Abstract: Odors are strong elicitors of affect, and they play an important role in guiding human behavior, such as avoiding fire or spoiled food. However, little is known about how risky decision making changes when stimuli are olfactory. We investigated this question in an experimental study of risky decision making with unpleasant odors and monetary losses in a fully incentivized task with real outcomes. Odor and monetary decisions were matched so that monetary losses corresponded to the amount of money participants were willing to pay to avoid smelling an odor. Hierarchical Bayesian analyses using prospect theory show that participants were less sensitive to probabilities when gambling with odors than when gambling with money. These results highlight the importance of taking the sensory modality into account when studying risky decision making.
5 DISCUSSION
To reach a better understanding of how decision making changes when outcomes are affect rich, unpleasant, olfactory stimuli compared with monetary losses, we asked participants in a laboratory experiment to make a series of decisions involving real consequences (monetary losses or smelling unpleasant odors) that were matched in subjective value. On a behavioral level, participants were more likely to choose the more risky option in the monetary gambles than in the odor gambles, suggesting that participants were less sensitive to differences in probabilities with odor gambles. In line with these findings, modeling participants' choices with CPT using a Bayesian hierarchical approach showed a more strongly curved probability weighting function for odors than for monetary gambles. These results correspond to the literature on the changes in decision processes when outcomes are affect rich (e.g., Lejarraga et al., 2016; Pachur et al., 2014; Rottenstreich & Hsee, 2001; Suter et al., 2016). They suggest that in decisions involving affect‐rich odors, participants' decision processes are less sensitive to probabilities. This result extends previous findings by Stancak et al. (2015) that unpleasant odors can increase loss aversion by showing that olfactory outcomes can also affect the subjective weighting or perception of probabilities. These insights are of direct importance for situations in which outcomes are olfactory. Furthermore, they support the initial findings by Ditto et al. (2006) showing a change in decision making when outcomes included an olfactory dimension. This suggests that odors will also affect risky decision making in situations in which odors are an integral and important feature of the outcomes, as in partner or food choice, for instance, when deciding whether food is still edible past its expiration date.
Moreover, our study provides clear evidence that affect‐rich outcomes change sensitivity to probabilities even when outcomes are real and decisions consequential. By using choices with real consequences, we were able to investigate whether the choices participants made with money and odors differed in “quality” in the sense that they affected the likelihood of losing. Participants chose the gamble with the higher expected value less frequently in the odor gambles than in the monetary gambles. Furthermore, participants for whom the payout gamble was an odor gamble were more likely to incur a loss than participants for whom the payout gamble was a monetary gamble. Thus, participants may be less able to choose options that maximize their earnings when decision outcomes contain affect‐rich outcomes such as unpleasant odors.
Although our results dovetail with those of previous studies using affect‐rich outcomes (e.g., Rottenstreich & Hsee, 2001), there were some noteworthy differences from studies that used real affect‐rich outcomes: Specifically, Krawczyk (2015) and Berns et al. (2007, 2008) did not find a decrease in sensitivity for the probabilities of affect‐rich outcomes. Krawczyk used vouchers in his study and measured affect richness with how excited participants were about receiving the voucher. Possibly, the observed differences between affect‐rich and affect‐poor vouchers in this study reflected differences not only in affect but also in perceived utility.
For the differences from the studies by Berns et al. (2007, 2008), there are at least two possible explanations. First, Berns et al. investigated risky decisions using real affect‐rich outcomes (i.e., electric shocks) but did not have a monetary control group and thus compared their findings with parameter estimates for gamma parameters within CPT reported in the literature (e.g., Abdellaoui, 2000; Tversky & Kahneman, 1992). In our study, we found differences in probability weighting, but the average probability weighting function estimated for the odor gambles actually resembled the parameter estimates reported in the above‐mentioned studies more closely than the probability weighting function in the monetary gambles. 7 Thus, it is possible that in the studies by Berns et al., differences in probability weighting would have appeared if the same gambles had been presented with matched monetary outcomes. Second, in Berns et al.'s studies, participants received immediate feedback after each choice, whereas in our task, participants experienced the odor at the beginning but then did not receive feedback until the payout gamble selected at the end of the experiment. Perhaps differences in probability weighting diminish over time when participants experience real affect‐rich outcomes repeatedly.
In addition, there are some limitations of our study. First, we had to exclude 20% of our participants because they did not perceive the odors as unpleasant enough to be willing to spend money to avoid smelling them again. Although we tried to include only participants with a normal sense of smell, we used a self‐report measure. Thus, it is possible that these (or some of these) participants had a reduced sensitivity to odors that they were not aware of or not willing to disclose. Regarding the generalizability of our results, it could mean that the overall influence of odors on decisions is less strong than our results indicate. Second, we equated monetary losses and unpleasant odors based on participants' WTP judgments. This relies on the assumption that participants are able to accurately price smelling an unpleasant odor. Difficulties in setting a price for smelling an unpleasant odor might have driven the differences in choices, suggesting an alternative explanation for why odors or affect‐rich outcomes in general lead to different choices than monetary outcomes (see also McGraw et al., 2010). What speaks against this explanation is that people's evaluations of unpleasant odors do not seem to change much over time and are not affected by familiarity (Delplanque et al., 2008; Delplanque, Coppin, Bloesch, Cayeux, & Sander, 2015), and participants' WTPs in our study were highly correlated with their odor ratings. Third, we used a combination of choice data and mathematical modeling to understand the changes in risky taking. However, to fully understand the cognitive processes underlying the observed changes in choices, we would need to use process‐tracing methods, such as eye tracking or mouse tracking, which would allow us to investigate whether the observed differences in risky decision making can be traced to information processing, such as the attention allocated to outcomes (e.g., Lejarraga, Schulte‐Mecklenbeck, Pachur, & Hertwig, 2019; Pachur, Schulte‐Mecklenbeck, Murphy, & Hertwig, 2018). Finally, in our study, outcomes were odors, whereas in many decisions such as when evaluating food items, a new car, or clothes that still smell of the chemicals used for dying, odors will be just one attribute of the outcome. Here, it will be important in the future to test whether odors still affect the sensitivity to probabilities when other attributes also influence the overall utility of an option.
In conclusion, our study shows a qualitative change in decision processes for affect‐rich olfactory outcomes, leading to a reduced sensitivity to probabilities. These results highlight the importance of taking olfactory stimulus dimensions into account when studying risky decision making. Furthermore, by using consequential decisions with real outcomes, the present study provides solid evidence that the affective intensity of outcomes is an important factor in risky decision making that should be taken into account to better understand the underlying cognitive processes.
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