The involvement of the dorsal stream in processing implied actions between paired objects: A TMS study

Perceiving and selecting the action possibilities (affordances) provided by objects is an important challenge to human vision, and is not limited to single-object scenarios. Xu et al. (2015) identified two effects of implied actions between paired objects on response selection: an inhibitory effect on responses aligned with the passive object in the pair (e.g. a bowl) and an advantage associated with responses aligned with the active objects (e.g. a spoon). The present study investigated the neurocognitive mechanisms behind these effects by examining the involvement of the ventral (vision for perception) and the dorsal (vision for action) visual streams, as defined in Goodale and Milner's (1992) two visual stream theory. Online repetitive transcranial magnetic stimulation (rTMS) applied to the left anterior intraparietal sulcus (aIPS) reduced both the inhibitory effect of implied actions on responses aligned with the passive objects and the advantage of those aligned with the active objects, but only when the active objects were contralateral to the stimulation. rTMS to the left lateral occipital areas (LO) did not significantly alter the influence of implied actions. The results reveal that the dorsal visual stream is crucial not only in single-object affordance processing, but also in responding to implied actions between objects.