A growing body of evidence suggests that we understand other people’s actions and intentions by simulating their movements in the motor pathways of our own brain. Now a study suggests that peripheral sensation and proprioception – the sense of where our limbs are in space – also play a role in this process, specifically when it comes to inferring other people’s expectations from the way they move.
Simone Bosbach (pictured) and colleagues tested two patients, IW and GL, who, because of sensory neuropathy, have the extremely rare condition of lacking any peripheral sensation or proprioception. The patients watched a video of a man lifting different boxes. When the man was always given correct information about the weight of the boxes, the patients, like controls, were able to correctly judge whether he’d lifted a heavy or light box. However, in a second experiment, when the man was occasionally given incorrect information about the boxes’ weight, the patients, unlike controls, were unable to judge from his movements whether or not a box weighed what he had expected (except when the task was made easier using larger boxes). Patient IW also couldn’t make this judgment correctly when he viewed videos of himself performing the same lifting task.
It’s not that the patients were incapable of forming a motor representation of the box lifting movements per se, otherwise IW wouldn’t have been able to lift the boxes. Rather, the authors believe the patients’ lack of peripheral sensation and proprioception affected their ability to activate or sustain a mental simulation of the lifting movements when watching them performed. The researchers said “[The patients’] reduced ability in the present task suggests that to judge mismatches between action preparation and performance in others, one has to access subconscious sensorimotor programmes, which IW and GL may lack”.
Bosbach, S., Cole, J., Prinz, W. & Knoblich, G. (2005). Inferring another’s expectation from action: the role of peripheral sensation. Nature Neuroscience, 8, 1295-1297.