Changes in pupil diameter can reflect high-level cognitive signals that depend on central neuromodulatory mechanisms. However, brain mechanisms that adjust pupil size are also exquisitely sensitive to changes in luminance and other events that would be considered a nuisance in cognitive experiments recording pupil size. We implemented a simple auditory experiment involving no changes in visual stimulation. Using finite impulse-response fitting we found pupil responses triggered by different types of events. Among these are pupil responses to auditory events and associated surprise: cognitive effects. However, these cognitive responses were overshadowed by pupil responses associated with blinks and eye movements, both inevitable nuisance factors that lead to changes in effective luminance. Of note, these latter pupil responses were not recording artifacts caused by blinks and eye movements, but endogenous pupil responses that occurred in the wake of these events. Furthermore, we identified slow (tonic) changes in pupil size that differentially influenced faster (phasic) pupil responses. Fitting all pupil responses using gamma functions, we provide accurate characterisations of cognitive and non-cognitive response shapes, and quantify each response's dependence on tonic pupil size. These results allow us to create a set of recommendations for pupil size analysis in cognitive neuroscience, which we have implemented in freely available software.

The normal variability in alertness we experience in daily tasks is rarely taking into account in cognitive neuroscience. Here we studied neurobehavioral dynamics of cognitive control with decreasing alertness. We used the classic Simon Task where participants hear the word "left" or "right" in the right or left ear, eliciting slower responses when the word and the side are incongruent -the conflict effect. Participants performed the task both while fully awake and while getting drowsy, allowing for the characterisation of alertness modulating cognitive control. The changes in the neural signatures of conflict from local theta oscillations to a longdistance distributed theta network suggests a reconfiguration of the underlying neural processes subserving cognitive control when affected by alertness fluctuations.

Conflict detection in sensory input is central to adaptive human behavior. Perhaps unsurprisingly, past research has shown that conflict may even be detected in absence of conflict awareness, suggesting that conflict detection is an automatic process that does not require attention. To test the possibility of conflict processing in the absence of attention, we manipulated task relevance and response overlap of potentially conflicting stimulus features across six behavioral tasks. Multivariate analyses on human electroencephalographic data revealed neural signatures of conflict only when at least one feature of a conflicting stimulus was attended, regardless of whether that feature was part of the conflict, or overlaps with the response. In contrast, neural signatures of basic sensory processes were present even when a stimulus was completely unattended. These data reveal an attentional bottleneck at the level of objects, suggesting that object-based attention is a prerequisite for cognitive control operations involved in conflict detection.

18Humans are remarkably capable of adapting their behaviour flexibly based on rapid situational 19 changes: a capacity termed cognitive control. Intuitively, cognitive control is thought to be affected by 20 the state of alertness, for example, when sleepy or drowsy, we feel less capable of adequately 21implementing effortful cognitive tasks. Although scientific investigations have focused on the effects 22 of sleep deprivation and circadian time, little is known about how natural fluctuations in alertness in 23 the regular awake state affect cognitive control. Here we combined a conflict task in the auditory 24 domain with neurodynamics -EEG recordings-to test how neural and behavioural markers of conflict 25processing are affected by fluctuations in arousal. Using a novel computational method, we 26 segregated alert and drowsy trials from a three hour testing session and observed that, although 27 participants were generally slower, the typical slower responses to conflicting information, compared 28to non-conflicting information, was still intact, as well as the effect of previous trials (i.e. conflict 29 adaptation). However, the behaviour was not matched by the typical neural markers of cognitive 30control -local medio-frontal theta-band power changes-, that participants showed during full alertness. 31Instead, a decrease in power of medio-frontal theta was accompanied by an increase in long-range 32 information sharing (connectivity) between brain regions in the same frequency band. The results 33show the resilience of the human cognitive control system when affected by internal fluctuations of 34 our arousal state and suggests a neural compensatory mechanism when the system is under 35physiological pressure due to diminished alertness. 36

Perception of sensory input is influenced by fluctuations in ongoing neural activity, most prominently driven by attention and neuromodulator systems. It is currently unknown if neuromodulator activity and attention differentially modulate neural activity and perception or whether neuromodulatory systems in fact control attentional processes. We pharmacologically enhanced cholinergic (through donepezil) and catecholaminergic (through atomoxetine) levels in humans performing a visual attention task to investigate the effects of neuromodulatory drive and spatial attention on neural activity and behavior. Attention and catecholaminergic enhancement both improved perceptual sensitivity by increasing the rate of evidence accumulation towards a decision threshold (cholinergic effects were negligible). Electroencephalographic recordings revealed that attention and catecholaminergic enhancement both modulated pre-stimulus cortical excitability, evoked sensory processes and parietal evidence accumulation. Crucially however, the spatial profile and timing of these effects were remarkably different. This suggests that selective attention and neuromodulatory systems shape perception largely independently and in qualitatively different ways.