Story of Psychology - Morton Hunt [348]
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.46
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.47
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.48
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