Using a Veto paradigm to investigate the decision models in explaining Libet-style experiments.

The question of whether free will exists or not has intrigued philosophers for centuries. About 40 years ago, cognitive neuroscientists such as Benjamin Libet have joined the discussion by demonstrating that an ERP component, the readiness potential (RP), precedes the reported time of decision to act by a few hundred milliseconds. Libet et al. (1983) argued that our brains unconsciously prepare the movement before we experience any conscious intention, which led some free will skeptics (e.g., Ebert & Wegner, 2011) to argue that free will does not exist. While Libet's interpretation of his findings initiated an intense philosophical debate, alternative interpretations have been put forward more recently (Bode et al., 2014; Brass et al., 2019; Schurger et al., 2012; 2021). Integration to bound models (ITB) of Libet-style experiments suggest that we accumulate information until an intention threshold is reached, which triggers our experience of intention and execution of voluntary behaviors. The RP, from this perspective reflects the decision process itself rather than the consequence of an unconscious decision. To determine if the ITB model better predicts behavioral patterns in Libet-style experiments, we added a whether-component to the classical Libet task (the Veto Libet task) and compared the behavioral measures in the Veto Libet task with the Classical Libet task. We hypothesized that the signal accumulation in the Veto Libet task would be less steep than in the Classical Libet task, resulting in longer wait times and earlier self-reported intentions to act (i.e., the W). The result in general supported our hypotheses. In addition, these behavioral differences between the Classical Libet task and the Veto Libet task established valuable behavioral correlates for future investigations into the vetoing phenomenon. Finally, this study was also the first application of the Libet task in an online setting, and the behavioral parameters were highly comparable to the previous offline studies, further supporting the possibility of using the online platform to study arbitrary decision-making.

Temporal context modulates cross-modality time discrimination: Electrophysiological evidence for supramodal temporal representation.

Although the peripheral nervous system lacks a dedicated receptor, the brain processes temporal information through different sensory channels. A critical question is whether temporal information from different sensory modalities at different times forms modality-specific representations or is integrated into a common representation in a supramodal manner. Behavioral studies on temporal memory mixing and the central tendency effect have provided evidence for supramodal temporal representations. We aimed to provide electrophysiological evidence for this proposal by employing a cross-modality time discrimination task combined with electroencephalogram (EEG) recordings. The task maintained a fixed auditory standard duration, whereas the visual comparison duration was randomly selected from the short and long ranges, creating two different audio-visual temporal contexts. The behavioral results showed that the point of subjective equality (PSE) in the short context was significantly lower than that in the long context. The EEG results revealed that the amplitude of the contingent negative variation (CNV) in the short context was significantly higher (more negative) than in the long context in the early stage, while it was lower (more positive) in the later stage. These results suggest that the audiovisual temporal context is integrated with the auditory standard duration to generate a subjective time criterion. Compared with the long context, the subjective time criterion in the short context was shorter, resulting in earlier decision-making and a preceding decrease in CNV. Our study provides electrophysiological evidence that temporal information from different modalities inputted into the brain at different times can form a supramodal temporal representation.

Musical Expertise Influences the Processing of Short and Long Auditory Time Intervals: An Electroencephalography Study.

Musical expertise has been proven to be beneficial for time perception abilities, with musicians outperforming nonmusicians in several explicit timing tasks. However, it is unclear how musical expertise impacts implicit time perception. Twenty nonmusicians and 15 expert musicians participated in an EEG recording during a passive auditory oddball paradigm with 0.8- and 1.6-sec standard time intervals and deviant intervals that were either played earlier or delayed relative to the standard interval. We first confirmed that, as was the case for nonmusicians, musicians use different neurofunctional processes to support the perception of short (below 1.2 sec) and long (above 1.2 sec) time intervals: Whereas deviance detection for long intervals elicited a N1 component, P2 was associated with deviance detection for short time intervals. Interestingly, musicians did not elicit a contingent negative variation (CNV) for longer intervals but show additional components of deviance detection such as (i) an attention-related N1 component, even for deviants occurring during short intervals; (ii) a N2 component for above and below 1.2-sec deviance detection, and (iii) a P2 component for above 1.2-sec deviance detection. We propose that the N2 component is a marker of explicit deviance detection and acts as an inhibitory/conflict monitoring of the deviance. This hypothesis was supported by a positive correlation between CNV and N2 amplitudes: The CNV reflects the temporal accumulator and can predict explicit detection of the deviance. In expert musicians, a N2 component is observable without CNV, suggesting that deviance detection is optimized and does not require the temporal accumulator. Overall, this study suggests that musical expertise is associated with optimized implicit time perception.

When the Heart Meets the Mind: Exploring the Brain-Heart Interaction during Time Perception.

Recent studies suggest that time estimation relies on bodily rhythms and interoceptive signals. We provide the first direct electrophysiological evidence suggesting an association between the brain's processing of heartbeat and duration judgment. We examined heartbeat-evoked potential (HEP) and contingent negative variation (CNV) during an auditory duration-reproduction task and a control reaction-time task spanning 4, 8, and 12 s intervals, in both male and female participants. Interoceptive awareness was assessed with the Self-Awareness Questionnaire (SAQ) and interoceptive accuracy through the heartbeat-counting task (HCT). Results revealed that SAQ scores, but not the HCT, correlated with mean reproduced durations with higher SAQ scores associating with longer and more accurate duration reproductions. Notably, the HEP amplitude changes during the encoding phase of the timing task, particularly within 130-270 ms (HEP1) and 470-520 ms (HEP2) after the R-peak, demonstrated interval-specific modulations that did not emerge in the control task. A significant ramp-like increase in HEP2 amplitudes occurred during the duration-encoding phase of the timing but not during the control task. This increase within the reproduction phase of the timing task correlated significantly with the reproduced durations for the 8 s and the 4 s intervals. The larger the increase in HEP2, the greater the under-reproduction of the estimated duration. CNV components during the encoding phase of the timing task were more negative than those in the reaction-time task, suggesting greater executive resources orientation toward time. We conclude that interoceptive awareness (SAQ) and cortical responses to heartbeats (HEP) predict duration reproductions, emphasizing the embodied nature of time.

From preparation to post-processing: Insights into evoked and induced cortical activity during pre-cued motor reactions in children and adolescents.

INTRODUCTION: The motor system undergoes significant development throughout childhood and adolescence. The contingent negative variation (CNV), a brain response reflecting preparation for upcoming actions, offers valuable insights into these changes. However, previous CNV studies of motor preparation have primarily focused on adults, leaving a gap in our understanding of how cortical activity related to motor planning and execution matures in children and adolescents. METHODS: The study addresses this gap by investigating the maturation of motor preparation, pre-activation, and post-processing in 46 healthy, right-handed children and adolescents aged 5-16 years. To overcome the resolution limitations of previous studies, we combined 64-electrode high-density Electroencephalography (EEG) and advanced analysis techniques, such as event-related potentials (ERPs), mu-rhythm desynchronization as well as source localization approaches. The combined analyses provided an in-depth understanding of cortical activity during motor control. RESULTS: Our data showed that children exhibited prolonged reaction times, increased errors, and a distinct pattern of cortical activation compared to adolescents. The findings suggest that the supplementary motor area (SMA) plays a progressively stronger role in motor planning and response evaluation as children age. Additionally, we observe a decrease in sensory processing and post-movement activity with development, potentially reflecting increased efficiency. Interestingly, adolescent subjects, unlike young adults in previous studies, did not yet show contralateral activation of motor areas during the motor preparation phase (late CNV). CONCLUSION: The progressive increase in SMA activation and distinct cortical activation patterns in younger participants suggest immature motor areas. These immature regions might be a primary cause underlying the age-related increase in motor action control efficiency. Additionally, the study demonstrates a prolonged maturation of cortical motor areas, extending well into early adulthood, challenging the assumption that motor control is fully developed by late adolescence. This research, extending fundamental knowledge of motor control development, offers valuable insights that lay the foundation for understanding and treating motor control difficulties.

Connection of social anxiety to impaired pattern of cognitive control and underlying motivational deficiencies: Evidence from event-related potentials.

Numerous studies have established a correlation between social anxiety and poor cognitive control. However, little is known about the cognitive control pattern of individuals with high social anxiety (HSAs) and the underlying mechanisms. Based on the Dual Mechanisms of Control framework and the Expected Value of Control theory, this study explored whether HSAs have an impaired cognitive control pattern (Experiment 1) and whether motivational deficiencies underlie the impaired control pattern (Experiment 2). In Experiment 1, 21 individuals with low social anxiety (LSAs) and 21 HSAs completed an AX-Continuous Performance Task. Results showed that HSAs had a smaller P3b amplitude than LSAs, indicating their weakened proactive control in the cue processing stage, but a larger contingent negative variation (CNV) on cue B as compensation for the negative effects of anxiety in the response preparation stage. No group difference was found in N2 and P3a amplitude on probes, suggesting that reactive control in HSAs was not affected compared to LSAs. In Experiment 2, 21 LSAs and 21 HSAs completed a cued-flanker task, where the likelihood of proactive control engagement was manipulated. The results revealed that HSAs exhibited motivation deficiencies in engaging in proactive control, as evidenced by P3b, CNV amplitude, and response times. These findings shed light on the impaired cognitive control pattern of HSAs and suggest that motivational deficiencies may be the crucial underlying factor.

Mismatch Negativity in Schizophrenia, Unaffected First-degree Relatives, and Healthy Controls.

BACKGROUND: Mismatch negativity (MMN) amplitude is attenuated in schizophrenia patients (SZ). However, variability in illness course among SZ samples and types of deviant stimuli used in MMN paradigms have contributed to inconsistent findings across studies. Though MMN is suggested to be impaired in schizotypy, the potential link between the two is yet to be systematically examined in unaffected first-degree relatives of schizophrenia patients (FDR). METHODS: The SZ sample had twenty-two drug-naïve or drug-free patients (dSZ) and thirty chronic/medicated patients (cSZ). dSZ and cSZ patients were compared with thirty-six unaffected FDR and thirty-two healthy controls (HC) using a two-tone passive auditory oddball MMN paradigm in an event-related potential experiment with two conditions (presented as separate blocks)-duration-deviant (duration-MMN) and frequency-deviant (frequency-MMN). Schizotypy scores and MMN indices were examined for correlation in FDR. RESULTS: Duration-MMN amplitude was significantly attenuated in both dSZ and cSZ compared to other groups. dSZ and cSZ did not differ on MMN indices. Psychopathology scores and features of illness (illness duration, medication dosage, etc.) did not correlate with MMN indices. In FDR, Schizotypal trait measures did not correlate with MMN indices. CONCLUSIONS: Duration-MMN emerged as a more robust indicator of prediction error signalling deficit in SZ. Frequency-MMN amplitude did not significantly differ among the groups, and MMN indices did not correlate with state and trait measures of schizophrenia-related psychopathology. These findings reiterates that auditory sensory processing captured by MMN is likely reflective of dynamic cognitive functions at the point of testing, and is unlikely to be an expression of enduring symptomatology.

Early and late contingent negative variation (CNV) reflect different aspects of deficits in schizophrenia.

Abnormal reward processing and psychomotor slowing are well-known in schizophrenia (SZ). As a slow frontocentral potential, contingent negative variation (CNV) is associated with anticipatory attention, motivation and motor planning. The present study aims to evaluate the early and late amplitude and latencies of CNV in patients with SZ compared to healthy controls during a reward processing task and to show its association with clinical symptoms. We recruited 21 patients with SZ and 22 healthy controls to compare early and late CNV amplitude and latency values during a Monetary Incentive Delay (MID) Task between groups. Patients' symptom severity, levels of negative symptoms and depressive symptoms were assessed. Clinical features of the patients were further examined for their relation with CNV components. In conclusion, we found decreased early CNV amplitudes in SZ during the reward condition. They also displayed diminished and shortened late CNV responses for incentive cues, specifically at the central location. Furthermore, early CNV amplitudes exhibited a significant correlation with positive symptoms. Both CNV latencies were linked with medication dosage and the behavioural outcomes of the MID task. We revealed that early and late CNV exhibit different functions in neurophysiology and correspond to various facets of the deficits observed in patients. Our findings also emphasized that slow cortical potentials are indicative of deficient motivational processes as well as impaired reaction preparation in SZ. To gain a deeper understanding of the cognitive and motor impairments associated with psychosis, future studies must compare the effects of CNV in the early and late phases.

Blocked versus interleaved: How range contexts modulate time perception and its EEG signatures.

Accurate time perception is a crucial element in a wide range of cognitive tasks, including decision-making, memory, and motor control. One commonly observed phenomenon is that when given a range of time intervals to consider, people's estimates often cluster around the midpoint of those intervals. Previous studies have suggested that the range of these intervals can also influence our judgments, but the neural mechanisms behind this "range effect" are not yet understood. We used both behavioral tests and electroencephalographic (EEG) measures to understand how the range of sample time intervals affects the accuracy of people's subsequent time estimates. Study participants were exposed to two different setups: In the "blocked-range" (BR) session, short and long intervals were presented in separate blocks, whereas in the "interleaved-range" (IR) session, intervals of various lengths were presented randomly. Our findings indicated that the BR context led to more accurate time estimates compared to the IR context. In terms of EEG data, the BR context resulted in quicker buildup of contingent negative variation (CNV), which also reached higher amplitude levels and dissolved more rapidly during the encoding stage. We also observed an enhanced amplitude in the offset P2 component of the EEG signal. Overall, our results suggest that the variability in time intervals, as defined by their range, influences the neural processes that underlie time estimation.

Neuroelectric indices of pre-motor planning and adiposity are selectively related to balance in children.

BACKGROUND: Motor function and weight status are components of physical fitness that have been implicated in childhood motor and cognitive development. The lateralized readiness potential (LRP), an index of motor planning and action, can provide context surrounding relationships between fitness and brain activity underlying cognitive and motor functions. This study evaluated the relationship between the LRP and motor skills, as well as associations between weight status and neural and behavioral motor functions. METHODS: Children aged 7-13 (n = 35) participated in a cross-sectional study, using the Movement Assessment Battery for Children 2nd edition (MABC-2) to assess balance, manual dexterity, and aiming/catching. The stimulus- (LRP-S) and response-locked (LRP-R) LRPs were elicited from a modified flanker task. Stepwise regressions tested the association between LRPs and MABC-2 components. Linear regressions were conducted to examine BMI and %Fat in relation to LRPs and MABC-2 components. RESULTS: Analyses revealed that LRP-S mean amplitude difference (ß = 0.401, P = 0.042) and reaction time interference scores (ß = 0.545, P = 0.004) were positively associated with balance, after adjusting for covariates. The LRP-S and interference scores did not predict other MABC-2 outcomes and LRP-R did not predict any MABC-2 components. Further, %Fat (ß = -0.439, P = 0.044), not BMI (ß = -0.364, P = 0.082), only predicted balance. CONCLUSION: We found that changes in the LRP-S amplitude were positively associated with balance, and %Fat was negatively related to balance. This evidence is that fitness components such as weight status and coordination are related to neural markers of motor function which may be useful in intervention designs aimed to improve brain function via improvements in physical fitness and health behaviors.

Biological motion perception in the theoretical framework of perceptual decision-making: An event-related potential study.

Biological motion perception plays a critical role in various decisions in daily life. Failure to decide accordingly in such a perceptual task could have life-threatening consequences. Neurophysiology and computational modeling studies suggest two processes mediating perceptual decision-making. One of these signals is associated with the accumulation of sensory evidence and the other with response selection. Recent EEG studies with humans have introduced an event-related potential called Centroparietal Positive Potential (CPP) as a neural marker aligned with the sensory evidence accumulation while effectively distinguishing it from motor-related lateralized readiness potential (LRP). The present study aims to investigate the neural mechanisms of biological motion perception in the framework of perceptual decision-making, which has been overlooked before. More specifically, we examine whether CPP would track the coherence of the biological motion stimuli and could be distinguished from the LRP signal. We recorded EEG from human participants while they performed a direction discrimination task of a point-light walker stimulus embedded in various levels of noise. Our behavioral findings revealed shorter reaction times and reduced miss rates as the coherence of the stimuli increased. In addition, CPP tracked the coherence of the biological motion stimuli with a tendency to reach a common level during the response, albeit with a later onset than the previously reported results in random-dot motion paradigms. Furthermore, CPP was distinguished from the LRP signal based on its temporal profile. Overall, our results suggest that the mechanisms underlying perceptual decision-making generalize to more complex and socially significant stimuli like biological motion.

Effort discounts reward-based control allocation: A neurodynamic perspective.

The amount of cognitive and neural resources allocated to a task is largely determined by the reward we can expect. However, it remains under-appreciated how this reward-expectation-based control allocation is modulated by effort expenditure. The present event-related potential study investigated this issue through the lens of neural dynamics. Thirty-four participants completed an effort-based monetary incentive delay task while their EEG was recorded. Effort demand was manipulated by adding no (low effort) or much (high effort) noise to the target. Behaviorally, participants exhibited reward-related speeding regardless of effort expenditure, as revealed by faster RTs for reward than neutral trials. Our ERP results demonstrated a widespread facilitatory influence of reward expectation on neural dynamics extending from cue evaluation as indexed by the cue-P3, to control preparation as indexed by the contingent negative variation (CNV), and finally to control engagement as indexed by the target-P3. Critically, the neural facilitation was discounted by effort expenditure during both the control-preparation and control-engagement stages instead of the cue-evaluation stage. Overall, this study provides neurodynamic evidence that control allocation is determined by reward and effort via a cost-benefit analysis.

Amplitude modulation of the contingent negative variation in psychopathy: A systematic review and meta-analysis.

The CNV is analyzed in tasks related to EEG studies, often with participants presenting psychopathic personality traits. A systematic search of the literature was conducted, to solve some inconsistencies regarding CNV amplitude modulation by psychopathy. Nine studies (N = 317) were retrieved for analysis. Three meta-analyses were run - CNV, iCNV, tCNV. A qualitative analysis - reporting CNV amplitudes modulated by psychopathy dimensional features - was also featured. Overall effects for CNV and iCNV were not significant. Larger tCNV amplitudes were found in participants reporting higher psychopathy traits, g = -0.58, 95% CI [- 0.94, - 0.22]. These findings were surprising when confronted with previous assumptions in the literature, especially considering that no significant heterogeneity between studies was found. Neither of the studies' characteristics was a significant moderator. Findings require the need to discuss key differences between adaptive/(mal)adjustment patterns in participants presenting psychopathic traits. Future studies dissociating iCNV and tCNV modulation by psychopathy, especially in community samples and through a dimensional lens, could help to better understand the construct of psychopathy.

Neurophysiological evidence of motor preparation in inner speech and the effect of content predictability.

Self-generated overt actions are preceded by a slow negativity as measured by electroencephalogram, which has been associated with motor preparation. Recent studies have shown that this neural activity is modulated by the predictability of action outcomes. It is unclear whether inner speech is also preceded by a motor-related negativity and influenced by the same factor. In three experiments, we compared the contingent negative variation elicited in a cue paradigm in an active vs. passive condition. In Experiment 1, participants produced an inner phoneme, at which an audible phoneme whose identity was unpredictable was concurrently presented. We found that while passive listening elicited a late contingent negative variation, inner speech production generated a more negative late contingent negative variation. In Experiment 2, the same pattern of results was found when participants were instead asked to overtly vocalize the phoneme. In Experiment 3, the identity of the audible phoneme was made predictable by establishing probabilistic expectations. We observed a smaller late contingent negative variation in the inner speech condition when the identity of the audible phoneme was predictable, but not in the passive condition. These findings suggest that inner speech is associated with motor preparatory activity that may also represent the predicted action-effects of covert actions.

Movement initiation and preparation in subjects with schizophrenia - The amplitude of the readiness potential as a biological marker for negative symptom severity.

OBJECTIVE: Despite extensive research, the etiology of negative symptoms is not well understood. Preliminary findings are linking motor disturbances to negative symptom severity. We aimed to further the understanding to what extent motor movement preparation influences negative symptom severity. METHODS: In a cohort of 31 subjects with schizophrenia and 20 control subjects we recorded the readiness potential amplitude over Cz during spontaneous movements of the right and left thumb. We further assessed negative and positive symptom severity (scale for the assessment of negative and positive symptoms) as well as neurological soft signs (NSS). RESULTS: In subjects with schizophrenia the severity of negative symptoms was best predicted by the readiness potential amplitude and the NSS subdomain motor coordination. The correlation between deficits in motor coordination and negative symptom severity was partially mediated by the readiness potential amplitude in subjects with schizophrenia. CONCLUSIONS: Deficits in motor processing are linked to negative symptom severity in schizophrenia. The readiness potential may represent a biological marker of these basal deficits. In combination with the assessment of NSS, the readiness potential may be a marker of the course of negative symptom severity and help clarifying interdependencies between (pre)frontal networks for action initiation and coordination, as well as negative symptoms.

Electrophysiological signatures of temporal context in the bisection task.

Despite having relatively accurate timing, subjective time can be influenced by various contexts, such as stimulus spacing and sample frequency. Several electroencephalographic (EEG) components have been associated with timing, including the contingent negative variation (CNV), offset P2, and late positive component of timing (LPCt). However, the specific role of these components in the contextual modulation of perceived time remains unclear. In this study, we conducted two temporal bisection experiments to investigate this issue. Participants had to judge whether a test duration was close to a short or long standard. Unbeknownst to them, we manipulated the stimulus spacing (Experiment 1) and sample frequency (Experiment 2) to create short and long contexts while maintaining consistent test ranges and standards across different sessions. The results revealed that the bisection threshold shifted towards the ensemble mean, and both CNV and LPCt were sensitive to context modulation. In the short context, the CNV exhibited an increased climbing rate compared to the long context, whereas the LPCt displayed reduced amplitude and latency. These findings suggest that the CNV represents an expectancy wave preceding a temporal decision process, while the LPCt reflects the decision-making process itself, with both components influenced by the temporal context.

Comparing monetary gain and loss in the monetary incentive delay task: EEG evidence.

What is more effective to guide behavior: The desire to gain or the fear to lose? Electroencephalography (EEG) studies have yielded inconsistent answers. In a systematic exploration of the valence and magnitude parameters in monetary gain and loss processing, we used time-domain and time-frequency-domain analyses to uncover the underlying neural processes. A group of 24 participants performed a monetary incentive delay (MID) task in which cue-induced anticipation of a high or low magnitude of gain or loss was manipulated trial-wise. Behaviorally, the anticipation of both gain and loss expedited responses, with gain anticipation producing greater facilitation than loss anticipation. Analyses of cue-locked P2 and P3 components revealed the significant valence main effect and valence × magnitude interaction: amplitude differences between high and low incentive magnitudes were larger with gain vs. loss cues. However, the contingent negative variation component was sensitive to incentive magnitude but did not vary with incentive valence. In the feedback phase, the RewP component exhibited reversed patterns for gain and loss trials. Time-frequency analyses revealed a large increase in delta/theta-ERS oscillatory activity in high- vs. low-magnitude conditions and a large decrease of alpha-ERD oscillatory activity in gain vs. loss conditions in the anticipation stage. In the consumption stage, delta/theta-ERS turned out stronger for negative than positive feedback, especially in the gain condition. Overall, our study provides new evidence for the neural oscillatory features of monetary gain and loss processing in the MID task, suggesting that participants invested more attention under gain and high-magnitude conditions vs. loss and low-magnitude conditions.

Encoding, working memory, or decision: how feedback modulates time perception.

The hypothesis that individuals can accurately represent temporal information within approximately 3 s is the premise of several theoretical models and empirical studies in the field of temporal processing. The significance of accurately representing time within 3 s and the universality of the overestimation contrast dramatically. To clarify whether this overestimation arises from an inability to accurately represent time or a response bias, we systematically examined whether feedback reduces overestimation at the 3 temporal processing stages of timing (encoding), working memory, and decisions proposed by the scalar timing model. Participants reproduced the time interval between 2 circles with or without feedback, while the electroencephalogram (EEG) was synchronously recorded. Behavioral results showed that feedback shortened reproduced times and significantly minimized overestimation. EEG results showed that feedback significantly decreased the amplitude of contingent negative variation (CNV) in the decision stage but did not modulate the CNV amplitude in the encoding stage or the P2-P3b amplitudes in the working memory stage. These results suggest that overestimation arises from response bias when individuals convert an accurate representation of time into behavior. Our study provides electrophysiological evidence to support the conception that short intervals under approximately 3 s can be accurately represented as "temporal gestalt."

(Non)-experiencing the intention to move: On the comparisons between the Readiness Potential onset and Libet's W-time.

A seminal study by Libet et al. (1983) provided a popular approach to compare the introspective timing of movement execution (the M-time) and the intention to move (the W-time) with respect to the onset of the readiness potential (RP). The difference between the W-time and the RP onsets contributed significantly to the current free-will discussion, insofar as it has been repeatedly shown that the RP onset unequivocally precedes the W-time. However, the interpretations of Libet's paradigm continuously attract criticism, questioning the use of both the W-time and the RP onset as indicators of motor intention. In the current study, we further probe whether the W-time is rather an intention-unrelated product of the participant's inference than an unambiguous temporal marker of the intention to move. Using behavioral reports and concurrent multichannel EEG, we investigated the relationship between the W-time and M-time introspective reports in two groups of participants who started an experiment with a series of different reports. Congruently with previous studies, we have shown that the W-time is affected by the experimental procedures: participants who had prior experience reporting the M-time provided significantly earlier W-time. However, contrary to previous papers, we revealed that even naive participants do introspectively differentiate the W-time and the M-time, which suggests that the W-time might actually reflect the intention to move, at least to some extent. We, therefore, suggest that training-based modulation of the W-time values may explain this finding. Moreover, we further confirm the absence of a direct link between the RP onset and the W-time by showing no covariation between them in both experimental groups. In turn, our findings question the overall interpretation of the comparison between these two time points. Overall, our study further emphasizes the ambiguity of Libet's paradigm, and suggests that the relatedness of both the RP and the W-time to the movement initiation processes should not be assumed a priori.

Physiological and introspective antecedents of tics and movements in adults with tic disorders.

OBJECTIVE: To investigate the subjective phenomenon and the neural underpinnings of tics compared with voluntary movements in patients with tic disorders. METHODS: We recorded electroencephalographic and electromyographic data while subjects completed a Libet clock paradigm. Patients and healthy volunteers reported the times of W (willing to move) and M (movement occurrence) while performing voluntary movements. This was repeated only for the patients for the tics. RESULTS: In the patients, W and M times preceding voluntary movements and tics did not significantly differ from voluntary movements of healthy volunteers. The Bereitschaftspotentials in the patients were similar to healthy volunteers. Tics were only assessable for 7 patients due to artifacts. Two subjects did not show Bereitschaftspotentials, and they reported the lowest levels of tic voluntariness. 5 subjects did not show beta band event-related desynchronization before tics. CONCLUSIONS: For patients, the sense of volition for tics is similar to that of their voluntary movements which is similar to normal. Patients showed dissociations between the Bereitschaftspotential and beta desynchronization for tics, with 5/7 showing normal Bereitschaftspotentials and 2/7 showing desynchronization. The absence of desynchronization may suggest attempts to suppress tics. SIGNIFICANCE: This physiology shows a difference for most tics compared with normal movements.