Zusammenfassung
Intention is an intermediate concept between will and action and is defined in this work as conscious or non-conscious preparation to act. The goal of this work is to identify a neural index of change of intention and characterize the conditions that lead to it. In order to obtain an electro-physiological model for 'change of intention' we used a masked priming paradigm while recording EEG. The task w as to press a right or left button following either a visible arrow cue ('instructed condition') or a visible 'free-choice' cue. The subjects were unaware of the presence of the masked prime, nevertheless we observed a behavioral effect of the prime: on Instructed trials performance was slower and less accurate when the prime and instruction cue pointed in different directions (i.e., incongruent trials), than on congruent trials; on free-choice trials performance was slower in the incongruent cases, and primes significantly biased freely chosen responses in the direction of the prime. We revealed a spatio-temporal electrophysiological signal around 250-350ms after prime onset which we interpret as an EEG signal induced by the prime, representing preparation to move right or left according to the prime cue direction. This signature allowed us to explain the behavior cost of incongruence, both in Instructed as well as in free-choice trials, by a 'change of intention' scenario rather than confusion or hesitation: the subject prepares the type of action indicated by the prime but 'changes his/her mind' and actually acts differently. In this experiment, the 'change of intention' is composed of an initial intention prompted exogenously by a masked prime, which is then overruled either by an exogenous instructing arrow in the Instructed case, or by an endogenous intention in the free-choice case. The results allowed us to reveal the process of change of intention in a second experiment in which both the initial and the overruling intention are endogenous.
