The effect of expectation on judgments of odor.

Abstract The effect of expectation on the accuracy of odor judgments was studied in two ways intended to simulate factors in real life. First, the relative frequency of the presentation of the odorant versus a nonodorous substance was varied. In addition, the appearance of the substances was manipulated by coloring some of them and not coloring others. The main finding is that both of these variables affect the subjects' tendency to make the error of reporting the perception of an odor when no odorant has in fact been presented. This tendency persisted even though the subjects were given immediate information ‘feedback’ about the accuracy of each judgment. It seems to reflect a strong and apparently unconscious response bias. The results are discussed in light of contemporary psychophysical detection theory.