The influence of stimulus concentration and odor intensity on relaxing and stimulating perceived properties of odors

It is generally assumed that intensity can be used as a proxy of the arousing properties of odors: the more concentrated an odorant, the more intense an odor and the more stimulating and the less relaxing the odor. The aim of the present study was thus to investigate the relationship between relaxing and stimulating properties of odors when judged on two independent scales, for different levels of stimulus concentration. Thirty-three volunteers judged relaxing, stimulating, pleasantness, familiarity and intensity properties of four odors, namely strawberry, lavender, coffee, and lemon, at five concentrations. Our findings show that for all odors, higher stimulus concentration was associated with higher perceived intensity and higher stimulating judgments whereas it was not associated with lower relaxing judgments. On the contrary, lavender and strawberry were also judged more relaxing when stimulus concentration increased whereas coffee and lemon relaxing properties remained the same overall whatever the concentration. Odor familiarity increased with stimuli concentration as well as pleasantness (with the exception of coffee odor). Our results underline the need to use two separate unipolar scales when assessing the relaxing and stimulating properties of odors in self-report questionnaires. They also question the suitability of the commonly used bidimensional framework (valence vs. arousal) to describe olfactory emotions.