Time Course of Motor Affordances Evoked by Pictured Objects and Words

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Correspondence effects based on the relationship between the left/right position of a pictured object’s handle and the hand used to make a response, or on the size of the object and the nature of a grip response (power/precision), have been attributed to motor affordances evoked by the object. Effects of this nature, however, are readily explained by the similarity in the abstract spatial coding of the features that define the stimulus and response, without recourse to object-based affordances. We propose that in the task context of making reach-and-grasp actions, pictured objects may evoke genuine, limb-specific action constituents. We demonstrate that when subjects make reach-and-grasp responses, there is a qualitative difference in the time course of correspondence effects induced by pictures of objects versus the names of those objects. For word primes, this time course was consistent with the abstract spatial coding account, in which effects should emerge slowly and become apparent only among longer response times. In contrast, correspondence effects attributable to object primes were apparent even among the shortest response times and were invariant across the entire response-time distribution. Using rotated versions of object primes provided evidence for a short-lived competition between canonical and depicted orientations of an object with respect to eliciting components of associated actions. These results suggest that under task conditions requiring reach-and-grasp responses, pictured objects rapidly trigger constituents of real-world actions.

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