6.5.2.2 How it works
This predictive process may also be at the root of why physical fights tend to escalate. Notice how tit-for-tat tussles between children (or indeed brawls between adults) intensify, with each person claiming that the other hit him harder. In a recent study,3 a motor was used to apply a brief force to the tip of each participant’s left index finger. Participants were then asked to match the force they felt using their right index finger to push down on their left index finger through a force transducer.
Results showed that participants consistently applied a stronger force than that which was applied to them. The authors suggest that, just as when we try to tickle ourselves, the brain predicts the sensory consequences of the self-generated force and then reduces the sensation. We can only predict the outcome of our own actions and not of someone else’s, so an externally generated force feels more intense. As a result, if you were to deliver a vengeful punch to match the force of your opponent’s blow, it is likely that you would overestimate the strength of the opponent’s punch and strike back harder.
Why have we evolved the inability to tickle ourselves? The force generation experiment shows that sensations that are externally caused are enhanced. Similarly, our reactions to tickling may have evolved to heighten our sensitivity to external stimuli that pose a threat. Our sensory systems are constantly bombarded with sensory stimulation from the environment. It is therefore important to filter out sensory stimulation that is uninterestingsuch as the results of our own movementsin order to pick out, and attend to, sensory information that carries more evolutionary importance, such as someone touching us. When a bee lands on your shoulder or a spider climbs up your leg, the brain ensures that you attend to these potentially dangerous external stimuli by ignoring feelings from your own movements. The predictive system therefore protects us and tickling may just be an accidental consequence.
6.5.3. End Notes
Blakemore, S-J, Wolpert, D. M., & Frith, C. D. (1998). Central cancellation of self-produced tickle sensation. Nature Neuroscience, 1(7), 635-640.
Blakemore, S-J, Frith, C. D., & Wolpert, D. W. (1999). Spatiotemporal prediction modulates the perception of self-produced stimuli. Journal of Cognitive Neuroscience, 11(5), 551-559.
Shergill, S., Bays, P. M., Frith, C. D., & Wolpert, D. M. (2003). Two eyes for an eye: The neuroscience of force escalation. Science, 301(5630), 187.
6.5.4. See Also
Weiskrantz, L., Elliot, J., & Darlington, C. (1971). Preliminary observations of tickling oneself. Nature, 230(5296), 598-599.
Wolpert, D. M., Miall, C. M., & Kawato, M. (1998). Internal models in the cerebellum. Trends in Cognitive Sciences, 2(9), 338-347.
Suparna Choudhury and Sarah-Jayne Blakemore
Taken from : Mind Hacks
