Influence of biological kinematics on abstract concept processing

During a random number generation task, human beings tend to produce more small numbers than large numbers. However, this small number bias is modulated when motor behaviour, such as a turn of the head, is performed during the random number generation task. This result fits with the finding that number representation is linked to laterally oriented actions, with small- and large-magnitude numbers generally linked to movement towards the left or the right side of space, respectively. To test whether this number-space association is specific to human motor behaviours or extends to any type of laterally oriented movements, we assessed whether the presentation of biological or nonbiological leftward or rightward movement affected a subsequent random number generation task. Biological and nonbiological movements were obtained by varying the kinematic parameters of the movements. Biological kinematics represented the tangential velocity actually observed in a human pointing movement; nonbiological kinematics represented equivalent movements but with an inverse tangential velocity along the path. The results show that only the observation of biological movements induces a space-number bias whereas observing nonbiological movements does not. This finding is the first evidence of a link between a biological marker and the semantic representation of a concept as abstract as number.