Observing learned object-specific functional grasps preferentially activates the ventral stream

In one popular account of the human visual system, two streams are distinguished, a ventral stream specialized for perception and a dorsal stream specialized for action. The skillful use of familiar tools, however, is likely to involve the cooperation of both streams. Using functional magnetic resonance imaging, we scanned individuals while they viewed short movies of familiar tools being grasped in ways that were either consistent or inconsistent with how tools are typically grasped during use. Typical-for-use actions were predicted to preferentially activate parietal areas important for tool use. Instead, our results revealed several areas within the ventral stream, as well as the left posterior middle temporal gyrus, as preferentially active for our typical-for-use actions. We believe these findings reflect sensitivity to learned semantic associations and suggest a special role for these areas in representing object-specific actions. We hypothesize that during actual tool use a complex interplay between the two streams must take place, with ventral stream areas providing critical input as to how an object should be engaged in accordance with stored semantic knowledge.