1 Introduction

The latest advances in the field suggest that disgust is involved in certain aspects of moral psychology [1–3]. Also, people are known to judge the actions of old people differently to those of young people [4,5]. Previous work in a vignette study and correlational research design [6] has found that disgust sensitivity affects how harshly moral violations of old adults are judged. However, evidence on the relationship between disgust sensitivity and moral judgments (i.e., judgments of a moral violation) towards the elderly is still scarce and requires further experimental studies. Building on the reviewed literature, the present research is intended to extend current research in this largely unexplored topic, by examining whether the influence of affective priming of disgusting pictures on moral judgments is sensitive to the target’s age.

The study of the cognitive/affective foundations of stigmatization indicates that disgust is a relevant variable in this process [3,7,8]. Disgust is at its core an emotional response that is elicited by cues of parasites and disease, experienced as a sense of revulsion, offense, notions of pollution, and a behavioral tendency to avoid a diverse pool of stimuli [9,10]. Disgust sensitivity (i.e., the degree to which people experience disgust) varies remarkably across individuals, cultures, and geographical regions [11–13]. There is evidence that disgust sensitivity decreases with age [14] and that women tend to be more sensitive to disgust than men [12,15]. Disgust sensitivity is associated with several areas of psychology, such as personality traits, psychiatric disorders, and social belief systems [16,17].

Although it is widely held that disgust evolved as a pathogen avoidance mechanism [18,19], some authors argued that disgust has come to be co-opted to be a sociomoral emotion, extending its original function to also protect the psyche from moral degradation [12,20]. Several studies suggest that disgust is involved in certain aspects of moral cognition [1–3]. Disgust can exert a causal role in moral judgments (i.e., judgments of a moral violation), can be a consequence of moral violations, or can “moralize” otherwise neutral acts and persons [21,22]. For instance, some studies found that disgust experienced incidentally makes moral judgments harsher [23,24], although this influence may be susceptible to certain moderators [25,26], such as individual sensitivity to bodily cues [27]. While recent studies have questioned the robustness of the link between incidental disgust and moral judgment [28–31], some authors highlight that more work is needed to determine which disgust inductions, if any, consistently produce carry-over effects on moral judgment [32].

Some authors claim that disgust triggered by a subclass of egregious moral violations (e.g., enjoyment of child pornography) can “degrade” the perpetrator, functioning as a guard against such actions being carried out [20]. Giner-Sorolla and colleagues [3] suggest that disgust not only helps people to value what is “good” or what is “rotten” socially, but also informs perceived intentions and characteristics of the social actors, especially judgments of moral character. Indeed, moral evaluations are not context-free, but are often influenced by the focus on the person being judged [33–34] Research by Giner-Sorolla et al. [3] and Uhlmann et al. [34] suggests that incidental disgust might have a stronger influence on evaluations of individuals, especially when morally irrelevant aspects, such as age, are considered. Since the disgusting is perceived as degraded and polluting [40], disgust establishes an implicit order in which the target of the repugnant is regarded as inferior and impure [35–37; 7]. Consistent with this, disgust influences negative attitudes to a variety of outgroups, such as immigrants, foreigners, socially deviant groups [8,40], obese people [41], and gay men [38,39]. Disgust, then, is an emotion with a great capacity to stigmatize, i.e., rejecting not just individuals but entire social groups [40,41].

One social group that is often included in the realm of disgust is older adults [5,42]. Some evidence suggests that older adults do not necessarily provoke disgust by themselves, but as representatives of old age per se [43]. That is, disgust towards old adults may be explained because of biases about aging as a whole. Perception of vulnerability to disease and awareness of ageing may contribute to this negative bias [44]. Thus, old age is rejected as much as it could transmit illnesses and, what is more, remind us of our mortality [45–47]. Although ageism (i.e., negative attitudes towards older adults) is pervasive in many societies, more research is needed on its correlates and predictors [48]. A consistent finding is that males are more ageist than females [49,50]. Ageing anxiety (anxiety about getting older) has been related to ageism in several studies [49,51,52, but see [53]. Some authors claim that ageism in younger people should be explained as part of a coping strategy to deal with unpleasant thoughts of mortality [54].

Despite anecdotal evidence supporting this link, empirical evidence on disgust towards old adults remains limited and offers mixed results. Nicol and his colleagues [48] found that prejudice towards older adults is related to disgust sensitivity, but that this relationship is mediated by perceived vulnerability to disease and ageing anxiety. A recent study [6] found that older adults were judged less morally harshly than younger adults, with higher disgust sensitivity being associated with harsher moral judgments, irrespective of the age of the perpetrator. Interestingly, lower disgust sensitivity was associated with less harsh (less severe) moral judgments towards older people than to younger people, (e.g.,) suggesting that low disgust sensitivity could partially underlie compassionate paternalism towards the elderly. Altogether, actual empirical research on the role of disgust in moral judgments toward the elderly suggest that this relationship may be more complex (e.g., sensitive to moderators) than predicted by theoretical assumptions and anecdotal evidence.

The fact that the influence of incidental affective responses on moral judgments appears to be largely automatic [55,56] encourages affective priming as a relevant tool for the study of moral cognition. This experimental paradigm is built on the assumption that the affective nature of the prime (e.g., a disgusting image) will impact the subject’s evaluation of the target stimulus (e.g., a moral dilemma). Indeed, affective priming often occurs independently of evaluative intention and of awareness of the prime [57]. Although affective priming has been effectively applied to a vast number of studies [58], this technique has scarcely been applied to moral research. There is evidence that erotic pictures presented in a suboptimal manner (but not other types of pleasant pictures) increase utilitarian moral judgments, which might be due to the erotic stimuli being more arousing [59]. Affective priming through disgusting pictures (depicting human mutilation) exclusively reduced the severity of moral judgments (with no effect on non-moral judgments [60]). The effect of disgust priming on moral judgments may be moderated by how sensitive the individual is to disgust: while disgusting pictures favoured utilitarian judgments in participants with higher disgust sensitivity, the same pictures favoured deontological judgments in participants with lower disgust sensitivity [61]. In sum, the few studies conducted on the effects of affective priming on moral judgments show mixed results, suggesting that more research is needed to disambiguate the direction of the effects of affective priming on the harshness of moral judgments. For instance, whether affective priming of disgusting pictures would have a different effect on the harshness of moral judgments than other types of affective pictures (i.e., depicting stimuli associated with different emotional responses) and whether this effect varies depending on the age of the person performing the action requires further research.

Building on the reviewed literature, which suggests that moral evaluations are often influenced by the focus on the person being judged [33–34], and proposing a stronger role for incidental disgust stemming from morally irrelevant aspects of the person or act in question [3], the present research aims to conceptually replicate and extend Aguiar and his colleagues’ [6] finding that disgust sensitivity responds to the target’s age in the making of moral judgments, by examining whether the influence of affective priming of disgusting pictures on moral judgments is sensitive to the target’s age in a pre-registered protocol. Consequently, we propose the following research questions (RQ) summarized in the following Table 1.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 1. Preregistered research questions.

https://doi.org/10.1371/journal.pone.0328392.t001

2 Materials and methods

2.4 Participants

An initial sample of 278 participants’ responses was collected (see Table 2 for descriptive statistics). We applied the filters specified in the protocol to remove participants and trials. We checked the open response to detect participants which were aware of the study hypothesis, we removed 10 participants (4%). Also, we excluded trials with responses time above 4000, this yield to the exclusion of 7% of trials. Also, we excluded participants which had less than 20 experimental trials after the high response times were removed which removed 32 participants (12%). We did not detect participants’ responses with zero variance. The final sample consisted of 235 participants ranging from 28 to 55 years.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 2. Descriptive statistics of main variables of interest by condition.

https://doi.org/10.1371/journal.pone.0328392.t002

Descriptive statistics showed little mean difference between conditions and similar standard deviations (see supplementary online material for statistics for each vignette). Mean responses were about the middle range of response options (see Table 2).

3 Results

3.1 Preregistered inferential results

We strictly followed our preregistered report protocol [69] for the inferential analysis. For inferential purposes we modeled the response (harshness moral judgment) with a linear mixed model effects regression. In the model we included the condition interaction (Young vs Old) with the disgust sensitivity score and condition interaction with prime type. As random effects we included participant and vignette identifiers which produced a convergent model. Regarding the inferential model, we found that the convergent model included item and participant as random effect (see Table 3). Judging by the intraclass correlation coefficient value the mixed model seems to be an adequate model for the data presented. The coefficients indicate a small negative effect of the Old Condition and no significant interaction effect between disgust sensitivity and condition. Specifically, disgust sensitivity led to harsher moral judgments in both conditions (see Fig 1, RQ1). Priming conditions resulted in no effect on the harness of moral judgements (RQ2). All the analysis showed the same pattern when the excluded participants and trials were included as sensitivity check (see online supplementary material for details).

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 3. Coefficients of main model.

https://doi.org/10.1371/journal.pone.0328392.t003

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 1. Predicted acceptability judgement as a function of disgust sensitivity score (centered).

The relationship is shown for both young (gray) and old (yellow) experimental conditions. Shaded areas are 95% confidence intervals. Marginal plots show the distributions of the predictor (top) and outcome (right) variables for each group.

https://doi.org/10.1371/journal.pone.0328392.g001

3.2 Planned exploratory inferential results

We explored the effects of affective pictures on the harshness of moral judgments, comparing outcomes between conditions featuring old versus young actors. Priming conditions resulted in a positive interaction of disgust prime, this is, disgust prime led to less severe judgements when paired to old themed vignette condition (Table 3).

When comparing between conditions (old vs. young), disgust priming facilitates less severe judgments in the old condition (RQ2). This result suggests that the influence of disgust priming on moral judgments is sensitive to the age of the target (see Fig 2). The analysis of interactions and paired contrasts between age groups (young and old) and types of prime stimuli (neutral, sad, and disgust) indicates that differences in reactions to these stimuli are moderated by the participant’s age. No statistically significant difference was found in reactions to neutral and sad stimuli between the young and old conditions (b = −0.10, SE = 0.09, z =−1.165, p = .244). In contrast, the reaction to disgust stimuli compared to neutral was significantly different (b = 0.20, SE = 0.09, z = 2.34, p = .019), showing that the young condition group responds differently to these stimuli compared to the old group. Most notably, the difference between reactions to sad and disgust stimuli was statistically significant (b = 0.312, SE = 0.089, z = 3.508, p = .0005), suggesting greater differential reactivity in the young group to these types of emotional stimuli.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 2. Predicted acceptability judgements for young (gray) and old (yellow) participants across four Moral Foundations.

Points are predicted means, and error bars are 95% confidence intervals.

https://doi.org/10.1371/journal.pone.0328392.g002

Also, we examined relationships between demographic traits (age, gender) and individual differences (ageism scores, disgust elicited by the word “old”, etc.) with primary outcome measures of judgments. Results showed no effects (see Table 4). Regarding the relationship between ageism scores and emotions elicited by old people, focusing on how this interacts with age condition and affects moral judgment harshness, we did not find any relevant relationship (see Table 4).

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 4. Model comparison for exploratory analysis.

https://doi.org/10.1371/journal.pone.0328392.t004

4 Discussion

According to our first research question, which investigates the role of disgust sensitivity in judging two age scenarios, our findings show that individuals with higher disgust sensitivity tend to make more severe moral judgments. This aligns with previous research suggesting that the experience of disgust can influence moral judgments [3,32,70]. The consistent relationship between disgust sensitivity and harshness of moral judgment across conditions underscores the robustness of this effect. However, contrary to our expectations and to previous studies [6], we did not find an interaction effect between disgust sensitivity and the experimental condition. According to these results, the vignette actor’s age has no influence on the effect of disgust sensitivity on moral judgment. Specifically, we found that the impact of disgust sensitivity on moral judgments remains consistent across different experimental contexts (i.e., age of the actor), suggesting that the influence of disgust on moral judgments is more general than initially hypothesized. It is important to note that our study differs from previous investigations in several methodological aspects (see [6]). Firstly, we employed a larger number of vignettes to assess moral judgments, potentially providing a more comprehensive evaluation of moral judgment. Additionally, our sample had an upper age restriction compared to previous studies. Disgust propensity has been shown to decline with age [70–72] so future studies should consider the age of the participants when we examine this effect.

These methodological differences could account for some discrepancies in the results and provide new insights into the disgust-morality relationship. These findings reinforce the notion that emotions, specifically disgust, play a significant role in our moral judgments. This has implications for our understanding of moral decision-making processes and could have applications in fields such as law, ethics, and public policy. The consistent effect of disgust sensitivity across conditions suggests that individual differences in disgust sensitivity might be a reliable predictor of the harshness of moral judgment [30,70].

The strength of the relationship between disgust sensitivity and moral judgments stands in contrast to recent debates regarding the impact of incidental disgust on moral judgments [28–31 but see [25–27]. As Donner and colleagues [70] note, research on disgust sensitivity does not take a stance on whether the causal influence of disgust on moral judgments is driven by disgust that is incidental or inherent to the moral judgment process. Therefore, it may be that people high in disgust sensitivity are more susceptible to experiencing incidental disgust or to misattributing it (or both). Conversely, disgust sensitivity may be indicative of a stronger propensity to experience intrinsic disgust, which may have attitudinal and behavioral moral consequences. Disgust may influence various aspects of social interactions, serving a pivotal function within the context of a preventive “behavioral immune system” [11], which relies on heuristic signals to avert contact with individuals perceived as potentially infectious. For example, individuals who are perceived as disgusting are often judged as more immoral [33].

A second aim of this research was to investigate the effect of affective pictures on the harshness of moral judgments (RQ2). Postulating that disgust is involved in certain aspects of moral judgments [1,3,58], such as how harshly moral violations of old adults are judged [6], we examined whether the influence of affective priming of disgusting pictures on moral judgments was sensitive to the target’s age. When exposed to disgust priming, the comparison between conditions shows that participants’ moral judgments were less harsh in the old condition than in the young condition. Therefore, our results show that the effects of disgust priming on moral judgments were sensitive to the experimental condition, that is, to the target’s age. This finding suggests that the age of the target may constitute a differential factor when making moral judgments when experiencing incidental disgust.

Our findings align with the work of Giner-Sorolla et al. [3] and Uhlmann et al. [34], which suggests that incidental disgust may exert a more significant influence on evaluations of individuals, particularly when morally irrelevant factors are considered. One such factor could be the target’s age. Indeed, Laurent and Li [33] propose that the influence of disgust within the moral domain is more likely to affect perceptions of moral character than judgments of specific moral behaviors. Further, our results are consistent with previous research showing that the direction of affective priming effects on moral judgements depends on certain moderating variables [73]. Altogether, our findings suggest that a fine-grained approach to the effects of incidental emotional stimuli on moral judgments should take account the interaction between the affective quality of the stimuli and specific features of the target (e.g., the age of the target performing the action).

As stated in RQ2, we expected that disgust pictures will have a different effect on the harshness of moral judgments than other affective pictures (sadness). Our results revealed that, unlike disgust priming, the effect of sadness pictures in moral judgments were insensitive to the target’s age. No effect of neutral priming was observed in any condition.

Prior research on the specific role of disgust in morality has shown that, relative to sadness, disgust more strongly influences moral judgments [56]. Other studies found no evidence that incidental sadness influenced moral judgments [74] Disparity between results may be explained by methodological differences, such as the intensity of the affective induction [64]. Our results add to the existing literature by showing that how the target is perceived may determine whether disgust and sadness affective inductions have differential effects on moral judgments.

Interestingly, disgust, induced through affective priming, did not cause harsher moral judgments. This finding is consistent with previous research on affective priming and moral judgments [58,59], suggesting that affective priming may be a particular case of an affective induction paradigm when it comes to moral research. One possibility is that emotional pictures presented at extremely short exposure times may fail to capture the more “cognitive” dimensions of the emotional response. For instance, research on the impact of short exposure times in affective priming indicates that rapid exposure can trigger initial emotional responses, while responses requiring more cognitive effort typically require longer exposure times for elicitation [75]. Since we did not measure the experience of disgust in the participants, this question requires empirical evidence. Future studies should examine whether the effects of different affective pictures on moral judgments are consistent when presented at longer exposure times.

Some limitations should be noted. Firstly, caution is warranted in drawing definitive conclusions about the affective priming effects on moral judgments. As noted earlier, the influence of induced disgust on moral judgments remains a contentious issue, with several studies highlighting the need for further investigation [28–30]. Secondly, we did not include non-moral situations. Therefore, we cannot claim that our results are restricted to moral judgments. While consistent evidence indicates that higher disgust sensitivity is associated with stronger condemnation of moral violations [32,70], this relationship may, in part, reflect a broader connection between disgust sensitivity (or potentially emotional reactivity more generally; [76]) and negative evaluations in social judgments. Our results suggest that the relationship between disgust and moral judgment may remain particularly relevant when considering specific factors, such as the target’s age. In addition, prior research showed that suboptimal affective priming by disgust and horror pictures only influenced moral judgments, with no effect on non-moral dilemmas [58]. This finding was explained as moral judgments recruiting affective information to a greater extent than non-moral judgments. In this vein, we did not measure the affective dimensions (i.e., valence and arousal) of moral dilemmas. It may be the case that the age of the target increases or decreases valence and/or arousal ratings of moral dilemmas, which may be informative in the context of this research. Finally, in this study we measured moral judgments using only self-reported measures. In future studies, it will be recommended to use some implicit measures to check if we find similar results.

In conclusion, this study makes a meaningful addition to the existing literature on disgust and moral judgment by showing the different effects of dispositional and induced disgust. Furthermore, the study highlights the nuanced role of affective priming in moral judgments. It shows that the effects of disgust on moral judgments is sensitive to the age of the target, leading to more lenient judgments when the target is an older individual. This finding suggests that the emotional responses elicited by the prime interact with the perceived characteristics of the moral agent, challenging the notion that disgust universally strengthens moral judgments. In addition, the research emphasizes the importance of considering individual differences in disgust sensitivity when studying moral judgments. The consistent effect of disgust sensitivity across age conditions suggests a broader, more pervasive influence of this trait on moral judgments, reinforcing its potential as a predictor of moral judgment severity.