Thesis objectives

As we described in section 2.2, numerous factors’ impact on olfactory pleasasntness evaluation and preferences have been studied. However, to the best of our knowledge, no study to date has systemically investigated to what extent decision-making processes can modulate olfactory pleasantness evaluation, and the mechanisms underyling such an influence.

The study of decision-making processes does not have a tradition of using chemosensory stimuli (Oud & Coppin, 2012). Köster (2002), describing the nineteenth century view of the “lower” sensory modalities, such as olfaction and taste, wrote that those sensory modalities “seem rather subjective and less universal – more related to

feelings and emotions than to thoughts and decisions” (p. 27). Perhaps the disregard of olfaction and decision-making processes derives historically from this view. Furthermore, it is often quite simply easier and less costly to present visual or auditory stimuli to participants.

Anosmia, i.e. the absence or loss of the sense of smell, has however anedoctally been described as impairing decision-making processes (e.g., Birnbaum, 2011; Doriez, 2005). The impact of decision-making processes on olfactory processes and olfactory evaluation flexibility remains an open question in terms of systematic experimental work that has seen an astonishing dearth of research.

To the best of our knowledge, there is one exception to the absence of investigation combining odors and decision-making processes: the work of Martin (1922). The goal of the study was to investigate the consequences of interfering with choices after they had already been made. Martin (1922) featured two experiments. In the first, participants were given hypothetical situations in which they had to make choices. Note that in these hypothetical situations, decisions were “impossible of immediate execution” (p. 6). In other words, while they may allow assessing predicted utility, something else is needed to assess experienced utility (Kahneman et al., 1997). As mentioned in section 2.1.5, predicted utility refers to the beliefs, prior to consumption, about the subjective pleasure that will be experienced with a particular stimulus, while experienced utility refers to the subjective pleasure experienced with a stimulus (Kahneman et al., 1997). With odors, this problem could be fixed: the chosen one was presented to the participant for two seconds. Hence, in the second experiment, participants made choices between odors. We agree with Martin (1922) that using odors presents the advantage of quite directly assessing experienced utility.

Considering the modulatory impact of decision-making processes on olfactory preferences, as well as the mechanisms underlying this influence, appears relevant for at least three other reasons.

First, the hedonic dimension of odors has been underlined in both non-scientific and scientific literature. Thus, “a central feature of odor perception is its hedonic or affective component” (De Araujo et al., 2004, p.671) and “it is clearly the hedonic meaning of odor that dominates odor perception” (Richardson and Zucco, 1989, p. 353; see also Engen, 1982; Yeshurun & Sobel, 2009). Because of the saliency of the hedonic dimensions

of olfactory stimuli, using them to investigate hedonic evaluative judgments, i.e.

preferences, seems particularly promising.

Second, the flexibility decision-making processes may introduce to preferences could have a particular relevance in the olfactory context.

Decision-making processes are omni-present in everyday life. Montague (2007) notaby describes life as a compilation of billions of choice moments where one outcome is selected and others forgone (p. 7).

Why might these (numerous) decision-making processes be relevant in the chemosensory context? Because “under natural conditions the olfactory system faces a particular problem not encountered in other sensory modalities, namely, the large numbers and inherent unpredictability of the potentially relevant stimuli. […] In an evolutionary sense, that has also made it difficult for the system to anticipate which features of the chemical environment are going to be of particular relevance” (Hudson &

Distel, 2002, p. 409). This means that the olfactory system can reap the benefits of flexibility that is induced by decision-making processes. This flexibility can then shape the relevance of certain stimuli (for instance, we can hypothesize that chosen stimuli are subsequently more relevant than rejected ones). Given the tight link between olfaction and approach/avoidance behaviors (Stevenson, 2010; Yeshurun & Sobel, 2009), increased or decreased relevance for particular stimuli may result in an efficient course of action.

Moreover, in relation with the main functions of olfaction (ingestion, avoidance of environmental hazards and social communication; see Stevenson, 2010, for details), those decision-making processes’ consequences could be important. For instance, by increasing liking for given smells or given tastes, they can facilitate social bonding, and in some extreme cases, decision-making processes’s could even have life-or-death consequences (e.g., when deciding whether to consume potentially toxic food).

Third, and maybe most importantly, using olfactory stimuli appears to be a promising way of studying implicit memory (e.g., Issanchou, Valentin, Sulmont, Degel, &

Köster, 2002). According to Köster (2002, 2005), olfactory memory is mainly implicit, functioning independently from naming. According to him, “since we can not stop breathing and should spit out poisonous food before swallowing, early detection of the unusual is more important than identification in olfaction and taste […] In “near senses”

there is little time for complex template matching and there is only one adequate reaction

upon danger (feeling, spitting out, or retracting, respectively), whereas in far senses there is time to identify and choose the proper reaction from a variety (hiding, hitting, running, freezing). Thus, a primitive episodic memory based on immediate feelings of (not) knowing, or detecting unexpected deviant odor notes in the situation, prevails in daily odor memory, rather than precise odor recognition in full scale template matching based on detailed feature analysis in working memory” (Köster, 2005, p. 237). Olfactory perception is consequently assumed to rely more on rapid implicit mechanisms than vision or audition. Regarding the nature of the mechanisms underlying preference modulation induced by decision-making processes, using olfactory stimuli consequently means having a valuable tool to investigate implicit mechanisms.

We were interested here in the consequences of decision-making processes, and not in its causes. More precisely, this thesis’ goal is three-fold: i) to investigate whether olfactory preferences can be modulated by decision-making processes; to do so, we notably investigated three alternative methods to control for Chen and Risen (2010)’s criticism according to which choice could simply reflect preferences (see experimental sections 3.3. to 3.6); (ii) to shed light on the level of processing (explicit vs. implicit) required for postchoice preference modulation to occur; (iii) to investigate the stability of this modulation.

We consequently believe we took Elliott and Devine (1994)’s advice of investigating “the inner workings of the affective and cognitive processes involved in the motivated-dissonance-induction-to-reduction sequence” (p. 392-393).