1.2. Varieties of intentions

The intentional typology we present below is primarily motivated by the necessity to take into account two dimensions of variation in the content of intentions that may make an important difference to the processes involved in their inference. The first dimension of variation concerns the scope of the intention; i.e., the more or less complex nature of its goal. Here we can draw a distinction between:

(i) Motor intentions: They are intentions directed at simple motor goals, i.e. goals that can be realized by basic actions (such as lifting an arm, pressing a button, reaching for an object, etc.). Motor intentions are sensorimotor representations where the goal is represented directly in terms of the motor commands needed to achieve it. The relation between motor intention and motor act is thus a one-one when that act is successfully completed.

(ii) Superordinate intentions: They are intentions directed at somewhat complex or general goals, the achievement of which typically involves the completion of a number of subgoals or substeps. Depending on the complexity of the general goal, these subgoals may themselves be decomposed into further subgoals, ultimately reaching the level of basic actions. The achievement of a superordinate intention will thus require the execution of a combination of basic actions each guided by a corresponding motor intention. Different combinations of motor acts can be used to accomplish the same general goal and, conversely, a same motor act (or even series of motor acts) can be part of combinations aimed at different general goals. As a result, when visual information on motor acts is noisy or incomplete, recognizing the superordinate intention driving these acts may become a challenge.

The second dimension of variation we were interested in concerns the target of the intentions. Neither motor nor superordinate intentions are necessarily directed at inanimate objects. They may also target a third party or be achieved in a context of social interaction (Searle, 1995; Blakemore & Frith, 2004; Sebanz, Bekkering, & Knoblich, 2006; Frith & Frith, 2007; Ciaramidaro et al., 2007). Intentional contents are thus also modulated by the relational structure in which an action takes place. We called intentions directed at an object, non-social intentions, and intentions directed ata third party, social intentions.

By combining these two dimensions, we obtain the following typology: i) non-social motor intention, ii) non-social superordinate intention, iii) social motor intention, and iv) social superordinate intention.

Owing to their different scopes and targets, motor and superordinate, social and non-social intentions are naturally assigned different functional roles, different types of content and different temporal scales. The present study aims at investigating whetherthese functional differences would be reflected in the respective contribution of perceptual information and prior expectations to intentional judgments.