Influences of hand action on the processing of symbolic numbers: A special role of pointing?

Abstract

Embodied and grounded cognition theories state that cognitive processing is built upon sensorimotor systems. In the context of numerical cognition, support to this framework comes from the interactions between numerical processing and the hand actions of reaching and grasping documented in skilled adults. Accordingly, mechanisms for the processing of object size and location during reach and grasp actions might scaffold the development of mental representations of numerical magnitude. The present study exploited motor adaptation to test the hypothesis of a functional overlap between neurocognitive mechanisms of hand action and numerical processing. Participants performed repetitive grasping of an object, repetitive pointing, repetitive tapping, or passive viewing. Subsequently, they performed a symbolic number comparison task. Importantly, hand action and number comparison were functionally and temporally dissociated, thereby minimizing context-based effects. Results showed that executing the action of pointing slowed down the responses in number comparison. Moreover, the typical distance effect (faster responses for numbers far from the reference as compared to close ones) was not observed for small numbers after pointing, while it was enhanced by grasping. These findings confirm the functional link between hand action and numerical processing, and suggest new hypotheses on the role of pointing as a meaningful gesture in the development and embodiment of numerical skills.

Fig 1. Graphical illustration of the experimental setup, see main text for details.

Panel a. Timeline of the experiment. Panel b. Experimental setting during the hand motor task. Panel c. Experimental setting during number comparison. Panel d. Illustration of the four conditions of the motor task. Panel e. Schematic illustration of the trial structure in number comparison.

Fig 2. Effects of action type.

Preregistered planned comparisons and the related results are reported in grey (grasp vs. control conditions; reach vs. control conditions), while additional planned comparisons and the related results are reported in blue. Error bars represent within-subjects SEM, computed only for illustration purposes [79].

Fig 3

Panel a. RTs as a function of number target and action type. Error bars represent within-subjects SEM, computed only for illustration purposes [74]. Panel b. Regression slopes representing the size of the distance effect for small or large digits in each action type condition. Error bars represent SEM. Results from exploratory analyses are written in blue. Panel c. Individual regression slopes as a function of numerical distance in the grasp–small number condition. Negative slopes indicate performance in the direction of the classical distance effect (i.e., faster responses for digits far from the reference as compared to closer ones). Red circles indicate more negative slopes for small numbers after grasping as compared to the other conditions. Grey crosses indicate more negative slopes for small numbers after tapping, pointing, and viewing as compared to the grasping condition. Panel d. Individual regression slopes as a function of numerical distance in the point–small number condition. Negative slopes indicate performance in the direction of the classical distance effect (i.e., faster responses for digits far from the reference as compared to closer ones). Blue triangles indicate less negative slopes for small numbers after pointing as compared to the other conditions. Grey crosses indicate less negative slopes for small numbers after tapping, grasping, and viewing as compared to the pointing condition.