The effect of object affordances on motor action priming used in rapid balance recovery actions


There is considerable evidence to suggest that object affordances (see Gibson, 1966) can serve to moderate volitional responses by "priming" the visuomotor system toward certain actions (e.g., Tucker & Ellis, 1998). Typically, these studies assume that shorter voluntary reaction time latencies reflect more efficient movement planning. Questions remain however, as to whether object affordances offer the same motor priming benefits in situations where the temporal window to initiate motor action precludes volitional movement planning (e.g., during an unexpected balance perturbation). In this study, participants sat in a custom-built chair that delivered posterior perturbations and, on each trial, were presented with two of three types of stimuli within their reach (two graspable poles and a flat non-graspable control surface). They were instructed to reach out and grasp one of the poles at the moment of perturbation so as to mitigate the "fall". To assess cortical activity that may be indicative of motor planning in response to the perception of object affordances, changes in oxyhemoglobin (HbO) in the right and left pre-motor and motor cortices were measured using a continuous wave fNIRS system. Results revealed a significant increase (F= 5.2, p= .03 ) in HbO in the right and left hemisphere (M = .004 mM) in response to objects that afford a grasping action, compared to when no grasping opportunity was present (M = -.034 mM). These results suggest that object affordances may be continuously perceived and integrated by the system to be utilized in a potential situation of balance threat.