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This paper discusses research on odor mixtures with a focus on perception. Conclusions about type of interaction, such as addition, subtraction, and synergism, are linked to theoretical and methodological issues; for example, stimulus-oriented methods (odor thresholds) and response-oriented methods (perceived intensity) give different outcomes. A quantitative model of odor interaction is presented that is congruent with a theory that relates odor intensity and quality of mixtures to type of percepts. The model states that the perceived intensity of mixtures is the vector sum of the perceived intensity of the constituents. It has been verified for several mixtures containing from two to five compounds. Possible predictions about mixture quality have also received some empirical support. The model has shown that nonodorous factors play a major role in the perceived odor intensity of complex gases such as pulp mill effluents.

Multidimensional analysis of twenty-one odors. Scand. J . Psychol., 1973, 14, 131-137.-The present paper reports an experiment on the application of multidimensional scaling to the sense of smell for the purpose of revealing basic psychophysical dimensions of odorants matched in perceived intensity and varying only in perceived quality. The results showed clear evidence for the existence of individuaI odor spaces, but in apparent contradiction to related studies in the literature individual differences were too large to establish a representative odor space for the whole group. For nearly all individual subjects one of the factors extracted seemed to represent a unique hedonic dimension apparently unrelated to the physical attributes of the odorants. It is suggested that such psychological factors may be as important a basis for the judgment of the similarity of odors as the physical attributes of the odorants. Both the interpretation of multidimensional analysis and the extent to which the sense of smell is analytic or synthetic depend on an understanding of this problem. Postal address: B. Berglund Psychological Laboratories University of Stockholm Box 6706 S-113 85 Stockholm Sweden Scand. J . Psychol. 14

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Previous evidence has shown that detection threshold in humans and olfactory neural discharge rate in animal preparations both depend on flow rate of odorous vapor. But no data have been reported that show the effects of flow rate in humans on perceived odor strength at suprathreshold intensities. Subjects learned to inspire at two flow rates, one twice as great as the other, by adjusting (on a cathode ray tube) the transduced trace of a sniff-produced pressure change to match either of two target contours. They then made magnitude estimations of odor strength, while producing either weak or strong sniffs, for odorants presented over a wide range of concentrations via a specially designed sniff-bottle system. The odorant, diluted in diethyl phthalate, was n-butanol in two experiments and n-amyl acetate in two others. Subject-controlled flow rate had no effect on odor strength for either odorant. There was an apparent contradiction between these data and those on neural discharge rate that may, however, be resolved by adopting an odor constancy model: When sniff intensity varies during the olfactory exploration of an odor source, information about the rate at which odorant molecules are established at the receptor site is combined with information about sniff vigor so that the resulting percept is of invariant odor strength.