Flavor-flavor and color-flavor conditioning in humans

Aversive conditioning is impaired in impulsive individuals: A study on learning asymmetries

BACKGROUND AND OBJECTIVES

Appetitive and aversive conditioning are thought to be involved in the development and maintenance of mental disorders including anxiety, mood, eating, and substance use disorders. However, few studies measure the relative strength of appetitive and aversive associations, and their relevance to the risk of mental disorders. This study aims to address this gap.

METHODS

We tested how readily healthy volunteers acquire appetitive vs. aversive associations. 150 participants associated complex 3D objects with either gain or loss and made decisions to gain or avoid losing points. We investigated the relationship of a learning asymmetry with neuroticism, impulsivity, and anhedonia, to test the hypothesis that a stronger learning asymmetry corresponds to more extreme scores on these traits.

RESULTS

Impulsivity was positively associated with the learning asymmetry (R2 = .10). This resulted from an inverse relation with the strength of aversive associations, indicating that impulsive individuals are worse at aversive learning. However, appetitive associations did not differ significantly. No correlations with neuroticism or anhedonia were found.

LIMITATIONS

Conditioning studies typically use primary reinforcers and a CS-. Lacking these may make these results less comparable to other studies.

CONCLUSIONS

We demonstrate that the learning asymmetry can measure individual differences linked to personality traits, and that impulsivity, normally linked with appetitive learning, also influences aversive learning. These results enable additional studies of learning asymmetry in relation to mental disorders, which could include measurements of mental health symptoms to provide further insight into how appetitive and aversive learning interacts with mental disorders.

Searching for perceptual similarity within, and between, the (chemical) senses

In this narrative historical review, I want to take a closer look at the concept of perceptual similarity both as it applies within, and between, the chemical senses (specifically taste and smell). The discussion is linked to issues of affective similarity and connotative meaning. The relation between intramodal and crossmodal judgments of perceptual similarity, and the putatively special status of those odorants that happen to take on taste qualities will also be discussed. An important distinction is drawn between the interrelated, though sometimes distinct, notions of perceptual similarity and crossmodal congruency, specifically as they relate to the comparison of chemosensory stimuli. Such phenomena are often referred to as crossmodal correspondences, or by others (incorrectly in my view), as a kind of ubiquitous synesthesia.

Visual cues associated with sweet taste increase short-term eating and grab attention in healthy volunteers

Most studies that examine responses to food cues use images of actual foods as stimuli. Since foods are rewarding in multiple ways, it then becomes difficult to try and partial out the role of the importance of different aspects of food reward. Here we aimed to evaluate the impact of novel visual cues specifically associated with the immediate sensory reward from a liked sweet taste. In the training phase, one visual cue (CSsweet) was associated with the experience of sweet taste (10%sucrose) and a second, control cue (CSneutral) with a neutral taste (artificial saliva) using a disguised training procedure. In Experiment 1, participants (n = 45) were given an ad libitum snack intake test 30 min post-training, either labelled with CSsweet or CSneutral. Total caloric consumption was significantly higher in the CSsweet (650 ± 47 kcal) than CSneutral (477 ± 45 kcal) condition, but ratings of liking for the snacks did not differ significantly between conditions. In Experiment 2, participants (n = 80) exhibited an overall attentional bias (22.1 ± 9.9 ms) for the CSsweet relative to CSneutral cue (assessed using a dot-probe task), however rated liking for the CSsweet did not change significantly after cue-sweet training. Likewise, measures of expected satiety for drinks labelled with CSsweet did not differ significantly from CSneutral. Overall these two experiments provide evidence that associations between neutral visual cues and the experience of a liked sweet taste leads to cue-potentiated eating in the presence of the CSsweet cue. With no evidence that cue-sweet training altered rated liking for the visual cues, and in keeping with extant literature on the dissociation of hedonic and rewarding properties of food rewards, we propose this potentiation effect to reflect increased incentive salience.

Explaining Crossmodal Correspondences Between Colours and Tastes

For centuries, if not millennia, people have associated the basic tastes (e.g., sweet, bitter, salty, and sour) with specific colours. While the range of tastes may have changed, and the reasons for wanting to connect the senses in this rather surprising way have undoubtedly differed, there would nevertheless appear to be a surprisingly high degree of consistency regarding this crossmodal mapping among non-synaesthetes that merits further consideration. Traditionally, colour-taste correspondences have often been considered together with odour-colour and flavour-colour correspondences. However, the explanation for these various correspondences with the chemical senses may turn out to be qualitatively different, given the presence of identifiable source objects in the case of food aromas/flavours, but not necessarily in the case of basic tastes. While the internalization of the crossmodal statistics of the environment provides one appealing account for the existence of colour-taste correspondences, emotional mediation may also be relevant. Ultimately, while explaining colour-taste correspondences is of both theoretical and historical interest, the growing awareness of the robustness of colour-taste correspondences would currently seem to be of particular relevance to those working in the fields of design and multisensory experiential marketing.

Odor-Taste Interactions in Food Perception: Exposure Protocol Shows No Effects of Associative Learning

Repeated exposure can change the perceptual and hedonic features of flavor. Associative learning during which a flavor's odor component is affected by co-exposure with taste is thought to be central in this process. However, changes can also arise due to exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of exposure without taste by repeatedly presenting one odor together with sucrose and a second odor alone. Sixty individuals attended two testing sessions separated by a 5-day Exposure Phase during which the stimuli were presented as flavorants in chewing gums that were chewed three times daily. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the notion that food preferences are modulated by exposure, odor pleasantness increased between the sessions independently of whether the odor (basil or orange flower) had been presented with or without sucrose. However, we found no evidence of associative learning in any of the tasks. In addition, exploratory equivalence tests suggested that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that the hypothesized effects of associative learning are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to evaluate the relative support for these explanations and, if experimental conditions can be identified that reliably produce such effects, to identify factors that regulate the formation of new odor-taste associations.

Memory and preparedness in evaluative conditioning in a smell-taste paradigm. A registered report

We investigate two questions, (1) the relevance of memory for evaluative conditioning (EC) effects based on smell-taste pairings, and (2) the potential preparedness of smell-taste combinations for yielding EC effects. The relevance of memory for EC effects is a subject of intense research. The majority of studies that investigate the memory-EC relation use visual stimuli and typically show no or relatively small EC effects without memory. For smell-taste combinations, only a few studies exist, with mixed results regarding the role of memory in EC. The idea that there might be a preparedness of smell and taste pairings comes from classical conditioning studies showing preparedness in food aversion and from research on joint processing of smells and tastes. In Experiment 1, we report a conceptual replication of previous studies with smell-taste and picture-taste pairings. In this experiment, we found no evidence for memory-independent EC overall. In a pre-registered Experiment 2, we used a design with smells, pictures, tastes, and sounds to test the role of memory more conclusively and test the preparedness hypothesis for smell-taste pairings. The results support the preparedness hypothesis for smell-taste pairings in EC. Furthermore, as in Experiment 1, we did not find evidence for memory-independent EC.

On the Relationship(s) Between Color and Taste/Flavor

Experimental psychologists, psychophysicists, food/sensory scientists, and marketers have long been interested in, and/or speculated about, what exactly the relationship, if any, might be between color and taste/flavor. While several influential early commentators argued against there being any relationship, a large body of empirical evidence published over the last 80 years or so clearly demonstrates that the hue and saturation, or intensity, of color in food and/or drink often influences multisensory flavor perception. Interestingly, the majority of this research has focused on vision's influence on the tasting experience rather than looking for any effects in the opposite direction. Recently, however, a separate body of research linking color and taste has emerged from the burgeoning literature on the crossmodal correspondences. Such correspondences, or associations, between attributes or dimensions of experience, are thought to be robustly bidirectional. When talking about the relationship between color and taste/flavor, some commentators would appear to assume that these two distinct literatures describe the same underlying empirical phenomenon. That said, a couple of important differences (in terms of the bidirectionality of the effects and their relative vs. absolute nature) are highlighted, meaning that the findings from one domain may not necessarily always be transferable to the other, as is often seemingly assumed.

A Declarative Memory Model of Evaluative Conditioning

I propose a Declarative Memory Model (DMM) of evaluative conditioning (EC). EC effects are changes in the valence of a conditioned stimulus (CS) due to previous pairings with a positive or negative unconditioned stimulus (US; e.g., De Houwer, 2007, https://doi.org/10.1017/S1138741600006491). According to the DMM, EC effects are found if (1) a memory trace is formed in the learning phase that links the CS to evaluative information from the US, if (2) this trace survives the retention interval, if (3) the trace or part of it is consciously retrieved when the CS is being evaluated, and if (4) the retrieved trace is used in the CS evaluation. For each of these stages, I make separate predictions about EC effects, many of which are based on empirical research on declarative memory. Where available, I report and discuss empirical evidence on EC that speaks to these hypotheses. The available empirical evidence is largely in line with the predictions of the DMM. Several predictions, however, have yet to be tested and some findings are ambiguous. While the DMM specifies conditions under which CS-US pairings should lead to a valence change, it does not deny the possibility that other processes might lead to a change in attitude as well. Advantages of the DMM are its foundation on declarative memory research, its applicability for attitude change effects in general, and its suitability for predictions of EC effects in the real world.

Rethinking the Negativity Bias

The negativity bias is a broad psychological principle according to which the negative is more causally efficacious than the positive. Bad, as it is often put, is stronger than good. The principle is widely accepted and often serves as a constraint in affective science. If true, it has significant implications for everyday life and philosophical inquiry. In this article, I submit the negativity bias to its first dose of philosophical scrutiny and argue that it should be rejected. I conclude by offering some alternative hedonic hypotheses that survive the offered arguments and may prove fruitful.

Flavour Liking and Preference Conditioned by Caffeine in Humans

When caffeine consumers repeatedly experience a novel flavoured drink containing caffeine, the rated pleasantness of the drink flavour increases progressively. These results could be interpreted in terms of the flavour acting as a Pavlovian conditioned stimulus (CS) predicting the consequences of caffeine ingestion. However, all studies of this phenomenon to date have used between-subjects designs, and one criticism of this is that changes in pleasantness might have arisen from nonspecific effects. A more rigorous test is to examine changes in pleasantness for two drinks, a CS+ flavour paired with caffeine and CS− paired with placebo. Accordingly, 20 moderate caffeine consumers consumed both CS+ and CS− drinks in counterbalanced order over eight conditioning trials at breakfast, with hedonic and sensory characteristics evaluated on each trial. As predicted, the rated pleasantness of the CS+ drink increased whereas pleasantness of the CS− drink did not change. Despite this, participants did not have an overall preference for the CS+ flavour posttraining. However, both those who chose the CS+ and those who chose the CS− at the end showed the same direction and rate of change in pleasantness for the two drinks during training, but spurious differences in baseline preference obscured this effect in terms of an overall change in preference. Overall these data suggest that changes in pleasantness of drinks paired with caffeine delivery are best explained in terms of Pavlovian associations between drink flavour and the postingestive effects of caffeine.

Negativity Bias, Negativity Dominance, and Contagion

We hypothesize that there is a general bias, based on both innatepredispositions and experience, in animals and humans, to give greater weight to negative entities (e.g., events, objects, personal traits). This is manifested in 4 ways: (a) negative potency (negative entities are stronger than the equivalent positive entities), (b) steeper negative gradients (the negativity of negative events grows more rapidly with approach to them in space or time than does the positivity of positive events, (c) negativity dominance (combinations of negative and positive entities yield evaluations that are more negative than the algebraic sum of individual subjective valences would predict), and (d) negative differentiation (negative entities are more varied, yield more complex conceptual representations, and engage a wider response repertoire). We review evidence for this taxonomy, with emphasis on negativity dominance, including literary, historical, religious, and cultural sources, as well as the psychological literatures on learning, attention, impression formation, contagion, moral judgment, development, and memory. We then consider a variety of theoretical accounts for negativity bias. We suggest that 1 feature of negative events that make them dominant is that negative entities are more contagious than positive entities.

Human diet and cognition

Cognition influences what, when and how much we eat, which in turn affects the brain and hence cognition. In this overview, focusing mainly on the human literature, we start by examining cognitive influences on food and eating. This includes food preferences and choices (e.g., effects of learning, advertising, and cultural taboos), food habits relating to when and how much to eat (e.g., the concept of meals, dieting, and hunger strikes), the perception of food (e.g., the influence of appearance, food labels, and conceptions of naturalness), and how food perception is influenced by expertise. We also review how these various influences are disrupted by abnormalities of cognition (e.g., Gourmand syndrome, amnesia, and anorexia nervosa). The second part of the overview focuses on how diet affects cognition. We start by looking at the acute effects of diet, notably the impact of breakfast on cognitive performance in children. This is followed by a review of the effects of extended dietary exposures-years and lifetimes of particular diets. Here we look at the impacts of protein-energy malnourishment and Western-style diets, and their different, but adverse affects on cognition, and the beneficial effects on cognition of breast-feeding and certain dietary practices. We then outline how diet and cooking may have allowed the evolution of the large energy-hungry human brain. This overview serves to illustrate the multiple interactions that exist between cognition and diet, their importance to health and disease, and their impact on thinking about the role of conscious processes in decision making. WIREs Cogn Sci 2014, 5:463-475. doi: 10.1002/wcs.1290 For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Learning to (dis)like: The effect of evaluative conditioning with tastes and faces on odor valence assessed by implicit and explicit measurements

Evaluative conditioning may be an important mechanism for learning food preferences and aversions; however, in both real life and experimental settings it has not been consistently successful. The current study aimed to gain more insight into which underlying factors may contribute to a successful outcome of olfactory evaluative conditioning. Two groups of 18 participants came in on three consecutive days, and were repeatedly exposed to four novel, neutral odors (CS) coupled to varying disliked, neutral, liked, or no stimuli (taste and/or pictures, US), following a 50% reinforcement schedule, leading to 40 odor presentations per session. Liking ratings, as well as changes in the autonomic nervous system were assessed before, during and after conditioning. We were able to induce negative, but not positive, affective changes by pairing neutral odors with tastes and pictures differing in valence. Negative as well as multimodal stimuli appear to be more potent US, since they may be considered more salient. Lastly, results of the current study imply that heart rate is responsive to changes in valence of olfactory stimuli, and perhaps even more sensitive than explicit ratings of liking.

Evaluative Conditioning with Facial Stimuli in Dementia Patients

We present results of a study investigating evaluative learning in dementia patients with a classic evaluative conditioning paradigm. Picture pairs of three unfamiliar faces with liked, disliked, or neutral faces, that were rated prior to the presentation, were presented 10 times each to a group of dementia patients (N = 15) and healthy controls (N = 14) in random order. Valence ratings of all faces were assessed before and after presentation. In contrast to controls, dementia patients changed their valence ratings of unfamiliar faces according to their pairing with either a liked or disliked face, although they were not able to explicitly assign the picture pairs after the presentation. Our finding suggests preserved evaluative conditioning in dementia patients. However, the result has to be considered preliminary, as it is unclear which factors prevented the predicted rating changes in the expected direction in the control group.

Evaluative Conditioning without Directly Experienced Pairings of the Conditioned and the Unconditioned Stimuli

Evaluative conditioning (EC) is the valence change of a stimulus (conditioned stimulus, CS) that is due to the previous pairing with another stimulus (unconditioned stimulus, US). We investigated whether EC can occur also when the CS–US pairings are not experienced directly by the participant but are implied by other events that the participant encounters. In two experiments, positive USs were presented in some trials and negative USs in other trials. Afterwards, participants were given information from which it was possible to conclude that CSs were covertly present during these trials. Finally, the valence of these CSs was registered using both implicit (Implicit Association Test, affective priming) and explicit measures (valence ratings). In line with the assumption that EC effects can be based on CS–US pairings that are not directly experienced, the valence of the CSs changed in the direction of the US with which they were covertly paired. This effect was observed both on explicit and on implicit measures. We argue that several aspects of our results are in line with propositional models of EC and fit less well with association formation models.

Evidence for the role of cognitive resources in flavour-flavour evaluative conditioning

One way that dis/likes are formed is through evaluative conditioning (EC). In two experiments we investigated the role of cognitive resources in flavour-flavour conditioning. Both experiments employed an EC procedure in which three novel flavoured conditioned stimuli (CSs) were consumed. One was consumed with a pleasant unconditioned stimulus (US; CS+ sugar), one with an aversive US (CS+ saline), and a third with plain water (CS-). Half of participants in each experiment performed a cognitive load task during conditioning. We measured EC using self-reported measures of liking (Experiments 1 and 2) and an indirect measure of liking: drink pick-up latency (Experiment 2). In both experiments, differential EC was observed in the no cognitive load condition but not in the cognitive load condition. This pattern of results was observed in self-reported measures of liking as well as in the drink pick-up latency data. Results from both experiments show that EC occurs only when there are sufficient cognitive resources available. The fact that this was observed using both self-reported and indirect measures suggests that insufficient cognitive resources affect learning itself rather than merely obstructing reporting.

Chemosensory learning and flavour: perception, preference and intake

Recent approaches to perception that have emphasised multi-sensory interactions have been crucial in developing a view of flavour as a cognitive construct derived from a synthesis of gustatory, olfactory and oral somatosensory inputs. The perceptual interactions between these distinct sensory channels provide evidence for the existence of a functional flavour system. This system is characterised by a dependence on associative learning in which odours and tastes come to share common features. In addition, studies in which attention is directed to the flavour or its elements during learning provide evidence for a view that flavour is encoded as a configural stimulus following spatial and temporal pairing of the different sensory inputs. Such encoding produces changes in the perceptual properties of odours/flavours - as illustrated by sweet-smelling odours - but is also responsible for changes in hedonic valence through flavour-flavour and flavour-consequence learning. In turn, flavour and odours can act as conditioned cues that have appetitive effects.

Does Evaluative Learning Rely on the Perception of Contingency?

An experiment is reported studying the impact of objective contingency and contingency judgments on cross-modal evaluative conditioning (EC). Both contingency judgments and evaluative responses were measured after a contingency learning task in which previously neutral sounds served as either weak or strong predictors of affective pictures. Experimental manipulations of contingency and US density were shown to affect contingency judgments. Stronger contingencies were perceived with high contingency and with low US density. The contingency learning task also produced a reliable EC effect. The magnitude of this effect was influenced by an interaction of statistical contingency and US density. Furthermore, the magnitude of EC was correlated with the subjective contingency judgments. Taken together, the results imply that propositional knowledge about the CS-US relationship, as reflected in contingency judgments, moderates evaluative learning. The data are discussed with respect to different accounts of EC.

Learning: from association to cognition

Since the very earliest experimental investigations of learning, tension has existed between association-based and cognitive theories. Associationism accounts for the phenomena of both conditioning and "higher" forms of learning via concepts such as excitation, inhibition, and reinforcement, whereas cognitive theories assume that learning depends on hypothesis testing, cognitive models, and propositional reasoning. Cognitive theories have received considerable impetus in regard to both human and animal learning from recent research suggesting that the key illustration of cue selection in learning, blocking, often arises from inferential reasoning. At the same time, a dichotomous view that separates noncognitive, unconscious (implicit) learning from cognitive, conscious (explicit) learning has gained favor. This review selectively describes key findings from this research, evaluates evidence for and against associative and cognitive explanatory constructs, and critically examines both the dichotomous view of learning as well as the claim that learning can occur unconsciously.