Accounts of visually directed actions usually assume that their planning begins with an intention to act. This article describes three experiments that challenged this view through the use of a stimulus-response compatibility paradigm with photographs of common graspable objects as stimuli. Participants had to decide as fast as possible whether each object was upright or inverted. Experiments 1 and 2 examined the effect of the irrelevant dimension of left-right object orientation on bimanual and unimanual keypress responses. Experiment 3 examined wrist rotation responses to objects requiring either clockwise or anticlockwise wrist rotations when grasped. The results (a) are consistent with the view that seen objects automatically potentiate components of the actions they afford, (b) show that compatibility effects of an irrelevant stimulus dimension can be obtained across a wide variety of naturally occurring stimuli, and (c) support the view that intentions to act operate on already existing motor representations of the possible actions in a visual scene.

Brain responses to handwritten and printed letters differentially depend on the activation state of the primary motor cortex.

It is suggested that seen objects potentiate a range of actions associated with them, irrespective of the intentions of the viewer. Evidence for this possibility is provided by the data from two experiments, both of which required a participant to make a binary motor response to an auditory stimulus. In the first experiment the response was a power or precision grip, which was performed whilst simultaneously viewing a real object which would normally be grasped using either a power or precision grip. A significant interaction of response and grip compatibility of the object was observed. Similar results were obtained in the second experiment when a wrist rotation of a given direction was used as a response, whilst viewing objects which would require wrist rotations if they were to be grasped. The effects of the seen objects on components of action are described as microaffordances which are said to be dispositional states of the viewer's nervous system.

No abstract

Behavioural data have shown that the perception of an object automatically potentiates motor components (affordances) of possible actions toward that object, irrespective of the subject's intention. We carried out an event-related fMRI study to investigate the influence of the intrinsic properties of an object on motor responses which were either compatible or incompatible with the action that the object affords. The subjects performed power or precision grip responses based on the categorization of objects into natural or man-made. The objects were either 'small' (usually grasped with a precision grip) or 'large' (usually grasped with a power grip). As expected, the motor responses were fastest to objects that afforded the same grip (congruent) and slowest to objects that afforded the other grip (incongruent). Imaging revealed activations which covaried with compatibility in the parietal, dorsal premotor and inferior frontal cortex. We suggest that the greater the difference in reaction times between congruent and incongruent trials, the greater the competition between the action afforded by the object and the action specified by the task, and thus the greater the activation within this network.