Nodding and shaking of the head as simulated approach and avoidance responses

Our recent study within the embodiment perspective showed that the evaluation of true and false information activates the simulation of vertical and horizontal head movements involved in nodding and shaking of the head (Moretti & Greco, 2018). This result was found in an explicit evaluation task where motion detection software was deployed to enable participants to assess a series of objectively true or false statements by moving them with the head vertically and horizontally on a computer screen, under conditions of compatibility and incompatibility between simulated and performed action. This study replicated that experiment, but with subjective statements about liked and disliked food, in both explicit and implicit evaluation tasks. Two experiments, plus one control experiment, were devised to test the presence of a motor-affective compatibility effect (vertical-liked; horizontal-disliked) and whether the motor-semantic compatibility found with objective statements (vertical-true; horizontal-false) could be a sub-effect of a more general and automatic association (vertical-accepted; horizontal-refused). As expected, response times were shorter when statements about liked foods and disliked foods were moved vertically and horizontally respectively by making head movements, even when participants were not explicitly required to evaluate them. In contrast, the truth compatibility effect only occurred in the explicit evaluation task. Overall results support the idea that head-nodding and shaking are simulated approach-avoidance responses. Different aspects of the meaning of these gestures and the practical implications of the study for cognitive and social research are discussed.