Theoretical implications

Theoretical and empirical parts of the present thesis have important implications for both theories of emotion and theories of attention. More particularly, the first empirical study together with the meta-analysis brought strong evidence that positive rewarding stimuli bias attention, and that, similarly to what has been shown for negative threatening stimuli, this attentional bias occurs rapidly and involuntarily independently of voluntary processes. These findings contradict the “fear module”

(Öhman & Mineka, 2001), which is one of the more influential theoretical models of

emotional attention. According to this model, attention is exclusively biased toward stimuli that have intrinsic perceptual features characteristic of threats to the species for which organisms have been biologically prepared or stimuli that have been associated with such threats. However, the present thesis indicates that attention is also rapidly and involuntarily biased toward positive rewarding stimuli.

In terms of mechanisms underlying the attentional bias, this thesis suggests that the properties of the rewards or reward associated stimuli per se matter less than their interaction with the individual’s current concerns. This is congruent with both the model of emotional attention derived from appraisal theories (Brosch, Sander, Pourtois, & Scherer, 2008; Brosch, Sander, & Scherer, 2007) and the incentive salience hypothesis (Berridge & Robinson, 1998). Both postulate that the ability of a reward or a reward-associated stimulus to bias attention critically depends upon the interaction between the stimulus and the motivational state of the individual and not on the stimulus pleasantness or valence, as it has been shown in the present thesis.

This thesis delineates the interest of reward for the main emotional theories.

For several years experimental research on emotion has been mainly focused on negative emotions, particularly fear, inspired from animal research on aversive conditioning. This focus on fear has led several scholars to hypothesize that fear had a special status compared with other emotions (Öhman & Mineka, 2001). Through experimental research on emotion inspired from animal research on appetitive conditioning, it is possible to show the existence of a similar functioning for positive rewarding stimuli and negative threatening stimuli, thereby supporting the idea that single emotions do not function independently from each other, but instead that they are underlain by common dimensions or mechanisms as postulated by circumplex and appraisal theories (Moors et al., 2013; Russell, 1980; Scherer, 2001; Yik, Russell, &

Barrett, 1999). More precisely, circumplex theories (Russell, 1980; Yik et al., 1999) stress that different emotions are underlain by two common dimentions: arousal and valence. The emotional attention model derived from this theory postulates that arousal determines the attentional bias for emotional stimuli (Anderson, 2005).

Appraisal theories (Moors et al., 2013; Scherer, 2001) stress that different emotions are triggered by common affective mechanisms. The emotional attention model derived from these theories postulates that affective relevance determines the attentional bias for emotional stimuli (Brosch et al., 2008; Brosch et al., 2007).

Therefore, for appraisal theories, the mechanism responsible for attentional bias resides in the emotion elicitation process, while for circumplex theories, it resides in one aspect of the emotional response. In this thesis, we provided evidence favoring the appraisal postulate over the circumplex postulate in predicting the size of the attentional bias for positive emotional stimuli (see chapter 2.1 for a detailed discussion).

More generally, we illustrated how the approach suggested by appraisal theories might be fruitful when investigating the relationship between emotions and other psychological constructs such as attention or motivation. According to appraisal theories (Sander et al., 2005; Scherer, 2001), affective relevance is a key mechanism to elicit an emotional response, however its influence on other psychological constructs such as attention or motivation is direct and not mediated by the emotional response. Congruently with this proposal, the theoretical and the empirical part of this thesis suggest that affective relevance, rather than the emotional response itself, directly modulates both the involuntary orienting of attention and the CS-triggered peak of wanting.

Implications for modeling ‘irrational reward seeking behaviors’

One of the most paradoxical and poorly understood phenomenon in human behavior is that under many situations individuals will invest a considerable amount of effort to obtain an object of their desire, even though once they obtain the object they do not experience it as pleasant. The theoretical and empirical parts of this thesis might shed some light into the underlying mechanisms that might sometime lead to irrational reward’s seeking behaviors where the amount of effort mobilized to obtain a reward is no longer justified by the reward ability to trigger hedonic pleasure. We showed that, as predicted by the incentive salience hypothesis (Berridge & Robinson, 1998), the ability of a CS to (a) bias attention and (b) trigger peaks of wanting to obtain the associated rewarding chocolate odor was directly modulated by the physiological state of individual, and that this mechanism is independent of the liking experience triggered by the chocolate odor consumption.

Our findings are congruent with a large corpus of animal literature that have shown that the CS’s ability to modulate wanting depends on the physiological state of

the organism when perceiving the CS (Dickinson & Balleine, 1994; Dickinson &

Dawson, 1987; Pecina, Cagniard, Berridge, Aldridge, & Zhuang, 2003; Robinson &

Berridge, 2013; Wyvell & Berridge, 2000). Research conducted on rodents has demonstrated that the CS’s ability to trigger peaks of wanting for the associated reward depended on several physiological states such as hunger (Dickinson &

Balleine, 1990; Dickinson & Dawson, 1987; Robinson & Berridge, 2013), the mesolimbic dopaminergic level (Wassum et al., 2011; Wyvell & Berridge, 2000, 2001), and stress (Pecina, Schulkin, & Berridge, 2006). In the empirical part of this thesis, we replicated these findings of stress on a human population. Critically, we showed that the interaction between the CS perception and the physiological state of stress of the individual increased CS-triggered wanting to obtain the associated chocolate odor, but not the actual liking experience when the chocolate odor was obtained.

Additionally, our findings showed that the CS’s ability to bias attention is also modulated by the physiological state of the individual: the attentional bias for a CS associated with a chocolate odor is no longer present once an individual has eaten chocolate until satiation. Congruently, other studies showed that the ability of stimuli that are naturally associated rewards, such as pictures of food or water, to bias attention is modulated by the physiological states of hunger, thirst and stress (Mazzietti, Sellem, & Koenig, 2014; Newman, O'Connor, & Conner, 2008; Piech, Pastorino, & Zald, 2010).

Together, this evidence suggests that the synergetic interaction between the CS and the current physiological state of the individual can explain some of the irrational reward seeking behaviors: The relevant physiological state increases the CS’s ability to bias attention, thereby increasing their likelihood to be perceived.

Once perceived, the CS triggers amplified peaks of wanting to obtain the associated reward, independently of the liking experience.

In the theoretical part of this thesis we proposed that the interaction between the individual’s current physiological state and the CS perception underlying wanting is independent from the expectations about the pleasantness of the reward (see Figure 4-1). According to the incentive salience hypothesis, expected plesantness determines cognitive desires which represent a distinct source of control of reward seeking behaviors.

This proposal is consistent with a theoretical framework which consists of three interacting systems excercing control of reward seeking behaviors: Pavlovian, habitual and goal-directed (for a review see Rangel, Camerer, & Montague, 2008).

The Pavlovian system assigns intrinsic affective properties of a reward (e.g., highly palatable food) to a neutral stimulus with which it has been systematically associated (e.g., a bell ringing). After the associative learning is completed, the Pavlovian stimulus acquires the ability to evoke reward-seeking behaviors originally triggered by the reward (e.g., salivating after hearing the bell ringing). The habitual system controls automatic instrumental actions triggered by environmental stimuli from the context in which the instrumental action has been learned (e.g., seeing the lever, pressing the lever; stimulus–response learning even in the absence of hunger). In the habitual system, the action is not accomplished with the intention of obtaining a reward, whereas in the goal-directed system, the representation of the reward is critical. The goal-directed system involves learning the association between a specific action (e.g., jogging) and a rewarding outcome (e.g., feeling fit; action-outcome learning). Therefore, goal-directed actions demand a higher load of cognitive resources and are slower compared with habits. However, the effort invested in goal-directed actions is flexibly proportional to the expected pleasantness of the reward that they are leading to.

Wanting, depending on the interaction between a Pavlovian stimulus and the current physiolgical state of the individual, relies on the Pavlovian system; whereas cognitive desires, depending on expectancies of the pleasantness of the reward, rely on the goal-directed system. But does it mean that wanting can be reduced to a

“Pavlovian reflex” as opposed to cognitive desires being a“non-cognitive” process?

Several studies suggest that this is not the case: the CS’s ability to trigger wanting peaks critically depends upon the representation of the relevant properties of the UCS for the current physiological state of the individual (Cardinal, Parkinson, Hall, & Everitt, 2002; Dayan & Berridge, 2014; Dickinson & Balleine, 1990;

Robinson & Berridge, 2013). Wanting is triggered by the perception of CS in a particular physiological state (e.g., hunger), however when an individual is in a particular physiological state, not all CSs trigger wanting peaks, but only those CSs that are associated with a UCS that is relevant for the physiological state of the said individual (e.g., food associated CS). The importance of the UCS’s representation has

been recently illustrated by Robinson and Berridge (2013), which have shown that rats in a sodium depleted-state approached the CS lever that had previously been associated with a salt outcome in a normal physiological state, but they did not change their behavior toward the CS lever associated with a sucrose outcome.

These new studies demonstrated that the identity of the UCS is thus predicted by the CS and that the UCS’s relevant properties for the current physiological state are directly evaluated. Based on this observation, Dayan and Berridge (2014) proposed that wanting is underlain by a Pavlovian model-based mechanism relying on the UCS’s identity representation. The distinction between model-based and model-free forms of computation has substantially been applied to instrumental learning.

Model-free learning consists of an incremental update of the value of an instrumental action via retrospective experience and prediction error without rich representations, whereas model-based learning relies on representations of the environment that are used to construct expectations, predictions and transformations of the value of an instrumental action in future or current conditions change (Daw, Niv, & Dayan, 2005). Model-based instrumental learning underlies the goal-directed system, whereas model free instrumental learning underlies that habitual system (Daw et al., 2005).

Initially the Pavlovian system has been considered to rely on model-free computations (e.g., Pearce & Hall, 1980), however, recent studies have suggested that model-based computations play a critical role in the Pavlovian system (e.g., Prévost, McNamee, Jessup, Bossaerts, & O'Doherty, 2013). Dayan and Berridge (2014) have suggested that such model-based computations in the Pavlovian system allow CS-triggered wanting to flexibly vary according to the relevance of the UCS for the current physiological state of the individual.

Therefore, the current state of the literature suggests that both cognitive desires and wanting are underlain by model-based mechanisms, requiring a cognitive representation of the reward, however different aspects of the reward are represented and evaluated. Wanting relies on the reward relevance for the current motivational state, whereas cognitive desires rely on its expected pleasantness.

Figure 4-1. Illustration of the mechanisms proposed in this thesis to be involved in wanting and liking.

Wanting is underlain by the perception of a Pavlovian stimulus (conditioned stimulus; CS) associated with a reward (unconditioned stimulus; UCS) that is relevant for the current concerns of the individual, it is distinct and potentially independent from the liking experience during the reward consumption or receipt as well as the expected pleasantness. The UCS relevance also determines the CS’s perceptual salience and its ability to bias attention. Liking consists in the hedonic experience during the reward consumption or receipt, expected pleasantness is built on the memories of these past liking experiences and determine cognitive desires. Cognitive desires rely on the goal-directed system and wanting relies on the Pavlovian systems, thus they represent two distinct motivational control system of reward seeking behaviors.

In conclusion, we propose that some irrational reward-seeking behaviors can be explained if we consider that reward-seeking behaviors are controlled by multiple systems. Wanting relies on the control of the Pavlovian system and is underlain by a mechanism that is distinct and potentially independent from expected pleasantness.

This implies that some rewards are sought, even if they are not expected to be liked and are not actually liked once they are consumed or received. We suggest that these behaviors that seem irrational, can be better understood if one considers that they rely on relevance rather than valence evaluations. Particularly, we proposed (chapter 2.2) that relevance relies on a larger variety of motives (i.e., current concerns based on socialization, personal sensitivity or momentary goals) than simple physiological state (e.g., hunger, thirst) that are organized in a dynamic hierarchy of priorities that can vary depending on the situation (Sander et al., 2005). The relevance of an outcome depends on the importance of the concern for which its properties are relevant. In the hierarchy of priorities, some are more important than others because they determine

CS

UCS Relevance Expected

Pleasantness

Reward-seeking behaviors Perceptual salience

Liking experience Wanting

Pavlovian System

Cognitive desires Goal-directed System

how individuals define themselves, but are not necessarily associated with a high expectation of pleasure.