If we have learned to solve problems by one method, we often have difficulty bringing new insight to similar problems. However, electrical stimulation of the brain appears to help subjects come up with fresh insight. In a recent experiment1 conducted at the University of Sydney in Australia, 40 participants were trained to solve problems in a certain way and then asked to solve an unfamiliar problem that required fresh insight. Half of the participants were randomly assigned to receive noninvasive electrical stimulation of the brain while the other half (control group) received sham stimulation as a placebo. The participants did not know in which group they were. In the control group, 20% of the participants successfully solved the problem while 60% of the participants who received brain stimulation solved the problem.
(a) Is this an experiment or an observational study?
(b) From the description, does it appear that the study is double-blind, single-blind, or not blind?