Research interests
• Cognitive science, Cognitive psychology, Developmental psychology, Cultural psychology, Cognitive science of religion, Cultural neurobiology
• Amazonian ethnology, Ethnohistory of South America, Cognitive anthropology, Experimental anthropology, Neuroanthropology
• Philosophy of mind, Philosophy of perception, Experimental philosophy
Research work
Collaborations.
In my ongoing work, I am collaborating with several labs, including:
-Cognitive Development and Learning Lab / UC Berkeley / Alison Gopnik
-Language and Cognition Lab / Stanford University / Michael C. Frank
-Psychology Department / Eötvös Loránd University / Sunae Kim
-Religion, Cognition and Behavior Lab / University of Amsterdam / Michiel van Elk
-Anthropology Department / Stanford University / Tanya Luhrmann
-Psychology Department / Ludwig Maximilian University of Munich / Markus Paulus
Fields, tools and methods.
My research work combines (1) conceptual analysis (analytic philosophy), (2) theorization based on existing empirical findings (mainly: anthropological, psychological, neuroscientific and biological findings), (3) collection of experimental/psychological data, and, (4) collection of ethnographic data.
My ethnographic fieldwork is located in Shipibo-Konibo communities of the Ucayali region, in the Peruvian Amazon. More recently, I have also started to work with Huni Kuin (Cashinahua) communities on the Peruvian side of the Purus region.
I what follows I outline the two lines of research that I have been investigating within the last few years: (1) "The structure of abstract knowledge in indigenous Amazonian cultures", and, (2) "Hallucinogens, culture, and neurobiology".
(1) First line of research: "The structure of abstract knowledge in indigenous Amazonian cultures"
(1.1) General background: Bayesian constructivism
The formation of abstract knowledge has been a matter of controversy: some have argued that it is innately present (nativism) and others that it is simply abstracted from regularities detected by the senses or is socially constructed (empiricism). A third proposal—Bayesian constructivism—suggests that abstract knowledge is more than the simple accumulation of sensory data and that it is gradually constructed through development rather than being innately given or directly taught (cf. Alison Gopnik, Fei Xu, Josh Tenenbaum, Charles Kemp, etc.). One implication of this view is that different abstract structures may be constructed given different kinds of experience. My work explores the fruitfulness of the Bayesian constructivist framework in studying how Amazonian indigenous people categorize and reason about the world.
(1.2) Essentialism
Psychological essentialism (PE) is the view that external properties are explained by inner ones and that identity is defined by inner and fixed properties rather superficial and malleable ones. According to most authors, PE is found in all cultures across the world (e.g., Gelman, Hirschfeld, Boyer). My work challenges such a claim. In particular, Cashinahua people resort to striking non essentialist lines of reasoning. For them, many inner properties are explained by external ones and are thus highly malleable. Cashinahua non-essentialism obtains both in the domain of ethnozoology (reasoning about different species of animals) and ethnosociology (reasoning about different ethnic groups).
The importance of non-essentialism in some Amazonian cultures has also implications in the field of anthropology. Anthropologists such as Descola and Viveiros de Castro have proposed that what is special in the way Amazonian people think is that they ascribe mental and bodily properties differently than we do (for example, as compared to us, they “over-ascribe” mental properties to animals and plants). What my work on non-essentialism suggests is that what really differentiates Amazonian thinking from our own thinking, is not so much how mental or bodily properties are ascribed to beings of the world, but rather whether these properties are deemed fixed or malleable. Typically, we tend to conceptualize many inner properties as being fixed while indigenous Amazonian people conceptualize them as being highly malleable.
(1.3) Ethnobiology
My work on ethnobiology is closely related to (1.2). In the domain of ethnobiology, essentialist thinking has often been associated to taxonomic thinking (cf. Atran). Here again, several authors (e.g., Berlin, Atran) have maintained that ethnobiological knowledge is universally organized in taxonomic trees. In line with the Bayesian proposal, I explore the hypothesis that a given domain can be organized around various structures. Preliminary findings suggest that, in Amazonian, abstract knowledge regarding biological beings is organized around complex and dynamical networks rather than taxonomic trees. This is consistent with previous work conducted in the Peruvian Amazon (cf. Lenaerts).
(1.4) Color categorization
Just like the domain of biology, the domain of color has been said to be organized around universal principles (cf. Berlin & Kay). However, several authors have disputed the claim that color categories are organized in the same way all over the world. For example, Surrallés has recently argued that the Candoshi of the Peruvian Amazon do not have any color category but instead use ad hoc and contextual words anchored in real objects of the world. My work among the Shipibo-Konibo brings to light 5 basic color terms that work consistently with the color categories described in the World Color Survey. However, in addition to that, the studies I have conducted also reveal the existence of a myriad of ad hoc color terms. For example, to refer to red, the Shipibo-Konibo often use the word “jimi” (“blood”) even though they have a basic color term specifically referring to red (“joshin”). The ad hoc color terms used by the Shipibo-Konibo are polysemous (i.e., they can be used to refer to different colors if the original anchor object features different colors) and if speakers are asked about their meaning, they will first mention non-color meanings (e.g., “jimi” will be said to mean “blood” before “red”). These two properties contrast with lexicalized basic color terms used in English that originate in real objects of the world (e.g., the word “orange” for the orange color). In sum, my work on color categorization among the Shipibo-Konibo questions the universality of classic color categorization, and above all, it shows that some indigenous cultures of Amazonia have developed categorization systems that strikingly contrast with ours in that they include highly context-sensitive and flexible concepts.
(1.5) Components of beings
The view that abstract knowledge can take only one form within a given domain is also illustrated by the way people conceptualize beings. Many psychologists have claimed that persons are universally conceived in a dualist fashion (e.g., Bloom, Bering, Cohen). I have studied how the Shipibo-Konibo ascribe abilities (“thinking”, “eating”, “crying”, “reasoning”, etc.) to different beings (animals, plants, natural inanimate objects, artefacts); and also how they ascribe “ontological components” (“shinan” = “thinking”; “kaya” = “soul”; “yora” = “body”, etc.) to the same beings. Preliminary findings contrast with the view that dualism is universal. Here again, it seems that the components of the beings are ascribed in a very dynamic and context-sensitive way.
This work also speaks to recent anthropological discussions around the concept of animism. As mentioned in (1.2), some anthropologists have it that a key feature of Amazonian cultures is that they over-ascribe mental properties to animals, plants and even non-living objects: in other words, there are animists. My work on the component of the beings provides a very different picture: nowhere did I find the kind of hyper-mentalization described by the proponents of the animistic model.
(1.6) Spirits and masters
The Amazonian world is replete with “supernatural” entities. Some of them are spirits and others are described as masters or guardians of the animals, of the river, of the land, etc. (some supernatural entities are purported to be both spirits and masters). I have explored the properties Shipibo-Konibo ascribe respectively to the master (ibo) of a plant (the ayahuasca vine), of a river (the Ucayali river) and of an animal (a white-lipped peccary). Interestingly, while the master of the plant is conceived as an immaterial spirit and as being the same for all the plants, the masters of the rivers and of the animals are taken to be other animals and each herd or each river possesses its own animal master. In the zoological and ecosystemic domains, the master seems to be defined by very specific ecological relationships. This work further questions some of the assumptions of approaches from both anthropology and the cognitive science of religion that over-emphasize the role of hyper-mentalization in folk intuitions about “supernatural” entities.
(1.7) Supernatural thinking
A very influential theory developed by several proponents of the cognitive science of religion has it that the main mechanisms of supernatural thinking lie in the violation of modular and universal domain-specific knowledge (e.g., Boyer, Barrett, Atran). This theory has recently received some criticism (e.g., Purzycki & Willard). In my work, I also point out some weaknesses of this theory and develop a new proposal. According to this new proposal, supernatural thinking is triggered by violations of randomness that cannot be explained by our ordinary causal schemas. This theory is largely inspired from previous work on randomness (cf. Griffiths & Tenenbaum), on probabilistic models of agency (cf. Xu, Kushnir) and causal reasoning (cf. Gopnik) and it contends that supernatural thinking is not a matter of modularity or domain-specific knowledge. This new proposal challenges many influential approaches to religious thinking developed within the cognitive science of religion.
(2) Second line of research: "Hallucinogens, culture, and neurobiology"
(2.1) Defining hallucinogens
Psychotropic substances are pharmacological compounds that have the power of altering cognition and/or consciousness. Hallucinogens are a subclass of psychotropic compounds: they specifically alter perception by generating (visual, auditory, haptic, etc.) contents which are not true. Importantly, many psychostimulants (e.g., coca, khat) or sedative substances (e.g., opiates, kava) are not hallucinogenic. My research bears only on hallucinogenic substances and not on psychotropic substances in general.
(2.2) Classes of hallucinogens
In my large review of the literature on hallucinogenic compounds and their effects, I have put forward a model that identifies 9 classes of hallucinogens: (i) serotoninergic hallucinogens (e.g., LSD, psilocybin); (ii) antimuscarinic hallucinogens (e.g., scopolamine, atropine); (iii) antihistaminergic hallucinogens (e.g., brompheniramine, diphenhydramine); (iv) κ-opioid hallucinogens (e.g., pentazocine, bremazocine); (v) antiglutamatergic hallucinogens (e.g., ketamine, phencyclidine); (vi) cannabinoid hallucinogens (e.g., THC, nabinole); (vii) nicotinic hallucinogens (e.g., nicotine, nornicotine); (viii) anticholinesterasic hallucinogens (e.g., harmine, harmaline); and (ix) GABAergic hallucinogens (e.g., muscimol, THIP). In addition to these 9 classes, a tenth class of hallucinogenic compounds should be added to classify compounds whose effects tap into several neurotransmission systems. Ibogaine and noribogaine are good illustrations of such hybrid compounds. It is worth noting that although 9 classes of hallucinogens can be identified, only 6 classes of hallucinogens have been widely used through history and across cultures (namely, (i), (ii), (vi), (vii), (viii), and (ix)).
(2.3) The pharmacodynamics/phenomenology one-to-one mapping
Most of the researchers currently investigating hallucinogens focus on serotoninergic hallucinogens. One of the main claims of my work is that key insights can be gained on the mechanisms of drug-induced hallucination by comparing classes of hallucinogens with one another. In this work, I sketch what a general comparative study of the 9 classes of hallucinogens would look like, but I only investigate two classes in detail – serotoninergics and antimuscarinics – because these two are the most well documented (antimuscarinics have been widely researched in the 1960s and 1970s). By comparing the underlying pharmacodynamics and resulting hallucinogenic effects of serotoninergics and antimuscarinics, I show how very neat one-to-one mappings can be established between the neuropharmacological and the phenomenological levels.
(2.4) Neurocognitive account of the phenomenology of hallucinogens
After showing how distinct neuropharmacological mechanisms correlate with distinct phenomenological contents, I put forward several neurocognitive models building the bridge between the cellular and the experiential levels. For example, a key feature of antimuscarinic hallucinations is that they are perfectly realistic and embedded in the non-hallucinatory environment. By contrast, serotoninergic hallucinations are mostly non-realistic and extraordinary in character and they present themselves as belonging to another “plane of reality”. This phenomenological contrast can be readily explained by the fact that serotoninergics importantly alter the early visual cortex as well as areas underlying object construction, while antimuscarinics mainly interfere in higher areas underlying scene construction.
(2.5) Towards a new theory of hallucination and perception
The investigation of the neuropharmacological and cognitive neuroscience of hallucinogens can provide crucial insights into the understanding of hallucination and perception. In particular, I debunk three “myths” endorsed by classical theories of hallucination and perception.
-The first myth is that perception can be defined by a relation to the world whereas hallucinations are to be defined as the lack of such relation. What my work shows is that hallucinatory states are always influenced by inputs from the world. The real difference between perception and hallucination does not lie in whether the central nervous system is related to the world (influenced by the world) or not, but in how stimuli from the world are being processed. A hallucinatory state may be induced exactly by the same input (i.e., by the same relation) as the non-hallucinatory state, but what makes it hallucinatory is the way it processes that input – i.e., what kind of output it generates given a certain input.
-The second myth is that there is such a thing as a perfect hallucination – i.e., a hallucinatory content that perfectly mimics a non-hallucinatory content. None of the different kinds of hallucination induced by the 9 classes of hallucinogens ever generates perfect hallucinations. This is equally true of other types of hallucinatory states: hallucinations caused by schizophrenia, neurodegenerative diseases, dreaming, etc. While hallucinations never perfectly mimic non-hallucinatory states, I duly acknowledge that they may subjectively seem to do so. How is it, then, that subjects can erroneously experience a hallucinatory state to be identical to a non-hallucinatory state while it is not? This happens every time the subject lacks metacognitive insights. This metacognitive faculty, I argue, is closely related to the activation of the dorsolateral prefrontal cortex.
-The third myth is that hallucinations are anomic, that is, that they are random (i.e., they can result in any kind of content and they are not governed by specific and predictable laws). This myth has been traditionally endorsed by authors such as Descartes and Malebranche. What my work shows is that each hallucinogen generates a specific kind of hallucinatory content and this specificity can be elucidated by the cellular and neurocognitive mechanisms underpinning the hallucinatory effects. Thus, a antimuscarinic hallucinogen – unlike a serotoninergic hallucinogen – will never induce extraordinary hallucinatory objects (such as a chimera). Therefore, like any representation in the brain, hallucinations are normatively constrained: they are governed by specific laws and these laws can be discovered by the neuroscience of hallucination.
In sum, philosophically, I reject both “disjunctivism” and “common factor theories” (i.e., most brands of intentionalism, sense-data, etc.). I reject disjunctivism because this theory claims that the key difference between the perceptual state and the hallucinatory state is to be understood in terms of relation to the world (present in one case and absent in the other). This amounts to endorsing the first myth. Conversely, I reject “common factor theories” because they endorse the second myth of “perfect hallucinations”. For that matter, I also reject predictive coding accounts of hallucinations which are also committed to the truth of the second myth (cf. “perception is a controlled hallucination”).
(2.6) Neuropharmacology and culture
In this work, I also explore interactions between neuropharmacology and culture. The question, briefly, is the following: when one entertains a given hallucinogenic experience, what part of the experience is caused by neuropharmacology and what part is caused by culture. A purely biological perspective would have it that the whole experience can be boiled down to the properties of the pharmacological compound. Conversely, a purely culturalist perspective, perspective would contend that the whole experience is determined by one’s mindset and by the setting in which the experience is taking place. My contribution to this debate consists in highlighting two main points. First, I show how fruitful the comparative approach is. By comparing the role of neuropharmacology and culture in hallucinogenic experiences induced by distinct classes of compounds (serotoninergics, antimuscarinics, κ-opioids, etc.) one is able to better assess the contribution of each factor. Second, I argue that the neuropharmacology vs. culture divide is misleading because the two factors are in fact deeply intertwined. For example, I show that it is precisely for neuropharmacological reasons that serotoninergic hallucinogens make people so sensitive to the mindset and the setting. The cultural shaping of such hallucinogenic experiences is governed by neuropharmacology. Such cases require us to go beyond the usual neuropharmacology vs. culture divide and to develop more interactive and dynamic concepts.
(2.7) Neuropharmacology and cultural evolution
Many authors (Furst, Ruck, Wasson, etc.) have made very strong claims about the role played by hallucinogens in cultural evolution. According to them, beliefs, artefacts and institutions are crucially shaped by hallucinogenic use. In other words, hallucinogenic use results in the emergence of very specific cultural traits. In order to assess such claims, I have reviewed all the key cultural traits that these authors take to be specifically related to hallucinogenic use; next, I have comparatively looked at traditional cultures in which hallucinogenic use was present and others in which it was absent and examined whether the latter type of culture lacks the cultural traits purported to be found only in hallucinogenic-driven societies. This investigation revealed that the cultural traits under scrutiny are encountered in all cultures regardless of whether hallucinogenic use is present or not. As a result, it seems reasonable to say that hallucinogens play only a limited role in cultural evolution; furthermore, their role may concern formal rather than contentual properties of culture. To take the example of beliefs, my point is that hallucinogens shape not so much what is believed – i.e., the content of beliefs – as the kind of attitude people entertain towards those contents. In other words, regardless of what belief is being entertained (believing in gods, in spirits, in dwarfs, etc.), hallucinogens have very specific attitudinal effects. Specifically, Van Leeuwen has proposed to distinguish between religious credence and factual belief. Importantly, Van Leeuwen (and others) have it that the attitude defined as factual belief is never found among religious believers. By contrast, I argue that hallucinogenic use precisely enables people to switch from religious credence to factual belief. Hallucinogens make people believe on a “factual belief mode” what they previously believed on a “religious credence mode”. Hence the general claim that the role hallucinogens play in cultural evolution is more a matter of attitudinal change than a matter of contentual change.
(2.8) The HUTHAC (Hallucinogenic Use Through History and Across Cultures) database
In order to further investigate the interactions between hallucinogenic use and culture, I am currently developing a database that includes hundreds of references from academic articles and books, explorers’ diaries, and historical chronicles. Each of these references specifies which hallucinogen was being use, where it was used, who was allowed to use it, what it was being used for (e.g., divinatory, political or healing purposes?), etc. To my knowledge, the HUTHAC is the first academic source exhaustively documenting hallucinogenic use through history and across cultures. The criteria used to insert data within the HUTHAC are particularly stringent. First, data included in the database concern only hallucinogenic use and not psychotropic use in general. Second, when building the HUTHAC, I made a distinction between use of hallucinogens at hallucinogenic doses and use of hallucinogens at sub-hallucinogenic doses (i.e., at doses too low to induce any hallucination). Sub-hallucinogenic uses of hallucinogens are not included in the HUTHAC. Also, since the 1950s, outlandish philological speculations have been made about the use of hallucinogens at different epochs and in different places in the world. The HUTHAC does not include the doubtful cases of hallucinogenic use advanced by these authors. It only includes uses of hallucinogens for which there is a good amount of evidence. This evidence may be first-person observation (by an ethnographer or an explorer), third-person report (provided that the report can be considered reliable), and archeological evidence.
(2.9) Main finding of the HUTHAC database
The main finding of the HUTHAC is that hallucinogenic use is fairly rare through history and across cultures. By and large, in the last hundreds years, hallucinogenic use has mainly flourished in the Americas and been absent elsewhere (with only a few exceptions). Even in the Americas, hallucinogenic use has been persistently absent from some areas – notably North America (with the exception of Southern California and the Southwest), the Southern Cone, and Eastern Brazil. Another finding is that hallucinogenic use has gradually increased through the centuries (for example, in South America, ayahuasca and mimosa use have developed only in the 18th century). These findings deeply challenge the view that hallucinogenic use is very ancient and belongs to an ancestral shamanic tradition that would have migrated from Siberia to the New World (cf. Furst, La Barre, Wasson, etc.). More broadly, they also challenge the view that most archaic cultures used hallucinogens. By contrast, these findings accord very well with the model championed by John Cooper and Joseph Wilbert according to which hallucinogenic use is relatively recent and related to horticultural/agricultural practices.
(2.10) Homo neurochemicus
Some neuroscientists argue that our brain is evolutionarily wired, and as a result, it is everywhere the same and generates everywhere similar behavioral outputs. Other neuroscientists argue that the brain is wonderfully plastic and that its wiring can be extensively modified through experience. My contention is that the study of hallucinogenic use provides us a view of the brain which radically differs from the two aforementioned stories. Regardless of whether our brain is malleable or not, what is so interesting about hallucinogens is that they can deeply modify behavior and experience without modifying anything in the underlying hardware. More specifically, when someone takes LSD, the wiring of the brain is exactly the same before and during the hallucinogenic experience (one can certainly observe dramatic functional changes in brain connectivity, but not any structural change). And yet, under LSD, consciousness will be so deeply altered, sounds will influence the content of vision, spatial dimensions will collapse, outlandish and folkloric characters will appear, new metaphysical beliefs will be endorsed, etc. Again, what is so outstanding is that all this takes place without any structural change in the brain.
By putting forward the concept of Homo neurochemicus, I intend to highlight that most of the flexibility of the human behavior stems from neurochemical changes (I am here speaking of the kind of flexibility scientists can observe in the lab and not so much the kind of flexibility they can de facto observe in the wild, as hallucinogenic use is precisely limited in the wild (cf. 2.9)). Proponents of evolutionary psychology and of fixist models of the wiring of the brain are mistaken in that they overlook the power of neurochemistry. All the behaviors and thoughts that they take to be universal and fixed can in fact be altered by introducing the right chemical compound in the central nervous system. Proponents of the plasticity of the brain are also mistaken because they think that diversity of behavior and experience can only stem from a change in the wiring of the brain; moreover, changes caused by neurochemical means are much more dramatic than those induced by the long-term plasticity of the brain.