Abstract
Sniffing, which is the active sampling of olfactory information through the nasal cavity, is part of the olfactory percept. It is influenced by stimulus properties, affects how an odor is perceived, and is sufficient (without an odor being present) to activate the olfactory cortex. However, many aspects of the affective correlates of sniffing behavior remain unclear, in particular the modulation of volume and duration as a function of odor hedonics. The present study used a wide range of odorants with contrasted hedonic valence to test: (1) which psychophysical function best describes the relationship between sniffing characteristics and odor hedonics (e.g., linear, or polynomial); (2) whether sniffing characteristics are sensitive to more subtle variations in pleasantness than simple pleasant-unpleasant contrast; (3) how sensitive sniffing is to other perceptual dimensions of odors such as odor familiarity or edibility; and (4) whether the sniffing/hedonic valence relationship is valid in other populations than young adults, such as the elderly. Four experiments were conducted, using 16–48 odorants each, and recruiting a total of 102 participants, including a group of elderly people. Results of the four experiments were very consistent in showing that sniffing was sensitive to subtle variations in unpleasantness but not to subtle variations in pleasantness, and that, the more unpleasant the odor, the more limited the spontaneous sampling of olfactory information through the nasal cavity (smaller volume, shorter duration). This also applied, although to a lesser extent, to elderly participants. Relationships between sniffing and other perceptual dimensions (familiarity, edibility) were less clear. It was concluded that sniffing behavior might be involved in adaptive responses protecting the subject from possibly harmful substances.
Highlights
One important characteristic of the human sense of smell is that it is a highly emotional sense
No linear regressions were significant for the pleasant odors (R2s < 0.23, ps > 0.110), whereas they were for the unpleasant odors (R2s > 0.71, ps < 0.0001 for sniff volume, and for duration with or without outlier)
Including a wide range of odorants spread over the hedonic continuum and repeating the experiment in different groups of participants allowed us to confirm previous conclusions that participants sniff unpleasant odors less, in volume and duration, than they do with pleasant odors (Warren et al, 1994; Bensafi et al, 2003, 2007; Johnson et al, 2006), and to more finely describe these relationships
Summary
One important characteristic of the human sense of smell is that it is a highly emotional sense. Especially the most obvious ones such as attraction and disgust, serve important adaptive functions (Stevenson, 2010). They are involved in the regulation of behavioral response to events in the surrounding environment. Other types of odor play a major role in sensory pleasure, modulating the ingestion of food, or contributing to social communication through attraction toward mates or attachment to kin. Such emotional responses to odors are expressed at different levels, from conscious and possibly verbalized subjective feelings to physiological changes and motor expression (e.g., Scherer, 2000). Measuring them requires differing methodological approaches, at the verbal (Churchill and Behan, 2010; Ferdenzi et al, 2013a), autonomic (e.g., Alaoui-Ismaïli et al, 1997; Bensafi et al, 2002a) and motor levels (such as sniffing behavior: Bensafi et al, 2003, 2007)
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