What Is It Like to Be an Emotion Researcher? Background and Scopes

Home , Affective neuroscience, Emotion (journal), Emotion perception

What Is It Like to Be an Emotion Researcher?

Tahn´eeEngelen1, Rocco Mennella1,2

July 2021

1 Cognitive and Computational Neuroscience Laboratory (LNC2), Inserm U960, Department of Cogni- tive Studies, Ecole´ Normale Sup´erieure,PSL University, 29 rue d’Ulm, 75005, Paris, France 2 Laboratory on the Interactions between Cognition, Action, and Emotion (LICAE) – Paris Nanterre University, 200 avenue de La R´epublique,92001 Nanterre Cedex, France.

Corresponding authors: Tahn´eeEngelen & Rocco Mennella Corresponding authors e-mails: [email protected] & [email protected] Corresponding authors telephone: +33144322638 Corresponding authors fax number: +33144322642

Abstract. The field of emotion has a rich history, yet given the amount of time researchers have been bending over critical questions such as ’what is an emotion’, the field has little consensus to show. The current paper focuses on one of the main topics of disagreement, namely the role of conscious feelings in emotion and their neural correlates. We argue that contemporary theories of emotional consciousness often rely on preliminary findings, stemming from both theoretical and methodological limitations. By drawing parallels with the field of perceptual consciousness, we highlight the unique methodological challenges of research on emotional consciousness. Finally, we make concrete propositions with the aim of moving the field forward. Keywords: Emotion, Consciousness, Theories of Emotion, Affective Neuroscience

Background and scopes lution and development in virtue of their adaptive value”. You should have seen the faces of the people from the world of cinema. What is it like to be an emotion researcher (Nagel, Both popular and scientific discord around the no- 1974)? Most differently from bats, emotion re- tion of emotion is not something new. Nonethe- searchers do not rely on echolocation to navigate less, a particularly intense debate is now ongoing their environment. In fact, one might guess that among renowned authors in the field of affective being an emotion researcher must feel, in many as- (neuro)science, about what emotions are and how pects, like being any other researcher. Against this to study them (Adolphs et al., 2019; D. J. An- fallacious intuition, we argue that it involves the derson Adolphs, 2014; Barrett, 2017; Berridge, unique quale of having no idea of what your own 2018; Fanselow Pennington, 2018; LeDoux, 2012, object of study is. 2021; Ledoux & Brown, 2017; Mobbs et al., 2019; Ironically, for an emotion researcher preparing a Panksepp et al., 2017). What seems to be the presentation, the most challenging slide is the first leading source for this impasse is that the con- one. As a real-life example, in a recent general cept of emotion still does not have a commonly public conference about emotions in science and accepted definition and is vague at the point of cinema, soon the time came for one of the authors not meeting the standards for a scientific construct to give a concise definition of human emotions. It (Izard, 2010; Russell, 2003, 2015). In this con- sounded like: “Well, it has to be highlighted that text of uncertainty, authors are nonetheless bring- several theories exist. I would say that, despite ing forward holistic theories of emotion, which are this diversity, most authors would agree that an in contradiction with one another on several lev- emotion is a set of behavioral, physiological, cog- els. Although such theories are typically successful nitive and subjective responses to environmental in wrapping up each author’s own discoveries in a stimuli, which have been selected throughout evo-

1 coherent framework, they risk creating a scenario and psychophysiological reactions (Darwin, 1872; in which it becomes impossible comparing these James, 1891) (but see Fridlund & Russell, 2021 same theories and definitions to one another. As for an interesting and radically different interpreta- clearly explained in a recent paper (Pessoa, 2019), tion of Darwin’s original perspective). This notion tight definitions can sometimes slow down scien- implied that emotional states, and correspond- tific progress by discouraging novel research ideas ing feelings, can be inferred from behavioral and which violate theoretical boundaries, rather than physiological responses and led to the development pushing them forward. In this context, we agree of modern behavioral paradigms for the study of that all of us should refrain from overtheorizing, emotional responses in animals and humans, ulti- taking a step back to the stage of testing specific mately opening the way to the birth of the mod- hypotheses, to accumulate knowledge that could ern affective (neuro)science (Panksepp, 2004). Af- be useful to explain humans’ and animals’ com- ter some decades of quiescence, today the debate plex behaviors (Adolphs & Anderson, 2018; Pes- around the role of conscious feelings in defining soa, 2019). emotions has risen again. For simplicity, we will Here, we write to push the debate forward, try- group theories into two global approaches (A1 and ing to cast two pairs of fresh eyes on one of the A2) and compare their arguments. Cited authors most strongly divisive topics, namely, the role of will excuse us for relying on this heuristic; we will conscious feelings in defining emotion. First, we try to highlight important differences where nec- will highlight how the contemporary discussion on essary, but the full complexity of each theory will emotion under many aspects is organized around not be covered. this main question. Second, we will suggest that On the one hand, some authors (A1) re-proposed existing theories of emotional consciousness rely on the idea that emotions equate to conscious feelings, insufficient evidence or overgeneralizations, stem- which can only be accessed through introspection ming from both theoretical ambiguity and method- (LeDoux, 2012; LeDoux & Hofmann, 2018). As ological pitfalls. Finally, we will end with practical a logical consequence, the core property of emo- suggestions for moving the debate forward. tion, the conscious feeling, can only be studied in humans, through subjective reports (LeDoux, 2021; Ledoux & Brown, 2017). For instance, the A broad view on the contemporary concept of “fear” ought to be attributed only to debate on emotion each human’s unique conscious experience when facing threat and not to the behavioral, physiolog- We identified what we think is the topic of debate ical and cognitive reactions to threat. The under- from which stem most of the controversies around lying idea is that, while humans and other animals the foundations of emotion as a scientific concept, share the neural circuits to respond to threat, face namely the conscious versus unconscious nature of aggression or seek rewards (LeDoux & Daw, 2018), emotion. In other words, the question is whether none of these circuits determines the precise con- an emotion is essentially a reportable conscious ex- tent of the accompanying subjective emotional experience, or whether it can be inaccessible to in- periences present in humans. In fact, although ba- trospective scrutiny or even unconscious. sic forms of bodily awareness and simple valenced The debate around the conscious versus uncon- states (positive/negative) probably exist in both scious nature of emotion has a long history, which humans and other animals, they are omnipresent we will not fully summarize here. However, it is in our cognitive life and not specific to emotional important to keep in mind that until relatively episodes (Barrett, 2017; Barrett et al., 2007). A1 recently, emotions were not considered a suitable authors do not deny the existence of behavioral phenomenon for experimental investigation. This and visceral reactions, but do not support a reli- was partly because emotions were viewed as in- able and specific causal relationship between these timate subjective experiences that could only be reactions and an instance of what we call emotion accessed through introspection. The equation be- (Barrett, 2017; Ledoux & Brown, 2017). Emo- tween emotion and conscious feelings was chal- tional consciousness, i.e., what emotion really is, lenged at the end of the XIX century by the idea is hierarchical: it is determined by a cognitive pro- that emotions are innate and universal functional cess which helps categorizing a range of somatic responses to environmental stimuli, selected by and visceral reactions into meaningful concepts. evolution, which map onto measurable behaviors

2 These concepts can then become conscious, when have proven useful to adapt to environmental chal- top-down modulatory effects bring them into work- lenges. This set of physiological and behavioral ing memory (Lane et al., 2015). This implies that responses is therefore a measurable and objective emotional feelings are “higher order” representa- indicator of the activation of the central emotion tions of both bodily states and low level cogni- generator. It is also highlighted that direct stimu- tive (e.g., perceptual) processes (Lane et al., 2015; lation of dedicated emotional neural circuits has Ledoux & Brown, 2017), conceivable as instances reinforcing effects on behavior (i.e., animals ac- of reportable access consciousness (Block, 1995). tively try to prolong or terminate the stimula- These emotional concepts are learned progressively tion) (Panksepp, 1998b, 1998a). This is some- through each individual’s development, ultimately times taken as evidence for these circuits being allowing for the attribution of meaning to our ex- responsible for a primitive phenomenological form periences in the world, through categorization and of emotional consciousness, which is nonetheless prediction of future outcomes (Barrett, 2006, 2017; more differentiated than a simple experience of Lane et al., 2015). Importantly, each person has something good or bad (Panksepp, 1998b, 1998a). their own unique emotional experiences, as the Of note, this is thought to be a “first order” con- way humans mentally represent, perceive, recog- scious experience (Block, 1995), very different from nize and express emotions is profoundly shaped the “higher order” form of consciousness proposed by life-history and socio-cultural influences (Bar- by A1 (Ledoux & Brown, 2017). Other authors rett et al., 2019; Crivelli & Fridlund, 2018, 2019; argue that such reinforcing effects on behavior, as R. E. Jack et al., 2012; Jackson et al., 2019). In well as typical emotion-related neural and phys- this view, while it is not impossible that other ani- iological activations, can be elicited even in re- mals have some form of basic affective experience, sponse to emotional stimuli which are not con- this is hardly comparable to the complex experi- sciously detected and in the absence of changes in ence available to humans and will never be directly subjective reports, supporting the idea that emo- accessible (LeDoux & Pine, 2016). In fact, it is tions can be totally unconscious (Berridge, 2018; proposed that unjustified inference of (subjective) Celeghin et al., 2015; Winkielman et al., 2005; emotion from objective behavioral and physiolog- Winkielman & Berridge, 2004). Depending on ical measures has led animal studies to produce the author, the functional properties of evolution- scarce results in developing new pharmacological arily conserved emotional circuits are thought to treatments for affective disorders, such as depres- be partially (Adolphs, 2017) or almost entirely sion and anxiety (LeDoux & Pine, 2016). (Panksepp, 1998a) conserved between humans and On the contrary, other authors (A2) argue that other animals. A2 largely acknowledges that hu- the conscious representation that allows humans to mans can further elaborate, reappraise and have produce verbal reports about what they feel (e.g., access to core emotional reactions to report them “I feel angry”) has no special status in defining verbally. Some authors even made the distinc- what an emotion is. In fact, reportable subjec- tion between “basic emotions” - the evolutionary tive feelings in humans are only one of the com- conserved emotional responses - and the associ- ponents of a functionally organized set of behav- ations between such emotions and cognitive re- ioral, physiological and cognitive responses to en- sponses, acquired through learning, called “emo- vironmental challenges, caused by “central genera- tion schemas” (Izard, 2007). In this view, an- tors” or “central states” of emotions (Anderson & imal studies are often thought to represent the Adolphs, 2014; Fanselow Pennington, 2018). Such gold standard for understanding the emotion prim- central generators would (at least in part) map itives, non-contaminated by subsequent cognitive onto dedicated neural systems (Adolphs, 2013), elaboration (Berridge, 2018; Fanselow & Penning- mostly subcortical (Panksepp, 2007), which have ton, 2018; Panksepp et al., 2017). This also been shaped by evolution. Accordingly, these an- stems from the possibility of directly stimulat- cient circuits control the execution of typical phys- ing/interfering with the central brain state with iological and behavioral responses, such as freezing invasive techniques and measure effects on behav- (Fanselow, 1994; Fanselow Lester, 1988), “want- ior, as well as provoking strong emotional states, ing” (Berridge et al., 1989; Berridge & Valenstein, which would be unethical in humans (Panksepp et 1991; Treit Berridge, 1990) or RAGE (Panksepp, al., 2017). Overall, it is expected that animal stud- 1998a), which have been conserved since they ies will be crucial (and for A2 they already have

3 been) for gaining a better understanding of psy- cases, an entirely unconscious phenomenon, mostly chopathology and how to treat it (Berridge, 2018; sub-cortically generated by evolutionary conserved Fanselow & Pennington, 2018; Panksepp et al., primitive brain structures, which humans share 2017). with other mammals. Here we will challenge some The abovementioned debate leaves the strong im- of the supposedly supportive findings for either A1 pression that A1 and A2 are not referring to the or A2, drawing parallels with the study of per- same thing. The question of what level of con- ceptual consciousness. In fact, despite remaining sciousness is necessary for the experience of an controversies, in the last twenty years this domain emotion seem to be at the core of the disagreement. has made great theoretical and methodological ad- The question is tightly linked to the debate con- vancements, especially concerning how conscious- cerning the neural correlates of consciousness and, ness is represented in the brain, the so-called neu- in particular, whether feelings can be fully subcor- ral correlates of consciousness (NCC). tically generated or whether they only arise when cortical areas, in particular prefrontal ones, are activated. As mentioned, beyond the theoretical Susceptibility of affective science to issue, this has far-reaching methodological conse- fall for over-generalizations quences: research on animals, as well as on infants, Before delving into the credibility of the claims for who share with adult humans several sub-cortical the mainly unconscious or conscious nature of emo- networks, but for whom the prefrontal cortex is tion, as well as its subcortical or cortical origin, only partially developed, might either be the gold there are, in our opinion, two over-generalizations standard for the study of emotion or be essentially on both sides of the argument, which are impor- useless (see Fanselow & Pennington, 2018), de- tant to point out to begin with: pending on the approach. Furthermore, method- a) Most theories of emotional consciousness at ological disagreement produces particularly strong present are predominantly based on findings in the statements by authors on both sides of the net, domain of fear, which in our opinion represents an which are in explicit contradiction. For LeDoux unwarranted over-generalization, contrary to other and Hofman (2018, p. 67), for instance, ”the most authors’ opinion (Ledoux & Brown, 2017). In the direct way to assess conscious emotional feelings field of consciousness, a distinction is made be- is through verbal self-report”. In the very same tween the general and the content specific Neural year, Adolphs and Anderson state that ”A sci- Consciousness Correlates (NCC; Koch, Massimini, ence of emotion should [...] use behavior, cogni- Boly, & Tononi, 2016). The general NCC are the tion, and neurobiology in its vocabulary. It should neural substrates supporting conscious experiences not be based on self-report of feelings in people” in their entirety, irrespective of their specific con- (Adolphs & Anderson, 2018, p. 51). By drawing tents; on the other hand, the content-specific NCC parallels to the study of (perceptual) conscious- are the neuronal mechanisms which determine a ness, we will use the following section to argue that particular phenomenal distinction within an expe- the full picture of emotional consciousness will not rience, such as the perception of a face. Therefore, be obtained by excluding specific research fields or the general NCC is the combination of the sets of methods of study, but on the contrary, by crossing content-specific NCC, for all possible contents of them. experience. Of note, an important difference exists between neural correlates, neural prerequisites, and neural consequences of consciousness (Aru et Studying emotional conscious- al., 2012; de Graaf et al., 2012). The neural prereq- ness and its neural correlates uisites of consciousness refer to those mechanisms that are necessary for the conscious experience to As highlighted above, several authors propose arise, but are not the locus of conscious experiences quite opposite views on levels of consciousness re- themselves, whereas neural consequences are the quired for emotional experience. A1 proposes that after-effects resulting from a conscious experience. emotional consciousness is a cortically generated A neural prerequisite can be identified by the fact form of high order consciousness. In an opposite that it will be active whenever a conscious experi- fashion, A2 defends the idea that emotion involves ence arises, irrespective of the content of that ex- a form of first order consciousness, or is, in some perience. For example, if a researcher were study-

4 ing house-related visual consciousness solely com- times done prematurely. There are several reasons paring consciously perceived versus non-perceived to believe the conscious experience of an emotion pictures of houses, they might erroneously take the might differ in certain aspects from, for example, areas found for the conscious percept as being an the perception of a flickering Gabor patch. For in- NCC. However, if they had additionally included stance, some authors argue that contributions of pictures of faces, they would have found many of subcortical areas distinct to those necessary for vi- the same areas responding to conscious faces. Gen- sual consciousness are a prerequisite for the subjec- eralizing results from one emotion (e.g., fear) to tive experience of fear to form (Fanselow & Pen- the others inflates the risk of taking neural pre- nington, 2018). Furthermore, the study of emo- requisites for neural substrates. The presentation tional consciousness has proven that even with- of fear-provoking stimuli, for instance, probably out reported conscious percepts, emotional stimuli activates brain areas that would have responded can elicit physiological responses and biasing of be- differently to joy-provoking ones (content specific) havior, similarly (but not identically) as would be as well as similarly (neural prerequisites, conse- observed when the stimulus would be reported as quences, or general NCC). Any neural substrate consciously perceived. In a phenomenon called af- active for all possible emotional conscious experi- fective blindsight, cortically blind patients are able ence is more likely to represent a neural prereq- to identify the emotional expressions of faces above uisite, rather than a neural substrate of conscious chance level, but are incapable of doing the same emotional experience. Interestingly, the idea that for facial attributes unrelated to the emotional ex- the entire range of emotions we are capable of expression, such as identity (Rossion et al., 2000), periencing would map onto one single brain area potentially arguing for a special role for this partic- or network is apparently refuted by both A1 and ular type of non-conscious perception (Tamietto & A2 approaches and irrespective of whether the au- de Gelder, 2010). Emotions seem deeply connected thors believe emotions to be discrete or continuous with unconscious aspects of our mental life, which in nature. For example, even opponents of studies manifest themselves as behavioral and physiolog- trying to map discrete neural signatures of emo- ical responses, possibly highlighting the necessity tions (e.g., Saarimäkiet al., 2016) would not ar- of the ’something extra’ that needs to be explained gue that any kind of emotional experience can be when forming a theory of emotional consciousness. mapped onto a single generalized emotion network As a matter of fact, a principle of parsimony would (Clark-Polner et al., 2017). It is therefore at odds suggest not to bother building separate theories of that theories of emotional consciousness sometimes emotional consciousness, if one is really convinced oversimplify this aspect. In our opinion, if indeed that emotional consciousness is alike any other more research has been conducted on fear, this is form of consciousness. This is not to say we cannot an incentive to broaden our research interest, to learn and be inspired by the field of consciousness, avoid overgeneralizing our findings. This said, it is but that current robust empirical support to do so not easy to conceive what a content-specific acti- is still lacking. Finally, even for theories assuming vation would be in the field of emotion before some that conscious emotional experiences are not spe- point of agreement is reached about what defines cial in that they are constructed similarly to any an emotional content. It has been shown that as- other conscious experience, the study of emotional signing experimental stimuli to specific emotional consciousness comes with unique methodological categories has an impact on the performance of su- challenges, which we will further elaborate on in pervised machine learning algorithms that look for section 2.3. their brain correlates, and that the same categories are sometimes not retrieved with non-supervised algorithms (Azari et al., 2020). This is a large Criticism of the neural correlates of point of discussion in and of itself, which we will emotional consciousness according to develop more in the final part of the paper (section A1 and A2 approaches 3.2), and which we believe calls for caution when Views in line with A1 argue that emotion refers to constructing theories of emotional consciousness. a conscious emotional experience and, in order for b) Secondly, we think that generalization of find- this experience to exist, higher order consciousness ings and theories stemming from the consciousness is necessary. In support of this claim, A1 reasons field to emotional consciousness has been some- that subcortical activations are insufficient for con-

5 scious emotional experiences to arise and that cor- support the claim about the necessity of higher or- tical activations are needed, particularly activation der consciousness as a prerequisite for emotional in the prefrontal cortex (LeDoux, 2021), which cor- consciousness is that activation of subcortical ar- relates with self-reported emotions (e.g., Williams eas is by itself not sufficient to elicit an emotional et al., 2006). To understand the evidence neces- experience. This is a rather interesting discussion sary to substantiate such claims, it is necessary point, which immediately brings us to the claims to put under scrutiny the validity of the measures made by theories of the A2 approach. A2 pro- by which conscious emotional experiences are cap- ponents often cite very similar research, however, tured. Introspection and verbal reports seem in- with the exact opposite interpretation, namely, dispensable, but with them comes a string of lim- that subcortical activation is sufficient to form a itations. An important question is whether, by conscious emotional experience and to influence asking participants to reflect upon their emotional subjective reports. So how did we get to a stage state, the neural correlates of introspecting and re- in which the same findings can be cited to defend porting conscious experiences are measured, rather complete opposing views? The answer might come than the neural correlates of emotional conscious- from the fact that findings are mixed and theoret- ness itself. A similar debate, has been ongoing in ical definitions are loose. Let us give an example, the field of consciousness. once again focusing on fear: the question exists There have been some particularly striking re- whether fear can or cannot be experienced with- sults obtained with so called no report paradigms out intact amygdalae. Here, evidence in support of (Tsuchiya et al., 2015). As the name already in- both sides comes either from patients who have ex- dicates, these paradigms require no subjective re- isting amygdalae damage, or patients in which the port of their participants and rely on the idea that amygdala can be invasively stimulated. Whereas conscious contents can be inferred from physiolog- A2 typically refers to lesion studies in which bilat- ical changes or subtle task manipulations. By in- eral amygdala damage impaired the recognition of ferring the perceived direction of competing mov- fearful faces, the subjective experience of fear, and ing stimuli under binocular rivalry from eye move- fear-related avoidance behaviors (Adolphs et al., ment, rather than a subjective report, it has been 1994; Feinstein et al., 2011), as well as stimulation demonstrated that right frontal activations that studies in humans that elicited conscious experi- were present during perceptual transition in the ences of fear and anxiety (Inman et al., 2018), A1 report task were absent in the no-report variant of often cites studies in which patients with amyg- the task (Frassle et al., 2014). While the debate on dala damage were still able to experience feelings of the necessity of prefrontal cortex in (visual) con- fear (Anderson Phelps, 2002; Feinstein, Adolphs, sciousness is far from resolved (e.g., Boly et al., Tranel, 2016; Feinstein et al., 2013). We should of 2017; Northoff & Lamme, 2020; Odegaard et al., course not be surprised by mixed findings, because 2017), the emotion community needs to take stock irrespective of the immense value of patient and to see where it stands in support of the involvement lesion data in providing causal insight into brain of prefrontal areas in emotional conscious experi- functioning (Adolphs, 2016; Vaidya et al., 2019), ence. There might be additional difficulty in imag- the limitations of such work is clear. On one hand, ining how a no report paradigm could be success- congenital lesions often result in plastic restruc- fully implemented in affective neuroscience. After turing of the brain (Wieloch & Nikolich, 2006); on all, even if the participant is aware of a fearful the other hand, stimulation studies can be diffi- face, one cannot assume that they are also expe- cult to generalize, as different stimulation param- riencing a corresponding emotion. This taps into eters (such as polarity and intensity) might create another experimental feature muddling the field, varying electric fields in different patients (Selim- namely the insufficient separation of emotion per- beyoglu, 2010). Both limitations, combined with a ception and emotion induction paradigms. To our profound disagreement about what fear (and emo- knowledge, rigorous evidence in the support of the tion) is and how to measure it, increase the likeli- necessity of prefrontal areas to form conscious emo- hood of mixed findings. tional experiences is still lacking; we will suggest Referring back to the field of visual consciousness, methodological strategies to obtain such evidence similar mixed findings emerged relating to primary in the final section. visual cortex. It is mostly undebated that stimu- Another argument often used by A1 theories to lation of primary visual cortex can elicit conscious

6 visual experiences, so called ‘phosphenes’, and the tantly, the contrast seen versus unseen cannot be blindsight phenomenon shows that some meta- equated to the contrast of felt vs unfelt. Whether awareness of visual information remains intact de- or not participants saw a particular emotional spite damage to primary visual cortex (Weiskrantz, stimulus gives no information about whether they 1986). In other words, primary visual areas can had a corresponding emotional experience. Here, directly give rise to a conscious percept, but their proponents of A1 might argue that this point is absence does not fully eradicate it. We also know irrelevant, as conscious emotions and unconscious that not everyone will experience phosphenes when emotions are two separate entities (or go even stimulated non-invasively, and we also know not all further and claim that unconscious emotions do cortically blind people will experience blindsight. not exist). On the other hand, proponents of A2 Yet, these results do not seem to create a division might argue the distinction is irrelevant because as in theories of visual consciousness even remotely long as either subcortical or physiological activa- similar to the one ignited by mixed findings orig- tions in response to an unseen emotional stimulus inating from work on the amygdala. None of the emerge, an emotion is somehow experienced. It is theories of visual consciousness propose that V1 evident that this contrast will not be able alone is the sole locus of visual awareness, but there is to accommodate between the different theories on a general consensus about the importance of V1 emotional consciousness. Therefore, the following in the formation of visual awareness, be it in a contrasts are equally necessary. hierarchical or interactive manner (Tong, 2003). 2. Experienced(felt) versus not experi- The debate is rather focused on how and where enced(unfelt/different) emotion: to be able to this area interacts with other brain regions to form reveal content-specific correlates of emotional con- conscious perception. The current constant reiter- sciousness, we need to be able to contrast con- ation in emotion research in which we count how ditions in which a stimulus elicits a reportable many studies do or do not find certain results based emotional experience, with conditions in which a on lesions or stimulation is somehow not helpful stimulus elicits either an alternative or no emo- in moving the field forward, given that a hundred tional experience. Again, several issues arise: as percent evidence in either direction will hardly be it has been highlighted, there is very little consen- found. sus on what would define an emotional content. Secondly, a truly emotionally neutral experience is probably unobtainable. Third, this contrast Then, how can we build proper relies inevitably on some measure of self-report: paradigms to measure emotional con- can self-report be trusted? Can behavioral and sciousness? verbal self-reports be equated? Whereas indeed accuracy of self-report based on metacognition We propose that there are three main experimen- abilities has been shown to be poor (Nisbett & tal contrasts which need to be combined to further Wilson, 1977), both consciousness and emotion our understanding of the neural correlates of emo- are first-person experiences, and are likely quite tional consciousness (see Figure 1): accurately accessible through introspection (Over- 1. Consciously versus unconsciously perceived gaard & Sandberg, 2012). But even if this is the emotional stimuli: this is a widely employed con- case, does the act of introspection for self-report trast in studies of emotional consciousness (for a influence our measurement (as already discussed in review see Mitchell & Greening, 2012). In some a previous paragraph)? General awareness is war- paradigms, such as masking or binocular rivalry, ranted concerning how validity of self-report can an emotional stimulus is either consciously per- be influenced by the way scales are constructed ceived by the participant or presented but not (e.g., dimensional vs. discrete), where the focus consciously perceived, on a trial-by trail basis. of introspective attention is placed, or the amount This contrast is limited in how much insight it can of elapsed time before the experience is captured give us into emotional consciousness in two ways. (e.g., A. I. Jack & Roepstorff, 2003; Overgaard & First, whatever neural correlates emerge from this Sandberg, 2012; Robinson & Clore, 2002). contrast will not be content-specific and are more An additional level of difficulty exists: an emotion likely to represent pre-requisites of emotional con- researcher might wonder if their stimulus evoked sciousness, rather than the true neural correlates of any feeling of fear in the participant, but that emotional consciousness. Second, and more impor-

7 Figure 1: We propose three experimental contrast as being necessary to study the neural correlates of emotional consciousness, namely consciously versus unconsciously perceived emotional stimulus, felt versus unfelt emotion, and objective versus subjective measures of emotion. Each contrast has its own limitations, therefore all three are necessary in order to obtain reliable evidence on the neural correlates of emotional consciousness. same stimulus might also have induced feelings of tion: Another way of trying to understand how a anger, panic, sadness, or no feeling at all. Nega- person might feel is measuring their peripheral re- tive and positive emotional states can co- exist at sponses, using for example their facial electromyo- the same time, so-called dialecticism (Bagozzi et graphy signals, as a proxy for emotional valence, al., 1999; Lindquist & Barrett, 2008). Therefore, or their skin conductance responses, as a proxy even if participants were immediately asked to in- for emotional bodily arousal. Nonetheless, while dicate how fearful they felt on a continuous scale, these subjective and objective measures of emo- we might be missing a great deal of relevant con- tion tend to be very well correlated at the group scious experiences. Or a participant might even level, they do not do so in a perfect manner at be primed to believe that what they had felt was the individual level. Early studies on the relation- fear, by framing the report measure in a particular ship between behavioral ratings and physiological way. Previous work has already shown that the responses showed that a correlation between zy- mere act of asking a participant to report on their gomatic and corrugator muscle responses with the feelings can change both physiological and neural rated experienced valence reached significance in responses to a particular stimulus or task (Creswell roughly 50% of the participants, and the corre- et al., 2007; Kassam & Mendes, 2013; Lieberman lations between skin conductance responses and et al., 2007). This is where the additional chal- experienced arousal reached significance in around lenge lies when studying emotional consciousness 30% of the sample (Lang et al., 1993). Of note, compared to perceptual consciousness. We are emotion coherence refers to the coordination be- therefore in need for alternate ways of measuring tween subjective, behavioral, and physiological emotions, which brings us to the final contrast. emotional responses. It has been demonstrated 3. Subjective versus objective measures of emo- that the strength of this coherence depends on

8 both inter-individual differences and the intensity periment’ approach, in which a single experiment of the experience (Mauss et al., 2005). Such find- is run to falsify a specific null hypothesis. As we ings have caused a recent interest in the question have shown above, this approach sometimes does whether subjective experience and physiological not lead to definitive conclusions. An alternative responses are driven by the same underlying brain is the synthesis of existing data: large scale meta- mechanisms. Using multivoxel pattern analysis, analyses, more and more possible thanks to the Taschereau-Dumouchel and colleagues (2019) pro- diffusion of open science practices, have the ad- vided evidence for some level of independence be- vantage of increasing statistical power and deter- tween the two types of measures. Results showed mining consistency of effects (Yarkoni et al., 2010). that despite a significant correlation between re- Yarkoni et al. (2010) likewise suggested that syn- ported subjective fear and measured objective fear thesis of large-scale data is equally useful for the using skin conductance responses on the group development of ontologies or descriptive frame- level, some areas were differentially involved in the works (more on which in section 3.2). Exploring all prediction of the two measures. As stated pre- possible combinations of the above-mentioned con- viously, unconsciously presented emotional stim- trasts, which would hardly be feasible in one single uli have the capacity of eliciting physiological re- experiment, would aid in the search for contrast- sponses in the absence of subjective awareness, invariant and content-specific correlates of emo- raising doubts on their common neural origin. tional consciousness. For instance, it would be in- That said, physiological and behavioral aspects of formative to test whether similar brain areas (or emotion remain central: DSM criteria for emotion- networks) are involved in objectively measured, related disorders, such as anxiety and depression, perceptually identified, consciously felt fear ver- encompass both the subjective experience and sus objectively measured, perceptually identified the somatic/physiological manifestations (Ameri- and non-consciously felt fear. And what about can Psychiatric Association, 2013), and coherence the difference with other emotions? Answering between subjective and physiological responses these questions might inform on some important has been proposed as being related to well-being aspects that possibly the community already in- (Brown et al., 2020). This emphasizes the need for tuitively knows, but which are not yet properly affective disciplines to consider both sides of the formalized and tested. Such evidence is needed for coin, without disregarding one or the other as not starting building theories of emotional conscious- pertinent for emotion research. ness on a solid ground. We therefore suggest the field could benefit from the synthesis of existing data, guided by the suggested experimental con- Where do we go from here? trasts, while at the same time remaining mindful regarding the conclusions which can and cannot With the above listed contrasts, measures, and be drawn from each of the contrasts alone. The their associated shortcomings, one might wonder implementation of open science practices, such as what sort of experimental evidence is needed and data sharing, will help making the above possible. sufficient to build a mature theory of emotional consciousness. We suggest two important steps which we think will move us closer to resolving Defining emotion ontologies through some of the biggest discrepancies between A1 and data-driven approaches A2 approaches. As highlighted earlier, very little agreement exists on the definition of emotion. Definitions of robust Pushing for open science and phenomena and well-defined constructs are essen- large-scale meta-analyses to explore tial for theory building (Eronen Bringmann, 2021) methodological contrasts. and at the same time premature definitions can hinder scientific progress (Pessoa, 2019). Recent If we examine the literature, it turns out that a lot development in data-driven approaches have sug- of the leg work has already been done with respect gested new ways of defining emotion concepts and to exploring the different experimental contrast, ontologies (R. E. Jack et al., 2018), which can pro- but one thing still missing is binding everything vide more agnostic solutions for moving forward in together. Science often relies on the ‘critical ex- situations of large disagreements between theoret-

9 ical accounts. For example, research into mapping trasts, namely conscious versus unconscious emo- the semantic space of emotional experience using tion, felt versus unfelt emotion, and subjectively several self-report measures in response to a wide versus objectively measured emotion, as well as array of emotionally evocative videos was able to what we can and cannot conclude from them. We identify 27 distinct categories of emotional expe- propose that future work ought to perform a syn- riences (Cowen Keltner, 2017). When presented thesis of existing data, through the incorporation with various emotionally evocative stimuli, distinct of open science practices. Data-driven approaches bodily sensation maps associated with subjective might help in defining emotion-related concepts in feelings can be dissociated (Nummenmaa et al., cases where theories cannot converge. Accordingly, 2014). Data-driven approaches have likewise been some theoretical convergence needs to be aimed used to define the characteristics that define dy- at in the long term. To this end, we suggest re- namic facial and bodily movements (de Gelder & fraining from overgeneralization, exacerbation of Poyo Solanas, 2021; R. E. Jack et al., 2014). These preliminary findings and over-theorizing, knowing examples show the promise of how new develop- that whereas disagreements per se are not a reason ments in methodology can also inform theories of for a field to be stuck, premature definitive state- emotions and leave open an interesting potential ments are. for using such methods for the study of emotional consciousness. Importantly, however, data-driven approaches are only partially agnostic, and are Acknowledgements thus not aimed at replacing theory building on the long term. Rather, we here suggest that, given T.E. is supported by funding from the Euro- the large disagreements on how to study emotions, pean Research Council (ERC) under the Euro- such methods can be a strong propulsor for new pean Union’s Horizon 2020 research and innova- discoveries, at the same time aiding in the definition program (grant agreement No 670325, Ad- tion of concepts and ontologies. Some authors have vanced grant BRAVIUS). R.M. was benefited from abandoned the concept of emotion altogether, re- a Gretty Mirdal Junior Fellowship at the Paris placing it with different scientific constructs. For Institute for Advanced Study (France) and was example, Russell (2003) argued that no scientific supported by Fondation de France (grant num- model could apply to all instances of an emotion, ber 00100076). Both authors benefited from the like for example fear, given the large number of Agence Nationale de la Recherche grant ANR- factors being able to elicit it and determine how it 17-EURE-0017 (EUR FrontCog). The authors is experienced. Other authors have even more rad- would like to thank Julie Grèzes,Catherine Tallon- ically proposed a shift in affective science from try- Baudry, Tom de Graaf, Minye Zhan, Klara Ko- ing to explain concepts (e.g., ”emotion”) to trying varski, Morgan Beaurenaut, Clémence Alméras to explain interesting complex behaviors, which and Victor Chung for their support and valuable often cross theoretical boundaries and disciplines feedback on the manuscript. (Pessoa, 2019). This is not the place for discussing in detail all possible implications of such sugges- References tions which we cite here as potentially insightful examples, but we would like to encourage the pro- Adolphs, R. (2013). The Biology of Fear. Current Biology, cess of iterative refinement of concepts and defi- 23(2), R79–R93. https://doi.org/10.1016/j.cub.2012.11.055 nitions through research, instead of what can feel Adolphs, R. (2016). Human Lesion Studies in like a theoretically imposed impasse. the 21st Century. Neuron, 90(6), 1151–1153. https://doi.org/10.1016/j.neuron.2016.05.014 Adolphs, R. (2017). How should neuroscience study emo- Conclusions tions? by distinguishing emotion states, concepts, and experiences. Social Cognitive and Affective Neuroscience, In this paper we tried to address one of the ma- 12(1), 24–31. https://doi.org/10.1093/scan/nsw153 jor disagreements in contemporary theories of emo- Adolphs, R., & Anderson, D. J. (2018). The Neu- tion: what is the role of conscious feelings in emo- roscience of Emotion. Princeton University Press. tion and what are their neural correlates? To help https://doi.org/10.2307/j.ctvc77b1j move the debate forward we have laid out what Adolphs, R., Mlodinow, L., & Barrett, L. F. (2019). What we think are three important experimental con- is an emotion? Current Biology, 29(20), R1060–R1064.

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