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Zion Golumbic, E.

Publications and source records attributed to Zion Golumbic, E..

At least 19 recordsLinked to original sources

Speech Tracking in fMRI Reveals a Distinct Response to Sentence Boundaries During Comprehension

Psycholinguistic research and linguistic theory suggest that comprehending continuous speech involves segmenting it into sentences. Yet, direct neuroimaging evidence for this process remains scarce, partly because sentence boundaries coincide with acoustic, prosodic, lexical, and syntactic changes. Here, we used whole-brain fMRI to test whether sentence boundaries elicit a neural response beyond these accompanying speech properties during spontaneous speech comprehension. We modelled BOLD responses to sentence-final words alongside continuous regressors characterizing accompanying speech properties. This approach revealed sensitivity to continuously varying features of speech across multiple brain regions. Notably, the acoustic envelope predicted BOLD responses in bilateral primary auditory cortices. Responses associated with prosodic breaks and emphasis were found in right temporal cortex, syntactic bottom-up node count in the left superior temporal sulcus, and word concreteness in the parahippocampal gyri. Critically, sentence-final words were associated with an increased activation in right temporal regions, after accounting for acoustic, prosodic, lexical, semantic and syntactic properties. These findings provide evidence for a neural response to sentence boundaries consistent with active sentence segmentation. More generally, this study demonstrates the value of continuous-regressor modelling for investigating speech comprehension with fMRI.

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Bouncing back: Transient, but not long-lasting, effects of background disturbances on speech processing

Processing and understanding speech in face of occasional background disturbances can be difficult and often leads to distraction and reduced comprehension. However, despite the vast literature on the detrimental effects of processing speech-in-noise, little is known about the time-course of these effects. Here we studied whether reduced speech processing is limited only to the period when disruptions mask target speech, or if processing difficulties linger even after disruptions end, suggesting longer lasting distraction. Using an ecologically-relevant experimental design, we measured neural activity and skin-conductance from participants as they watched an educational video-lecture. Short background speech comments, mimicking plausible classroom disruptions, were occasional embedded in half of the lecture segments. Speech disruptions elicited robust neurophysiological orienting responses, reflected in a neural auditory ERP and a phasic increase in skin conductance. Importantly, when disruptions were presented, we observed a marked reduction in neural tracking of the lecture, increased inter-subject correlation (ISC), and decreased alpha power, suggesting a brief diversion of processing resources away from the target speech. However, these effects were transient in nature, with all neural measures returning to baseline immediately after disruption offset, showing no evidence for prolonged disruption-related costs or impaired comprehension. Interestingly, neurophysiological responses to disruption and return to baseline were not correlated with self-reported symptoms of attention-deficits (ADD). These findings highlight the resilience of auditory attention, demonstrating its ability to maintain a robust representations of target speech over time, despite of transient ecological disturbances.

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Testing the Cross-Paradigm Convergence of Behavioral and Neural Measures of Attention

Attention abilities, that are critical for most real-life cognitive task, can vary greatly across individuals. A plethora of behavioral and neural metric are commonly utilized to quantify attention; however, these often yield inconsistent and non-replicable results, raising questions as to which measures reliably account for and capture individual differences. To address this tension, here we employed a within-subject cross-paradigm design and quantified both behavioral and EEG-based neural measures associated with attention functioning, to test which measures converged across a gradient of artificial and ecological tasks. We found Inter-Subject Correlation (ISC), which quantifies the similarity in the pattern of neural response across individuals, captured consistent individual differences across both an artificial (Auditory Oddball) and ecological (Attention to Speech) task, with some correlation with performance. Moreover, we found that P300 neural responses to surprising events were qualitatively similar across artificial and ecological tasks, supporting their generalization across contexts. Interestingly, traditional cognitive-behavioral measures of attention - both from speeded response-time tasks and self-report of ADHD symptoms (ASRS) were not correlated with each other nor did they explain variance in neural metrics, nor were they explained by variation in general cognitive abilities (working memory or fluid intelligence). While these results demonstrate the shortcomings of many established measures of attention to generalize across contexts, they also point to the potential of neural measures, and specifically ISC, to serve as reliable indicators of individual differences and to bridge the gap between artificial and ecological studies of attention functioning.

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Toward precision EEG: Assessing the reliability of individual-level ERPs across EEG Systems

Event-related potentials (ERPs) are among the most established tools for studying the neural mechanisms of perception and cognition. Advancing toward precision EEG, however, places new demands for a better understanding of how reliable neural markers are at the individual subject level. We conducted two complementary experiments to examine the reliability of N100 and P300 components in an auditory oddball paradigm with three sounds (Standard, Target, and Novel). In Experiment 1, we evaluated the consistency at both the group level and the individual level across four EEG systems: one research-grade wired system (BioSemi) and three mobile devices--Smarting, DSI-24, and EPOC X. At the group level, all systems demonstrated the canonical N100 and P300 components; however, the EPOC X system showed a significantly reduced signal-to-noise ratio compared to the others. At the individual level, temporal and spatial clustering analyses showed that N100 and P300 components were detectable in most individuals (70-85%), with additional significant responses appearing outside this range. We further calculated the similarity of individual responses across participants ("typicality index"), which revealed highly consistent responses to Standard and Novel sounds, alongside divergent patterns of responses to Targets. In Experiment 2, we assessed the within-participant reliability of N100 and P300 using a test-retest design. Results indicated high within-participant consistency of response patterns for all three stimuli, demonstrating that individual ERPs remain reliably stable over time, even when they deviate from canonical group-level patterns. The current study contributes to the ongoing discussion regarding the utility and reliability of ERP-based metrics for precision imaging and highlights important methodological considerations for their practical implementation.

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Neurophysiological Patterns of Attention and Distraction during Realistic Virtual-Reality Classroom Learning in Adults with and without ADHD

Many people, and particularly individuals with Attention Deficit (Hyperactivity) Disorder (AD(H)D), find it difficult to maintain attention during classroom learning. However, traditional paradigms used to evaluate attention do not capture the complexity and dynamic nature of real-life classrooms. Using a novel Virtual Reality platform, coupled with measurement of neural activity, eye-gaze and skin conductance, here we studied the neurophysiological manifestations of attention and distractibility, under realistic learning conditions. Individuals with AD(H)D exhibited higher neural responses to irrelevant sounds and reduced speech tracking of the teacher, relative to controls. Additional neurophysiological measures, such the power of alpha-oscillations and frequency of gaze-shifts away from the teacher, contributed to explaining variance in self-reported AD(H)D symptoms across the sample. These ecologically-valid findings provide critical insight into the neurophysiological mechanisms underlying individual differences in the capacity for sustained attention and the proneness to distraction and mind-wandering, experienced in real-life situations.

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An ecological investigation of the effect of background noise on speech processing in a Virtual Classroom

Many real-life situations can be extremely noisy. Psychoacoustic studies have shown that background noise can have a detrimental effect on the ability to process and understand speech. However, most studies use stimuli and task designs that are highly artificial, limiting their generalization to more realistic contexts. Moreover, to date, we do not fully understand the neurophysiological consequences of trying to pay attention to speech in a noisy place. To address this lab to real-life gap and increase the ecological validity of speech in noise research, here we introduce a novel audiovisual Virtual Reality (VR) experimental platform. Combined with neurophysiological measurements of neural activity (EEG), eye-gaze and skin conductance (GSR) we studied the effects of background noise in a realistic context where the ability to process and understand continuous speech is especially important: A VR Classroom. Participants (n=32) sat in a VR Classroom and were told to pay attention to mini-lecture segments by a virtual teacher. Trials were either Quiet or contained background construction noise, emitted from outside the classroom window, which was either Continuous (drilling) or Intermittent (air hammers). Result show that background noise had a detrimental effect on learning outcomes, which was also accompanied by reduced neural tracking of the teachers speech. Comparison of the two noise types showed that the intermittent construction noise was more disruptive than continuous noise, as index by both behavioral and neural measures, and it also elicited higher skin-conductance levels, reflecting heightened arousal. Interesting, eye-gaze dynamics were not affected by the presence of noise. This study advances our understanding of the neurophysiological effects of background noise and extends it to more ecologically relevant contexts. It also emphasizes the role that temporal dynamics play for processing speech in noise, highlighting the need to consider the features of realistic noises, as we expand speech in noise research to increasingly realistic circumstances.

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Neural Speech-Tracking During Selective Attention and Attention-Switching Between Concurrent Talkers: A spatially realistic audiovisual study

Paying attention to a target talker in multi-talker scenarios is associated with its more accurate neural-tracking relative to competing non-target speech. This "neural-bias" to target speech has largely been demonstrated in experimental setups where target and non-target speech are acoustically controlled and interchangeable. However, in real-life situations this is rarely the case. For example, listeners often look at the talker they are paying attention to while non-target speech is heard (but not seen) from peripheral locations. To enhance the ecological-relevance of attention research, here we studied whether neural-bias towards target speech is observed in a spatially realistic audiovisual context, and how this is affected by switching the identity of the target talker. Group-level results show robust neural-bias towards target speech, an effect that persisted and generalized after switching the identity of the target talker. In line with previous studies, this supports the utility of the speech-tracking approach for studying speech processing and attention in spatially realistic settings. However, a more nuanced picture emerges when inspecting data of individual participants. Although reliable neural speech-tracking could be established in most participants, this was not correlated with neural-bias or with behavioral performance, and >50% of participant showed similarly robust neural tracking of both target and non-target speech. These results indicate that neural-bias toward the target is not a ubiquitous, or necessary, marker of selective attention (at least as measured from scalp-EEG), and suggest that individuals diverge in their internal prioritization among concurrent speech, perhaps reflecting different listening strategies or capabilities under realistic conditions. Significance StatementThis work contributes to ongoing efforts to study the neural mechanisms involved in selective attention to speech under ecologically relevant conditions, emulating the type of speech materials, multisensory experience, and spatial realism of natural environments. Group-level results show that under these more realistic conditions, the hallmark signature of selective attention - namely the modulation of sensory representation, and its robustness to switches in target-identity - is conserved, at least at the group level. At the same time, results point to an underlying diversity among participants in how that this modulation manifests, raising the possibility that differences in listening strategies, motivation or personal traits lead to differences in the way that individuals encode and process competing stimuli, under ecological conditions.

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"Um... it's really difficult to... um.. speak fluently": Neural tracking of spontaneous speech

Spontaneous real-life speech is imperfect in many ways. It contains disfluencies and ill-formed utterances and has a highly variable rate. When listening to spontaneous speech, the brain needs to contend with these features in order to extract the speakers meaning. Here, we studied how the neural response is affected by four specific factors that are prevalent in spontaneous colloquial speech: (1) the presence of non-lexical fillers, (2) the need to detect syntactic boundaries in disfluent speech, and (3) variability in speech rate. Neural activity (EEG) was recorded from individuals as they listened to an unscripted, spontaneous narrative, which was analyzed in a time-resolved fashion to identify fillers and detect syntactic boundaries. When considering these factors in a speech-tracking analysis, which estimates a temporal response function (TRF) to describe the relationship between the stimulus and the neural response it generates, we found that the TRF was affected by both of them. This response was observed for lexical words but not for fillers, and it had an earlier onset for opening words vs. closing words of a clause and for clauses with slower speech rates. These findings broaden ongoing efforts to understand neural processing of speech under increasingly realistic conditions. They highlight the importance of considering the imperfect nature of real-life spoken language, linking past research on linguistically well-formed and meticulously controlled speech to the type of speech that the brain actually deals with on a daily basis.

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Covert detection of own-name and semantic violations in task-irrelevant speech, in a realistic Virtual Cafe

Detecting that someone has said your name is one of the most famous examples for incidental processing of supposedly-unattended speech. However, empirical investigation of this so-called "cocktail party effect" has yielded conflicting results. We present a novel empirical approach for revisiting this effect under highly ecological conditions, by immersing participants in a multisensory virtual cafe environment and using realistic stimuli and tasks. Participants listened to conversational speech from a character sitting across from them, while a barista in the back of the cafe called out food orders. Unbeknownst to them, the barista sometimes called orders containing their own name or semantic violations. We used combined measurements of brain activity (EEG), eye-gaze and galvanic skin response to assess the response-profile to these two probes in the task-irrelevant barista-stream. Both probes elicited unique neural and physiological responses relative to control stimuli, indicating that the system indeed processed these words and detected their unique status, despite being task-irrelevant. Interestingly, these responses were covert in nature and were not accompanied by gaze-shifts towards the barista character. This pattern demonstrates that under these highly ecological conditions, listeners incidentally pick up information from task-irrelevant speech, emphasizing the dynamic and non-binary nature of attention in real-life environments.

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Capacity and tradeoffs in neural encoding of concurrent speech during Selective and Distributed Attention

Speech comprehension is severely compromised when several people talk at once, due to limited perceptual and cognitive resources. Under some circumstances listeners can employ top-down attention to prioritize the processing of task-relevant speech. However, whether the system can effectively represent more than one speech input remains highly debated. Here we studied how task-relevance affects the neural representation of concurrent speakers under two extreme conditions: when only one speaker was task-relevant (Selective Attention), vs. when two speakers were equally relevant (Distributed Attention). Neural activity was measured using magnetoencephalography (MEG) and we analysed the speech-tracking responses to both speakers. Crucially, we explored different hypotheses as to how the brain may have represented the two speech streams, without making a-priori assumptions regarding participants internal allocation of attention. Results indicate that neural tracking of concurrent speech did not fully mirror their instructed task-relevance. When Distributed Attention was required, we observed a tradeoff between the two speakers despite their equal task-relevance, akin to the top-down modulation observed during Selective Attention. This points to the systems inherent limitation to fully process two speech streams, and highlights the complex nature of attention, particularly for continuous speech.

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Memory-paced tapping to auditory rhythms: Effects of rate, speech and motor-engagement

Humans have a near-automatic tendency to entrain their motor actions to rhythms in the environment. Entrainment is hypothesized to play an important role in processing naturalistic stimuli, such as speech and music, which have intrinsically rhythmic properties. Here we studied two facets of entraining ones rhythmic motor actions to an external stimulus: (1) synchronized finger tapping to auditory rhythmic stimuli, and (2) memory-paced reproduction of a previously heard rhythm. Using modifications of the Synchronization-Continuation tapping paradigm, we studied how these two rhythmic behaviours were affected by different stimulus and task features. We tested synchronization and memory-paced tapping for a broad range of rates, from sub-second to supra-second, both for isochronous tone-sequences and for rhythmic speech stimuli (counting from one to ten), which are more ecological yet less strictly isochronous. We also asked what role motor engagement plays in forming a stable internal representation for rhythms and guiding memory-paced tapping. Results show that individuals can flexibly synchronize their motor actions to a very broad range of rhythms. However, this flexibility does not extend to memory-paced tapping, which is accurate only in a narrower range of rates, around ~1.5Hz. This pattern suggests that intrinsic rhythmic-defaults in the auditory/motor systems influence the internal representation of rhythms, in the absence of an external pace-maker. Interestingly, memory-paced tapping for speech rhythms and simple tones shared similar optimal rates, although with reduced accuracy, suggesting that internal constraints on rhythmic entrainment may generalize to more ecological stimuli. Last, active synchronization led to more accurate memory-paced tapping vs. passive listening, which emphasizes the importance of action-perception interactions in forming stable entrainment to external rhythms.

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Assessing the sensitivity of EEG-based frequency-tagging as a metric for statistical learning

AO_SCPLOWBSTRACTC_SCPLOWStatistical Learning (SL) is hypothesized to play an important role in language development. However, the behavioral measures typically used to assess SL, particularly at the level of individual participants, are largely indirect and often have low sensitivity. Recently, a neural metric based on frequency-tagging has been proposed as an alternative and more direct measure for studying SL. Here we tested the sensitivity of frequency-tagging measures for studying SL in individual participants in an artificial language paradigm, using non-invasive EEG recordings of neural activity in humans. Importantly, we use carefully constructed controls, in order to address potential acoustic confounds of the frequency-tagging approach. We compared the sensitivity of EEG-based metrics to both explicit and implicit behavioral tests of SL, and the correspondence between these presumed converging operations. Group-level results confirm that frequency-tagging can provide a robust indication of SL for an artificial language, above and beyond potential acoustic confounds. However, this metric had very low sensitivity at the level of individual participants, with significant effects found only in 30% of participants. Conversely, the implicit behavior measures indicated that SL has occurred in 70% of participants, which is more consistent with the proposed ubiquitous nature of SL. Moreover, there was low correspondence between the different measures used to assess SL. Taken together, while some researchers may find the frequency-tagging approach suitable for their needs, our results highlight the methodological challenges of assessing SL at the individual level, and the potential confounds that should be taken into account when interpreting frequency-tagged EEG data.

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Linguistic processing of task-irrelevant speech at a Cocktail Party

Paying attention to one speaker in noisy environments can be extremely difficult, because to-be-attended and task-irrelevant speech compete for processing resources. We tested whether this competition is restricted to acoustic-phonetic interference or if it extends to competition for linguistic processing as well. Neural activity was recorded using Magnetoencephalography as human participants were instructed to attended to natural speech presented to one ear, and task-irrelevant stimuli were presented to the other. Task-irrelevant stimuli consisted either of random sequences of syllables, or syllables structured to form coherent sentences, using hierarchical frequency-tagging. We find that the phrasal structure of structured task-irrelevant stimuli was represented in the neural response in left inferior frontal and posterior parietal regions, indicating that selective attention does not fully eliminate linguistic processing of task-irrelevant speech. Additionally, neural tracking of to-be-attended speech in left inferior frontal regions was enhanced when competing with structured task-irrelevant stimuli, suggesting inherent competition between them for linguistic processing. Impact StatementSyntactic structure-building processes can be applied to speech that is task-irrelevant and should be ignored, demonstrating that Selective Attention does not fully eliminate linguistic processing of competing speech.

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Motor-evoked neural responses in auditory cortex are associated with improved sensitivity to self-generated sounds

Sensory perception is a product of complex interactions between the internal state of an organism and the physical attributes of a stimulus. One factor that modulates the internal state of the perceiving agent is voluntary movement. It has been shown across the animal kingdom that perception and sensory-evoked physiological responses are modulated depending on whether or not the stimulus is the consequence of voluntary actions. These phenomena are often attributed to motor signals sent to relevant sensory regions (efference copies), that convey information about expected upcoming sensory consequences. However, to date, there is no direct evidence in humans for efferent signals underlying these motor-sensory interactions. In the current study we recorded neurophysiological (using Magnetoencephalography) and behavioral responses from 16 healthy subjects performing an auditory detection task of faint tones. Tones were either generated by subjects voluntary button presses or occurred predictably following a visual cue. By introducing a constant temporal delay between button press/cue and tone delivery and applying source-level analysis we decoupled motor-evoked and auditory-evoked activity in auditory cortex. We show motor-related evoked-responses in auditory cortex following sound-triggering actions and preceding sound onset. Such evoked-responses were not found for button-presses that were not coupled with expected sounds. Furthermore, the amplitude of these evoked-responses corresponded with subsequent sound detection, suggesting their functional relevance to auditory processing. Our results provide first direct evidence for efferent signals in sensory cortex that are evoked by voluntary actions coupled with sensory consequences.

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Irrelevant Predictions: Distractor Rhythmicity Modulates Neural Encoding in Auditory Cortex

Dynamic Attending Theory suggests that predicting the timing of upcoming sounds can assist in focusing attention towards them. However, whether similar predictive processes are also applied to background noises and assist in guiding attention away from potential distractors, remains an open question. Here we address this question by manipulating the temporal predictability of distractor sounds in a dichotic listening selective attention task. We tested the influence of distractors temporal predictability on performance and on the neural encoding of sounds, by comparing the effects of Rhythmic vs. Non-rhythmic distractors. Using Magnetoencephalography (MEG) we found that, indeed, the neural responses to both attended and distractor sounds were affected by distractors rhythmicity. Baseline activity preceding the onset of Rhythmic distractor sounds was enhanced relative to Non-rhythmic distractor sounds, and sensory response were suppressed. Moreover, when distractors were Rhythmic, responses to attended sounds were more strongly lateralized to the contra-lateral hemisphere. Behavioral performance also improved in the Rhythmic condition. These combined behavioral and neural results suggest that not only are temporal predictions formed for task-irrelevant sounds, but that these predictions bear functional significance for promoting selective attention and reducing distractibility.

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The Role of Spatial Separation on Selective and Distributed Attention to Speech

AO_SCPLOWBSTRACTC_SCPLOWProcessing speech in multi-speaker environments poses substantial challenges to the human perceptual and attention system. Moreover, different contexts may require employing different listening strategies. For instance, in some cases individuals pay attention Selectively to one speaker and attempt to ignore all other task-irrelevant sounds, whereas other contexts may require listeners to Distribute their attention among several speakers. Spatial and spectral acoustic cues both play an important role in assisting listeners to segregate concurrent speakers. However, how these cues interact with varying demands for allocating top-down attention is less clear. In the current study, we test and compare how spatial cues are utilized to benefit performance on these different types of attentional tasks. To this end, participants listened to a concoction of two or four speakers, presented either as emanating from different locations in space or with no spatial separation. In separate trials, participants were required to employ different listening strategies, and detect a target-word spoken either by one pre-defined speaker (Selective Attention) or spoken by any of the speakers (Distributed Attention). Results indicate that the presence of spatial cues improved performance, particularly in the two-speaker condition, which is in line with the important role of spatial cues in stream segregation. However, spatial cues provided similar benefits to performance under Selective and Distributed attention. This pattern suggests that despite the advantage of spatial cues for stream segregation, they were nonetheless insufficient for directing a more focused attentional spotlight towards the location of a designated speaker in the Selective attention condition.

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The Preferred Period Hypothesis Revisited: Rhythmic Preferences and Motor Tapping Precision in ADHD Adults and Controls

Many aspects of human behavior are inherently rhythmic, requiring production of rhythmic motor actions as well as synchronizing to rhythms in the environment. It is well-established that individuals with ADHD exhibit deficits in temporal estimation and timing functions, which may impact their ability to accurately produce and interact with rhythmic stimuli. In the current study we seek to understand the specific aspects of rhythmic behavior that are implicated in ADHD. We specifically ask whether they are attributed to imprecision in the internal generation of rhythms or to reduced acuity in rhythm perception. We also test key predictions of the Preferred Period Hypothesis, which suggests that both perceptual and motor rhythmic behaviors are biased towards a specific personal default tempo. To this end, we tested several aspects of rhythmic behavior and the correspondence between them, including spontaneous motor tempo (SMT), preferred auditory perceptual tempo (PPT) and synchronization-continuations tapping in a broad range of rhythms, from sub-second to supra-second intervals. Moreover, we evaluate the intra-subject consistency of rhythmic preferences, as a means for testing the reality and reliability of personal default-rhythms. We used a modified operational definition for assessing SMT and PPT, instructing participants to tap or calibrate the rhythms most comfortable for them to count along with, to avoid subjective interpretations of the task. Our results shed new light on the specific aspect of rhythmic deficits implicated in ADHD adults. We find that individuals with ADHD are primarily challenged in producing and maintaining isochronous self-generated motor rhythms, during both spontaneous and memory-paced tapping. However, they nonetheless exhibit good flexibility for synchronizing to a broad range of external rhythms, suggesting that auditory-motor entrainment for simple rhythms is preserved in ADHD, and that the presence of an external pacer allows overcoming their inherent difficulty in self-generating isochronous motor rhythms. In addition, both groups showed optimal memory-paced tapping for rhythms near their counting-based SMT and PPT, which were slightly faster in the ADHD group. This is in line with the predictions of the Preferred Period Hypothesis, indicating that at least for this well-defined rhythmic behavior (i.e., counting), individuals tend to prefer similar time-scales in both motor production and perceptual evaluation.

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Paying Attention to Speech: The Role of Cognitive Capacity and Acquired Experience

Managing attention in multi-speaker environments is a challenging feat that is critical for human performance. However, why some people are better than others in allocating attention appropriately, remains highly unknown. Here we investigated the contribution of two factors - Cognitive Capacity and Acquired Experience - to performance on two different types of Attention task: Selective Attention to one speaker and Distributed Attention among multiple concurrent speakers. We compared performance across three groups: Individuals with low (n=20) and high cognitive capacity (n=26), and Aircraft Pilots (n=25), who have gained extensive experience on both Selective and Distributed attention to speech through their training and profession. Results indicate that both types of Attention benefit from higher Cognitive Capacity, suggesting reliance on common capacity-limited resources. However, only Selective Attention was further improved in the Pilots, pointing to its flexible and trainable nature, whereas Distributed Attention seems to suffer from more fixed and hard-wired processing-bottlenecks.

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