Discussion
We replicated Ganel and Goodale’s (2003) results in the perceptual classification and grasping
tasks. In the former task, variation in the task-irrelevant dimension clearly affected participants’ classifications
of the task-relevant dimension, indicating that adults process these two dimensions in
interaction with one another. In the grasping task, the task-irrelevant dimension did not influence
adults’ grasping of the task-relevant dimension. Thus, we conclude that adults process these dimensions
independent of each other in action.
Furthermore, the grasping with pulling task showed that the task-irrelevant dimension did not
influence adults when they grasped the object to pull it in terms of either their grasping reaction times
(start and MGA times) or their MGAs. The change in procedure did not influence participants’ underlying
processing strategy. Consequently, the task-irrelevant dimension effect on grasping in the original
action task is not confounded by an obstacle avoidance mechanism. Therefore, our results confirm
and extend those of Ganel and Goodale (2003) and provide additional evidence that adults process
task-relevant dimensions independent of task-irrelevant dimensions in action. As a result, the grasping
task’s procedure is a robust design that can be adapted for use with children.
In addition, we confirmed that the type of shutter device (i.e., PLATO goggles vs. shutter window)
did not influence participants’ object processing strategies. Participants in both shutter groups processed object dimensions as interactive in the perception task and as independent in the action
task. Thus, we assume that the shutter window can be used with children without concern.