Is consciousness required to withhold an impending action?: Evidence from event-­related brain potentials

This thesis explores whether a decision to withhold an impending motor action can be initiated unconsciously. There is much evidence to suggest that both voluntary actions and reactions to external events can be initiated without consciousness. However, there is some debate as to whether inhibition or control of behaviour can occur unconsciously. Libet et al. (1985) proposed that while consciousness is not required to initiate an action, it may be essential in allowing the action to be vetoed. Similarly, evidence from tasks involving response conflict points to a close association between inhibition/control of behaviour and conscious awareness. In particular, both fMRI and EEG correlates of control are seen to be absent when response conflict is unconscious. The research in this thesis aimed to clarify whether the no-go N2 and P3, ERP correlates of the no-go response, can be modulated by an unconscious prime. In each of five EEG experiments, target-related N2 and P3 components were significantly affected by the nature of the unconscious primes. More specifically, when the unconscious information coded for a no­go response, N2 and P3 amplitude was significantly reduced, suggesting that inhibition of the imminent response was primed by the unconscious stimuli. In addition, there was evidence that the unconscious primes were able to directly engage frontal inhibition/control mechanisms. In experiments 1, 2 and 5 early ERP differences were observed over frontocentral electrodes that were entirely dependent on the nature of the unconscious prime. Furthermore, experiment 5 showed that this early modulation of ERP activity was directly related to the extent to which the participants were influenced by the unconscious primes. These findings suggest that inhibition of an impending motor action can be initiated by an unconscious stimulus. These conclusions are discussed in relation to previous research, and the possible role of consciousness in behaviour. The limitations of the current research and suggestions for future work are also considered

Action prediction modulates both neurophysiological and psychophysical indices of sensory attenuation

Sensory attenuation refers to the observation that stimuli that are predicted based on one’s action are attenuated. This phenomenon has primarily been observed as a neurophysiological phenomenon, with reduced Event-Related Potential (ERP) (e.g., Bäss et al., 2008) and BOLD (e.g., Blakemore et al., 1998). However, psychophysical investigations (e.g., Sato, 2008; Cardoso-Leite et al., 2010; Roussel et al., 2013) have confirmed that action prediction also influences the perception of sensory action effects. The present study recorded both neurophysiological and psychophysical measures in a single experiment, to confirm whether the two phenomena are related. In addition, by measuring the ERP modulations of both stimulus contrast and prediction congruency, we sought to directly relate the neurophysiological phenomenon to the magnitude of sensory processing in the brain. Participants performed left- and right-hand voluntary actions that were previously associated with the letters A and H. In the test phase, participants were presented with these same two letters, at one of two possible contrasts. Participants were required to report which of the two possible contrasts had been presented. We observed both reduced contrast discrimination (in line with Roussel et al., 2013) and a reduced ERP response for congruent action-effects. Furthermore, our congruency modulation was observed on the same component that differed as a function of stimulus contrast. Taken together these results strongly suggest that neurophysiological indices of sensory attenuation reflect reduced sensory processing of voluntary action effects

The temporal dynamics of metacognition: Dissociating task-related activity from later metacognitive processes

In recent years, neuroscience research spent much effort in revealing brain activity related to metacognition. Despite this endeavor, it remains unclear exactly when metacognitive experiences develop during task performance. To investigate this, the current study used EEG to temporally and spatially dissociate task-related activity from metacognitive activity. In a masked priming paradigm, metacognitive experiences of difficulty were induced by manipulating congruency between prime and target. As expected, participants more frequently rated incongruent trials as difficult and congruent trials as easy, while being completely unable to perceive the masked primes. Results showed that both the N2 and the P3 ERP components were modulated by congruency, but that only the P3 modulation interacted with metacognitive experiences. Single-trial analysis additionally showed that the magnitude of the P3 modulation by congruency accurately predicted the metacognitive response. Source localization indicated that the N2 task-related activity originated in the ACC, whereas the P3-interplay between task-related activation and metacognitive experiences originated from the precuneus. We conclude that task-related activity can be dissociated from later metacognitive processing

The effect of cognitive effort on the sense of agency

While we are performing a demanding cognitive task, not only do we have a sense of cognitive effort, we are also subjectively aware that we are initiating, executing and controlling our thoughts and actions (i.e., sense of agency). Previous studies have shown that cognitive effort can be both detrimental and facilitative for the experienced sense of agency. We hypothesized that the reason for these contradictory findings might lie in the use of differential time windows in which cognitive effort operates. The current study therefore examined the effect of cognitive effort exerted on the current trial, on the previous trial or across a block of trials on sense of agency, using implicit (Experiment 1) and explicit (Experiment 2) measures of sense of agency. We showed that the exertion of more cognitive control on current trials led to a higher explicit sense of agency. This surprising result was contrasted to previous studies to establish potential reasons for this surprising finding and to formulate recommendations for future studies

Recruitment dynamics of cognitive control in insomnia

Study Objectives Individuals with insomnia disorder (ID) commonly report complaints of cognitive control functioning. Conversely, both behavioral and neurological evidence supporting subjective cognitive control impairments in insomnia remain remarkably scarce and inconclusive. To investigate this discrepancy, the present study used next to behavioral measures, event-related potentials (ERPs) to assess proactive control and reactive control in insomnia. Methods Individuals with insomnia disorder (n = 18) and good sleeper controls (GSC; n = 15) completed the AX-Continuous Performance Task, while electroencephalography (EEG) was recorded. This task required participants to maintain specific cue-information active in order to prepare an adequate response to a subsequent probe, which allowed us to measure participants’ reliance on both proactive and reactive control. Results The results indicate that, although ID show a comparable level of performance as GSC, they show a reduced proactive engagement of cue-induced maintenance and response preparation processes (as reflected by the P3b and the contingent negative variation components). Moreover, in contrast to GSC, ID fail to engage reactive control (as indexed by the P3a component) in order to overcome invalid response tendencies. Conclusions This study provides neurological evidence for impairments in cognitive control functioning in insomnia. As such, our study contributes to a better understanding of the discrepancy between the commonly reported cognitive impairments in insomnia and the scarce objective evidence supporting these cognitive complaints

Individual differences in sensory integration predict differences in time perception and individual levels of schizotypy

To interact functionally with our environment, our perception must locate events in time, including discerning whether sensory events are simultaneous. The Temporal Binding Window (TBW; the time window within which two stimuli tend to be integrated into one event) has been shown to relate to individual differences in perception, including schizotypy, but the relationship with subjective estimates of duration is unclear. We compare individual TBWs with individual differences in the filled duration illusion, exploiting differences in perception between empty and filled durations (the latter typically being perceived as longer). Schizotypy has been related to both these measures and is included to explore a potential link between these tasks and enduring perceptual differences. Results suggest that individuals with a narrower TBW make longer estimates for empty durations and demonstrate less variability in both conditions. Exploratory analysis of schizotypy data suggests a relationship with the TBW but is inconclusive regarding time perception

Behavioral and neural dynamics of cognitive control in the context of rumination

Rumination is a characteristic feature of several clinical disorders (e.g., major depressive disorder, insomnia disorder). Emerging evidence suggests that a reduced flexibility in the balance between proactive and reactive control might be related to trait rumination. This study aimed to investigate the proactive-reactive control balance in the context of trait rumination. In the current study, we investigated behavioral performance and event-related potentials (ERPs) while participants were performing an AX- Continuous Performance Task, to evaluate whether a shift towards more reactive control (i.e., conflict monitoring and resolution) at the expense of proactive control (i.e., maintenance and updating of task-relevant information) is associated with increased trait rumination. Our behavioral results as well as our ERP results did not demonstrate that a shift towards more reactive control at the expense of proactive control was associated with increased trait rumination. Future research is needed to investigate the proactive-reactive control balance in the context of trait rumination. This study is the first to explore the recruitment dynamics of cognitive control using behavioral as well as electrophysiological measures in the context of rumination

The Role of Action-Effect Contingency on Sensory Attenuation in the Absence of Movement

Stimuli that have been generated by a person's own willed motor actions generally elicit a suppressed electrophysiological, as well as phenomenological, response than identical stimuli that have been externally generated. This well-studied phenomenon, known as sensory attenuation, has mostly been studied by comparing ERPs evoked by self-initiated and externally generated sounds. However, most studies have assumed a uniform action–effect contingency, in which a motor action leads to a resulting sensation 100% of the time. In this study, we investigated the effect of manipulating the probability of action–effect contingencies on the sensory attenuation effect. In Experiment 1, participants watched a moving, marked tickertape while EEG was recorded. In the full-contingency (FC) condition, participants chose whether to press a button by a certain mark on the tickertape. If a button press had not occurred by the mark, a sound would be played a second later 100% of the time. If the button was pressed before the mark, the sound was not played. In the no-contingency (NC) condition, participants observed the same tickertape; in contrast, however, if participants did not press the button by the mark, a sound would occur only 50% of the time (NC-inaction). Furthermore, in the NC condition, if a participant pressed the button before the mark, a sound would also play 50% of the time (NC-action). In Experiment 2, the design was identical, except that a willed action (as opposed to a willed inaction) triggered the sound in the FC condition. The results were consistent across the two experiments: Although there were no differences in N1 amplitude between conditions, the amplitude of the Tb and P2 components were smaller in the FC condition compared with the NC-inaction condition, and the amplitude of the P2 component was also smaller in the FC condition compared with the NC-action condition. The results suggest that the effect of contingency on electrophysiological indices of sensory attenuation may be indexed primarily by the Tb and P2 components, rather than the N1 component which is most commonly studied

ERP and behavioral evidence of increased sensory attenuation for fear-related action outcomes

Voluntary action selection entails the representation of the expected consequences of the action. Previous evidence suggests that accurate action-effect prediction modulates both ERP and behavioral markers of sensory processing-a phenomenon know as sensory attenuation. This may play an important role in monitoring the success or failure of our actions, or attributing agency. Nonetheless, the vast majority of studies in this domain focus on simplistic visual and auditory stimuli. Given that we rarely perform voluntary actions with the aim of generating such stimuli in social contexts, this provides little indication of the extent to which sensory attenuation operates in everyday behavior. The present study investigated ERP and behavioral measures of sensory attenuation for fearful and neutral facial expressions. Participants were trained to associate one voluntary action with the presentation of a fearful face, and another action with a neutral face. We measured both ERP responses and behavioral ratings following presentation of faces whose emotional content was either consistent or inconsistent with the action prediction. We observed significant modulation for fearful outcomes only, suggesting that sensory attenuation is heightened to stimuli of high social relevance. The N170 response was significantly attenuated for congruent fearful faces, but not for congruent neutral faces (in comparison to incongruent faces). Similarly, behavioral ratings were modulated only for fearful faces but not neutral faces. This provides new insight into how social and affective outcomes modulate sensory attenuation and may have implications for implicit sense of agency for socially relevant stimuli

Temporal binding window and sense of agency are related processes modifiable via occipital tACS

The temporal binding window refers to the time frame within which temporal grouping of sensory information takes place. Sense of agency is the feeling of being in control of one’s actions, and their associated outcomes. While previous research has shown that temporal cues and multisensory integration play a role in sense of agency, no studies have directly assessed whether individual differences in the temporal binding window and sense of agency are associated. In all three experiments, to assess sense of agency, participants pressed a button triggering, after a varying delay, the appearance of the circle, and reported their sense of agency over the effect. To assess the temporal binding window a simultaneity judgment task (Experiment 1) and a double-flash illusion task (Experiment 2 and 3) was also performed. As expected, the temporal binding window correlated with the sense of agency window. In Experiment 3, these processes were modulated by applying occipital tACS at either 14Hz or 8Hz. We found 14Hz tACS stimulation was associated with narrower temporal biding window and sense of agency window. Our results suggest the temporal binding window and the time window of sense of agency are related. They also point towards a possible underlying neural mechanism (alpha peak frequency) for this association