Another example of the work in the area of cognitive psychology comes from the studies of Saul Sternberg in the 1960's at Bell Laboratories. Sternberg examined how additional information in memory influences the speed of mental operations in retrieving information stored in memory. Stern-berg's task was fairly simple. He presented his subjects with a list of numbers; the list might range from one to six numbers. After the subjects saw this initial list, a single number (called a probe) was presented. People were asked to identify whether the probe number was on the initial list of numbers. The list might be 2, 3, 9, and 5, for example, and the probe might be 3.
Sternberg's primary interest was in studying how the length of the initial list affected the time it took to make the required yes-or-no decision. Two possibilities typically emerge when people consider this problem. The concept called serial processing holds that the comparison of the probe to each number in the initial list takes time, so that the more items in the initial list, the longer the memory search takes. An alternative idea, parallel processing, suggests that people instantaneously scan all the items in the memory set, and the number of items in the initial list does not make a difference. Another way of saying this is that all the items are scanned at once, in parallel fashion. Sternberg found that people search their memories using the technique of serial processing. In fact, he was able to calculate precisely the amount of additional search time needed for each added item in the memory set—38 milliseconds (a millisecond is a thousandth of a second). Although the search may seem fast, even instantaneous, the more there is to think about, the more time it takes to think.
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