The Story of Psychology (103 page)

Much of what was learned about how all these kinds of information are organized was the product of reaction-time experiments such as asking subjects to name, in a brief period of time, as many things as they can that are red, or that are fruit, or that start with a given letter. Using that technique, Elizabeth Loftus found that in one minute volunteers could, on average, name twelve instances of “bird” but only nine of “yellow.” Her conclusion was that we cannot readily look directly in memory for examples of a property but instead locate categories of objects (birds, fruit, vegetables), and scan each for that property.
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Similarly, as Loftus and a colleague, Allan Collins, found, it takes people longer to answer “true” or “false” to the statement “An ostrich is a bird” than to the statement “A canary is a bird.” The implication: A canary is a more typical bird than an ostrich, is closer to the center of the category, so it requires less time to identify. Collins and Loftus, on the basis of such data, symbolically portrayed long-term semantic memory as an intricate network that is hierarchical (a general category is surrounded by specific instances) and associative (each instance is linked to a number of traits). They envisioned it as shown on p. 611.
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FIGURE 41
One portrayal of the long-term semantic memory network

This is only a minuscule sample of the semantic memory network. Every node shown here is connected to many other chains of nodes not shown: “Swim” might be linked to “cetaceans,” “human swimmers,” “sports,” “healthful exercises,” and each of those to other instances, characteristics, traits, and so on, and on.

A much later and much more detailed representation of the memory network relating to birds is bewilderingly complex; it is on page 612, as
FIGURE 42
, for those who care to puzzle it out.

Memory research has been so far-ranging and multifaceted over the last several decades that we must limit ourselves now to a handful of brief reports of major research findings and theories, and then move on.

Memory systems:
The memory system portrayed in
FIGURE 40
, on p. 608, is now seen as too simple. According to the results of many studies, there are a number of interacting memory systems that encode and store different kinds of information in different ways. The memories stored about how to swim, drive a car, or sail a boat are very different from those concerning the names and identities of people you know, how to
perform arithmetical procedures, or what a collie looks like. Each of these kinds of memory, and many others, require their own forms of processing and storage, and differ in the amount and kinds of effort required to enter and retain it in long term memory.

FIGURE 42
Network and connectionist representations of concepts relating to birds

Moreover, memory researchers distinguish among types of memory in other ways: Explicit memory refers to information or knowledge that we can bring to mind and to personal experiences, and implicit memory to information that is available without conscious effort, including motor skills and automatic responses (such as avoiding bumping into others on the sidewalk), built-in attitudes and reactions to people, objects, and situations—all of these requiring different memory systems.
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Other studies have investigated the differing process of recognition and recall—a distinction familiar enough in everyday experience (we all recognize a great many words that we cannot easily or at all summon up voluntarily). In a socially valuable application of the difference, a series of studies tested whether witnesses to a crime (a staged one before groups of students who were not told what was going on until later) would be more likely to identify the actual culprit in a lineup or by seeing a number of suspects one at a time. The latter method proved so much the better that many police departments are now changing their standard lineup procedures.
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Cognitive neuroscientists have lately done brain scans during different kinds of memory activity and come up with an answer to an old question: Where are memories stored? The answer, in the past, has vacillated between “locally” and “widely distributed.” Brain scans now show that “widely distributed” is the answer—and that different kinds of memories are differently distributed.
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Categorization:
Much research indicates that the human mind has a tendency to spontaneously group similar objects in memory and, from their similarities, develop general concepts or categories. Even infants only a few months old seem to do simple categorizing. One research team showed four-month-old babies patches of varied blues, greens, yellows, and reds. After seeing a number of patches of one color group, the babies showed a preference for a patch of any other color. The conclusion: Hue categorization is either innate or develops soon after birth.
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Many other studies have documented how, as children acquire language, they gradually develop such categories as “animal” after experiences of dogs, cats, squirrels, and others. Parents, to be sure, teach these concepts to their children, but in part the tendency seems to be built in. It is so general among all people as to be presumed an innate human trait. The anthropologist Brent Berlin found that people in a dozen different primitive societies group plants and animals in remarkably similar fashion, namely, hierarchically, starting with subgroups similar to biological
species, combining these in larger headings similar to biological genera, and lumping these together in categories similar to biological plant and animal kingdoms.
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The ability to categorize was probably selected by evolution. It has survival value, since from such groupings we can make valid inferences about things that are new to us. Rochel Gelman and a colleague showed subjects pictures of a flamingo, a bat, and a blackbird. The blackbird was portrayed so that it looked much like the bat. Subjects were told about the flamingo, “This bird’s heart has a right aortic arch only,” and about the bat, “This bat’s heart has a left aortic arch only.” Then they were asked about the blackbird, “What does this bird’s heart have?” Almost 90 percent answered “right aortic arch only,” correctly basing their answer not on the visual similarity of bat and blackbird but the common membership in the bird category of flamingo and blackbird. Even four-year-old children, when given a similar but simpler test, based their answers almost 70 percent of the time on category membership.
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Representation:
Researchers were long at odds about the form in which the material is stored in long-term memory. Some believed it is represented both in images and words and that there is communication between the two data banks. Others, drawing on information theory and the computer model, argued that information is recorded in memory only in the form of “propositions.” A proposition is a simple “idea unit” or bit of knowledge embodied in a conceptual relationship like that between bat and wings (a bat has them) or bat and mammal (a bat is one).

In the first view, a bat would be recorded in memory as an image, along with verbal statements about it; in the second view it would be recorded in the form of relationships (as in the bits of semantic networks in the figures above) which, though not verbal, are equivalent to “bat has wings,” “salmon is red,” and so forth. Another example of the propositional view is seen in these sentences:

The princess kissed the frog,

and its passive version,

The frog was kissed by the princess,

which mean the same thing; they are verbal expressions, differently focused, of the same proposition or unit of relationship knowledge.
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The proponents of each view have good evidence to back them up. The “mental rotation” experiments of Roger Shepard that we saw earlier indicate that we see objects “in the mind’s eye” and deal with those images as if they were three-dimensional objects. Later studies by others confirmed and extended this finding. Several years ago, Stephen Kosslyn, who has long explored mental imagery, took a different tack: He had subjects memorize a map of a small roughly pear-shaped island with various things located here and there, among them a hut at one end, a lake nearby, a cliff somewhat farther off, a large rocklike object at the farthest end, and so on. Later, his subjects were asked to close their eyes, summon up the remembered image, focus on one location such as the site of the hut, and then find another named site and push a button as soon as they found it. The times of each mental search were recorded; most remarkably, the farther the second location was from the first, the longer it took them to find it. Obviously, they were scanning across the mental image.
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But the advocates of propositional representation have equally good grounds for their view. They contend that images cannot convey such relationships as “has,” “causes,” and “rhymes with,” or represent categories and abstract concepts. Herbert Simon and William Chase found that chess masters could reproduce an entire board position after viewing it for just a few seconds—but only if it was a true board position in an actual game. If it was a random arrangement of the pieces, they could not. The implication: The masters’ memory was not visual but was based on the geometrical relations—the attack and defense move potentials—of the pieces. Finally, information in computer programs is stored in propositional form, and if computability is a good model of cognition, it stands to reason that the mind stores information similarly.
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Quite reasonably, a third position has been taken for some time by many theorists: There are several types of representation—propositions, mental models, and images, each encoding information at a different level of abstraction. Finally, a fourth position is that different types of mental imagery use different brain networks: imagery involving spatial relations (as in imaginary rotation of an object) relies on a network in the parietal lobes, while imagery involving high-resolution shapes relies on a network in the occipital lobes.
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(Even if true, that position doesn’t help us understand how the masses of neuronal impulses arriving by either network get to be “seen” by us as mental images.)

Schemas:
In 1932 the English psychologist Frederic Bartlett told subjects folk tales from non-Western sources and then asked them to recall
the tales. They remembered the stories inaccurately, inadvertently filling in gaps, modifying events so as to provide reasons for what happened, and omitting details that made no sense to Western minds. Bartlett concluded that “remembering is not the re-excitation of innumerable fixed, lifeless, and fragmentary traces” but “an imaginative reconstruction, or construction” based on our own organized mass of experiences. He called that organized mass “schemata”; others prefer the anglicized version “schemas.”
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Bartlett’s idea has been revived and elaborated in recent years. Schemas—also known as “frames” and “scripts”—are now thought of as packages of integrated information on various topics, retained in memory, on which we rely to interpret the allusive and fragmentary information that ordinary conversation—and even most narrative writing—consists of. In 1978, David Rumelhart, then of the University of California in San Diego, reported on experiments in which he read stories, sentence by sentence, to his subjects to see how and when they formed a clear idea of what the stories were about. When, for instance, they heard this: “I was brought into a large white room, and my eyes began to blink because the bright light hurt them,” some 80 percent at once assumed they were hearing either a hospital or interrogation scene, and supplied a wealth of information to the few words they had heard. If the next sentence or two contradicted this supposition, they changed it and filled out the story anew from a different schema.
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Much other recent work on schemas and a related type of information package known as a “script” has firmly established that it is by drawing on our expectations and organized knowledge structures that we understand and interpret—or often misinterpret—what we hear, read, and experience. Memory, in sum, is not only an information register to be consulted as needed but a program that directs our thinking.
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