Are tool properties always processed automatically? The role of tool use context and task complexity.

Previous work with healthy adults supports the idea that perception of the orientation of a tool's handle may automatically activate cognitive components for grasping and use. An important source of evidence for this automatic activation view comes from studies showing interference when automatically activated action representations are inconsistent with the behaviors demanded by a task (e.g., Tucker and Ellis, 1998). Here, we evaluated whether such effects occur in a grip selection task in which responses were chosen based on a learned rule (Rule task) versus anticipatory planning (Plan task). Participants were asked to pantomime grasping horizontally presented objects with handles. In the Rule task, a color cue indicated on which side of the tool's handle the thumb had to be placed. In the Plan task, participants had to choose the most comfortable way to grasp and rotate the object into a specific end-position. Across three experiments we found evidence of interference on grip selection exclusively during the Rule task, and only when it was preceded by a prime task that involved tool use. These findings suggest that prior activation of cognitive components through use of tools can be effective over time and interferes with grip selection based on use of a pre-learned rule. Absence of interference effects during the plan task, even when preceded by the Use task, suggest that engagement of similar mechanisms during active planning overwrites this automatic activation of previously effective components. Possible cognitive and neural mechanisms are discussed.