Thinking More Lowers Hand Waving: Dual Task Damps Hand Movements During Mental Rotation

Thinking More Lowers Hand Waving: Dual Task Damps Hand Movements During Mental Rotation Sanjay Chandrasekharan (sanjayan@cc.gatech.edu) School of Interactive Computing, College of Computing, Georgia Institute of Technology, Atlanta, USA Samudragupta Bora (samudragupta12@gmail.com) Dilip Athreya (athreyadilip@yahoo.com) Narayanan Srinivasan (ammuns@yahoo.com) Centre for Behavioural and Cognitive Sciences University of Allahabad, Allahabad 211002, India Abstract The ideomotor view argues for a common coding between actions (motor activation) and observation of actions (perceptual activation). This common coding allows the latter to generate the same physical effects as the former. Models that draw on this idea postulate that the brain automatically mimics perceived movements in the world (Brass & Heyes, 2005; Prinz, 2005). This automatic activation of movement is considered to usually stay covert due to inhibition, but this covert ‘simulation’ of movement is believed to contribute towards cognition. In some cases, the automatic activation does not stay covert – it leads to the execution of overt actions that are complementary to the perceived movement. We have developed a model to explain how such overt actions are generated, using a mental rotation task where such complementary actions compatible to the observed stimuli are naturally activated (Chandrasekharan, Athreya & Srinivasan, 2006). The model assumes the ideomotor idea that the observation of movement leads to the brain automatically activating actions compatible with the observed stimuli, but these actions remain covert due to inhibition. However, in our model, as cognitive load rises, processing resources move away from this ‘caretaker’ inhibitory process, which keeps the actions covert. This results in the ‘orphaning’ of the covert activation, leading to overt execution of the action. This ‘orphan’ model of complementary action generation extends the ideomotor idea beyond automatic activation and inhibition, to cognitive-load-modulated inhibition. It explains two puzzles related to complementary actions: 1) why are such actions generated mostly in high cognitive load conditions? and 2) why are non-compatible actions never generated? It also explains why actions non- compatible with cognitive tasks lower performance (see next section for a brief review). In this paper, we report an experiment that investigated the orphan model further, using the same mental rotation task. The objective of the experiment was to see whether there is a threshold of cognitive load, beyond which covert activation of movement becomes overt action. We used a dual task paradigm to investigate this question. Surprisingly, rather than generating more overt actions, the dual task actually lowered the overt activation of action. The paper is organized as follows: section 1 outlines the complementary action problem, the experimental paradigm used to investigate it, and a summary of earlier results. We report a dual task experiment investigating complementary actions (such as hand movements) that arise during cognitive tasks (such as counting). The ‘orphan model’ of the mechanism underlying such parallel actions predicts that a dual task would raise the frequency of such actions. However, rather than leading to more complementary actions, the dual task actually lowered usage of hands during mental rotation. This result fits models that consider motor area activation to be modulated by working memory load, such as models where motor area recruitment is initiated and driven by mental rotation, rather than by movement perception, as assumed by the orphan model. But studies on mental rotation show that there is no activation of the motor area during mental rotation of objects. Given this conflict, we propose two models that explain the dual task’s damping effect on hand activation, and outline current experiments to test these models. Keywords: Complementary Actions; Orphan Model; Mental Rotation; Situated Cognition; Ideomotor Theory Introduction Once upon a time, there lived a naive hen and a wily fox on the edge of a forest. The sight of the hen made the fox drool, but as soon as the hen saw the fox, she flew to the branch of a tree. The fox tried many times to coax the hen to come down, but she was never enticed by his sweet words. The fox then hit on an interesting idea: instead of persuading the hen to come down, he decided to run round and round under the tree. The hen, following the fox’s movement intently, grew dizzy and fell down, and became the fox’s dinner. This Indian folktale illustrates how observing an action can have the same effect as doing an action (going round and round can make you dizzy, but equally, watching something go round and round can also make you dizzy). The ideomotor principle (Prinz, 2005), first outlined by William James, explains this effect: Every representation of a movement awakens in some degree the actual movement which is its object; and awakens it in a maximum degree whenever it is not kept from doing so by an antagonistic representation present simultaneously in the mind (James, 1890)