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by Chris Woodford. Last updated: January 6, 2016.

Why do we do the things we do? Why do some people like hot chocolate while others prefer coffee? Why do some live to surf while others would rather stay home and read a book? How can some of us put a name to every single person we've ever met while others struggle even to remember our own telephone number? Why do some people always seem happy and successful while others see no choice but to end their painful lives in suicide? These are the sorts of questions we can try to answer through psychology: the science of human behavior. In this short article, we'll briefly explore the different branches of psychology and get a quick overview of the kinds of things psychologists do.

Photo: Everything you do, think, and feel involves your brain, shown here as it appears in a PET scan. Understanding how the brain works, how it gives rise to the mind, and why it makes us do the things we do is the prime goal of psychology. Photo courtesy of Lawrence Berkeley National Laboratory and US Department of Energy.

What are the different kinds of psychology?

We can divide psychology into two big areas called experimental psychology and social psychology.

Of course, we can study social psychology in a lab using rigorous experiments, just as we can carry out meticulous experiments in the real world; the division I've drawn between experimental and social psychology is arbitrary and artificial, but it reflects the way psychology is often taught in schools and colleges, and how it's written up in textbooks and scientific papers. The reason for that is largely historical: in the late 19th-century, when psychology was still a very new field, psychologists were keen to be taken seriously as scientists, so they tried to adopt scientific methods to cloak the things they studied in respectability. To this day, there's a certain stigma attached to social psychology and sociology (the study of how individuals and groups behave in society); whether fairly or not, some people see them as soft sciences lacking academic rigor. At Cambridge University in England, for example, the psychology department still calls itself the "Department of Experimental Psychology" and its curriculum includes relatively little social psychology.

Branches of psychology

Humans are the most complex of all the animals, which explains why psychology is such a vast subject. Within the psychology department of a typical university, you'll find people working in a huge range of different areas. There are people who study perception (such as how our eyes and ears work), learning (how we develop as children and how we make sense of the world as adults), memory (why we remember and how we forget), language, thinking, and reasoning. While some psychologists study "normal" human behavior, others specialize in "abnormal" psychology, which includes how people behave when their brains are damaged or degenerate over time and what causes psychiatric disorders. Social psychologists study everything from the best way to design a computer mouse to whether we can really trust the evidence we get from people who witness crimes. Let's look at the various branches of psychology in turn, in a bit more detail.


Close-up of the iris in a blue eye.

You can think of people as living machines who receive information from the world, process it in various ways, and then act on it. In the mid-20 century, it was fashionable to talk about animals (including people) receiving a stimulus through their senses (maybe seeing a chocolate-chip cookie appearing in front of you), which then led to some kind of response (salivating and reaching out); according to a school of thought known as behaviorism, human behavior was all about the way a certain stimulus produced an appropriate response (and exactly what went on inside the brain to make the connection wasn't thought to be especially important: behaviorism was literally "mindless"). Since the 1960s and 1970s, psychologists have tended to view the human brain as a kind of computer, taking in information as "input," processing and storing it in various ways, and then producing "output" (some kind of visible behavior); this approach is known as cognitive psychology and we'll consider it again a little later. However you react to the world, your behavior usually starts with sensory perception: the way your five main senses (vision, hearing, smell, touch, and taste), plus other, lesser-known sensory abilities such as proprioception (your sense of where your limbs are and how your body is moving), feed information into your brain.

Photo: A huge part of your brain is devoted to processing information gathered by your eyes.

For most people, vision is easily the most important sense, closely followed by hearing; that also explains why perceptual psychologists have traditionally devoted most effort to studying vision, closely followed by hearing (comparatively speaking, the other senses have barely been explored at all). Most of us assume that we see with our eyes, but it's far more accurate to say that we see with our eyes and our brains. While we can't see without our eyes, it's also true that our brains carry out a huge amount of processing on the sensory impressions they receive—and in all kinds of interesting ways. One very obvious example is that we see things in three dimensions using separate, two-dimensional images that our brain fuses together from our two eyes. But we also see things based on what we expect to see, which is what causes most of the things we call optical illusions; for example, we see faces in clouds because our brains try to make sense of the world very quickly based on the things we've seen in the past (an awful lot of faces), the things we expect to see in the future (an awful lot more faces), and the things that matter most to us (the faces of people we love, work with, and have to interact with). We can get some idea of just how complex the human visual system is by considering how little progress computer scientists and robot engineers have made designing machines that can "see" in anything like the same way. Why are our own brains so good at seeing? It's estimated that something like 30 percent of the cortex (the outer and, in evolutionary terms, "newest" part of the human brain) is devoted to vision. That's a very impressive illustration of the sheer complexity of making sense of the world entirely by studying light rays that enter two big holes in your head.


One of the things that marks out humans from "lesser" creatures is our ability to make sense of our environment and learn from it. It's obviously untrue to suggest that humans are the only creatures that learn things: you can teach a chimpanzee to use a symbolic language, you can train a dog not to defecate on your carpet, a rat will quickly learn to run through a maze to reach a food reward, and even a simple sea-slug can learn a couple of basic tricks.

Learning goes hand-in-hand with survival, but it's a surprisingly large and complex subject. At one end of the spectrum, psychologists study the process of conditioning, which is how animals come to associate a particular stimulus with a certain response. One of the first people to look into this was Russian scientist Ivan Pavlov (1849–1936), who famously rang a bell when he delivered food to his dogs; eventually, he found the dogs would salivate simply when he rang the bell, even when there was no food around, because they'd been conditioned to associate salivating with the sound of the bell. When behaviorism was fashionable, some psychologists thought all kinds of complex human behavior might be broken down into patterns of stimulus and response. That's why, for example, you often see attempts to blame violence on TV and in the movies for wider violence in society. Now we know complex human behavior is much more than a simple knee-jerk reflex from stimulus to response.

A spider monkey copies a human drinking water.

One of the great things about psychology, which differentiates it from older sciences such as physics and chemistry, is that its relevance to everyday life is often more immediate and apparent. One branch of the psychology of learning is called developmental psychology and it concerns how babies develop into children and adults: for example, how they learn language, how they turn specific, concrete examples of things they see around them into much more general, abstract principles (the rules by which we have to live to survive), and the relative importance of "nature" (genetic factors—things we're born with) and "nurture" (environmental factors—things we're taught and learn). Developmental psychology has played a huge role in pedagogy and the scientific, theoretical approach to education; it's also a fascinating subject to study if you're a parent.

Photo: Mirror neurons? Sometimes we mimic one another's behavioral unconsciously, such as when two friends stand next to one another and, quite unawares, adopt exactly the same posture. Psychologists think our brains contain "mirror neurons," which are activated both when we do things and when we see other people doing those things. That encourages us to copy other people's behavior, and possibly explains how we feel empathy with others. Photo by Kasey Close courtesy of US Navy.

Cognitive psychology

Thousands of years ago, before humans started to create fixed settlements and developed agriculture, we lived much like other animals and day-to-day survival was our only preoccupation. How different things are now. Although the world's poorest people still experience life as a horrible daily battle to survive, most of us, thankfully, get to lead lives that alternate between (reasonably tolerable) work and (extremely tolerable) pleasure. Both of these things involve using our brains as much as or more than our bodies; both see us functioning as living computers—"human information processors"—that take in information, process or store it in our brains, and then output results. The way we process and store information is what cognitive psychologists study. How do we understand a simple sentence whispered into our ears? How can we remember everything from how to ride a bicycle to the names, in order, of all the American presidents? And is there any fundamental difference between these two types of memory (knowing how to do something, which is called procedural memory, and knowing facts about the world, which is declarative memory)?

Where behaviorists liked to pretend that "internal mental processes" didn't matter, didn't exist, or probably both, cognitive psychologists spend their time teasing out the precise nature of those processes, typically coming up with flowchart models that break such things as memory and language processing (a field of its known, often known as psycholinguistics) into sequences of discrete components. Applying this to the study of memory, for example, has given us models of mind that suggest memory breaks into separate long-term and short-term stores, with the short-term or "working" memory itself divided into distinct areas that process visual impressions, snippets of spoken language, and so on.

Ulric Neisser's cognitive psychology diagram

Artwork: Ulric Neisser's famous caricature of cognitive psychology from his 1976 book Cognition and Reality.

Cognitive psychology is not limited to how we process the structure of information, but also what information means. The word cognition is a synonym for thinking and reasoning, two areas that cognitive psychologists have also studied using computational models. How do we make informed judgements about things, such as whether one car is a better buy than another? Why do we live in absolute fear of things like terrorist attacks but happily cross roads, drive cars, ride bicycles, drink alcohol, or smoke cigarettes (all of which pose far greater risk to our safety and health)? Why do we play lotteries when the chances of winning are so much less than the odds of being struck by lightning? These are the sorts of questions cognitive psychologists consider under the broad umbrella of thinking and reasoning.

Examples of the capital letter A printed in various different sizes and fonts.

Photo: The psychology of typography: Although you might think these letters contain identical information (the capital letter A), each is printed in a different font. Thanks to things you've read and seen previously, you read words printed in different fonts with a slightly different meaning and emotion: elegant, relaxed, friendly, imperative, hostile, or whatever it might be. That's one of the key principles of graphic design—and it happens in your mind, not on the page.


Though related to cognition, intelligence, which we might define as a general ability to solve problems, is a separate area of study, and it's much less fashionable than it used to be several decades ago. There are several reasons for this. From Sir Cyril Burt (a prominent British psychologist who allegedly faked research data about his studies of intelligence) to William Shockley (the co-inventor of the transistor who, predictably, became embroiled in controversy when he dared to suggest that there was a link between race and intelligence that made white people intellectually superior to blacks), the study of intelligence has often proved intensely controversial. The controversies, though important, distract from a much more fundamental difficulty: how should we define intelligence and is it even a meaningful concept? Some cynics have defined intelligence as the mere ability to pass intelligence tests, but although psychometric testing is as popular as ever in recruitment for jobs, intelligence tests are not, and never have been, a predictor of people's ability to live happy, worthwhile, successful lives.


When you study psychology, it's remarkably easy to forget that most of the cool and fascinating things you discover happen inside the brain—an apparently unremarkable organ often compared to "two fistfuls of porridge." Neuropsychology is all about figuring out how the brain is structured and how different parts of it have different functions. One extreme, early example of neuropsychology, known as phrenology, famously involved quack doctors claiming they could tell interesting things about someone's personality by feeling their skull for bumps. Although the idea seems risible today, the central idea of phrenology—that the brain is modular, with discrete regions having specialized functions—is now known to be essentially correct. However, it's an unhelpful oversimplification to suggest, for example, that the right half of the brain is dreamily creative while the left half is clinically rational; for most of the things we do, many different parts of the brain are involved, either working in parallel or in complex serial circuits.

NMR body scanner

Photo: Brain scanners have revolutionized psychology. By showing up the activity inside our brains when we think certain thoughts or do certain things, they can help to reveal which areas of the brain do what. Photo by courtesy of Warren Grant Magnuson Clinical Center (CC) and US National Institutes of Health (NIH) Image Gallery.

If cognitive psychology can break things like memory or language into separate areas or processes, is it possible to locate parts of the brain where those things happen? That's the basic thinking behind a hugely successful field called cognitive neuropsychology, which involves trying to map abstract processes and functions discovered through cognitive psychology onto very concrete areas of the brain that neuropsychologists have discovered (and vice-versa). Some psychologists—modern-day mental Mercators—get carried away in a frenzy to map the brain, forgetting that the ultimate goal is not to draw a tourist's guide to the inside of your head but to produce a scientific explanation of the mind: who we are and why we do the things we do.

While neuropsychologists do study healthy, functioning brains, they also devote a lot of their time to researching people whose brains have become damaged through such things as head injuries, strokes, or degenerative diseases like Alzheimer's. We can discover much about how things like memory and language processing work by studying what people can no longer do when specific areas of their brain are damaged or destroyed. In the most spectacular cases, it's possible to find people with very localized brain damage who can no longer do very specific things (for example, recognizing faces or reading words); we can infer from this that the damaged brain areas play a key role in whatever function has been lost—and that helps us build up a map of which parts of the brain do what.

Abnormal psychology

People are hugely diverse and different—that's one of the things that makes life interesting. While it's difficult to define "normal" behavior, it's somewhat easier to point to examples of abnormal behavior, which is harmful to people and those around them. Neuropsychological problems following brain injuries are one example, but behavior can also become abnormal for a wide variety of other reasons, which we might broadly divide into behavioral, cognitive, and neurochemical/biological. Eating disorders such as anorexia and bulimia are believed to be largely behavioral and cognitive, for example: you might develop an eating disorder if you convince yourself you're fat, after becoming obsessed with skinny catwalk models. Illnesses such as Parkinson's disease are more to do with neurochemistry and biology: Parkinson's is believed to occur when nerve cells in the brain stop producing dopamine, an essential chemical neurotransmitter that sends messages around the brain.

Psychiatric disorders such as depression and schizophrenia are hugely complex and still imperfectly understood. Depression can occur for many different reasons, which might be behavioral (you feel nothing you do makes any difference and become miserable through "learned helplessness"), cognitive (you analyze the world around you in a way that persistently makes you unhappy), neurochemical/biological (for one reason or another, the chemicals or the basic structure of your brain are geared to unhappiness), or some combination of these things. The study of schizophrenia has a fascinating history, with attempts to explain it shifting from anatomical/biological causes, through cognitive and behavioral ones, and back again. Originally described as a kind of premature dementia ("dementia praecox"), by the 1960s it was being painted (by such figures as R.D.Laing) as a kind of sane reaction to an insane world, and now it's much more likely to be considered a consequence of a person's particular brain chemistry.

You'd think understanding the cause of a psychiatric problem would be the first step toward treating it but, remarkably, psychiatry has often worked in willful ignorance of what was happening in the mind, partly through the influence of behaviorism, partly through the challenge of anti-psychiatrists who refused to believe in what they called the "myth of mental illness," and also because the underlying causes of psychiatric problems were genuinely not known. Treatments for psychiatric disorders were largely doled out on the basis of what seemed to work and what didn't; if clinical trials found that drugs cured more depressive patients than, say, group therapy (talking about your problems with other patients), drugs became the treatment of choice. It didn't necessarily matter why they worked or how, providing the patients showed an improvement. That's how hugely controversial psychiatric treatments such as lobotomy (surgical removal or destruction of parts of the brain) and electroconvulsive therapy (electrical shocks to the brain) became popular in the mid-20th century. Just as psychology tried to cloak itself in experimental and Emo emotional robot with a computer-controlled mouth and eyes scientific rigor, so 20th-century psychiatry latched onto the respectability of medicine, often masking a substantial ignorance of how and why disorders actually occurred. Today, thanks to advances in neurology, neuropsychology, and neurobiology, we have a much clearer understanding of how the brain works and why it can malfunction—but many questions remain.

How will psychology develop in future?

In the 150 years or so since psychology became a science, huge amounts have been discovered about why people behave as they do and how we can relate different aspects of human behavior to what goes on inside our heads. Even so, teasing out the many, remaining mysteries of the brain remains one of the last great challenges of science. Apart from being hugely interesting in its own right, another important prospect is the discovery of effective treatments for terrible degenerative diseases such as Parkinson's and Alzheimer's. A further interesting direction is the development of artificial intelligence, including computers and robots that can "think" and act in more humanlike ways. Will probing the mysteries of the mind help us perfect electro-mechanical rivals who make us obsolete? Or will the act of developing intelligent machines sharpen our sense of what it means to be human, making us happier and more fulfilled? Psychologists, you can be sure, will find the answer!

Photo: Psychologists are helping computer scientists to develop emotional robots like this one, pictured at Think Tank, the science museum in Birmingham, England.

A brief history of psychology

Sigmund Freud

Here are a few key milestones from the history of psychology and psychiatry over the last few hundred years.

Photo: Sigmund Freud. Photo courtesy of US Library of Congress.

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