When artificial post-response outcomes did not modulate the Potentiation Effect of Grasping Behaviours

Seeing large (e.g., pears) or small objects (e.g., cherries) potentiates power and precision grip, respectively. According to the motor simulation account, this potentiation effect reflects an automatic access to object representation, including the grip usually associated with the object. Alternatively, this effect might be due to an overlap between magnitude codes used to represent both manipulable objects and response outcomes. In Experiment 1, participants saw objects usually grasped with a power or precision grip and had to mimic these gestures on a specific device. In the corresponding and non-corresponding conditions, each response generated low-pitch or high-pitch tone (i.e., a large vs. small perceptual outcome, respectively). In line with the ideomotor theories according to which voluntary actions are carried out due to the anticipation of their outcomes, each response generated a low-pitch or high-pitch tone. Response times were shorter when the object and the response were compatible than when they were not, independently of the magnitude of the artificial post-response outcome. Our results suggest that the potentiation effect could, under some circumstances, be immune to post-responses outcomes, which could be consistent with both motor simulation and magnitude coding accounts. To further disentangle these explanations, we conducted a second experiment with the device set horizontally to eliminate the grasping component of the responses. As in Heurley et al. (2020), the results revealed a potentiation-like effect, suggesting that the underlying process in our experiments could be better explained by the magnitude coding account.