times relative to subjects real-time electrocardiogram, manipulating whether pulses occurred during cardiac systole, when baroreceptors signal to the brain that the heart has contracted, or in diastole when baroreceptors are silent. The influential "Baroreceptor Hypothesis" predicts the effect of baroreceptive input on visual perception should be uniformly suppressive. In contrast, we observed that dominance durations increased for systole-entrained stimuli, inconsistent with the Baroreceptor Hypothesis. Further, we show that this cardiac-dependent rivalry effect is preserved in subjects who are at-chance discriminating between systole-entrained and diastole-presented stimuli in a separate interoceptive awareness task, suggesting that our results are not dependent on conscious access to heartbeat sensations.

neuroscience↗

bioRxiv2023

Illusion of agency over involuntary muscle movements reveals temporal dynamics of neural activity underlying self-agency judgments

Our muscles are the primary means through which we affect the external world, and the sense of agency (SoA) over the action through those muscles is fundamental to our self-awareness. However, SoA research to date has focused almost exclusively on agency over action outcomes rather than over the musculature itself, as it was believed that SoA over the musculature could not be manipulated directly. Drawing on methods from human-computer interaction and adaptive experimentation, we use human-in-the-loop Bayesian optimization to tune the timing of electrical muscle stimulation so as to robustly elicit a sense of agency over electrically-actuated muscle movements in male and female human subjects. We use time-resolved decoding of subjects EEG to estimate the time course of neural activity which predicts reported agency on a trial-by-trial basis. Like paradigms which assess SoA over action consequences, we found that the late (post-conscious) neural activity predicts SoA. Unlike typical paradigms, however, we also find patterns of early (sensorimotor) activity with distinct temporal dynamics predicts agency over muscle movements, suggesting that the "neural correlates of agency" may depend on the level of abstraction (i.e., direct sensorimotor feedback vs. downstream consequences) most relevant to a given agency judgement. Moreover, fractal analysis of the EEG suggests that SoA-contingent dynamics of neural activity may modulate the sensitivity of the motor system to external input. Significance StatementThe sense of agency - the feeling of "I did that" - when directing ones own musculature is a core feature of human experience. We show that we can robustly manipulate the sense of agency over electrically actuated muscle movements, and we investigate the time course of neural activity that predicts the sense of agency over these actuated movements. We find evidence of two distinct neural processes - a transient sequence of patterns that begins in the early sensorineural response to muscle stimulation and a later, sustained signature of agency. These results shed light on the neural mechanisms by which we experience our movements as volitional.

neuroscience↗

bioRxiv2023

Permutation-based group sequential analyses for cognitive neuroscience

Cognitive neuroscientists have been grappling with two related experimental design problems. First, the complexity of neuroimaging data (e.g. often hundreds of thousands of correlated measurements) and analysis pipelines demands bespoke, non-parametric statistical tests for valid inference, and these tests often lack an agreed-upon method for performing a priori power analyses. Thus, sample size determination for neuroimaging studies is often arbitrary or inferred from other putatively but questionably similar studies, which can result in underpowered designs - undermining the efficacy of neuroimaging research. Second, when meta-analyses estimate the sample sizes required to obtain reasonable statistical power, estimated sample sizes can be prohibitively large given the resource constraints of many labs. We propose the use of sequential analyses to partially address both of these problems. Sequential study designs - in which the data is analyzed at interim points during data collection and data collection can be stopped if the planned test statistic satisfies a stopping rule specified a priori - are common in the clinical trial literature, due to the efficiency gains they afford over fixed-sample designs. However, the corrections used to control false positive rates in existing approaches to sequential testing rely on parametric assumptions that are often violated in neuroimaging settings. We introduce a general permutation scheme that allows sequential designs to be used with arbitrary test statistics. By simulation, we show that this scheme controls the false positive rate across multiple interim analyses. Then, performing power analyses for seven evoked response effects seen in the EEG literature, we show that this sequential analysis approach can substantially outperform fixed-sample approaches (i.e. require fewer subjects, on average, to detect a true effect) when study designs are sufficiently well-powered. To facilitate the adoption of this methodology, we provide a Python package "niseq" with sequential implementations of common tests used for neuroimaging: cluster-based permutation tests, threshold-free cluster enhancement, t-max, F-max, and the network-based statistic with tutorial examples using EEG and fMRI data.

neuroscience↗