The Future of Psychology Connecting Mind to Brain

Psychological states such as thoughts and feelings are real. Brain states are real. The problem is that the two are not real in the same way, creating the mind–brain correspondence problem. In this article, I present a possible solution to this problem that involves two suggestions. First, complex psychological states such as emotion and cognition can be thought of as constructed events that can be causally reduced to a set of more basic, psychologically primitive ingredients that are more clearly respected by the brain. Second, complex psychological categories like emotion and cognition are the phenomena that require explanation in psychology, and, therefore, they cannot be abandoned by science. Describing the content and structure of these categories is a necessary and valuable scientific activity. Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world. —Einstein & Infeld (1938, p. 33) The cardinal passions of our life, anger, love, fear, hate, hope, and the most comprehensive divisions of our intellectual activity, to remember, expect, think, know, dream , with the broadest genera of aesthetic feeling, joy, sorrow, pleasure, pain, are the only facts of a subjective order which this vocabulary deigns to note by special words. —James (1890, p. 195) From its inception in the early 18th century (as an amalgam of philosophy, neurology, and physiology), psychology has always been in a bit of an identity crisis, trying to be both a social and a natural science. Psychologists attempt to bridge the social and natural worlds using the conceptual tools of their time. Throughout our history, the link between the two has felt less like a solid footbridge and more like a tightrope requiring lightness of foot and a really strong safety net. Mind–brain, and relatedly, behavior– brain, correspondence continue to be central issues in psychology, and they remain the largest challenge in 21st-century psychology. The difficulty in linking the human mind to behavior on the one hand and to the brain on the other is rooted, ironically enough, in the way the human brain itself works. Human brains categorize continuously, effortlessly, and relentlessly. Categorization plays a fundamental role in every human activity, including science. Categorizing functions like a chisel, dividing up the sensory world into figure and ground, leading us to attend to certain features and to ignore others. Via the process of categorization, the brain transforms only some sensory stimulation into information. Only some of the wavelengths of light striking our retinas are transformed into seen objects, and only some of the changes in air pressure registered in our ears are heard as words or music. To categorize something is to render it meaningful. It then becomes possible to make reasonable inferences about that thing, to predict what to do with it, and to communicate our experience of it to others. There are ongoing debates about how categorization works, but the fact that it works is not in question. The brain’s compulsion to categorize presents certain unavoidable challenges to what can be learned about the natural world from human observation. Psychologists know that people don’t contribute to their perceptions of the world in a neutral way. Human brains do not dispassionately look upon the world and carve nature at its joints. We make self-interested observations about the world in all manner of speaking. And what holds true for people in general certainly holds for scientists in particular. Scientists are active perceivers, and like all perceivers, we see the world from a particular point of view (that is not always shared by other scientists). We parse the world into bits and pieces using the conceptual tools that are available at a particular point in time and with a particular goal in mind (often inextricably linked to said conceptual tools). This is not a failing of the scientific method per se—it is a natural consequence of how the human brain sees and hears and feels . and does science. An example of how categorization shapes science comes from the study of genetics. When molecular biologists first began to study the units of inheritance, they (inspired by Mendel) searched Address correspondence to Lisa Feldman Barrett, Department of Psychology, Boston College, Chestnut Hill, MA 02467; e-mail: barretli@bc.edu. Of course, psychology is not now, nor has it ever been, a unified discipline with a single approach to science. It encompasses many different topics, methods, and assumptions, as well as much diversity in its level of interest toward and treatment of the brain. PERSPECTIVES ON PSYCHOLOGICAL SCIENCE 326 Volume 4—Number 4 Copyright r 2009 Association for Psychological Science for and found genes: bits of DNA that make the proteins needed to constitute the human body. Yet, only a small proportion of human DNA (somewhere between 2% to 5%, depending on which paper you read) are genes; the rest of the stuff (that does not directly produce proteins) was labeled ‘‘junk’’ on the assumption that it was largely irrelevant to the biological understanding of life. As it turns out, however, ‘‘junk DNA’’ has some rather important functions, including regulating gene expression (i.e., turning on and off protein production) in a contextually sensitive fashion (for a generally accessible review, see Gibbs, 2003). Scientists have discovered that much of what makes us human and makes one person different from another lurks in this junk. The result has been nothing short of a revolution in molecular genetics. Genes do not, in and of themselves, provide a sufficient recipe for life. The unit of selection is not the gene, but the individual, who, for the purposes of molecular genetics, can be thought of as a bundle of genes that are turned on and off by the rest of our DNA that regulates the epigenetic context. And, the more they learned about junk DNA, the more scientists realized that it is not so easy to define what is a gene and what is not. Some molecular geneticists now try to avoid the word ‘‘gene’’ altogether. Instead they use the more mechanistic term transcriptional unit. In this article, I argue that perhaps psychology needs to reconsider its vocabulary of categories. Like any young science, psychology has been practicing a very sophisticated form of phenomenology, observing the psychological world using categories derived from our own experiences. We then use common sense words to name these categories, leading us to reify them as entities. We then search for the counterparts of these categories within the brain. These two practices—carving and naming— have a far-reaching consequence: Psychology may more or less accept the Kantian idea that the knowledge stored in a human brain contributes to thoughts, feelings, memories, and perceptions in a top-down fashion, but at the same time we accept without question that emotions, thoughts, memories, the self, and the other psychological categories in folk psychology reflect the basic building blocks of the mind. We do this in much the same way that Aristotle assumed that fire, earth, air, and water were the basic elements of the material universe; as if the categories themselves are not constructed out of something else more basic. In our causal explanations, psychologists talk about psychological facts as if they are physical facts. But what if psychological facts are not physical facts? What if the phenomena we want to explain—emotions, cognitions, the self, behaviors—are not just the subject matter of the human mind, but are also the creations of that mind? What if the boundaries for these categories are not respected in the very brain that creates them? Such a state of things might lead some scientists to conclude that psychological categories are not real, or that psychology as a science can be dispensed with. That all scientists need to do is understand the brain. But nothing can be farther from the truth. The main point I make in this article is that, in psychology, we simultaneously take our phenomenology too seriously and not seriously enough: too seriously when trying to understand how the mind corresponds to the brain and not seriously enough when we want to understand psychological phenomena as real and scientifically valuable, even in the face of spectacular and unrelenting progress in neuroscience. Changing this state of affairs is a central task for the future. THE METAPHYSICS OF WHAT EXISTS Scientific Ontology The vocabulary of categories in any field of science segregates the phenomena to be explained and in so doing makes them real. Yet not all categories are real in the same way. Natural sciences like physics deal with scientific categories that are assumed to be observer independent (they are real in the natural sense and can be discovered by humans). These kinds of categories function like an archaeologist’s chisel—we need a mind to discover and experience instances of these categories, but they do not depend on our minds for their existence. In 2007, I discovered that philosopher John Searle (in writing about social institutions and social power; Searle, 1995) called these ontologically objective categories or ‘‘brute facts. ’’ They are also called natural kind categories. At times, human experience can lull scientists into using the wrong categories at first (e.g., genes and junk DNA), but the phenomena themselves (e.g., DNA, RNA, proteins, and so on) exist outside of human experience and can have a corrective influence on which categories are used. Here, the presumption is that the scientific method takes us on what can seem like a long, slow, carnival ride toward discovering and explaining the material world. Social sciences like sociology or economics deal with categories that are observer dependent (and are real because they are invented and shared by humans). Observer-dependent categories functio