Cognitive Psychology: Connecting Mind, Research and Everyday Experience, 3rd Edition

124 • CHAPTER 5 Short-Term and Working Memory

or heard, as occurs for multiple-choice questions on an exam. Recognition tests can also be used

to test STM, but we will consider recognition tests in more detail in Chapter 6, when we discuss

some recognition memory experiments used to test long-term memory.

WHAT IS THE DURATION OF SHORT-TERM MEMORY?

John Brown (1958) in England and Lloyd Peterson and Margaret Peterson (1959)

in the United States used the method of recall to determine the duration of STM. In

their experiments, participants were given a task similar to the one in the following

demonstration.

DEMONSTRATION Remembering Three Letters

You will need another person to serve as a participant in this experiment. Read the following

instructions to the person:

I will say some letters and then a number. Your task will be to remember the letters. When

you hear the number, repeat it and begin counting backwards by 3s from that number.

For example, if I say ABC 309, then you say 309, 306, 303, and so on, until I say “Recall.”

When I say “Recall,” stop counting immediately and say the three letters you heard just

before the number.

Start with the letters and number in trial 1 below. It is important that the person count out loud

because this prevents the person from rehearsing the letters. Once the person starts counting,

time 20 seconds, and say “recall.” Note how accurately the person recalled the three letters and

continue to the next trial, noting the person’s accuracy for each trial.

Trial 1: F Z L 45

Trial 2: B H M 87

Trial 3: X C G 98

Trial 4: Y N F 37

Trial 5: M J T 54

Trial 6: Q B S 73

Trial 7: K D P 66

Trial 8: R X M 44

Trial 9: B Y N 68

Trial 10: N T L 39

We will return to your results in a moment. First let’s consider what Peterson

and Peterson found when they did a similar experiment in which they varied the time

between when they said the number and when the participant began recalling the let-

ters. Peterson and Peterson found that their participants were able to remember about

80 percent of the letters after counting for 3 seconds but could remember an average of

only 12 percent of the three-letter groups after counting for 18 seconds (● Figure 5.7a).

They interpreted this result as demonstrating that participants forgot the letters because

of decay. That is, their memory trace decayed because of the passage of time after hear-

ing the letters. However, when G. Keppel and Benton Underwood (1962) looked closely

at Peterson and Peterson’s results, they found that if they considered the participants’

performance on just the fi rst trial, there was little falloff between the 3-second and the

18-second delay (Figure 5.7b). How does this compare to your results? Did performance

become worse on later trials? Apparently, the poor memory at 18 seconds reported by

Peterson and Peterson was caused by a drop-off in performance after the fi rst few trials.

Why would memory become worse after a few trials? Keppel and Underwood

suggested that the drop-off in memory was due not to decay of the memory trace, as

Peterson and Peterson had proposed, but to proactive interference (PI)—interference

Brown-Peterson

Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.