Successful social communication is based, above all, on theability to understand the actions of other people. But how can weimagine what other people are thinking, or what intentions they have?Psychologists and neuroscientists trace it back to a kind of simulationthat goes on in our brain as soon as we observe a person acting. Theactions of the observed person are, so-to-speak, internally imitated.Indeed, researchers at the Max Planck Institute for Cognitive andNeurosciences in Munich, in cooperation with scientists from theUniversity of Bournemouth in England and Rutgers University in Newark,New Jersey, have shown that we understand the actions of anotherperson, apparently, on the basis of our own "action inventory". Inother words, our own mind and body give us the foundation to understandwhat other people are doing, thinking, or feeling. Evidence for thiscomes out of an experiment involving two patients that, because of anextremely rare illness, lost the ability to perceive their own body.(Nature Neuroscience, October 2005).
In the recently published study, Simone Bosbach and Wolfgang Prinzshowed, with their colleagues, that two specific patients have deficitsin their ability to interpret the actions of other people. These twopatients are currently the only known cases worldwide with this kind ofclinical picture. Its psychological consequences are dramatic. Bothpatients report that, at the beginning of their illness, most of all,they had the feeling that they had "lost" their entire body. Sincethen, they have learned to carry out simple body movements. However inorder to do that they have to be able to see their body. In the dark,the patients lose complete control over their bodies, because they areno longer able to determine, for example, the position of their armsand legs relative to the body, with the help of the sensory receptorcells in the joints and muscles.
Normal people can do this without any problems, thanks to theself-perception of their own body (proprioceptive feedback). Thisself-perception also lets our brains know when, and in which range,muscles contract or expand, and to which extent joints bend or stretch.This sense makes us able to pose in certain body positions and to carryout movements, and it is also decisive for the psychologicalconsciousness of having a body.
Bosbach and her colleaguesconfronted the patients with short video films in which people areasked to lift boxes. Each box was a different weight. Both patientswere given the task, in the first part, of guessing the weight of thebox that the person in the film was lifting. The patients received noother clues; they had to guess the weight of the box solely from themotion sequence of the lifter. It turned out that the patients wereable to complete the task as correctly and unerringly as the controlsubjects. Apparently they were able solve the problem using theirknowledge that, for example, a slow body movement signifies a heavyload and a faster movement, which gives the impression the subject wasunloading something, suggests a lower weight.
In the second partof the task, the patients also saw videos of people who were liftingboxes. However, this time, in some cases, the people in the film weredeceived about the actual weight of the boxes. So the actor, forexample, received the information before lifting the box that he waslifting 18 kilograms - when indeed the box weighed only three. Thepatients then had to state whether the person in the video had theright or the wrong expectation regarding the weight of the box. Again,the only source of information for the patients to make their judgmentwas body movement. If the people in the film were deceived about theweight of the box, they tended to show a characteristic discrepancy inthe movement, between the phases in which they prepared themselves tolift the box (expecting a heavy one) and the phase in which they wereactually lifting the box (which was clearly lighter than expected).This discrepancy was not present when the person had a correctexpectation of the weight.
In the second task, normal controlsubjects didn’t have a problem correctly evaluating the situation. Thetwo patients, on the other hand, had great difficulties. They werenotably poorer than the control subjects in determining whether theperson in the video had guessed correctly the weight of the boxcorrectly, or had been deceived.
Finally, in a further experimentthe scientists inverted the task. They asked the patients themselves tolift boxes and filmed them while they did so. During the recording, insome cases, the patients were deceived about the weight of the boxbefore they lifted it. Then, healthy control subjects had to judge,after they saw the video, whether the patient had expected the corrector the false weight. In this task, the control subjects failed, becausethe sequence of motion of the patient, in the case of the falseexpectations, did not show the characteristic discrepancy between thepreparation for the movement and its carrying out. This means that thepatients, because of their lack of self-perception, were unable toadjust their movements to their expectations of the weight of the box.In other words, the patients did not have the option to attunethemselves to the weight of the box before trying to pick it up. Forthe same reason, they were not able to judge other people’sexpectations based on their movement.
Models of movement, whichare activated in the brain when we observe the actions of anotherperson, hold information and knowledge about the way our own bodyfunctions. The possibilities and limitations of movement of our ownbody are the reference from which we process and interpret the actionsof another person. In other words, we understand in others that whichwe can do ourselves, and what we cannot do ourselves, we cannot alsounderstand in others. Feedback from our own bodies apparently plays arole in our intuitive knowledge of the intentions of other people. Inthis way, we can predict not only the consequences of other people’sactions, but we are able to "put ourselves in the position" of theother person. Such a mechanism is the basis for sympathy and empathy,and thus decisive for the success and continuity of socialrelationships.
Bosbach, S., Cole, J., Prinz, W. & Knoblich, G.
Inferring another's expectation from action: the role of peripheral sensation
Nature Neuroscience online : 28 August 2005, Print-Version: Nature Neuroscience (2005), Vol. 8, 1295-1297
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