Brain Hemisphere Activity

Have a right-handed friend tap on a sheet of paper with a pencil held in the right hand for one minute. Then have the person do the same with the left hand, using a fresh sheet of paper. Finally, repeat the procedure, having the person talk at the same time as tapping. For most people, talking will decrease the rate of tapping—but more for the right hand than for the left, probably because both activities involve the same hemisphere (the left one), and there is competition between them. (Left-handed people vary more in terms of which hemisphere is dominant for language, so the results for them will be more variable.)