Interaction between cognitive effort and biomechanical cost in motor decision-making during a transitive inference task

Decision-making can be influenced by motor costs, often with a bias toward choices requiring lower physical effort. Although this effect has been demonstrated in perceptual decision tasks, if similar effects are present when decisions depend on internal cognitive representations remains an open question. To test whether motor cost interacts with these representations in determining choice, participants performed a two-choice transitive inference (TI) task in which they first learned the rank order of a set of stimuli and then used this knowledge to infer ordinal relationships between pairs of items. Responses were made by releasing a left or right button to indicate the higher-ranking item, while the force exerted on each mouse button was monitored throughout the task. Just as the degree of similarity between stimuli affects accuracy and response latency in perceptual tasks, similarity between item ranks produces a comparable interference in TI tasks. This effect is known as the symbolic distance (SD) effect: the smaller the rank difference, the harder the decision. TI can be further influenced by the spatial association between side of the effector used to respond and the rank of the item (spatial effector-rank association; sERA), which facilitates decision outcomes if a higher-ranking item is paired with a right-hand movement. Using logistic regression analyses, we found that when the responding finger exerted greater force, the SD and sERA effects were reduced. This supports the hypothesis that the physical effort required to initiate an action directly influences the evaluation of decision options.