When does action comprehension need motor involvement? Evidence from upper limb aplasia

Abstract

Motor theories of action comprehension claim that comprehending the meaning of an action performed by a conspecific relies on the perceiver's own motor representation of the same action. According to this view, whether an action belongs to the motor repertoire of the perceiver should impact the ease by which this action is comprehended. We tested this prediction by assessing the ability of an individual (D.C.) born without upper limbs to comprehend actions involving hands (e.g., throwing) or other body parts (e.g., jumping). The tests used a range of different visual stimuli differing in the kind of information provided. The results showed that D.C. was as accurate and fast as control participants in comprehending natural video and photographic presentations of both manual and nonmanual actions, as well as pantomimes. However, he was selectively impaired at identifying point-light animations of manual actions. This impairment was not due to a difficulty in processing kinematic information per se. D.C. was indeed as accurate as control participants in two additional tests requiring a fine-grained analysis of an actor's arm or whole-body movements. These results challenge motor theories of action comprehension by showing that the visual analysis of body shape and motion provides sufficient input for comprehending observed actions. However, when body shape information is sparsely available, motor involvement becomes critical to interpret observed actions. We suggest that, with natural human movement stimuli, motor representations contribute to action comprehension each time visual information is incomplete or ambiguous.

Typical action perception and interpretation without motor simulation

“…Our findings thus considerably extend previous results obtained with IDs or congenital paralysis (19,(32)(33)(34)(35). It has been shown that individuals with congenital paralysis of facial muscles recognize facial expressions despite their inability to perform facial movements (32).…”

“…The observation reported here that IDs 1, 2, and 3 were better at recognizing non-upper limb actions than upper limb actions in experiment 2 (see also ref. 19) and that ID3 was impaired in predicting the outcome of the basketball free shot in experiment 5 also point to this possibility (although this difficulty also could be explained by the IDs having different visual experiences of these actions). Collectively, these results call for the development of fresh hypotheses about how knowledge acquired through motor experience helps shape visually and conceptually based computations of body actions.…”

“…In comparison with the controls both ID 4 and 5 performed relatively better for upper limb actions (both modified t tests, ts = 1.19) than for lower limb actions (both modified t tests, ts = 0.52). (C) All the IDs were as efficient as the controls in discriminating learned from novel actions [all modified t tests, ts ( under adverse perceptual conditions (13,19,23,24). Experiment 2 used point-light animations to test this hypothesis.…”

“…14-16). However, to date, the interpretation of the results from neuroimaging, behavioral, neuropsychological, and transcranial magnetic stimulation (TMS) studies that have been cited in support of motor simulation theories of perception remains unsettled (SI Discussion, 1) (17)(18)(19).…”

Typical predictive eye movements during action observation without effector-specific motor simulation

“…Participant D.C. is a 53-year-old man whose performance in various experiments has already been reported (Vannuscorps, Pillon & Andres, 2012;Vannuscorps, Andres & Pillon, 2013, 2014. He has a master's degree in psychopedagogy.…”