Experimenters' expectation and subjects' knowledge of hypotheses in simple reaction time to lateralized visual stimuli.

Researchers in experimental neuropsychology usually recruit "naive" normal subjects. In this preliminary study, we attempt to consider the role of such a selection. Sixty-four normal, right-handed subjects were enlisted for an experiment on simple reaction times to laterally displayed visual stimuli for which, according to the literature, no cerebral asymmetry is expected. In the course of the experiment, the subjects were "informed" about the hypothesis of the current research. Four subgroups of 16 subjects received four different kinds of information, one for each subgroup; moreover, in each subgroup, half the subjects were examined by an experimenter who hoped to modify the performance and the other half by an experimenter who supposed that information would not affect the behavior of the subjects. The results do not reveal any effect of instructions or experimenters and are discussed to plan future research.