Biology subjects

Zoefel, B.

Publications and source records attributed to Zoefel, B..

14 recordsLinked to original sources

bioRxiv2026

Manipulating speech perception with amplitude-modulated kilohertz magnetic perturbation (AM-kTMP)

Speech perception has been hypothesized to exploit neural activity that entrains to the rhythmic properties of the utterance. Perceptual sensitivity varies with the phase of oscillatory activity induced by speech, and with an external oscillatory perturbation induced by transcranial alternating current stimulation (tACS) over the temporal lobe. Here we used a new form of non-invasive brain stimulation (NIBS), kilohertz transcranial magnetic perturbation (kTMP), in which a low frequency perturbation is created by the amplitude modulation (AM) of a continuous high-frequency carrier signal (3.5 kHz). As a magnetic induction method, kTMP can produce much higher electrical fields at the cortical surface than tACS and reduces cutaneous co-stimulation. Human participants (n=40) listened to sequences of rhythmic speech while receiving kTMP with an AM component of 3.125 Hz. The phasic modulation of perceptual sensitivity was greater during AM-kTMP than during sham stimulation, suggesting that AM-kTMP entrains neural activity underlying speech perception. Participants ratings of rhythmic sensations and other side effects did not differ between AM-kTMP and sham stimulation. Together with its reduced peripheral stimulation, our results highlight kTMP as a promising NIBS method for modulating frequency-specific brain dynamics in speech perception.

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bioRxiv2026

Neurofeedback enhances a neural signature of selective attention to speech in cocktail-party settings

Understanding speech in noisy situations is challenging and often fails due to attentional rather than sensory deficits. We report here that neurofeedback can enhance a neural signature of selective attention to speech in a cocktail-party setting. Neural responses to speech were quantified in participants electroencephalogram (EEG) while they attended to one of two audiobooks, presented simultaneously. After each 22s-segment of speech, the participants N1 component was extracted from the temporal response function (TRF). The N1 component is known to be sensitive to attention. During a [~]49-min training session, N1 amplitude values were displayed visually to participants so that they could learn to strengthen their neural responses to target speech and minimise their responses to distracting speech. During neurofeedback training, we found an enhanced N1 component in the response to target audiobooks that was specific to EEG channels used to provide feedback, and not present in a control group that received sham feedback. At right-lateralised fronto-central channels, enhanced N1 components correlated with improvements in a measure of speech comprehension (multiple-choice content questions). These results indicate that neural responses to speech can be regulated through neurofeedback and open up new possibilities to train attentional listening in populations struggling to understand speech in noise.

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bioRxiv2025

A phase-based mechanism of attentional selection in the auditory system

Perceptual targets are often easier to detect and process if they occur at a predictable time. This perceptual benefit of temporal predictability suggests that neural resources are allocated to specific moments predicted to be most informative, or away from those predicted to be distracting. The sensitivity to sensory information changes with the phase of neural oscillations. An alignment of oscillatory phase according to the predicted time and relevance of expected events has therefore been proposed as a mechanism underlying attentional selection. This hypothesis predicts that opposite phases are aligned to relevant and distracting events so that the former are amplified and the latter suppressed, but such an effect remained to be demonstrated. We presented 25 human participants with acoustic stimuli that occurred at a predictable or unpredictable time during a pitch-discrimination task. Temporal predictability did not only lead to faster reaction times, but it also aligned the phase of beta oscillations in the electroencephalogram (EEG) in anticipation of the stimulus. Crucially, the aligned phase was opposite, depending on whether the stimulus was relevant or a distractor for the task. Single-trial deviations from the mean aligned phases slowed down behavioural responses, demonstrating functional significance of the observed neural effects. All effects occurred in the absence of rhythmic stimulation, an important but rarely tested criterion to rule out spurious phase alignment from preceding events in a stimulus sequence. We therefore conclude that the alignment of oscillatory phase underlies the selection of sensory information in time. We speculate that beta oscillations allocate neural resources in networks comprising auditory and sensorimotor regions to the expected time of auditory information, facilitating behavioural responses to upcoming events.

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bioRxiv2024

The inattentional rhythm in audition

The detection of temporally unpredictable visual targets depends on the preceding phase of alpha oscillations (~7-12 Hz). In audition, however, such an effect seemed to be absent. Due to the transient nature of its input, the auditory system might be particularly vulnerable to information loss that occurs if relevant information coincides with the low excitability phase of the oscillation. We therefore hypothesised that effects of oscillatory phase in audition will be restored if auditory events are made task-irrelevant and information loss can be tolerated. To this end, we collected electroencephalography (EEG) data from 29 human participants (21F) while they detected pure tones at one sound frequency and ignored others. Confirming our hypothesis, we found that the neural response to task-irrelevant but not to task-relevant tones depends on the pre-stimulus phase of neural oscillations. Alpha oscillations modulated early stages of stimulus processing, whereas theta oscillations (~3-7 Hz) affected later components, possibly related to distractor inhibition. We also found evidence that alpha oscillations alternate between sound frequencies during divided attention. Together, our results suggest that the efficacy of auditory oscillations depends on the context they operate in, and demonstrate how they can be employed in a system that heavily relies on information unfolding over time. Significance StatementThe phase of neural oscillations shapes visual processing, but such an effect seemed absent in the auditory system when confronted with temporally unpredictable events. We here provide evidence that oscillatory mechanisms in audition critically depend on the degree of possible information loss during the oscillations low excitability phase, possibly reflecting a mechanism to cope with the rapid sensory dynamics that audition is normally exposed to. We reach this conclusion by demonstrating that the processing of task-irrelevant but not task-relevant tones depends on the pre-stimulus phase of neural oscillations during selective attention. During divided attention, cycles of alpha oscillations seemed to alternate between possible acoustic targets similar to what was observed in vision, suggesting an attentional process that generalises across modalities.

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bioRxiv2024

Entrainment Echoes in the Cerebellum

Historically, researchers have considered the cerebellum a coordinator of motor programs that ensures precise timing of movements and their adaptation to external events1. However, it has become increasingly clear that this role is not restricted to the motor system2. Rather, the cerebellum seems to play an important role in temporal prediction in general, as shown in its involvement in multiple functions that rely on precise event timing3. Although previous work suggested that the cerebellum exclusively predicts the interval between two events4, rather than tracking a global rhythm, it is also active when a rhythmic stimulus changes in rate5. The latter finding is in line with a cerebellar role in speech processing6 that entails frequent rate changes7. Neural mechanisms underlying the cerebellums involvement in speech processing, however, remain poorly understood. Moreover, there is a lack of studies contrasting speech and non-speech stimuli to establish speech-specificity of the observed effects8. In a re-analysis of magnetoencephalography (MEG) data9, we found that activity in the cerebellum aligned to rhythmic sequences of noise-vocoded speech, irrespective of its intelligibility. We then tested whether these "entrained" responses persist, and how they interact with other brain regions, when the rhythmic stimulus stopped and temporal predictions had to be updated. We found that only intelligible speech produced rhythmic responses in the cerebellum that outlasted the stimulus. During this "entrainment echo", but not during rhythmic speech itself, cerebellar activity was coupled with that in the left inferior frontal gyrus (IFG), and specifically at rates corresponding to the preceding stimulus rhythm. This finding represents unprecedented evidence for specific cerebellum-driven temporal predictions in speech processing and their relay to cortical regions.

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bioRxiv2023

Neural entrainment to both target and distracting speech causally contributes to speech perception in a multi-speaker scenario

Segregating important stimuli from distractors is crucial for successful speech perception. Neural activity synchronized to speech, also termed "neural speech tracking", is thought to be instrumental for this purpose. However, the relative contribution of neural tracking of targets and distractors for speech perception in a setting with multiple competing speakers remained unclear. In 61 human participants, we used transcranial alternating current stimulation (tACS) to manipulate neural tracking of two simultaneously presented sequences of rhythmic speech while participants attended to one of them. A random temporal relationship between speech streams allowed us to disentangle effects of tACS on target and distractor processing, and to examine their combined effect on a behavioural measure of speech perception. We found that the phase relation between tACS and both target and distracting speech modulated word report accuracy to a similar degree. This effect was observed during bilateral tACS over auditory regions, the inferior frontal gyrus (IFG) and, importantly, in a control group that received near-identical cutaneous stimulation but [~]50% reduced brain stimulation. These results imply that, although neural tracking of both target- and distracting speech causally modulates speech perception, the cutaneous stimulation that goes along with tACS can cause phase effects in speech perception that resemble those for conventional tACS. Our finding illustrates the urgent need to control for cutaneous stimulation in tACS studies. Significance StatementNeural activity synchronised to speech ("neural speech tracking") plays an important role in speech perception, yet its exact role in multi-speaker scenarios remains underexplored. We here use tACS to manipulate neural tracking in such scenarios. We find that neural tracking of both target and distracting speech causally modulates speech perception, irrespective of whether tACS is applied to target auditory cortex, inferior frontal gyrus, or in a control condition designed to produce similar cutaneous stimulation, but [~]50% reduced direct brain stimulation. Although our results demonstrate a causal role of neural tracking for speech perception in multi-speaker scenarios, they also illustrate the urgent need to control for effects of cutaneous stimulation in future tACS work on speech perception and beyond.

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bioRxiv2023

Opposing neural processing modes alternate rhythmically during sustained auditory attention

During continuous tasks, humans show spontaneous fluctuations in performance, putatively caused by varying attentional resources allocated to process external information. If neural resources are used to process other, presumably "internal" information, sensory input can be missed and explain an apparent dichotomy of "internal" versus "external" attention. In the current study, we extracted presumed neural signatures of these attentional modes in human electroencephalography (EEG): neural entrainment and -oscillations ([~]10-Hz), linked to the processing and suppression of sensory information, respectively. We tested whether they exhibit structured fluctuations over time, while listeners attended to an ecologically relevant stimulus like speech and completed a task that required full and continuous attention. Results showed an antagonistic relation between neural entrainment to speech and spontaneous -oscillations in two distinct brain networks - one specialized in the processing of external information, the other reminiscent of the dorsal attention network. These opposing neural modes underwent slow, periodic fluctuations around [~]0.07 Hz and were related to the detection of auditory targets. Our study might have tapped into a general attentional mechanism that is conserved across species and has important implications for situations in which sustained attention to sensory information is critical. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/560684v3_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@43f7d9org.highwire.dtl.DTLVardef@44fd09org.highwire.dtl.DTLVardef@1407de9org.highwire.dtl.DTLVardef@10a7acc_HPS_FORMAT_FIGEXP M_FIG C_FIG

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bioRxiv2022

RHYTHMIC ENTRAINMENT ECHOES IN AUDITORY PERCEPTION

Rhythmic entrainment echoes - rhythmic brain responses that outlast rhythmic stimulation - can evidence endogenous neural oscillations entrained by the stimulus rhythm. We here tested for such echoes in auditory perception. Participants detected a pure tone target, presented at a variable delay after another pure tone that was rhythmically modulated in amplitude. In four experiments involving 154 participants, we tested (1) which stimulus rate produces the strongest entrainment echo and (2) - inspired by auditions tonotopical organisation and findings in non-human primates - whether these are organized according to sound frequency. We found strongest entrainment echoes after 6-Hz and 8-Hz stimulation, respectively. Best moments for target detection (in or in anti-phase with the preceding rhythm) depended on whether sound frequencies of entraining and target stimuli matched, in line with a tonotopical organisation. However, for the same experimental condition, best moments were not always consistent across experiments. We provide a speculative explanation for these differences that relies on the notion that neural entrainment and repetition-related adaptation might exercise competing, opposite influences on perception. Together, we find rhythmic echoes in auditory perception that seem more complex than those predicted from initial theories of neural entrainment.

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bioRxiv2022

Intelligibility improves the perception of speech rhythm

Auditory rhythms are ubiquitous in music, speech, and other everyday sounds. Yet, it is unclear how perceived rhythms arise from the repeating structure of sounds. For speech, it is unclear whether rhythm is solely derived from acoustic properties (e.g., rapid amplitude changes), or if it is also influenced by the linguistic units (syllables, words, etc.) that listeners extract from intelligible speech. Here, we present three experiments in which participants were asked to detect an irregularity in rhythmically spoken speech sequences. In each experiment, we reduce the number of possible stimulus properties that differ between intelligible and unintelligible speech sounds and show that these acoustically-matched intelligibility conditions nonetheless lead to differences in rhythm perception. In Experiment 1, we replicate a previous study showing that rhythm perception is improved for intelligible (16-channel vocoded) as compared to unintelligible (1-channel vocoded) speech - despite near-identical broadband amplitude modulations. In Experiment 2, we use spectrally-rotated 16-channel speech to show the effect of intelligibility cannot be explained by differences in spectral complexity. In Experiment 3, we compare rhythm perception for sine-wave speech signals when they are heard as non-speech (for naive listeners), and subsequent to training, when identical sounds are perceived as speech. In all cases, detection of rhythmic regularity is enhanced when participants perceive the stimulus as speech compared to when they do not. Together, these findings demonstrate that intelligibility enhances the perception of timing changes in speech, which is hence linked to processes that extract abstract linguistic units from sound.

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bioRxiv2020

Human hippocampal neurons track moments in a sequence of events.

An indispensable feature of episodic memory is our ability to temporally piece together different elements of an experience into a coherent memory. Hippocampal "time cells" - neurons that represent temporal information - may play a critical role in this process. While these cells have been repeatedly found in rodents, it is still unclear to what extent similar temporal selectivity exists in the human hippocampus. Here we show that temporal context modulates the firing activity of human hippocampal neurons during structured temporal experiences. We recorded neuronal activity in the human brain while patients learned predictable sequences of pictures. We report that human time cells fire at successive moments in this task. Furthermore, time cells also signaled inherently changing temporal contexts during empty 10-second gap periods between trials, while participants waited for the task to resume. Finally, population activity allowed for decoding temporal epoch identity, both during sequence learning and during the gap periods. These findings suggest that human hippocampal neurons could play an essential role in temporally organizing distinct moments of an experience in episodic memory. Significance StatementEpisodic memory refers to our ability to remember the "what, where, and when" of a past experience. Representing time is an important component of this form of memory. Here, we show that neurons in the human hippocampus represent temporal information. This temporal signature was observed both when participants were actively engaged in a memory task, as well as during 10s-long gaps when they were asked to wait before performing the task. Furthermore, the activity of the population of hippocampal cells allowed for decoding one temporal epoch from another. These results suggest a robust representation of time in the human hippocampus.

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bioRxiv2020

Sustained neural rhythms reveal endogenous oscillations supporting speech perception

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or "entrained") to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research - including neural entrainment and tACS - and reveal endogenous neural oscillations as a key underlying principle for speech perception.

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bioRxiv2019

Perception of rhythmic speech is modulated by focal bilateral tACS

Several recent studies have used transcranial alternating stimulation (tACS) to demonstrate a causal role of neural oscillatory activity in speech processing. In particular, it has been shown that the ability to understand speech in a multi-speaker scenario or background noise depends on the timing of speech presentation relative to simultaneously applied tACS. However, it is possible that tACS did not change actual speech perception but rather auditory stream segregation. In this study, we tested whether the phase relation between tACS and the rhythm of degraded words, presented in silence, modulates word report accuracy. We found strong evidence for a tACS-induced modulation of speech perception, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). These results were only obtained when data was analyzed using a statistical approach that was identified as optimal in a previous simulation study. The effect was driven by a phasic disruption of word report scores. Our results suggest a causal role of neural entrainment for speech perception and emphasize the importance of optimizing stimulation protocols and statistical approaches for brain stimulation research.

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bioRxiv2019

Theta-phase dependent neuronal coding during sequence learning in human single neurons.

The ability to maintain a sequence of items in short-term memory (STM) is a fundamental cognitive function. In the rodent hippocampus, the representation of sequentially organized spatial locations is reflected by the phase of action potentials relative to the theta oscillation (phase precession). We investigated whether the timing of neuronal activity relative to the theta brain oscillation also reflects sequence order in the medial temporal lobe of humans. We used a task in which human subjects learned sequences of pictures and recorded single neuron and local field potential activity with implanted electrodes. We report that spikes for three consecutive items in the sequence (the preferred stimulus for each cell, as well as the stimuli immediately preceding and following it) were phase-locked at distinct phases of the theta oscillation. Consistent with phase precession, spikes were fired at progressively earlier phases as the sequence advanced. These findings generalize previous findings in the rodent hippocampus to the human temporal lobe and suggest that encoding stimulus information at distinct oscillatory phases may play a role in maintaining their sequential order in STM.

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bioRxiv2019

How to test for oscillatory modulation of neural function and behaviour

Research on whether perception or other processes depend on the phase of neural oscillations is rapidly gaining popularity. However, it is unknown which methods are optimally suited to evaluate the hypothesized phase effect. Using a simulation approach, we here test the ability of different methods to detect such an effect on dichotomous (e.g., \"hit\" vs \"miss\") and continuous (e.g., scalp potentials) response variables. We manipulated parameters that characterise the phase effect or define the experimental approach to test for this effect. For each parameter combination and response variable, we identified an optimal method. We found that methods regressing single-trial responses on circular (sine and cosine) predictors perform best for all of the simulated parameters, regardless of the nature of the response variable (dichotomous or continuous). In sum, our study lays a foundation for optimized experimental designs and analyses in future studies investigating the role of phase for neural and behavioural responses. We provide MATLAB code for the statistical methods tested.

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