Biology subjects

Travers, E.

Publications and source records attributed to Travers, E..

3 recordsLinked to original sources

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.

neuroscience↗

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.

neuroscience↗

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.

neuroscience↗