Broken affordances, broken objects: a TMS study

It is well known that specific components of motor programs are automatically activated when they are afforded by object related pragmatic features. Among these features the handle appears to be particularly salient for interacting with an object. The aim of this study was to test the modulation of the motor system when object features, particularly relevant for the action, like the object's handle, are violated. In order to address this issue a TMS paradigm was used in which familiar objects with a whole or broken handle, positioned to the right or to the left, were centrally presented. A control condition was also included in which a symbol ('#' character) was shown in the right or in the left visual field. Participants had to watch stimuli carefully. The left hemisphere hand motor area was magnetically stimulated 200 ms after stimulus presentation. Results showed that MEP areas were larger when the handle was located to the right side consistent with the visuomotor role of this feature, but only when the handle was complete. The present data (1) suggest a more active role of the dorsal stream in building up object knowledge and (2) allow one to rule out the role of any asymmetrical aspect of an object in motor coding.