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Study Shows Why We Can't Tickle Ourselves By Jennifer Viegas, Discovery News type size: [A] [A] [A] March 6, 2006 Healthy humans cannot tickle themselves or attribute their own voices to those of other people, according to a new study that determined that individuals anticipate their own actions, which can beneficially alter their sense of perception. Since it is now believed that a breakdown in this anticipation process may underlie the delusions of schizophrenics, the finding may lead to a better understanding of this mental disorder. According to the National Institute of Mental Health, around 51 million people worldwide suffer from schizophrenia. The study also solves the long-standing mystery as to why most humans and animals cannot tickle themselves. "It's well known that you can't tickle yourself," said Randy Flanagan, one of the study's authors. "One explanation is that since all the sensations are completely predictable, we do 'sensory attenuation,' which reduces our touch perception." Flanagan, a psychologist at Queen's University in Ontario, Canada, added, "If we try to deal with all the sensory information directed at us at any given time, it's overwhelming. We can't focus attention on crucial changes in our environment that aren't a function of our own motions." Scientists previously speculated that we either filter out unnecessary information after the motion or sensation occurs, or that we predict our own actions, which could allow us to mostly ignore unnecessary sensations, such as the feel of our vocal chords while we speak, or the constant tapping our fingers experience while typing at a keyboard. To determine which of the two mechanisms is at work, the researchers had 20 right-handed individuals tap with one index finger on a force sensor that was sandwiched between the tapping finger and the other hand's passive index finger. With each finger tap, the sensor would deliver a tapping sensation to the passive finger. Similar to self-tickling, the test subjects reported that the tap received by the passive finger was weak because they had anticipated the sensation. This occurred even when part of the force sensor was removed during surprise trials where the active finger just wound up tapping the air, while the passive finger still received the expected tap. Findings are published in the February Public Library of Science Biology journal. "We are constantly predicting the consequences of our actions," Flanagan told Discovery News. "When we act on ourselves and on the world around us we predict in real time as we move." Flanagan also explained that a breakdown in this prediction process could be why delusional schizophrenics "hear voices" and mumble to themselves. "If a healthy person murmurs to himself, he knows that he is hearing his own voice," Flanagan said. "Now imagine that the person has a deficit in the predictive mechanism. He murmurs and then suddenly hears murmuring but cannot label it as himself. As he tries to make sense of the alien voice, the explanation for it could be quite bizarre, such as thinking it is coming from a wall or the pavement." He is not certain whether some schizophrenics can tickle themselves, but since their falsely alien sensations often are accompanied by feelings of fear and paranoia, it is likely that the experience would not be pleasurable. Chris Frith, a professor of neuropsychology and deputy director of the Leopold Müller Functional Imaging Laboratory at University College London, told Discovery News that he "was very impressed" by the new study. Both Frith and Flanagan hope that the findings will help schizophrenics. Frith said, "What is (currently) lacking are robust techniques for measuring the magnitude of the (prediction) breakdown. If techniques like the one described in the PLoS Biology paper can be used with patients, then this will have a major impact on diagnosis and the monitoring of the effects of treatment." -- Your representative owes you, not his industry only, but his judgment; and he betrays instead of serving you if he sacrifices it to your opinion. Edmond Burke ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Message: http://www.houseoffusion.com/lists.cfm/link=i:5:198987 Archives: http://www.houseoffusion.com/cf_lists/threads.cfm/5 Subscription: http://www.houseoffusion.com/lists.cfm/link=s:5 Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=11502.10531.5 Donations & Support: http://www.houseoffusion.com/tiny.cfm/54
