Categorization and sensorimotor interaction with objects.

Three experiments were aimed at verifying whether the modality of interaction with objects and the goals defined by the task influences the weight of the properties used for categorization. In Experiment 1 we used everyday objects (cups and glasses), in order to exclude that the results depended on pre-stored categorical knowledge and to assess the role of a purely perceptual property such as colour. Novel objects were used respectively in Experiment 2 and Experiment 3. Participants experienced objects in different modalities of interaction: Vision, Vision+Action, Action, and Mirror (they observed an experimenter touching and lifting them), then they were submitted to a similarity evaluation task and to a more action-based sorting task. Objects varied in intrinsic properties which had a different degree of interactivity: Grip, Shape, Size and Colour. Overall Grip, the most interactive property, was relevant for categorization, together with Size in Experiment 1 and with Shape in Experiment 2 and Experiment 3. The relevance of Grip in the sorting task confirms that goal-relevant properties are more weighted. The absence of a modality effect is discussed in the framework of the theories arguing that the vision of objects and of conspecifics interacting with objects automatically activates motor information.