The Story of Psychology (102 page)

Best of all, from the cognitive researcher’s viewpoint, if the subject performs some prescribed mental task while being scanned, the resulting fMRI (functional MRI) scan gives an intimate look at exactly which brain areas and substructures are active, and how active, during that kind of mental activity. Accordingly, the fMRI quickly became the workhorse of cognitive neuroscience. A dozen years ago, a mere handful of
studies based on fMRI scans appeared in a year’s worth of research literature; today, the annual output is several thousand.
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What has all this done to psychology, the science of the human mind? That depends on who is assessing the situation.

Most psychologists, focused on mental processes rather than wetware, continue to use research methods that were available before the advent of scanning, but many of them also rely on the help of scanning. They no longer see cognitive psychology and cognitive neuroscience as distinct and unrelated fields. As Robert J. Sternberg, a notable cognitive psychologist, says, “Biology and behavior work together. They are not in any way mutually exclusive.”
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Some use stronger terms to appraise the impact of cognitive neuroscience: Psychologists Stephen Kosslyn and Robin Rosenberg write, “It is fair to say that neuroimaging techniques have transformed psychology, allowing researchers to answer questions that were hopelessly out of reach before the mid-1980s.”
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Does that suggest that cognitive neuroscience will become the psychology of the future? Not according to cognitivist Michael Posner, who has worked in both camps and whose work has been admired by researchers in both: “An impressive aspect of the anatomical methods such as PET and fMRI is how much they have supported the view that cognitive measures can be used to suggest separate neural structures,” and he stresses the importance of the contributions of both fields to understanding brain function.
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But some cognitive neuroscientists think it possible, even likely, that their field will come to dominate mental science. Martha Farah, when asked if cognitive neuroscience would eventually become the overarching theory of psychology, said, “Yes, because it’s a broader and more heterogeneous approach to studying the mind which encompasses cognitive psychology. It’s a molecular-cellular-systems explanation of how the brain acts during all the classical processes of cognitive psychology—how we learn, think, behave, why we differ from each other, the sources of personality. All these things are in principle explainable by various levels of brain activity at various levels of description.”
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We seem to be at the top of the ninth, score tied, and will have to see how the game plays out.

Now let us return to the story of cognitive psychology and look more closely at several of its major themes of recent decades.

In the 1960s, the cognitive revolution rapidly won the allegiance, at least in academia, of some senior psychologists, most junior ones, and most graduate students of psychology. At first, they concentrated on perception, the first step of cognition, but fairly soon they shifted their attention to the uses the mind makes of perceptions—its higher-level mental processes. By 1980, John Anderson, a theorist of those processes, defined cognitive psychology as the attempt “to understand the nature of human intelligence and how people think.”
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In information-processing theory, the essential first step is the storing of incoming data in memory, whether for part of a second or for a lifetime. As James McGaugh said in a 1987 lecture:

How crucial memory is to thought is painfully apparent to anyone who has known a person suffering from advanced Alzheimer’s disease. He may frequently forget what he wants to say partway through a sentence, get lost walking down the driveway to his mailbox, fail to recognize his children, and become upset by the unfamiliarity of his own living room.

In 1955—before the start of the cognitive revolution—George Miller had given an address at a meeting of the Eastern Psychological Association that has been called a landmark for cognitive theorists working on memory. In his typically breezy manner, Miller called the talk “The Magical Number Seven, Plus or Minus Two,” and began by saying, “My problem is that I have been persecuted by an integer.” The integer was 7, and what seemed to Miller both magical and persecutory about it was, as many experiments had shown, that it is the number of digits that one can usually hold in immediate memory.
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(It is easy to remember briefly, after a moment’s study, a number like 9237314 but not one like 5741179263.)

It is both noteworthy and mysterious that immediate memory, the limiting factor in what we can pay attention to, is so tiny. The limitation serves a vital purpose: it drastically prunes the incoming data to what the mind, at any moment, urgently needs to attend to and make decisions about, a function that undoubtedly helped our primitive ancestors survive
life in the jungle or the desert.
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But it raises perplexing questions. How can so small a field of attention handle the flood of perceptions we must attend to when driving a car or skiing? Or the welter of sounds and meanings when someone is talking to us—or when we are trying to say something to them?

One answer, Miller said, making good use of an idea that had lain fallow in psychology for a century, is that immediate memory is not limited to seven digits but to seven—more or less
—items:
seven words or names, for instance, or “chunks” such as FBI, IBM, NATO, telephone area codes, or familiar sayings, all of which contain far more information than single digits but are as easily remembered.

But even with chunking, the capacity of immediate memory is insignificant compared with the enormous amount of material—everyday experiences, language, and general information of all sorts—that we learn and store away in long-lasting memory and call up again as needed.

To explain this disparity and determine how memory works, cognitive psychologists conducted a great many experiments during the 1960s, 1970s, and 1980s; the findings, pieced together, gave shape to an information-processing picture of human memory. In it, memory consists of three forms of storage, ranging from a fraction of a second to a lifetime. Experiences or items of information needed only for an instant fade away as soon as used, but those needed longer are transformed and held for longer, or even worked into the semipermanent or permanent register of long-term memory. Researchers and theorists portrayed the three types and the transfer of information among them in flow charts something like the one on p. 608.

The briefest form of memory consists of sensory “buffers” in which incoming sensations are first received and held. By means of the tachistoscope, researchers verified that buffers exist and also measured how long memories endure in them before disappearing. In a classic experiment in 1960, the psychologist George Sperling flashed on a screen, before attentively watching volunteers, patterns of letters like this:

The letters appeared for a twentieth of a second, too brief a time for the volunteers to have seen all of them, although immediately afterward
they could write down the letters of any one line. (A tone, right after the flash, told them which line to record.) They could still “see” all three lines when they heard the tone, but by the time they had written down one line, they could no longer remember the others; the memory had vanished in less than a second. (Experiments by others yielded comparable results with sounds.) Evidently, incoming perceptions are stored in buffers, from which they vanish almost at once—fortunately, for if they lasted longer, we would see the world as a continuous blur.
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FIGURE 40
An information-processing model of human memory

Since, however, we need to retain somewhat longer the things we are currently concerned with, there must be another and longer-lasting form of temporary storage. When we pay attention to material in a sensory buffer, we process it in any of several ways. A digit becomes not just a perceived shape but a symbol—a 4 gets a name (four) and a meaning (the quantity it stands for); similarly, words we read or hear get meanings. This processing transfers whatever we are attending to from the buffers to the immediate or short-term memory that Miller was talking about.

In lay usage, short-term memory refers to the retention of events of recent hours or days, but in technical usage it denotes whatever is part of current mental activity but is not retained after use. This form of memory is brief. We have all looked up a phone number, dialed it, gotten a busy signal, and had to look up the number again to redial it. Yet we can retain it for many seconds or even minutes by continuously repeating it
to ourselves—psychologists call this activity “rehearsal”—until we have used it.

To measure the normal duration of short-term memory, therefore, researchers had to prevent rehearsal. A team at Indiana University did so by telling their subjects that they were to try to remember a set of three consonants, a very easy task, but that as soon as they had seen them, they were to count backward by threes in time with a metronome; this preempted their attention and made rehearsal impossible. The researchers cut the volunteers’ backward counting short at different times to see how long they would retain the three consonants; none did so longer than eighteen seconds. Many later experiments confirmed that the decay rate of short-term memory is between fifteen and thirty seconds.
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Later, other studies distinguished between two kinds of short-term memory (not shown in the above diagram). One is verbal: the immediate memory for numbers, words, and so on that we have been discussing. The second is conceptual: the memory of an idea or meaning conveyed in a sentence or other expression of several parts (an algebraic equation, for instance). In a 1982 experiment, subjects were shown sentences, a word at a time, at a tenth of a second per word; they could easily remember plausible (though not necessarily true) sentences like this:

But they fared badly with nonsensical sentences of the same length, like:

A number of studies showed that we easily retain the message of a sentence in short-term memory but swiftly forget its exact words. Similarly, we retain in long-term memory for months, years, or a lifetime the content or meaning of some conversations we have had and books we have read, the gist of courses we have taken, and innumerable facts we have learned, but none, or at most a few, of the exact words in which any of these were couched. The mass of material stored away in this fashion is far larger than most of us can imagine: John Griffith, a mathematician, calculated that the lifetime capacity of the average human memory is up to 10
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(one hundred trillion) bits,
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or five hundred times as much information as is contained in the
Encyclopaedia Britannica.
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New information in short-term memory is forgotten after we use it, unless we make it part of long-term memory by subjecting it to further processing. One form of processing is rote memorizing, as schoolchildren memorize multiplication tables. Another is the linking of new information to some easily remembered structure or mnemonic device, like a singsong jingle (the preschool alphabet song) or a rhyming rule (“When the letter C you spy, / Put the E before the I”).

But a far more important kind, as became clear in the research performed in the 1960s and 1970s, is “elaborative processing,” in which the new information is connected to parts of our existing organized mass of long-term memories. We splice it into our semantic network, so to speak. If the new item is a mango and we have never seen one before, we link the word and concept to the appropriate part of long-term memory (not a physical location—ideas and images are now thought to be scattered throughout the brain—but a conceptual one: the category “fruit”), along with the mango’s visual image, feel, taste, and smell (each of which we also link to the categories of images, tactile qualities, and so on), plus what we learn about where it grows, what it costs, how to serve it, and more. In the future, when we try to think of a mango, we retrieve the memory in any one of many ways: by recalling its name, or thinking about fruit, or about fruit with a green skin, or about yellow sweet slices, or any other category or trait with which it is linked.