Manipulable objects and the dynamic representation of hand actions

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Motor representations form part of our knowledge of everyday objects like calculators and spray-cans. There is increasing evidence that such representations, determining our ability to hold and use manipulable objects, are invoked dynamically during language and perceptual tasks. For example, spatial attention is modulated in unexpected ways when observers view graspable objects. The computational role played by higher level motor systems in cognition is therefore of fundamental interest, as is the nature of the processes that determine a particular hand representation in a given task context. Any manipulable object affords a range of familiar actions. For example, we learn to pick up or move a pocket calculator with an inverted open grasp, but we learn to use it according to its conventional function by poking the keys with an extended forefinger. I therefore distinguish between volumetric grasps, having to do with the shape and weight properties of an object for lifting or moving, and functional grasps, those hand interactions evoked when we wish to carry out an object's function. I have developed a novel experimental method to assess the evocation of specific hand action representations to words, objects or sentences in real time. This approach requires subjects to carry out speeded reach and grasp actions on an eight-element response apparatus. Each element affords a unique action and subjects learn to produce a given manual action in response to a visual cue. We then measure the influence of an object, word or sentence (a priming event) on reach and grasp performance, time-locked to the visual cue, yielding evidence on the nature and time course of the motor representations evoked by the priming event. I describe a series of experiments designed to assess the time course of functional and volumetric grasp representations for pictures and words. In addition, I wish to assess the role of hand action representations in spatial attention to manipulable objects. This research provides valuable convergent methods that will clarify evidence available from functional imaging research and from neuropsychology.