On the connection between perception, motor activity and emotion
The importance of the perception of one’s own body is already evident when four-legged Aibo robots play soccer. The little kicking machines don’t track if and how they hit the ball, but have to wait until it rolls back into their camera’s field of view. A human being, on the other hand, already has a sense of whether the shot has succeeded or not when he touches the ball. Two studies have now looked at how this internal perception works.
In the current ie of the journal Science, a team of U.S. researchers reports on an experiment designed to help distinguish the brain regions that control the execution of movements from those that perceive those movements. Subjects were asked to trace the outline of an ellipse on a screen with a cursor. In doing so, they could not see their own arm with which they controlled the cursor. During several successive trials, the movements of the cursor in the horizontal plane were gradually reduced, so that at the end the subjects had to describe a circle with their hand in order to create an ellipse on the screen. Nevertheless, all were convinced to have executed ellipses also by hand. In the conflict between eyes and body perception, the eyes won out.
In order to clarify where exactly in the brain this conflict takes place, neurobiologist Andrew B. Schwartz, University of Pittsburgh, team conducted the experiment with monkeys, whose brain activity was measured in the process. Based on earlier findings, special interest was directed at the ventral pramotor cortex, which is associated with the coordination of perception and movement, and the primary motor cortex, which controls goal-directed movements. Decoding of neuronal activity showed that the primary motor cortex followed the actual movements of the hand, whereas the ventral pramotor cortex followed visual perception. The researchers suggest that the ventral pramotor cortex could represent a node that connects the perception of a particular object with the resulting movement.
Assigning perceptual functions to the ventral pramotor cortex challenges common notions of how the brain works. Jacqueline Gottlieb and Pietro Mazzoni of New York’s Columbia University therefore call for further research in a commentary article before this view can be widely accepted. Finally, the coding of sensory signals does not automatically mean that the respective brain area controls perception. Rather, such signals could also serve to plan movement. The results of the study by Schwartz et. al. therefore had to be related even more strongly to observations of visual perception.
The assessment of one’s own heartbeat
A different form of body perception is the subject of a study conducted by a team of British researchers led by Hugo D. Critchley, University College London, published in Nature Neuroscience. Here, the subjects were asked to judge the extent to which their own heartbeat was synchronized with an acoustic signal. On the one hand, this involved using imaging techniques to identify the brain regions that control this internal perception (insula and operculum). On the other hand, the scientists looked for correlations with the respective subjective sensitivities of the test subjects.
It turned out that the subjects who scored most accurately on the heartbeat test were the most emotional. This initially confirms theories that understand emotions as subjective perception of physical reactions to external stimuli. However, the correlation could only be observed for negative emotions such as anxiety and depression. The authors could not find any connection between the accuracy of the inner body perception and the experience of positive emotions.
For the designers of soccer robots, who want to teach their players goal instinct and ball feeling, the study may nevertheless be a reason to think more about the connection between inside and outside perception.