What Is in a Reach? Domain-General Spatial Modulation of Motor Responses by Number Representations
Authors
Santiago Alonso-Diaz
Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA
Elon Gaffin-Cahn
Department of Psychology, New York University, New York, NY, USA
Bradford Z. Mahon
Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA; Department of Neurosurgery, University of Rochester Medical School, Rochester, NY, USA; Center for Visual Science, University of Rochester, Rochester, NY, USA
Jessica F. Cantlon
Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA
Abstract
Gaze, pointing, and reaching movements are thought to provide a window to internal cognitive states. In the case of numerical cognition, it has been found that the left-right deviation of a reaching movement is modulated by the relative magnitude of values in a number comparison task. Some have argued that these patterns directly reflect the representation of a logarithmically compressed mental number line (direct mapping view). However, other studies suggest that the modulation of motor outputs by numerical value could be a more general decision-making phenomenon (response competition view). Here we test the generality of interactions between the motor system and numerical processing by comparing subjects' reach trajectories during two different nonverbal tasks: numerosity comparison and facial expression comparison. We found that reaching patterns were practically identical in both tasks – reach trajectories were equally sensitive to stimulus similarity in the numerical and face comparisons. The data provide strong support for the response competition view that motor outputs are modulated by domain-general decision processes, and reflect generic decision confidence or accumulation of evidence related to mental comparison.
