Despite the conventional belief that olfaction is not as efficient and functional in humans as in other mammals, humans have a very good sense of smell (Stoddart, 1990; Schaal and Porter, 1991; Wyatt, 2014; Wyatt and, 2015; McGann, 2017). Humans are reported to be able to discriminate one trillion olfactory stimuli (Bushdid et al., 2014) and at best an innumerable amount of odors (Gerkin and Castro, 2015). Humans use this sensory channel extensively and chemical communication plays an important role in our everyday life, consciously or unconsciously. Odorants may induce basic emotions: a sniff of lavender odor will activate the autonomic nervous system and elicit “happiness,” while the odor of butyric acid will induce negative emotions such as “anger” and “disgust” (Vernet-Maury et al., 1999). Odorants have an effect on taste perception by enhancing or suppressing both sweet and sour tastes (Stevenson et al., 1999). Perhaps one of the most surprising ways by which odorants influence human behavior is through the modulation of other sensory inputs. For instance, we automatically adjust the spread of our fingers to match the size of an object when grasping. However, if we smell the odor of an orange when grasping a strawberry the amplitude of our hand opening will be larger than when the odor evokes an object of a similar size as the target; conversely, if we smell the odor of a small object (e.g., an almond) when grasping a large item (e.g., a peach) the amplitude of hand opening is reduced (Castiello et al., 2006). Odorants presented at a sub-threshold level, and thus not consciously perceived, can affect visual processing by facilitating the identification of an object in a complex scene that is congruent with the odor (e.g., looking at the picture of an orange among 12 other items after being exposed to orange odor; Seigneuric et al., 2010).

Humans, as well as other animals, are constantly exposed to olfactory stimuli in the environment, some of which may modulate attitudes, behavior, and physiology. In particular, we are regularly exposed to compounds produced by our own body and those of others. Among these are 16-unsaturated C19 steroids (16-androstenes), which have been found in human axillary sweat, saliva, semen, and milk (reviewed in Havlicek et al., 2010). During the last couple of decades, studies have focused on three of these androstenes supposedly produced prevalently, or in greater amounts, by men: 5α-androst-16-en-3-one (androstenone), 5α-androst-16-en-3α-ol (androstenol), and 4,16-androstadien-3-one (androstadienone) (reviewed in Havlicek et al., 2010; Wyatt and, 2015). This does not imply that these androstenes are the only possible candidates for human semiochemicals (cf. Wyatt and, 2015); yet, generally in laboratory experiments, these compounds appear to play a significant role in modulating human behavior, psychology, and physiology, usually in a gender-specific manner (e.g., Gustavson et al., 1987; Bensafi et al., 2003). For instance, androstenes increase: (i) women's ratings of attractiveness of both men and women (Cowley et al., 1977; Kirk-Smith et al., 1978; Saxton et al., 2008; but see Ferdenzi et al., 2016; Hare et al., 2017 where effects are not gender-specific); (ii) positive mood (Jacob and McClintock, 2000; Jacob et al., 2002); and (iii) social interactions with the opposite sex (Cowley and Brooksbank, 1991). Results are not always consistent possibly because different compounds play different roles, for example they might be involved in either intersexual (i.e., in regulating attractiveness of men to women) or intrasexual (i.e., in regulating male-male competition) processes (Havlicek et al., 2010). In addition to effects on behavior, exposure to androstenes may modulate physiological responses such as variation in skin conductance, respiration rate and heart rate, sometimes with opposite effects in men and women (Grosser et al., 2000; Bensafi et al., 2003). Being exposed to one of the commonly investigated androstenes, androstadienone, raises the level of cortisol in women, a hormone linked to arousal and mood (Wyart et al., 2007). If the chemistry of sexual attraction involves states of mind, such as being relaxed, being in a good mood or being open to men's or women's advances, then androstenes may help in “setting the stage” for physical attraction. Yet, androstenol and androstenone did not seem to increase female sexual arousal in response to erotic prose (McCollough et al., 1981; Benton and Wastell, 1986).

In the various experimental studies available in the literature, only one or two of these androstenes have been tested with the same protocol (reviewed in Havlicek et al., 2010). We thus believe that it is important to test the effect of these three different androstenes using the same experimental paradigm, in order to assess their relative importance as potential chemosignals. In the present study we investigated whether and how exposure to androstenes may have an impact on linguistic processing. Our rationale is based on previous studies showing that the semantic value or the emotional valence of olfactory stimulations can interact with lexical access. For instance, by using a lexical decision task in the presence of an odor, Holland et al. (2005) found that odors facilitated the recognition of odor-related words in a lexical decision task (the possible effect of gender was not tested). In a study manipulating the affective valence of stimuli, Hermans et al. (1998) found that the response time to evaluate words as “positive” or “negative” was shortened if preceded by an affectively congruent odor compared to an affectively incongruent odor. This result was only observed in female participants, and interpreted by the authors as being related to general gender differences in odor perception.

Recently, androstadienone has been suggested to specifically increase attention to visual stimuli with emotional significance (Hummer and McClintock, 2009). To our knowledge, this is one of the few studies using, among other psychological tests, a language paradigm, namely the “Stroop task” (Stroop, 1935; for a review, see MacLeod, 1991) in which participants are required to identify the ink color of written words. Naming response (reaction) times are recorded. The Stroop effect occurs when a psychological process (word reading) interferes with the goal of the task (naming the ink color of words). In Hummer and McClintock's (2009) experiment, the emotional Stroop effect was defined by calculating the difference between naming times of the ink color of emotional words (positive or negative valence such as holiday and pathetic) and of control pseudo-words. The authors also compared matching and mismatching words (e.g., green written in green and green written in blue) to control pseudo-words. Androstadienone slowed ink color identification only for emotional words, both positive and negative, and the effect was similar in men and women. The authors suggested a selective effect of androstadienone on emotional attention, i.e., the lexical emotional content was more difficult to ignore when exposed to androstadienone. This opens novel research questions aimed at exploring the possible role of odor-active compounds, and specifically of androstenes, in the modulation of linguistic processes.

The aim of the present study was to investigate possible interactions between androstenes and language by testing cross-modal modulation between the presentation of androstenes and the processing of words. In particular, we investigated whether androstenone, androstenol, and androstadienone may affect the processing of emotional words with a paradigm classically used in psycholinguistic studies (e.g., Meyer and Schvaneveldt, 1971; Neely, 1991; McNamara, 2005; Bueno and Frenck-Mestre, 2008). In the lexical decision task, participants must determine whether or not a letter string is a real word (for instance, in English: boat vs. trui). Response times and errors are recorded. In our experiment, three types of words were studied representing three emotional conditions: positive emotion words (e.g., love), competitive emotion words (e.g., fight), and control, neutral words (e.g., portion). We used positive and competitive words because the effects of androstenes might be linked to positive (intersexual) or competitive (intrasexual) cue processing. There were three experimental groups of participants (exposed to either androstenone, androstenol, or androstadienone) and one control group (mineral oil), each of which composed of about half women and half men (Table 1). All participants performed the lexical decision task.

In the present study, participants were tested in the context of the priming paradigm, generally used in a large variety of circumstances (e.g., McRae and Boisvert, 1998; Plaut and Booth, 2000; review in McNamara, 2005; Bueno and Frenck-Mestre, 2008). In the experimental condition, participants are exposed to a first event (the prime) that is supposed to facilitate the recognition/categorization/naming (and more generally the psychological or motor behavior) of a second one, the target, whenever they are linked. In the control condition, this prime is replaced by another prime not related to the target. If a mental relationship exists between the prime and the target, then the target is processed more rapidly in the experimental condition. For instance, presenting a prime word such as doctor facilitates (i.e., accelerates) the recognition of the target word nurse (pinpointing the semantic proximity of these concepts in memory), compared to the situation where the prime (e.g., window) is not related to the same target word nurse. The present study falls into the framework of the semantic priming effect since it compares the exposure to one event (the androstrene treatment) and its effect on a target word.

We expected that exposure to androstenes would influence processing of emotional words, and that these processing effects might differ according to emotional valence of words (positive, competitive, or neutral). In a lexical decision task, we recorded response times (the latency to decide whether a sequence of letters is a real word or not) and error rates (correctly distinguishing between words and pseudo-words). In lexical decisions, responses to positive stimuli are generally faster than to negative stimuli (review in Kuperman et al., 2014).

We hypothesized that androstenes could act at two levels. First, at the level of attentional processes. Knowing that androstadienone enhances attention to emotional stimuli (e.g., Hummer and McClintock, 2009), we expected that androstenes would increase attention to emotional words, compared to control words. Moreover, given that androstadienone enhances the feeling of being focused (Lundström et al., 2003), we expected that error rates in androstene-exposed groups would be lower than in the control group.

The second level addresses the possible function of androstenes in sexual selection. If androstenes are involved in inter-sexual relationships, exposure to androstenes would facilitate the processing of positive words. We would therefore expect faster response time and lower error rates for positive words compared to the other categories of words in androstene-exposed participants. Moreover, if androstenes are involved in intra-sexual processes, we would expect that the processing of competitive words may be facilitated (faster responses, lower error rate) compared to the other categories of words. Different androstenes may differ in their effects; this is why it is important to test different androstenes using the same protocol.

The effects of androstenes have been shown to be gender-specific in some studies (e.g., Saxton et al., 2008) but not in others (e.g., Ferdenzi et al., 2016). Therefore, we could not formulate a clear prediction in this respect; however, we tested whether the effects of androstenes on response time and error rates were modulated by sex.

In this study we used a lexical decision task to investigate the possible effect of exposure to 16-androstenes on language processing. Slower responses in the task indicate increased attentional allocation to the presented words. We tested the effects of three androstenes most commonly used in previous research: androstenone, androstenol and androstadienone. Previous studies typically used only one of these compounds in a given experimental paradigm (e.g., Hummer and McClintock, 2009), which precludes the possibility to determine whether reported effects are elicited by any androstene or whether they are compound-specific (Havlicek et al., 2010). We compared effects of these androstene compounds on three categories of target words. We had three emotional conditions: positive emotion words, competitive emotion words, and control words. Our results show that priming of distinct androstene compounds had different effects on linguistic processes. We report two main findings. First, we analyzed the response time of participants in a lexical decision task, i.e., the latency to make a decision whether a sequence of letters is a real word or not. We show a modulating effect of one androstene on response time to words with different valence: androstenone differentially altered the response time of words with competitive and positive valence, independently of the participants' gender (Figure 1). Both men and women exposed to androstenone were slower when presented with competitive words than with positive words. This effect was not observed for the other two compounds, suggesting a compound-specific effect on semantic processing. When comparing the androstenone-exposed group and the control group (exposed to mineral oil), we observed that, for both sexes, the response time to positive words was faster in the androstenone group (Figure S1). Second, we analyzed the occurrence of errors (false negatives, i.e., a real word was not identified as such). Here, we observed gender-specific errors modulated by a different androstene: men exposed to androstenol made significantly fewer errors compared with those in the no-odor control group (Figure 3). Such an effect was not observed in women.

These results support the hypothesis that androstenes modulate attentional processes. Several studies suggest that attention is disengaged more slowly from negative stimuli than from positive ones and the consequence of this delayed disengagement is slower responding in lexical decisions (review in Kuperman et al., 2014). Our results that exposure to androstenone induced a slower response time to competitive words compared with positive (but not neutral) words is in agreement with these findings. Slower response times may indicate greater allocation of attentional resources toward emotional information contained in this category of words, which hold attention longer. This might be important in the context of partner choice and/or intrasexual signaling. However, our predictions stemming from the sexual selection hypothesis were not verified.

Regardless of treatment, women were overall slower to react to competitive than positive (but not neutral) words (Figure 2); women may particularly attend to competitive words because they reveal something about male competitive attitude (where high competitiveness is desirable), or alternatively because the use of competitive words in a conversation might reveal high dominance or aggressiveness in men, characteristics that may be undesirable for long-term relationships (Puts et al., 2012; Valentine et al., 2014). It appears that androstenone accentuates the impact of emotional information conveyed by words because positive words, which in general elicit lower response time (Kuperman et al., 2014), were identified even faster under androstenone exposure compared to exposure to control (Figure S1).

A different androstene had an effect on error rates, and this effect was sex-specific (Figure S2). Men exposed to androstenol made fewer errors than controls (Figure 3), thus appearing more focused on the task under this prime. This could be the effect of general arousal and/or feeling in a competition context when perceiving certain 16-androstenes. Indeed, previous studies showed that men avoid sitting on chairs that were treated with androstenone in a waiting room (Kirk-Smith and Booth, 1980; Pause, 2004) and exposure to androstenol made men consumers evaluate male magazines as more masculine (Ebster and Kirk-Smith, 2005). Interestingly, the effect of androstenol was sex-specific in a study showing that men avoided androstenol-sprayed stalls in restrooms while women showed no preference. This was interpreted as supporting the idea of androstenol as “human spacing signal,” which would be relevant particularly in male-male competition (Gustavson et al., 1987). Although the effects of androstenes on, for instance, ratings of attractiveness appeared to be gender-specific in some studies (e.g., Cowley et al., 1977; Kirk-Smith et al., 1978; Saxton et al., 2008) but not in others (Ferdenzi et al., 2016; Hare et al., 2017), our results are partially consistent with studies in which sex differences have been described in semantic processing and in priming processes. Using event-related potentials, for example, Wirth et al. (2007) showed that women and men differ in the depth of semantic elaboration and integration; in general, women appear to conduct a deeper semantic analysis than men. However, gender-specific effects might be amplified when women participants face a male experimenter, or vice versa. The effects of androstenes have indeed been shown to be context-dependent, the reactions of women being more prevalent in presence of a male experimenter (Jacob et al., 2001; Lundström and Olsson, 2005). Future research in this area should consider systematic counterbalancing of the experimenter's gender.

In our dataset, androstadienone exposure did not induce statistically significant effects, despite it being a widely used and “popular” compound (see Wyatt and, 2015), which is often associated with changes in behavior. Several studies suggest that androstadienone enhances women's feeling of being focused and modulates positively psychological arousal and mood (Lundström et al., 2003; Lundström and Olsson, 2005). In particular, Hummer and McClintock (2009) obtained positive results using the Stroop task (see introduction). The difference between the current and these previous studies might be due to the fact that the information processing strategy needed for lexical decisions is different from that underlying identification (reading aloud) of words (Schmidt et al., 2013). Furthermore, although we tested the responses to differently valenced words in the same participants, tests of the effects of treatment (exposure to one of three different androstene compounds or mineral oil control) were carried out between-subjects. Further tests of compound-specific effects might benefit from exposing the same participants to the different odor compounds. Although Holland et al. (2005) have shown an effect of odor priming on linguistic and other overt and covert behavioral processes, the present study investigated such effects using three distinct human-produced odorant androstenes. The priming effect induced separately by two of these androstenes had an influence on the response times (or error rate) to the subsequent linguistic material, thus confirming a direct link between chemo-perception and activation of high-level integration processes such as memory and language comprehension. Further steps should involve investigating the effects of androstenes in experiments using larger linguistic units such as sentences. If androstenes can truly affect behavior, their effects should be revealed in the processing of sentences describing obviously conflicting or positive situations, for instance. We thus expect that androstenes would also modulate response times in complex linguistic tasks. Another point open to future enquiry relates to the fact that these androstenes are emitted as mixtures in human body secretions/excretions. Thus, another step would be to assess the priming effects of mixtures of androstenes, possibly in the context of other odor-active compounds of body odor headspace.

In conclusion, whole body odors, including axillary odor, have been shown to influence a range of human judgments, attitudes and behaviors, just as they do in other animals (e.g., Gosling and Roberts, 2001; Wyatt, 2014). There is currently uncertainty concerning the nature of the odorants conveying such effects, and individual androstenes have been intensively assessed for their particular and specific influence on behavior (Havlicek et al., 2010; Wyatt and, 2015). We concede that androstenes are just one set of compounds within a much larger and complex mixture (e.g.,Curran et al., 2005; Gallagher et al., 2008; Dormont et al., 2013), and therefore we do not wish to make claims about whether the effects reported in the literature are exclusively produced by androstenes. Other types of odorants present in the body odor mixture need indeed to be tested. However, androstene compounds certainly contribute to axillary odor profiles and could therefore provide functional cues (or even signals) that are used in inter-individual assessment. Our results are consistent with other studies in showing that they elicit measurable behavioral effects, and suggest some androstenes at least have the potential to make a contribution to the effects seen using whole body odor. Furthermore, because we set out to compare effects of three different androstene compounds, and in view of the results in which we find compound-specific effects, it is possible that individual androstene compounds (or their relative concentrations) may have functional effects in modulating social interactions. Androstenes, which are produced in higher quantities in males, might be involved in intersexual and intrasexual communication (Pause, 2012; Lübke and Pause, 2015), and particularly in modulating responses to words in social contexts that are associated with specific emotions.

Pd, SB, HM, and AS conceived the study; Pd, SB, HM, AS, BS, and SR designed the study; Pd, SB, HM, and AS carried out the experimental work with the help of students and prepared the dataset; HR analyzed the data; Pd and HR wrote the manuscript with the contribution of SB and SR. All authors read, commented, and approved the manuscript.