1. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
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.

2. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
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).

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

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

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

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

7. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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.
TON
E
This is called the “probe”.
Probe

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

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

10. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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).
TON
E
Probe
4
Recall
+1+ 1 +1 +1 + 1 +1+ 1+ 1+ 1+ 1 +1 +1 = 12
Slow Presentation (Seconds)

11. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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.
TON
E
Probe
4
Fast Presentation (Seconds)
1 + 1 + 1 = 3

12. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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.
TON
E
Probe
4
Fast Presentation (Seconds)
1 + 1 + 1 = 3

13. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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.
TON
E
Probe
4
Fast Presentation (Seconds)
1 + 1 + 1 = 3
Both decay and displacement predict an increase in recall
as the probe gets closer to the tone.

14. Forgetting from Short-Term Memory:
Decay or Displacement?
ST
M
LT
M
The Probe-Digit Procedure
(Waugh & Norman, 1965)
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
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.
TON
E
Probe
4
Fast Presentation (Seconds)
1 + 1 + 1 = 3
Results

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