Figure 1.

Parametrically varied odor stimuli. We prepared nine opaque bottles containing mixtures of brown sugar (Odor A) and black pepper (Odor B). Two additional bottles served as standards, one containing only brown sugar and the other containing only black pepper. Standard bottles were labeled A and B, respectively, and participants were allowed to reference these bottles throughout the experiment to aid in their judgments. The nine unlabeled stimulus bottles contained combinations of brown sugar and black pepper in varying proportions. The weights of the bottles were equated, and the overall quantities of brown sugar and black pepper were chosen to roughly equate the perceived intensity of the two when each was smelled in isolation (see in "Methods" section).