Does size really matter? Exploring the interference effects of size and orientation within a sequential grasping task


Previous research has suggested that orientation might be more influential in sequential tasks than size information. However, recent evidence from our lab has shown that preparing an action to the second object does not produce interference to the first action, but attending to its size for verbal judgment does. Specifically, as the size of the second object increased, the amplitude of peak grip aperture (PGA) towards the first object also increased when performing the perception condition. The current study was designed in order to incorporate both size and orientation within a sequential task. Participants were required to grasp a cylinder (5cm in diameter) place it on an identified target area and than either grasp or make a perceptual judgment to the second object. The second object was either 3cm or 7cm in length and was either presented on a 45degree angle towards the left or the right. Based on the action-centered model of attention, it was predicted that both conditions would yield similar results when analyzing the interference of the size and orientation of the second object when grasping the cylinder. It was shown that participants' time to reach PGA was faster when the second object was the 3 cm object relative to the 7cm within the action condition. No such differences were found in the perception condition. Reaction times were overall faster in the action condition in comparison to the perception condition. Preliminary analyses provide a hint that orientation information affected grip posture more so than size information.