The hand and the object: the role of posterior parietal cortex in forming motor representations

The hypothesis of several subsystems for processing visual information is expanded to the context of visuomotor functions. It is proposed that object-oriented actions involve three main types of processing whether the object is to be localized, identified, or grasped and manipulated. Neurological evidence from patients is provided, showing that each type of processing pertains to a distinct pathway. Whereas identification is impaired by lesions affecting the occipitotemporal pathway, localization and grasping are processed in posterior parietal cortex. A new clinical case with a parietal lesion is presented, where the grasping deficit contrasted with preservation of both identification and localization. This result suggests separate representations for localizing and grasping within parietal cortex.