Motor imagery vividness does not predict the ability to judge object weight from observed hand actions

Observing others' actions and imagining oneself performing the same actions (motor imagery) have been linked in the literature in several ways. They have been shown to have overlapping neural representations, both seem to relate to one's ability to move, and both have been shown to positively affect movement rehabilitation. Whether these overlaps reflect a direct functional relationship between motor imagery and the ability to derive relevant information from observed kinematics (action understanding) has not yet been investigated. A previous study found that individuals with low self-reported imagery vividness exhibit weaker motor system engagement during action observation than those with typical imagery vividness. The present study provides the first behavioural test of the relationships between motor and general visual imagery vividness and a quantifiable behavioural measure of action understanding-specifically, the ability to judge the weight of objects based on observing someone else lift them. To test the research question across the full imagery spectrum, our recruitment strategy included a high proportion of individuals with very low imagery vividness (often referred to as 'aphantasia'). An online sample (N = 392) completed a weight judgement task alongside a matched speed judgement control task. Neither motor imagery vividness (Vividness of Movement Imagery Questionnaire-2) nor general visual imagery vividness (Vividness of Visual Imagery Questionnaire) predicted action understanding, with a Bayesian analysis suggesting moderate evidence against any relationship. Overall, our findings suggest that self-reported motor and general visual imagery vividness are functionally independent from action understanding of manual interactions.