Predictability of action sub-steps modulates motor system activation during the observation of goal-directed actions

Abstract

Action perception and execution are linked in the human motor system, and researchers have proposed that this action-observation matching system underlies our ability to predict observed behavior. If the motor system is indeed involved in the generation of action predictions, activation should be modulated by the degree of predictability of an observed action. This study used EEG and eye-tracking to investigate whether and how predictability of an observed action modulates motor system activation as well as behavioral predictions in the form of anticipatory eye-movements. Participants were presented with object-directed actions (e.g., making a cup of tea) consisting of three action steps which increased in their predictability. While the goal of the first step was ambiguous (e.g., when making tea, one can first grab the teabag or the cup), the goals of the following steps became predictable over the course of the action. Motor system activation was assessed by measuring attenuation of sensorimotor mu- and beta-oscillations. We found that mu- and beta-power were attenuated during observation, indicating general activation of the motor system. Importantly, predictive motor system activation, indexed by beta-band attenuation, increased for each action step, showing strongest activation prior to the final (i.e. most predictable) step. Sensorimotor activity was related to participants' predictive eye-movements which also showed a modulation by action step. Our results demonstrate that motor system activity and behavioral predictions become stronger for more predictable action steps. The functional roles of sensorimotor oscillations in predicting other's actions are discussed.

Reduced Mu Power in Response to Unusual Actions Is Context-Dependent in 1-Year-Olds

“…This is in line with research on adults demonstrating increased motor activation in response to deviating or unusual action outcomes (e.g., Manthey et al, 2003 ; Koelewijn et al, 2008 ). Motor system activity in adults was even sensitive to the degree of prediction with increased activation in response to highly predictable action outcomes ( Braukmann et al, 2017 ).…”

Action predictability is reflected in beta power attenuation and predictive eye movements in adolescents with and without autism

“…EEG statistical analysis. In order to maximise comparability with the original study (Braukmann et al, 2017), to quantify the effect of action step and occlusion on motor system activation, average values of mu (8-12 Hz) and beta (15-25 Hz) power recorded at Cz during each action step were extracted for each participant. We then ran one-tailed one-way t-tests on each frequency band to determine whether power during action observation was on average lower than power during baseline, to test for overall attenuation during action observation.…”

“…Eye-tracking data processing. The eye-tracking data were also analysed according to the previous study (Braukmann et al, 2017). Data were classified into fixations with a minimum duration of 50ms and a peak velocity of 40°/s in BeGaze 3.0 software (SensoMotoric Instruments GmbH, Teltow, Germany).…”

“…In order to quantify this, we measured observers' mu and beta power and predictive eye movements during observation of multi-step actions that become incrementally more predictable. We expected that mu power would be reduced during action observation compared to baseline, but that it would be unaffected by predictability during the unfolding of the multi-step actions in non-autistic participants (Braukmann et al, 2017). If action predictability is indeed the source of the mixed findings described above, then we should also see group differences in mu modulated by predictability.…”

“…In contrast, we expected that beta power would be modulated by predictability in non-autistic participants (Braukmann et al, 2017). We therefore expected that this would be the critical comparison between autistic and non-autistic individuals,…”