How manipulation-related and visually-guided information is processed when interacting with unusual versions of familiar objects: cognitive and anatomical bases

Object-directed actions involve properties linked to both long-term, sensorimotor representations of object manipulation (i.e. stable affordances) and visually-guided analysis of their structure (i.e. variable affordances). They are processed by the Function and the Structure systems, respectively. Aiming at clarifying how these systems are modulated during the phases of object-directed actions, unusual objects were created by modifying the structure of usual (i.e. traditional) familiar objects. Their function was still recognizable, but their structural variation required a greater recruitment of online visual guide, modulating the role of the two systems. A first study compared the processing of usual vs. unusual objects in a function categorization task. Results demonstrated that usual and unusual objects were both processed with the same strategy (Experiment 1), and that stable properties extended the time to “plan” the action, while variable properties were quickly processed during the movement “execution” (Experiment 2). A second study investigated the temporal features of object processing through kinematics. Participants grasped and used the usual and unusual objects in conditions of full view or view occlusion (with or without a temporal delay). During delayed actions without vision, the effect of the rapid visual decay on kinematics was evident for usual objects, which rely more on long-term representations (Function system), while unusual objects exploited more the visual information (Structure system). Additionally, a qualitative error analysis indicated a computational interference between the two systems in the case of unusual objects. Lastly, a functional magnetic resonance study demonstrated that categorizing unusual objects recruited more the neural correlates of both the Function and the Structure System (i.e. the ventro-dorsal and the dorso-dorsal stream, respectively) than usual objects did. Together, results demonstrated a different contribution in processing and timing of the two systems during object-directed actions, and the theoretical relevance of using unusual objects.