Relative Contribution of Odour Intensity and Valence to Moral Decisions

Abstract

Meta-analytic evidence showed that the chemical senses affect moral decisions. However, how odours impact on morality is currently unclear. Through a set of three studies, we assess whether and how odour intensity biases moral choices (Study 1a), its psychophysiological responses (Study 1b), as well as the behavioural and psychophysiological effects of odour valence on moral choices (Study 2). Study 1a suggests that the presence of an odour plays a role in shaping moral choice. Study 1b reveals that of two iso-pleasant versions of the same neutral odour, only the one presented sub-threshold (vs. supra-threshold) favours deontological moral choices, those based on the principle of not harming others even when such harm provides benefits. As expected, this odour intensity effect is tracked by skin conductance responses, whereas no difference in cardiac activity - proxy for the valence dimension - is revealed. Study 2 suggests that the same neutral odour presented sub-threshold increases deontological choices even when compared to iso-intense ambiguous odour, perceived as pleasant or unpleasant by half of the participants, respectively. Skin conductance responses, as expected, track odour pleasantness, but cardiac activity fails to do so. Results are discussed in the context of mechanisms alternative to disgust induction underlying moral choices.

Alexithymia and emotional reactions to odors

“…Detection threshold was determined using a two-alternative forced-choice ascending staircase paradigm with seven reversals and no feedback 36 . Each trial included one target (a bottle with the diluted odor) and one control stimulus (a bottle with the diluent only).…”

“…Indeed, the olfactory system is anatomically connected to the limbic system through brain regions including the amygdala, piriform cortex, insula, orbitofrontal cortex and anterior cingulate cortex 30 , 32 , 33 . This preferred link is manifested in the noteworthy ability of odors to automatically induce mood changes 31 and to impact cognition and behavior 34 – 36 .…”

Social odors (even when masked) make you more emotional: behavioral and neural insights

“…However, this paradigm has also other advantages: it allowed studying the effects of the social odor when they are unconsciously perceived. As seen in a previous study 63 , odor effects can emerge irrespective of the perceiving the presence of an odor; moreover, masking the social odor limited the inter-individual differences in odor intensity and pleasantness that can significantly affect decisions, as it seemed in the previous cases when intensity and pleasantness differences across odor conditions were evident 17,63 . Here we succeeded in making these conditions perceptually similar for intensity, familiarity and pleasantness, removing the possible confounding effect of these factors on the differences in the moral decisions.…”

“…Additionally, Schnall et al 17 demonstrated that the presence of a disgusting odor toughens the judgment on vignettes without moral content. Also, we have previously shown that the subliminal exposure to a neutral (non-social) odor can bias moral choices towards options characterized by harm avoidance (deontological options 18 ). Generally speaking, a harm is justified (or to some extent forgiven) if it comes as the side-effect of a moral action carrying a greater benefit compared to an intentional harm with the same outcome 19,20 .…”

“…To our knowledge, previous studies have only explored the behavioral effects of olfactory contextual stimuli on moral choices 17,18 . However, whether and how the social context might impact moral decision making when induced via sensory subliminal stimulation, and the neural underpinnings of moral choices under the exposure of masked social odors are still unknown.…”