Olfactory stimulus can form human’s perceptions and evaluations of an individual after detecting ambient odor or body odor. Scientists have long made significant revelations in olfactory sensing mechanisms. However, most of said this progress primarily focused on visual and auditory cues, with studies on how odors influence social decision (e.g., trustworthy, attractive, cooperativeness) still remaining as a novel scholarly perspective and is only scattered in various empirical studies with an overall lack of systematic summaries and reviews. This paper reviews existing research on the olfaction-decision making, thereby describing new insights into the mechanisms on how odor sensory experience might influence individuals’ decision making on social domain from five perspectives: phylogenesis (evolutionary hypothesis), body interaction (pharmacological hypothesis), emotion-induced (emotion-induced hypothesis), cognition (embodied metaphor hypothesis), and interpersonal interaction(social construction hypothesis).
From an evolutionary framework, the olfactory sense is perceived as an "adaptor" evolved by humans to address early pressures from survival and reproduction, creating an entire set of approach or avoidance behaviors across the course of human evolution. The sense of olfaction, as it relates to flavor perception, is adept at discriminating flavors from cooked food, working with various brain circuits to create food perceptions that humans want and crave, allowing us to recognize food and detect potentially harmful substances in its environment. Olfaction also plays an important role in partner selection through detect the degree of matching of MHC genes, and the decline in health of individuals due to cognitive disease processes affecting the normal function of olfaction or brain projection pathways. Human integrate multiple sources of information to make adaptive decisions in uncertain environments. In this way, olfaction serves as a safety mechanism, alerting us of the presence of harmful or offensive objects and predators, thus increasing our chances of survival and increase quality of life.
The pharmacological hypothesis proposes that various odors can directly interact with and impact the autonomic central nervous system and/or endocrine systems, thus leading to changes in mood, physiology, and behavior. This, in turn, potentially influences our social judgements and decisions. Olfactory stimulation via scents has been shown to result in rapid alterations in physiological parameters such as changes in blood pressure, pupil dilation, skin temperature, pulse rate, brain activity, and so on. Although psychologists have long utilized human psychophysical data to construct hypothetical models for information processing in cognitive and perceptual tasks, there remains much debate surrounding said approach.
The emotion-induced hypothesis is one of the most widely accepted hypotheses. Current studies show extensive evidence of odors having hedonic valence and can thus regulate moods and emotions either overtly or subliminally, thereby influencing decision-making behavior. In most studies, odors were found to induce not only pleasantness and disgust, but also emotions such as fear and anxiety. Growing evidence also suggests that humans possess the ability to deduce emotional states in conspecifics exclusively through ambient scent and body odor. Neuroimaging studies show that olfactory processes and emotional processing systems are highly overlapping in both human and non-human animal models.
Following the embodiment theories, the individual's body functions act as a mediator between the external environment and the mind. Odors experienced by an individual play a role in organizing their understanding of various entities. Some studies found that scents affect the feeling of body heat, implying that prior associations with odors may impact bodily self-consciousness. The cognitive aspects of odor relate to an individual's sensory inputs and physical affordances, the way in which their actions shape their perceptions and concepts, and the information obtained from external environments. In comparison to other bodily contingencies, such as visuo-tactile sensations, scents may produce a milder cue to elicit illusory embodiment given its ability to operate at a subconscious level.
Social constructivism argues that the routines and practices of daily life may exist independently of our conscious thought, and that their particular authenticity bears clear, current traces of such undeniable social origins and evolution of culture and the arts. The sense of smell activates an individual's innate cultural heritage, which then influences their decision making. Linguistic and socio-cultural norms triggered by odor stimuli may alter individuals’ emotional and cognitive meaning of odors and sub-consciously influence an individual’s social judgement and decision-making. Some reports of strong associations between certain odors and cultures imply that such odor-culture associations are likely acquired and may vary across different cultures. Indeed, smelling can also be lexicalized in complex ways, thus reflecting how people in different environments use and think about odors.
Studies also show the methodological issues with dependent measures and stimuli, as well as a greater awareness of the effects of context and individual differences that shape odor effects (e.g., age, gender, cultural background, odor experience, and preferences), ultimately leading to inconsistencies in the data. Clearly, olfaction pervades all aspects of life, influencing mate selection, conception, and disease. Despite it having various issues that need further addressing, and it still remains an area worthy of further study.
