Dissociations between action and awareness in simple reaction time and in pointing tasks

by Axel Cleeremans

We typically act congruently with our expectancy of what will happen next. Indeed, this link between action and expectancy constitutes a litmus test for agency, for it would seem irrational to do otherwise (i.e., act against our expectancies). However, there are conditions in which the two can dissociate. Here, we focus on two such paradigms: A simple reaction time task, and a pointing task. The simple reaction time task is inspired from conditioning paradigms. On each trial, a tone occurs and people are to press as fast as possible on a single key in response to the appearance of a white square on the screen (the imperative stimulus). Tones are only followed by the imperative stimulus in 50% of the cases. Shortly before the onset of the tone, people are also required to indicate whether the white square will appear. We observed a complete dissociation between reaction times to the white square and expectancy in this paradigm, suggesting that reaction time responses are not dependent on conscious expectancy. To explore awareness of action, we subsequently adapted this paradigm to a pointing task. People reached for a target, which unpredictably jumped to the side on 50% of the trials. On each trial, participants (1) expressed their expectancy of a target jump, (2) pointed at the target, adjusting their movement towards the shift if required and (3) reproduced the movement they had just made (as a measure of their motor awareness). We analysed the spatial disparity between the initial and the reproduced movements on those trials with a target shift. Negative values (undershoots), suggest │motor pessimism▓ in which motor awareness only reflects a sluggish, reconstructed awareness of the actual movement, while positive values (overshoots) suggest │motor optimism▓ in that the reproduced movement is influenced more by participants╣ prior intention to point to the shifted target than by their actual movement. Using these measures, we found that expectancy strongly influenced the experience of action. Further, the occurrence of delays between the three components of each trial (expectancy, action, reproduction) had no effect on visuomotor adjustment but strongly influenced action awareness: Delays boosted undershoots, suggesting increased reliance on a time-limited memory for action. Experience of action is thus strongly influenced by prior thoughts and expectations, but only over a short time period. Thus, awareness of action is a dynamic and relatively flexible mixture of what we intend to do and of what our motor system actually does.

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