Olfactory facilitation of dual-task performance.

We investigated the differential effects of olfactory stimulation on dual-task performance under conditions of varying task difficulty. Participants detected visually presented target digits from amongst a stream of visually presented distractor letters in a rapid serial visual presentation (RSVP) task. At the same time, participants also made speeded discrimination responses to vibrotactile stimuli presented on the front or back of their torso. The response mapping was either compatible or incompatible (i.e., lifting their toes for front vibrations and their heel for back vibrations, or vice versa, respectively). Synthetic peppermint odor or clean air (control) was delivered periodically for 35 s in every 315 s. The results showed a significant performance improvement in the presence of peppermint odor (as compared to air) when the response mapping was incompatible (i.e., in the difficult task) but not in the compatible condition (i.e., in the easy task). Our results provide the first empirical demonstration that olfactory stimulation can facilitate tactile performance, and also highlight the potential modulatory role of task-difficulty in odor-induced task performance facilitation.