Grounding object concepts in perception and action: evidence from fMRI studies of tools.

Studies of categories of objects, including tools, have spurred the development of the sensory-motor model of object concept representation. According to this model, information about objects is represented in the same neural subsystems that are active when we perceive and use them. In turn, this model has provided insight into the brain mechanisms of tool use. For tools, three types of information are especially important for identification: the characteristic motion with which they move (such as the up and down motion of a hammer), their visual form, and the way that they are manipulated. Evidence from neuropsychological, non-human primates, and neuroimaging studies suggest a mapping between specific brain regions and these fundamental identifying properties of tools. We focus on neuroimaging studies of the left posterior middle temporal gyrus. This brain region is active both when subjects perceive moving tools and when they answer questions about tools, and is responsive to the type of visual motion characteristic of tools: rigid, unarticulated motion. We describe a simple model that explains how low-level receptive field properties like those known to exist in area MT/V5 could give rise to the high-level category-related representations observed in functional imaging experiments.