Biology subjects

Haggard, P.

Publications and source records attributed to Haggard, P..

30 records · Page 2Linked to original sources

bioRxiv2020

A neural turning point - the EEG P3 component tracks unfolding changes of mind

The ability to change ones mind is a key feature of human cognition. Yet, the neural mechanisms underpinning our capacity to change our minds remain poorly understood. Here, we investigated the neural correlates of evidence accumulation and changes of mind in a two-step sequential sampling task. Participants provided a first, quick guess regarding the relative frequencies of target letters in a visual stream, followed by a slower, more deliberate decision. We found that the P3 amplitude evoked by successive target letters tracks an internal signed decision variable and predicts choices on a single-trial level. Moreover, this neural decision variable offers new insights into the dynamics of changes of mind. In particular, we show that the start of evidence accumulation after the early decision constitutes a neural turning point: the P3 evoked by the first letter contrary to the initial decision can be used to predict subsequent changes of mind. Our results highlight a critical interaction between the processing of external evidence and endogenous modulations of decisional parameters that facilitate reversing an original decision.

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bioRxiv2020

EEG frequency tagging reveals neural entrainment to people moving in synchrony

Humans and other animals have evolved to act in groups, but how does the brain distinguish multiple people moving in group from multiple people moving independently? Across three experiments, we test whether biological motion perception depends on the spatiotemporal relationships among people moving together. In Experiment 1, we apply EEG frequency tagging to apparent biological motion and show that fluently ordered sequences of body postures drive brain activity at three hierarchical levels of biological motion processing: image, body sequence, and movement. We then show that movement-, but not body- or image-related brain responses are enhanced when observing four agents moving in synchrony. Neural entrainment was strongest for fluently moving synchronous groups (Experiment 2), displayed in upright orientation (Experiment 3). Our findings show that the brain preferentially entrains to the collective movement of human agents, deploying perceptual organization principles of synchrony and common fate for the purpose of social perception.

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bioRxiv2020

Somatosensory evoked potentials indexing lateral inhibition are modulated according to the mode of perceptual processing: comparing or combining multi-digit tactile motion

Many perceptual studies focus on the brains capacity to discriminate between stimuli. However, our normal experience of the world also involves integrating multiple stimuli into a single perceptual event. Neural circuit mechanisms such as lateral inhibition are believed to enhance local differences between sensory inputs from nearby regions of the receptor surface. However, this mechanism would seem dysfunctional when sensory inputs need to be combined rather than contrasted. Here, we investigated whether the brain can strategically regulate the strength of suppressive interactions that underlie lateral inhibition between finger representations in human somatosensory processing. To do this, we compared sensory processing between conditions that required either comparing or combining information. We delivered two simultaneous tactile motion trajectories to index and middle fingertips of the right hand. Participants had to either compare the directions of the two stimuli, or to combine them to form their average direction. To reveal preparatory tuning of somatosensory cortex, we used an established event-related potential design to measure the interaction between cortical representations evoked by digital nerve shocks immediately before each tactile stimulus. Consistent with previous studies, we found a clear suppressive interaction between cortical activations when participants were instructed to compare the tactile motion directions. Importantly, this suppressive interaction was significantly reduced when participants had to combine the same stimuli. These findings suggest that the brain can strategically switch between a comparative and a combinative mode of somatosensory processing, according to the perceptual goal, by preparatorily adjusting the strength of a process akin to lateral inhibition.

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bioRxiv2020

Evidence accumulation under uncertainty - a neural marker of emerging choice and urgency

To interact meaningfully with its environment, an agent must integrate external information with its own internal states. However, information about the environment is often noisy. In our task participants had to monitor a stream of discrete visual stimuli over time and decide whether or not to act, on the basis of either strong or weak evidence. We found that the classic P3 event-related potential evoked by sequential evidence items item of evidence tracked decision-making processes and encoded participants choice, both when evidence was strong and when it was weak. We also found that the readiness potential, a classic marker of self-paced actions, was observed preceding all actions - even when those were strongly driven by external evidence. Computational modelling showed that both neural dynamics and behavioural results can be explained by a combination of (a) competition between mutually inhibiting accumulators for the two categorical choice outcomes, and (b) a context-dependent urgency signal.

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bioRxiv2020

The Readiness Potential reflects expectation, not uncertainty, in the timing of action

Actions are guided by a combination of external cues, internal intentions and stored knowledge. Self-initiated voluntary actions, produced without any immediate external cue, may be preceded by a slow EEG Readiness Potential (RP) that progressively increases prior to action. The cognitive significance of this neural event is controversial. Some accounts link the RP to the fact that timing of voluntary actions is generated endogenously, without external constraints, and perhaps even randomly. Other accounts take the RP as reflecting the unique role of planning, therefore of temporal expectation, in voluntary actions. In many previous experiments, actions are both unconstrained by external cues, but also potentially involve preplanning and anticipation. To separate these factors, we developed a reinforcement learning paradigm where participants learned, through trial and error, the optimal time to act. If the RP reflects freedom from external constraint, its amplitude should be greater early in learning, when participants do not yet know the best time to act. Conversely, if the RP reflects planning, it should be greater later on, when participants have learned, and know in advance, the time of action. We found that RP amplitudes grew with learning, suggesting that this neural activity reflects planning and anticipation for the forthcoming action, rather than freedom from external constraint.

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bioRxiv2019

Two Ways to Change Your Mind: Effects of Intentional Strength and Motor Costs on Changes of Intention.

Changes of Mind are a striking example of the human ability to flexibly reverse decisions after commitment to an initial choice, and to change actions according to circumstances. Previous studies of Changes of Mind largely focused on perceptual choices. Here we investigate reversals of voluntary, endogenous action decisions. In a novel version of the random-dot motion task, participants moved to a target that matched both the perceived dot-motion direction and an internally-generated intention (which colour target to move to). Movement trajectories revealed whether and when participants 1) perceived a change in dot-motion direction, or additionally 2) changed the colour that they chose to move to ( Change of Intention). Changes of Intention were less frequent in participants with strong colour intentions, as indicated by high performance costs in trials where perceptual information conflicted with the endogenous intention (Exp. 1). Additionally, Changes of Intention were more frequent when motor costs of intention pursuit were high (Exp. 2). These findings were simulated using an attractor network model that continuously integrates voluntary intentions, sensory evidence, and motor costs. This argues in favour of a unifying framework for dynamic decision-making processes, in which voluntary actions emerge from a dynamic combination of internal action tendencies and external environmental factors.

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bioRxiv2019

Prospective and retrospective contributions to intention awareness in voluntary action

Spontaneous, voluntary actions are often accompanied by motor intentions, that is the experience of \"being about to move\". The emergence of this experience is contentiously discussed, culminating in two opposing views of motor intention. While prospective theorists hold that an intention to move genuinely precedes the action, retrospective theorists suggest that an intention is reconstructed only after action execution. As such, both theories offer radically different predictions about the possibility of voluntary control over action intention. We assess here the respective contributions of prospective and retrospective factors in motor intention awareness in a real-time EEG setup. Participants performed self-paced movements with intermittent interruption by cues, signalling to either move or not to move. Cues were triggered by a brain-computer interface upon detection of either the presence or absence of a readiness potential (RP), a signal known to precede self-paced voluntary actions. Subsequently, participants reported their intention to move at the time of the cue. We found that participants were more likely to report an intention to move when the cue was followed by a movement than no movement, highlighting the effect of retrospection on awareness of intention. Interestingly, however, an intention to move was also more frequently reported when the cue was elicited by an RP, compared to when no RP was present, suggesting that awareness of intention is also informed by motor preparation processes, congruent with prospective theories. Overall, our findings show that intention awareness in voluntary action relies on both prospective and retrospective components, and we describe here how these two factors are dynamically integrated over time.

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bioRxiv2019

The Readiness Potential reflects internal source of actions, not decision uncertainty

Voluntary actions are preceded by a Readiness Potential (RP), a slow EEG component generated in medial frontal cortical areas. The RP is classically thought to be specific to internally-driven decisions to act, and to reflect post-decision motor preparation. Recent work suggests instead that it may reflect noise or conflict during the decision itself, with internally-driven decisions tending to be more random, more conflictual and thus more uncertain than externally-driven actions. To contrast accounts based on endogenicity with accounts based on uncertainty, we recorded EEG in a task where participants decided to act or withhold action to accept or reject visually-presented gambles, and used multivariate methods to extract an RP-like component.. We found no difference in amplitude of this component between actions driven by strong versus weak evidence, suggesting that the RP may not reflect uncertainty. In contrast, the same RP-like component showed higher amplitudes prior to actions performed without any external evidence (guesses) than for actions performed in response to equivocal, conflicting evidence. This supports the view that the RP reflects the internal source of action, rather than decision uncertainty. Significance StatementThe EEG Readiness Potential (RP) seen prior to self-initiated actions is often taken as a neural marker of volition (Shibasaki & Hallett, 2006). It has been argued that the RP may instead reflect conflict and uncertainty in the decisions leading up to these actions, raising questions about decades of previous findings. We directly tested these explanations by asking participants to decide whether to act or not in a gambling task, while manipulating both uncertainty and the source of the information (internal or external) guiding the decision. Only the source of information affected the presence of the RP. Therefore, the RP remains a marker of internally-generated voluntary action, not a marker of uncertainty.

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bioRxiv2019

Choosing and learning: outcome valence differentially affects learning from free versus forced choices

Positivity bias refers to learning more from positive than negative events. This learning asymmetry could either reflect a preference for positive events in general, or be the upshot of a more general, and perhaps, ubiquitous, \"choice-confirmation\" bias, whereby agents preferentially integrate information that confirms their previous decision. We systematically compared these two theories with 3 experiments mixing free- and forced-choice conditions, featuring factual and counterfactual learning and varying action requirements across \"go\" and \"no-go\" trials. Computational analyses of learning rates showed clear and robust evidence in favour of the \"choice-confirmation\" theory: participants amplified positive prediction errors in free-choice conditions while being valence-neutral on forced-choice conditions. We suggest that a choice-confirmation bias is adaptive to the extent that it reinforces actions that are most likely to meet an individuals needs, i.e. freely chosen actions. In contrast, outcomes from unchosen actions are more likely to be treated impartially, i.e. to be assigned no special value in self-determined decisions.

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bioRxiv2018

Evidence for metacognitive bias in perception of voluntary action

Studies of metacognition often measure confidence in perceptual decisions. Much less is known about metacognition of action, and specifically about how people estimate the success of their own actions. In the present study, we compare metacognitive abilities between voluntary actions, passive movements matched to those actions, and purely visual signals. Participants reported their confidence in judging whether a brief visual probe appeared ahead or behind of their finger during simple flexion/extension movement. The finger could be moved voluntarily, or could be moved passively by a robot replaying their own previous movements. In a third condition, participants did not move, but a visual cursor replayed their previous voluntary movements. Metacognitive sensitivity was comparable when judging active movements, during passive finger displacement and visual cursor reply. However, a progressive metacognitive bias towards overconfidence was found for passive and for voluntary movements. Taken together, our results may partly explain some of the peculiarities that arise when one judges ones own actions.

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bioRxiv2018

Dissociating cognitive and motoric precursors of human self-initiated action

Across-trial variability of EEG decreases more markedly prior to self-initiated than prior to externally-triggered actions, providing a novel neural precursor for volitional action. However, it remains unclear whether this neural convergence is an early, deliberative stage, or a late, execution-related stage in the chain of cognitive processes that transform intentions to actions. We report two experiments addressing these questions. Self-initiated actions were operationalized as endogenous skip responses while waiting for target stimuli in a perceptual decision task. These self-initiated skips were compared to blocks where participants were instructed to skip. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions, replicating previous findings.\n\nImportantly, this EEG convergence was stronger at fronto-midline electrodes than at either the electrode contralateral or ipsilateral to the hand assigned to the skip action in each block (Experiment 1). Further, convergence was stronger when availability of skip responses was rationed, encouraging deliberate planning before skipping (Experiment 2). This suggests that the initiation of voluntary actions involves a bilaterally-distributed, effector-independent process related to deliberation. A consistent process of volition is detectable during early, deliberative planning, and not only during late, execution-related time windows.

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bioRxiv2017

Human Self-Initiated Action Is Preceded By A Reliable Process Of Noise Reduction

A gradual buildup of electrical potential over motor areas precedes self-initiated movements. Recently, such \"readiness potentials\" (RPs) were attributed to stochastic fluctuations in neural activity. We developed a new experimental paradigm that operationalised self-initiated actions as endogenous skip responses while waiting for target stimuli in a perceptual decision task. We compared these to a block of trials where participants could not choose when to skip, but were instead instructed to skip. Frequency and timing of motor action were therefore balanced across blocks, so that conditions differed only in how the timing of skip decisions was generated. We reasoned that across-trial variability of EEG could carry as much information about the source of skip decisions as the mean RP. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions. This convergence suggests a consistent preparatory process prior to self-initiated action. A leaky stochastic accumulator model could reproduce this convergence given the additional assumption of a systematic decrease in input noise prior to self-initiated actions. Our results may provide a novel neurophysiological perspective on the topical debate regarding whether self-initiated actions arise from a deterministic neurocognitive process, or from neural stochasticity. We suggest that the key precursor of self-initiated action may manifest as a reduction in neural noise.

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