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What is Psychology’s Single Most Brilliant Discovery?

Multiple minds reside in your one head

A couple of months ago, I asked several of my distinguished colleagues to nominate psychologists who would merit the label “genius.”

But Mark Schaller suggested that I was asking the wrong question; I should instead be asking about which ideas from psychology deserved to be called ingenious. Schaller’s position is especially defensible if you assume that most scientific discoveries involve brilliant people standing on one another’s shoulders, sharing good ideas and improving them bit-by-bit. In fact, when I made up my own list of psychological geniuses, I was impressed by the fact that most of the people I admired had worked hand-in-hand with brilliant teachers and students, had collaborated with other brilliant researchers, often developing ideas that were “in the air” at the time. Rather than single earth-breaking discoveries, these ingenious researchers each made mini-discoveries, and those mini-discoveries combined to produce major advances in the way we think about human thought and behavior.

Has psychology given us any genuinely brilliant discoveries? I think the answer is yes, and I will nominate one that I think is especially noteworthy:

The human mind (and the human brain) is modular.

In everyday terms, we could say there is more than one “thinker” inside your head. Or even more boldly: We are all multiple personalities, with several different selves insides our heads. Those different selves pay attention to different kinds of information, remember different past experiences, have different feelings, and aim to accomplish different goals.

At first blush, it seems counterintuitive to think there is more than one “me” inside my head. My conscious experiences certainly seem to hang together in one continuous stream, and the reserved intellectual-you who is reading this blog posting can probably easily remember the extraverted-you who went to a party last night, the neurotic-you who worried about being mugged in the dark parking lot after the party, and the romantic-you who first fell head over heels for the love of your life. But your conscious continuity can be deceiving, and a number of pioneering findings suggest that there is a lot more going on behind the scenes, at the non-conscious level. Here is a very brief summary of some of the pioneering findings that led to that conclusion:

"Blausen gallery 2014". Wikiversity Journal of Medicine.
Source: "Blausen gallery 2014". Wikiversity Journal of Medicine.

Neuroscientific Evidence

Perhaps the most important discoveries about modularity were made during the 1860s and 1870s, when researchers in France and Germany found that very different types of speech disabilities were linked to damage in particular areas of the cerebral cortex. Damage to one area (dubbed Broca’s area after one of the discoverers) resulted in an inability to form words, even though the patient could understand language and communicate using nonverbal cues (such as nods and hand motions; Broca’s classic case was able to hold up fingers to indicate the number of years that had passed since he lost the ability to speak). Damage to a nearby area of the cortex, on the other hand (dubbed Wernicke’s area) resulted in a problem opposite to that observed by Broca - an inability to comprehend other people’s speech, despite a continuing ability to speak.

Another classic finding originated in a 1957 paper by William Scoville and Brenda Milner. That paper reported the classic case of H.M., who had lost most of his hippocampus and some of the surrounding areas of his temporal lobes during surgery for epilepsy. After the surgery, he was unable to report on new experiences (such as naming the current president of the United States, even if he’d heard the name several times). But H.M. was able to learn new nonverbal tasks (such as the pursuit rotor task, which requires a person to track a dot as it moves around on a turntable). This suggested that different types of memory are affected by different regions of the brain.

In the 1960s Roger Sperry and Michael Gazzaniga reported on several cases of individuals whose left and right cerebral hemispheres had been separated (also as a treatment for epilepsy). One consequence of this operation was that the left side of the brain could not communicate with the right side. If the researchers showed an image (a picture of a spoon, for example) to the subjects’ (more verbally adept) left brain by flashing it into the right half of their visual field, the person was able to name it. But if the same image was shown to the right brain, the person could point to a spoon with his left hand, but was unable to name it. Gazzaniga described how a split brain patient whose right brain saw an emotional picture would try to “explain” his emotions as due to something about Gazzaniga’s appearance or behavior (since the verbally adept left brain was unaware of the picture, so had to make up a plausible story). This work, which became a cornerstone of modern neuroscience and eventually won a Nobel Prize, challenged the idea of a unified consciousness. It showed that our conscious experiences could be very different depending on which part of the brain was currently active and processing incoming information.

Domain-specific learning and memory processes

Other work suggesting that the brain has multiple information-processing systems comes indirectly, from research on memory and learning.

It was once believed that learning processes such as classical and operant conditioning were “domain general” – that is, the same rules applied to conditioning of all sorts. That would seem to be a parsimonious way for a big single-system brain to process information. But a classic study by John Garcia and Robert Koelling suggested that learning to avoid potentially poisonous foods does not follow the same rules as other kinds of learning. If you ring a bell before feeding your pet dog Ivan, he will learn to salivate at the sound of the bell, but only if the bell is rung immediately before the food is delivered, and only if your pair the food and bell several times. That is classical conditioning in its classic form. But if an animal gets sick after eating a novel food, he will learn to avoid the food taste even if he ate the food several hours before, and it will only take a single trial, violating more than one of the general principles of classical conditioning.

In a paper published in Psychological Review, David Sherry and Daniel Schacter noted that certain kinds of learning could not easily be handled by the same brain mechanisms, because they require mutually exclusive kinds of processing. Birds learn songs early in life, with no practice, do not use that information till months later, and the learning is irreversible. But they remember where they stored seeds at any time throughout their lives, and they also remember which food stores they have eaten and which they have not. Both of these types of learning are incompatible with the rules for learning to avoid poisonous substances, and with the standard rules of classical conditioning.

Furthermore, the rules that apply to specific types of learning change in different ways for different species, depending on the category of information, and the kinds of information they must typically learn in their natural environments. In a classic paper in Science, Hardy Wilcoxon, William Dragoin and Paul Kral found that rats preferentially condition nausea to the distinctive smell or taste of foods that made them nauseous, whereas bobwhite quail preferentially condition nausea to what the food looks like. In their natural environments, rats find their food in the dark (they do not see that well, but have a highly developed sense of taste and smell), whereas quail find their food in broad daylight (and use their highly developed visual sense to locate foods, such as seeds, that do not give off much in the way of odor).

Broader Implications of Modularity for Human Social Behavior

Thinking in terms of modularity and domain specificity has helped us understand how the brain handles diverse inputs from sound, taste, temperature, touch, color, shape, and movement using different mechanisms that operate in parallel. But there are many other implications of the discovery that learning and memory are not under the influence of one big brain that processes all information in the same way.

Thinking about information processing in modular terms even has implications for understanding the complex judgments we make about other people, in ways that are not yet fully understood, but are certainly intriguing. For example, psychologists used to assume that homosexual men’s preferences were simply learning “feminine” as opposed to “masculine” preferences and roles. However, research has suggested that it is much more complicated than that. Homosexual men are like women in one way – they prefer men as sexual partners. But their preferences are unlike women’s in several other ways – they tend to prefer relatively younger partners, and to emphasize another man’s physical attractiveness over his social status. In many ways, homosexual men’s preferences are like those of heterosexual men – who also seek younger physically attractive partners with little regard for social status. In heterosexual men, these preferences make evolutionary sense, since they lead to the choice of partners who are fertile and likely to be healthy mothers. An older heterosexual man’s preference for a younger partner might also be reciprocated, if the man has sufficient social status. But in older homosexual men, a preference for younger partners is neither biologically necessary, nor is it likely to be reciprocated. These findings suggest that mate preferences, rather than being under the control of one simple switch, set to either “masculine” or “feminine,” are instead under the control of numerous switches. In homosexual males, although the basic preference for women is switched, most of the other switches seem to remain in their “default” settings.

One way to envision modular processing is to think about emotional and motivational systems (Kenrick, Griskevicius, Neuberg, & Schaller, 2010). The social world is quite complex, and we cannot pay attention to and remember every detail of every interaction with every person we encounter on a moment-to-moment basis. What were the different heights, hairstyles, shirt colors, and accents of the people you passed in the shopping mall, what were the different children yelling at one another and at their parents? We can’t process all that information, so need to be selective, but we need to be selective in different ways at different times. The evidence has begun to suggest that different emotional and motivational systems direct the brain’s information selectivity in different ways. We pay attention to different things about different people when our fearful self-protective subself is in control, as compared to when our erotic mate acquisition subself or our status-seeking subself is in control. Thinking about the way the brain processes information in modular terms can even help us understand why an advertising technique can sometimes backfire, and sometimes work really well (as I discussed in my review of Bob Cialdini’s new book Pre-Suasion).

And there are many implications of this way of thinking for understanding human decisions about choosing mates, cooperating with coworkers, investing our money, and making other decisions of all sorts (see Kenrick & Griskevicius, 2013, for an in-depth discussion of these implications).

How all of this works is still unfolding. How many different modules does the brain have? How are those modules organized? Are most of the brain’s modules spatially localized (as in the case of Broca’s and Wernicke’s areas), or are they distributed across different areas of the brain? How is information shared across different modules? How much can neural plasticity during development compensate for damage to particular modular structures? For an excellent review of the issues involved in thinking about modularity, I recommend a paper in Psychological Review by Clark Barrett and Rob Kurzban.

Despite all the remaining issues, though, one thing is clear – the brain is not simply one big unprogrammed collection of neurons, it is not like the stomach, which applies the same simple process to everything that passes through. The brain is more like a multi-layered organization like Apple Computers rather than a fruit stand that sells only MacIntosh apples.

P.S. If you have another discovery you'd nominate instead as psychology's most important, I'd love to hear from you in the comments.

Douglas Kenrick is author of: -The Rational Animal: How evolution made us smarter than we think. And

-Sex, Murder, and the Meaning of Life: A psychologist investigates how evolution, cognition, and complexity are revolutionizing our view of human nature.

Related blogs:

Are there any geniuses in the field of psychology?

Who are psychology’s geniuses: Part II

Rate yourself on the new motivational pyramid: A new scale of fundamental evolved motives.

How a passing mood can alter your economic decisions.

Deep rationality: Evolutionary psychology meets behavioral economics.


Barrett, H. C., & Kurzban, R. (2006). Modularity in cognition: framing the debate. Psychological review, 113(3), 628-647.

Broca, P. (1861). Perte de la parole, ramollissement chronique et destruction partielle du lobe antérieur gauche du cerveau. Bull Soc Anthropol, 2(1), 235-238.

Garcia, J., & Koelling, R. A. (1966). Relation of cue to consequence in avoidance learning. Psychonomic Science, 4(1), 123-124.

Gazzaniga, M. S. (1985). The social brain: Discovering the networks of the mind. New York: Basic Books.

Kenrick, D. T., & Griskevicius, V. (2013). The rational animal: How evolution made us smarter than we think. New York: Basic Books.

Kenrick, D. T., Griskevicius, V., Neuberg, S. L., & Schaller, M. (2010). Renovating the pyramid of needs contemporary extensions built upon ancient foundations. Perspectives on psychological science, 5(3), 292-314.

Kenrick, D. T., Keefe, R. C., Bryan, A., Barr, A., & Brown, S. (1995). Age preferences and mate choice among homosexuals and heterosexuals: A case for modular psychological mechanisms. Journal of Personality and Social Psychology, 69(6), 1166-1172.

Scoville, W. B., & Milner, B. (1957). Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery & Psychiatry, 20(1), 11-21.

Sherry, D. F., & Schacter, D. L. (1987). The evolution of multiple memory systems. Psychological review, 94(4), 439-454.

Sperry, R. W. (1968). Hemisphere deconnection and unity in conscious awareness. American Psychologist, 23(10), 723-733.

Wilcoxon, H. C., Dragoin, W. B., & Kral, P. A. (1971). Illness-induced aversions in rat and quail: Relative salience of visual and gustatory cues. Science, 171, 826-828.

Wernicke, C. (1874). Der aphasische Symptomencomplex: eine psychologische Studie auf anatomischer Basis. Cohn.


Brain image: By BruceBlaus. staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. - Own work, CC BY 3.0,

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