STM LTM Forgetting from ShortTerm Memory Decay or

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? After information enters STM, a copy may or may not be sent to LTM. Soon, however, that information will disappear from STM. Two processes could cause information to disappear from STM: decay and displacement.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? Decay: information that is not rehearsed disappears as time passes. Displacement: information being held in STM is pushed out by newly arriving information. Displacement is most likely to occur when the capacity limit of STM has been reached (about 7 units of information).

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? B R D Q L T H Displacement is most likely to occur when the capacity limit of STM has been reached (about 7 units of information). J

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? B R D Q L T H J Displacement is most likely to occur when the capacity limit of STM has been reached (about 7 units of information).

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? B R D Q L T H The original version of the Atkinson-Shiffrin model emphasized decay as the main cause of forgetting J in STM. Their later version emphasized displacement. Here is a study that compared decay to displacement and showed a much greater effect of displacement.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) You are read a list of 16 digits: 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 After the last digit, you hear a tone. . . TONE

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 TONE The tone is a signal to recall one of the digits. The last digit before the tone (8) occurs only once at an earlier point in the list. This is called the “probe”.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 TONE Recall The subject’s task is to recall the digit following the probe. Between the digit, 4, and the tone, two things happen: (1) time passes, and (2) more digits are presented.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 TONE Recall Which is more important in causing forgetting, time or the additional digits? The decay principle implies time; the displacement principle implies digits.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe Slow Presentation (Seconds) +1+ 1 +1 +1 + 1 +1+ 1+ 1 +1 +1 = 12 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 TONE Recall Time and digits are correlated (confounded). To separate them, Waugh & Norman used two rates of presentation: slow (1 digit per second) and fast (4 digits per second).

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 1 Fast Presentation (Seconds) + 1 = 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 3 TONE More time passes between the digit and the tone with slow presentation (12 seconds) than with fast presentation (3 seconds). According to the decay principle, the chances of recalling the digit should be lower with slow than with fast presentation.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 1 Fast Presentation (Seconds) + 1 = 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 3 TONE According to the displacement principle, the chances of recalling the digit should be the same with fast and slow presentation because the number of digits before the tone is the same in both conditions.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 1 Fast Presentation (Seconds) + 1 = 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 3 TONE Waugh & Norman made this comparison with the probe digit in each of the following positions: 3 (shown here), 5, 7, 9, 10, 12, 13, or 14. Both decay and displacement predict an increase in recall as the probe gets closer to the tone.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 1 Fast Presentation (Seconds) + 1 = 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 3 TONE Results There was slightly (but not significantly) higher recall with fast than with slow presentation when the probe was near the beginning of the list. Recall dropped sharply as the probe was moved from the end toward the beginning.

STM LTM Forgetting from Short-Term Memory: Decay or Displacement? The Probe-Digit Procedure (Waugh & Norman, 1965) Probe 1 Fast Presentation (Seconds) + 1 = 7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8 3 TONE Conclusion As time passes, what mainly causes forgetting from short-term memory is exposure to additional information, not the passage of time.