Luciano Fadiga

Five experiments investigated whether preparation of a grasping movement affects detection and discrimination of visual stimuli. Normal human participants were required to prepare to grasp a bar and then to grasp it as fast as possible on presentation of a visual stimulus. On the basis of the degree of sharing of their intrinsic properties with those of the to-be-grasped bar, visual stimuli were categorized as "congruent" or "incongruent." Results showed that grasping reaction times to congruent visual stimuli were faster than reaction times to incongruent ones. These data indicate that preparation to act on an object produces faster processing of stimuli congruent with that object. The same facilitation was present also when, after the preparation of hand grasping, participants were suddenly instructed to inhibit the prepared grasping movement and to respond with a different motor effector. The authors suggest that these findings could represent an extension of the premotor theory of attention, from orienting of attention to spatial locations to orienting of attention to graspable objects.

This chapter reviews experimental evidence and presents new data supporting the idea that human language may have evolved from hand/mouth action representation. Some of the findings include the discovery that the listener's motor system becomes active as if pronouncing the listened words during speech listening and that hand gestures where the hand is not explicitly visible activate the hand-related mirror neuron system, including Broca's region. This chapter concludes that the property of recursion, considered peculiar to human language, may have been introduced to hand actions by the fabrication of tools.