CoActions Lab

Cognition and Actions Lab

When given a choice between actions that yield the same reward, we tend to prefer the one that requires the least effort. Recent studies have shown that humans are remarkably accurate at evaluating the effort of potential reaching actions, and can predict the subtle energetic demand caused by the non-isotropic biomechanical properties of the arm. Here, we investigated the time course over which such information is computed and comes to influence decisions. Two independent approaches were used. First, subjects performed a reach decision task in which the time interval for deciding between two candidate reaching actions was varied from 200 to 800 ms. Second, we measured motor-evoked potential (MEPs) to single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) to probe the evolving decision at different times after stimulus presentation. Both studies yielded a consistent conclusion: That a prediction of the effort associated with candidate movements is computed very quickly and influences decisions within 200 ms after presentation of the candidate actions. Furthermore, while the MEPs measured 150 ms after stimulus presentation were well correlated with the choices that subjects ultimately made, later in the trial the MEP amplitudes were primarily related to the muscular requirements of the chosen movement. This suggests that corticospinal excitability (CSE) initially reflects a competition between candidate actions, and later changes to reflect the processes of preparing to implement the winning action choice.

Ignasi Cos1,3,4, Julie Duque2, and Paul Cisek1

1Groupe de recherche sur le système nerveux central (GRSNC), Département de Neuroscience, Université de Montréal, Montréal (QC), CANADA

2Cognition and Action Laboratory, Institute of Neuroscience, Université Catholique de Louvain, 1200 Brussels, BELGIUM

3UPMC, Univ Paris 06, UMR 7222, ISIR, 4 Place Jussieu, 75005 Paris, FRANCE

4CRNS, UMR 7222, ISIR, 4 Place Jussieu, 75005 Paris, FRANCE

Few studies have looked at the relation between mental fatigue (MF) and motivation. In particular, it remains unclear whether the reduced performance sometimes observed following MF is caused by a progressive loss of cognitive resources or by a decrease in motivation to engage in mental activity. To tackle this question 18 healthy subjects were asked to participate in a 3,5 hour-long experiment where MF was induced by performing Sudoku tasks. The behavioural effects of MF were then measured at regular intervals, by means of a Simple Reaction Time task (SRT) and a Working Memory task (WMT) in which motivation was manipulated by different levels of monetary reward. Psychophysiological measurements (Pupillometry, Skin conductance, EEG and ECG) were also conducted during the execution of each task. Results in the SRT showed that the subjects were faster for higher incentives indicating the validity of the reward manipulation. We found that during the WMT, the participants’ performance got gradually worse across block repetition, reflecting the appearance of MF. Psychophysiological and behavioural measures concur in showing that this performance drop was not associated to decreased motivation and that the level of mental effort exerted during the task was maintained. This suggests that MF is mainly the consequence of a decline in mental resources.

M. Gergelyfi1, E. Olivier1 and A. Zénon1

1University of Louvain, Brussels, 1200, Belgium

Several aspects of implicit learning have already been explored since Reber first defined it in 1967, from sequence to statistical learning and from artificial grammar learning to contextual cueing in visual search. In the current study, our aim was to investigate a new facet of implicit learning based on a stimulus-response association. Particularly, the participants had to report the motion direction of a single patch of dots, either left/right in a first experiment or top/down in a second one. In each trial the patch can be of three different colors, and unbeknownst to the participants, two of these colors were always associated with the same direction/response, while the third color was completely uninformative. In the first experiment, using the performance of the participants trial by trial, we fitted a Bayesian model in order to assess the level of implicit learning of information conveyed by the color. In the second experiment, using the same model, we disentangled the association between color and motion, and color and response, in order to test which association was actually learnt by the participants. The results highlight, despite a high interindividual variability, a robust implicit learning of the stimulus-response association, both in the first and second experiment. In addition, the second experiment shows how the participants independently learn stimulus-response and stimulus-stimulus associations. Future studies will focus on the neural correlates of this type of learning, and on the causes of such variability between subjects.

Andrea Alamia1, J.J. Orban de Xivry1, Etienne Olivier1, Alexandre Zenon1

1. Université Catholique de Louvain, Institute of Neuroscience, Bruxelles

During saccadic eye movements, the processing of visual information is transiently interrupted by a mechanism known as "saccadic suppression" [1] that is thought to ensure perceptual stability [2]. If, as proposed in the premotor theory of attention [3], covert shifts of attention rely on sub-threshold recruitment of oculomotor circuits, then saccadic suppression should also occur during covert shifts. In order to test this prediction, we designed two experiments in which participants had to orient towards a cued letter, with or without saccades. We analyzed the time course of letter identification score in an "attention" task performed without saccades, using the saccadic latencies measured in the "saccade" task as a marker of covert saccadic preparation. Visual conditions were identical in all tasks. In the "attention" task, we found a drop in perceptual performance around the predicted onset time of saccades that were never performed. Importantly, this decrease in letter identification score cannot be explained by any known mechanism aligned on cue onset such as inhibition of return, masking, or microsaccades. These results show that attentional allocation triggers the same suppression mechanisms as during saccades, which is relevant during eye movements but detrimental in the context of covert orienting.

Alexandre Zénon1, Brian D. Corneil2,3, Andrea Alamia1, Nabil Filali-Sadouk1, Etienne Olivier1

1 Institute of Neuroscience, University of Louvain, Brussels, Belgium
2 Departments of Physiology & Pharmacology, Psychology, Western University, London, Ontario, Canada
3 Robarts Research Institute, London, Ontario, Canada

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