Same-different reaction times to odors: some unexpected findings

Two experiments were carried out using olfactometers that delivered two stimuli with an interval of, respectively, 0.2 s (experiment 1) and 4.0 s (experiment 2) in a same–different paradigm. In experiment 1 (four men, age 38.5¿±¿15.2 and six women, age 25.8¿±¿1.2), four odors and in experiment 2 (nine men, age 23.4¿±¿2.6 and ten women, age 22.7¿±¿1.9), another eight odors were used in all pairs and pair-member orders. Subjects received each combination twice and responded as soon as possible after arrival of the second stimulus. Pair member similarity and odor pleasantness were measured in experiment 1 and odor complexity, familiarity, pleasantness, and self-reported odor imagining ability (high vs. low) in experiment 2. Results showed three independent effects: (1) “Same” responses took longer than “different” responses. (2) High imagers reacted faster than low imagers. (3) Reversing pair member order led to non-reciprocal similarity and reaction times. In different odor pairs, similarity and reaction time (Rt) correlated strongly and prime-familiarity and Rt correlated negatively. Edibility had an effect via prime-familiarity. Pleasantness had an effect only when a less pleasant odor followed a more pleasant one. All these latter effects were unrelated to the effects of participants’ imaging ability.