The Study of Memory

1
The Study of Memory Part 1 Short Term Memory
2

• Three questions
• Why did people originally believe in STM
  independent of LTM?
• What do we think of those reasons now?
• Do we need the STM construct?

3

• Why did people originally believe in STM
  independent of LTM?
• Because of STM LTM differences in
• Patient data
• Capacity
• Duration
• Type of code
• Serial position effect
• Mechanism of loss

4
Patient data.
5
Patient data Issue is there a patient with a
selective inability to add to LTM , with sparing
of STM? If so, that selective impairment could
be used in an argument for an independent
STM. The most famous of all memory patients is
HM.
6

• HM (Scoville Milner, 1957)
• Surgery to relieve severe epilepsy, in 1953, at
  age 27.
• bilateral excision of medial temporal lobe
• after surgery, HM had profound anterograde
  amnesia. Capable of little if any new learning.
• Some retrograde amnesia.

7
In HMs words "At this moment everything looks
clear to me, but what happened just before?
That's what worries me. It's like waking from a
dream I just don't remember".
8

• Psychological studies by Brenda Milner.
• HM has
• Good vocabulary and language normal IQ
• No attention disorder.

9
HM does not know, for example where he
lives who cares for him what he ate at his last
meal what year it is who the President of the
United States is or how old he is. In 1982, he
failed to recognize a picture of himself that had
been taken on his 40th birthday in 1966.
10
Declarative tasks asking HM what he knows HM
cannot learn (and later recall) new photographs
of people verbal material sequences of
digits complex geometric designs nonsense
patterns. Cannot expand his digit span.
11

• Procedural tasks observing what HM can do.
• Milner (1962) trained H. M. on a mirror-drawing
  task.
• HM, like normal people, improves with practice.
  But he denies having practice.
• Cohen and Corkin (1981) showed a similar result
  on the Tower of Hanoi puzzle.

12
HM Conclusion Though HM can learn procedures
he cannot acquire new declarative learning. LTM
impaired. But STM spared. Argument in favour of
view that STM and LTM are independent.
13
Capacity
14
Capacity Issue is STM different from LTM in
capacity? If so, that supports view that LTM and
STM are independent. Capacity of LTM is
essentially infinite. What is capacity of STM?
15

• Capacity
• Shepard Tehgtsoonian (1961)
• Presented 200 3-digit numbers in a row.
• E.g. 492, 865, 931, 758 865,
• Task report when you hear a repeated number

16

• Shepard Teghtsoonian (1961)
• I.V. Interval between 1st and 2nd appearance
• D.V. Probability of noticing repetition
• Repetition can only be noticed if first
  occurrence is still in memory.
• Question Are there separate forgetting
  functions for LTM and STM?

17

• Shepard Teghtsoonian (1961)
• Result
• P(noticing repetition) fell dramatically at
  first
• Steep decline ended at interval 7 items
• P(noticing) then fell more gradually,
  asymptoting at 60

18

• Shepard Teghtsoonian (1961) Interpretation
• Initial steep decline in P (noticing) occurs
  because response coming from STM.
• More gradual occurs when response depends upon
  LTM.
• Two forgetting functions two memory stores,
  one large and one small.

19
Question Why should STM have so small a
capacity? Sensory memory has large capacity. LTM
has large capacity. Why did we evolve a limited
capacity store between two large capacity stores?
20
Answer If STM was any larger, it would take too
long to search through. When we need information
from STM, to choose or guide a response, we need
it fast. Things have to be processed fast in STM
21
Duration
22
Duration. Issue how long do STM traces
last? LTM traces last a long time possibly
your whole life. If STM traces last less time,
that supports the view that STM and LTM are
independent.
23
Duration how long does stuff last in
STM? Brown (1958) and Peterson Peterson
(1959) Task subjects see a simple stimulus
(e.g., BRG) and have to report it back after an
interval. Rehearsal is prevented by having them
count backwards during retention interval. I.V.
length of interval in seconds.
24
Correct as function of delay in Brown/Peterson
task
25
Brown / Peterson Result after 18 seconds,
subjects can no longer report stimulus. Interpret
ation there is a memory system in which things
must be rehearsed, or they are lost. But we
dont have to rehearse things in LTM so there
must be a second memory system STM.
26
Type of code
27
Type of code. Issue every stimulus has multiple
aspects e.g. colour brightness shape category n
ame All are found in LTM. Which are found in STM?
28

• Brown/Peterson task
• Many similar studies reported in the 60s.
• Most errors phonological e.g., P for T.
• Errors based on shape were rare e.g., C for O.
• No semantic errors observed (or possible).
• Conclusion STM uses a phonological code.

29
Serial Position Effect
30
Serial Position Effect In ordered recall,
subjects recall a list in the order it was
given. Out-of-order responses are counted as
errors. Accuracy is higher for the beginning and
end of the list, lower for the middle of the list.
31

Position in list
32
Serial Position Effect Better performance at
beginning of list is called Primacy
Effect. Better performance at end of list is
called Recency effect. Theory Primacy produced
by LTM. Recency produced by STM
33
Mechanism of Loss
34
How are things lost from memory if at
all? Decay? Interference? Retrieval
failure? Originally, LTM loss was blamed on
interference and STM loss was blamed on decay
as in Brown / Peterson paradgim.
35
2. What do we think of those reasons now?
36

• Differences between STM and LTM (taken in
  slightly different order this time)
• Type of code
• Serial position effect
• Mechanism of loss
• Patient data
• Capacity
• Duration
• Do these reasons survive?

37

• Type of code
• Original argument any kind of code in LTM, only
  phonological codes in STM.
• We now know that STM can contain any kind of
  code.
• See, for example, Brooks (1968), and Wickens
  Release from Proactive Inhibition studies.

38
Serial Position Effect Original argument
Primacy effect produced by LTM, Recency effect
produced by STM. We now know that both Primacy
and Recency effects can be found in pure LTM
studies (e.g., recalling U.S. Presidents). Thus,
recency effect cannot be taken as empirical
signature of STM.
39
Mechanism of loss Original argument
information lost from STM through decay, from LTM
through interference. We now know that
information can be lost from STM through
interference.
40

• Duration
• Original argument
• newly-acquired memories must be rehearsed to
  survive
• but older memories do not need to be
• therefore, new and old memories must be in
  separate stores.

41

• Duration
• Alternative account
• traces in LTM are vulnerable until they have
  been consolidated.
• new items are more vulnerable to loss than
  established items.

42
HM If traces in LTM are vulnerable until they
have been consolidated, then HMs problem is that
he cannot consolidate. He has normal digit span
because new items can be inserted in LTM. But he
has anterograde amnesia because new items cannot
be consolidated in LTM.
43

• That leaves only Capacity
• Capacity is capacity of the Articulatory Loop
  which is used for rehearsal of information and
  for planning articulation.
• AL is not a short-term memory.
• For example, you cannot search your articulatory
  loop, the way you can search memory.

44
Articulatory loop. Capacity is determined by rate
of loss. You can rehearse about 7 items. If you
try to rehearse more than 7 items, the first ones
will be lost before you finish one cycle through
the list and go back to the beginning.
45
Articulatory loop in action Memory load r l z
t c j a Articulatory loop rehearses r l z t c
j a .. r l z t c j a .. r l z t c j a .. r is
still in loop when you finish a.
46
Articulatory loop in action Memory load r l z
t c j a m k s c p y Articulatory loop
rehearses r l z t c j a m k s c p y .. r is
no longer in loop by the time you finish y so
cannot be rehearsed is lost.
47
3. Do we need the STM construct?
48

• No.
• We can explain all memory phenomena in terms of
  LTM and the articulatory loop.
• All we need is two premises
• Limited capacity in articulatory loop.
• Items in LTM are vulnerable to loss until they
  have been consolidated.