Biology subjects

Kosem, A.

Publications and source records attributed to Kosem, A..

9 recordsLinked to original sources

bioRxiv2026

A touch that lingers: synchronized patting strengthens neural tracking of auditory rhythm in newborns

Rhythmic auditory stimulation in early life rarely occurs in isolation. Caregivers naturally combine singing and speech with rhythmic touch, rocking, and visual cues. Newborns are sensitive to auditory rhythm from birth, yet little is known about how temporally aligned information across sensory modalities shapes the neural encoding of auditory rhythmic structure. Here, we tested whether rhythmic touch can alter how the newborn brain tracks an ongoing auditory signal beyond the period of tactile stimulation. We recorded high-density electroencephalography from full-term newborns (N = 40), 1-3 days after birth, while they were exposed to recorded French lullabies presented either alone or accompanied by gentle patting synchronized with the metrically strong beat. Patting was delivered intermittently, allowing us to compare neural responses to lullabies across conditions, notably during periods without concurrent tactile stimulation. We quantified neural tracking of the lullabies using brain-stimulus coherence and temporal response function modeling. Newborns' neural activity synchronized with the rhythmic structure of the lullabies at frequencies corresponding to both the beat and the metrically accented strong beat. Critically, neural tracking was stronger when the lullabies had been accompanied by synchronized touch than when they were presented alone, and this enhancement persisted during subsequent periods in which no touch was delivered. Although rhythmic touch enhanced tracking in newborns with both weaker and stronger auditory-only tracking, there was a larger gain in those who initially showed weaker auditory tracking. Together, our findings reveal that the newborn brain exploits rhythmic touch to strengthen its encoding of auditory rhythm, and that this benefit outlasts the touch itself. This provides neural evidence that patting an infant in time with a song, a caregiving practice shared across cultures, does more than simply provide a tactile stimulation. It shapes how the newborn brain encodes the song's rhythm.

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bioRxiv2026

Impaired temporal prediction mechanisms in dyslexia

Effective speech analysis involves deconstructing the acoustic signal into identifiable linguistic units, which depends on the ability to recognize and anticipate temporal patterns within the speech stream. However, these processes may be less efficient in individuals with dyslexia. This study investigated the effects of temporal context and related temporal predictions in dyslexic adult participants and matched control participants, using an auditory oddball task with non-verbal stimuli. Pure tones were presented in sequences, and participants were requested to discriminate the pitch of target stimuli. The temporal intervals between the sounds varied in regularity across the sequences, thereby creating contexts with different levels of temporal predictability. At the end of each sequence, participants were prompted to evaluate the perceived rhythmicity of the sequence and to assess their own performance in the auditory discrimination task. Dyslexic participants demonstrated overall lower accuracy in discriminating target sounds than controls. They also showed reduced influence of the temporal context of the sequences on response times, while controls responded faster in sequences that were temporally more regular and predictable. Additionally, individuals with dyslexia perceived the rhythmicity of sound sequences less accurately, overestimating the temporal regularity in irregular sequences and underestimating it in regular sequences. They also reported lower overall confidence in their ability to perform the task compared to control participants. Altogether, these findings provide converging evidence for altered temporal prediction abilities in dyslexia, which may impact auditory perception and then impair language processing.

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bioRxiv2023

What is a rhythm for the brain? The impact of contextual temporal variability on auditory perception

Temporal predictions can be formed and impact perception when sensory timing is fully predictable: for instance, the detection of a target sound is enhanced if it is presented on the beat of an isochronous rhythm. However, natural sensory stimuli, like speech or music, are not entirely predictable, but still possess statistical temporal regularities. We investigated whether temporal expectations can be formed in non-fully predictable contexts, and how the temporal variability of sensory contexts affects auditory perception. Specifically, we asked how "rhythmic" an auditory stimulation needs to be in order to observe temporal predictions effects on auditory discrimination performances. In this behavioral auditory oddball experiment, participants listened to auditory sound sequences where the temporal interval between each sound was drawn from gaussian distributions with distinct standard deviations. Participants were asked to discriminate sounds with a deviant pitch in the sequences. Auditory discrimination performances, as measured with deviant sound discrimination accuracy and response times, progressively declined as the temporal variability of the sound sequence increased. Temporal predictability effects ceased to be observed only for the more variable contexts. Moreover, both global and local temporal statistics impacted auditory perception, suggesting that temporal statistics are promptly integrated to optimize perception. Altogether, these results suggests that temporal predictions can be set up quickly based on the temporal statistics of past sensory events and are robust to a certain amount of temporal variability. Therefore, temporal predictions can be built on sensory stimulations that are not purely periodic nor temporally deterministic. Significance statementThe perception of sensory events is known to be enhanced when their timing is fully predictable. However, it is unclear whether temporal predictions are robust to temporal variability, which is naturally present in many auditory signals such as speech and music. In this behavioral experiment, participants listened to auditory sound sequences where the timing between each sound was drawn from distinct gaussian distributions. Participants ability to discriminate deviant sounds in the sequences was function of the temporal statistics of past events: auditory deviant discrimination progressively declined as the temporal variability of the sound sequence increased. Results therefore suggest that auditory perception is sensitive to prediction mechanisms that are involved even if temporal information is not totally predictable.

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bioRxiv2022

The Interaction of Context Constraints and Predictive Validity during Sentence Reading

Words are not processed in isolation, instead they are commonly embedded in phrases and sentences. The sentential context influences the perception and processing of a word. However, how this is achieved by brain processes and whether predictive mechanisms underlie this process remains a debated topic. To this end we employed an experimental paradigm in which we orthogonalized sentence context constraints and predictive validity, which was defined as the ratio of congruent to incongruent sentence endings within the experiment. While recording electroencephalography, participants read sentences with three levels of sentential context constraints (high, medium and low). Participants were also separated into two groups, which differed in their ratio of valid congruent to incongruent target words that could be predicted from the sentential context. For both groups we investigated modulations of alpha power before, and N400 amplitude modulations after target word onset. The results reveal that the N400 amplitude gradually decreases with higher context constraints. Contrary, alpha power is non-monotonically influenced, displaying the strongest decrease for high context constraints over frontal electrode sites, while alpha power between medium and low context constraints does not differ. This indicates that both neural correlates are influenced by the degree of context constraint but are not affected by changes in predictive validity. The results therefore suggest that both N400 and alpha power are not unequivocally linked to the predictability of a target word based on larger contextual information.

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bioRxiv2022

Neural tracking of speech does not unequivocally reflect intelligibility

During listening, brain activity tracks the rhythmic structures of speech signals. Here, we directly dissociated the contribution of neural tracking in the processing of speech acoustic cues from that related to linguistic processing. We examined the neural changes associated with the comprehension of Noise-Vocoded (NV) speech using magnetoencephalography (MEG). Participants listened to NV sentences in a 3-phase training paradigm: (1) pre-training, where NV stimuli were barely comprehended, (2) training with exposure of the original clear version of speech stimulus, and (3) post-training, where the same stimuli gained intelligibility from the training phase. Using this paradigm, we tested if the neural responses of a speech signal was modulated by its intelligibility without any change in its acoustic structure. To test the influence of spectral degradation on neural tracking independently of training, participants listened to two types of NV sentences (4-band and 2-band NV speech), but were only trained to understand 4-band NV speech. Significant changes in neural tracking were observed in the delta range in relation to the acoustic degradation of speech. However, we failed to find a direct effect of intelligibility on the neural tracking of speech in both theta and delta ranges. This suggests that acoustics greatly influence the neural tracking response to speech signals, and that caution needs to be taken when choosing the control signals for speech-brain tracking analyses, considering that a slight change in acoustic parameters can have strong effects on the neural tracking response.

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bioRxiv2019

Biasing the perception of spoken words with tACS

Recent neuroimaging evidence suggests that the frequency of entrained oscillations in auditory cortices influences the perceived duration of speech segments, impacting word perception (Kosem et al. 2018). We further tested the causal influence of neural entrainment frequency during speech processing, by manipulating entrainment with continuous transcranial alternating current stimulation (tACS) at distinct oscillatory frequencies (3 Hz and 5.5 Hz) above the auditory cortices. Dutch participants listened to speech and were asked to report their percept of a target Dutch word, which contained a vowel with an ambiguous duration. Target words were presented either in isolation (first experiment) or at the end of spoken sentences (second experiment). We predicted that the frequency of the tACS current would influence neural entrainment and therewith how speech is perceptually sampled, leading to a perceptual over- or underestimation of the vowel duration. Experiment 1 revealed no significant result. In contrast, results from experiment 2 showed a significant effect of tACS frequency on target word perception. Faster tACS lead to more long-vowel word percepts, in line with previous findings suggesting that neural oscillations are instrumental in the temporal processing of speech. The different results from the two experiments suggest that the impact of tACS is dependent on the sensory context. tACS may have a stronger effect on spoken word perception when the words are presented in a continuous stream of speech as compared to when they are isolated, potentially because prior (stimulus-induced) entrainment of brain oscillations might be a prerequisite for tACS to be effective.

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bioRxiv2019

Dual-site high-density 4Hz transcranial alternating current stimulation applied over auditory and motor cortical speech areas does not influence auditory-motor mapping

BackgroundVerbal repetition of auditory speech requires the mapping of a sensory acoustic input onto articulatory motor plans (auditory-motor mapping). Recent evidence indicates that auditory-motor mapping could rely on low frequency neural synchronization (i.e., theta oscillatory phase coupling) between sensory and motor speech areas.\n\nObjectiveIn the present study, we apply dual-site high-density (HD) Transcranial Alternating Current Stimulation (TACS) above the auditory and motor cortex to induce, or disrupt, theta phase coupling between the two areas. We predicted that functionally coupling the two areas would strengthen auditory-motor mapping, compared with functionally decoupling them. We assessed the strength of auditory-motor mapping using a verbal repetition task.\n\nResultsWe found no significant effect of TACS-induced theta phase coupling on auditory-motor mapping as indexed by verbal repetition performance.\n\nConclusionAuditory-motor mapping may rely on a different mechanism than we hypothesized, for example, oscillatory phase-coupling outside the theta range. Alternatively, modulation of interregional theta-phase coupling may require more effective stimulation protocols, for example, TACS at higher intensities.

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bioRxiv2018

Distracting linguistic information impairs neural entrainment to attended speech

Listening to speech is difficult in noisy environments, and is even harder when the interfering noise consists of intelligible speech as compared to unintelligible sounds. This suggests that the competing linguistic information interferes with the neural processing of target speech. Interference could either arise from a degradation of the neural representation of the target speech, or from increased representation of distracting speech that enters in competition with the target speech. We tested these alternative hypotheses using magnetoencephalography (MEG) while participants listened to a target clear speech in the presence of distracting noise-vocoded speech. Crucially, the distractors were initially unintelligible but became more intelligible after a short training session. Results showed that the comprehension of the target speech was poorer after training than before training. The neural tracking of target speech in the delta range (1-4 Hz) reduced in strength in the presence of a more intelligible distractor. In contrast, the neural tracking of distracting signals was not significantly modulated by intelligibility. These results suggest that the presence of distracting speech signals degrades the linguistic representation of target speech carried by delta oscillations.

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bioRxiv2017

Neural entrainment determines the words we hear

Low-frequency neural entrainment to rhythmic input has been hypothesized as a canonical mechanism that shapes sensory perception in time. Neural entrainment is deemed particularly relevant for speech analysis, as it would contribute to the extraction of discrete linguistic elements from continuous acoustic signals. Yet, its causal influence in speech perception has been difficult to establish. Here, we provide evidence that oscillations build temporal predictions about the duration of speech tokens that directly influence perception. Using magnetoencephalography (MEG), we studied neural dynamics during listening to sentences that changed in speech rate. We observed neural entrainment to preceding speech rhythms persisting for several cycles after the change in rate. The sustained entrainment was associated with changes in the perceived duration of the last words vowel, resulting in the perception of words with radically different meanings. These findings support oscillatory models of speech processing, suggesting that neural oscillations actively shape speech perception.

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