(As I am rapidly losing time, I am providing you with the following notes,
so that I can talk about other aspects of memory that I think you should know
about. I've included the outline headings to help keep this organized.)
A. Introduction
1. The Brown-Peterson Paradigm
2. Baddeley's Coding Study
B. Atkinson & Shiffrin's Multistore Model {we already talked }
1. Overview of Stores & Processes {about these in the }
2. Sensory Memory {last lecture }
3. Short-Term Store
a. Neurological Evidence
b. Characteristics
c. Search & Retrieval in Short-Term Memory
If STS is a memory system, then we can also inquire about how we locate
information that currently resides within this system. That was the point of
a famous experiment by Sternberg. Sternberg asked a very simple question:
Does the time it takes to locate information in STS depend on how many
memory traces are currently there? To start with, he talked about two
possibilities: That it would matter (a serial search model), and that it
wouldn't (a parallel model). Here's how these models operate:
The serial self-terminating model is the easiest to understand. According to
this model, you check the memories in STS one by one until you find the
memory you're looking for. So, on average, the more memories there are in
STM, the longer it'll take you to find what you're looking for. This is called
a serial model because you have to check things serially: one at a time. It
is also called a self-terminating model because you stop once you've found the
right memory. So, to give you an example, if you are looking for a particular
book on your text shelf at home, you start scanning the titles of the books
from left to right, until you come across the title you wanted. At that
point, you stop searching since, obviously, you've found the desired book.
What about the parallel search model? According to this model, you can check
all your memories at the same time, instead of checking them one by one. So,
it shouldn't matter how many memories there are in STM, it's going to take you
the same amount of time regardless of whether there are one or seven. As an
example, we do parallel searches when recognizing a friend's face: You can see
the eyes, lips, nose, hairline, etc., all at the same time; you do not need to
first check to see if it's the right pair of eyes, and then go on to check if
the nose is ok, and after that, the lips.
Now that we have our two models, how do we set up an experiment to test which
is right? Sternberg set up the experiment by using a probe technique. In
this task, you are seated in front of a screen, and see -- on a given trial --
anywhere from one to six letters. They come at you at something like one
letter every second. These letters constitute what is called the memory set.
Your job is to keep these in STS. Presumably, if you have six letters, then
you are loading six memories into STS, whereas if you have only a single
letter, then on that trial you need keep only one memory in STS. In any case,
after seeing the memory set, you get a warning cue to let you know a memory
test is about to happen. That test involves presenting another letter, called
the probe. All you have to do is decide whether it's a member of your memory
set or not. If it's one of the ones that was in your STS, then you press a
"true" button; if it's not, then you press a "false" button. So, the probe
can be one of two sorts: a target (one of the items we asked you to memorize),
or a distractor (a letter not in the memory set).
What does the serial self-terminating model predict in this case? Let's start
with targets. Generally, the more items there are in your memory set, the
longer you should take to hit the "true" key. The reason is, on average, you
ought to find the memory you're looking for about half way through your search.
So, for a memory set of one item, you have to check that one item to see if it
matches. For a memory set of two items, half the time you'll find a match
after checking the first item, and half the time you'll find a match only after
checking the second item, as well. Thus, on average, you find a match after
checking 1.5 items. For a memory set of 3 items, of course, you should
generally find a match after checking 2 items. And so on. But, if you think
about what happens with distractors, you'll see a very different prediction:
Since the distractor is not in the memory set, by definition, you need to
check all of the items. So, to look at what should happen, let's make a
chart of the average number of searches per memory set:
Size of Memory Set
1 2 3 4 5 6
----------------------------------------------------------------
Average Number
of Searches for:
Target Probe 1 1.5 2 2.5 3 3.5
Distractor Probe 1 2 3 4 5 6
----------------------------------------------------------------
Assuming that it takes a bit of time for each search, what you can see is that
reaction time will increase for both targets and distractors as memory set size
increases, but it will increase much more for the distractors.
What about parallel searches? By definition, it doesn't matter how many items
you have in STS if you do a parallel search. So, regradless of the size of the
memory set, you ought to have the same time for targets. By the same token,
we can also predict that you should have the same time for all distractors,
although maybe distractors will take you a bit longer than targets (since it's
generally easier to execute a "true" response than a "false" response).
So, now that we have a method, we can go out and do the experiment (which I do
have on computer, if you want to put yourself through this to get a clearer
feel for what is going on). And when Sternberg does, it turns out that neither
model adequately describes what subjects do. As memory set size increases, so
do the reaction times, as predicted by a serial model. However, unlike the
prediction from the chart above, distractors don't show a bigger effect than
targets: the reaction times for distractors and targets are identical. Thus,
Sternberg found results claiming people do a serial exhaustive search, rather
than a self-terminating one. It's as if, once you locate the book you want on
your shelf, you still go ahead and check the other titles.
Why would anyone want to waste time checking additional memories? That result
strikes a number of people as counter-intuitive. To explain these results,
Sternberg hypothesized that it takes very little time to check a probe against
a memory in STS, but it takes a long time to decide what to do about the results
(whether to go on to the next item, or to press one or the other button). So,
he argued that it may actually be more efficient to check the probe against all
of the memories in STS, and just make one decision at the end, rather than a
decision after each item. That's one explanation for this otherwise seemingly
odd result. There's another, however, and it can be seen by considering the
times involved in this process. What Sternberg found was that each additional
item in the memory set added 38 msec to the response time. Let's round that
up to 40 msec, and let's assume that we have our full set of six items in STS.
In that case, we're talking about 240 msec to check all six items. If we
round that figure up to 250 msec, you can see that you can check six items in
under a quarter of a second. That is such a fast time that maybe the mind
doesn't have enough time to signal the search process to stop once it's found a
match. Consisten with this argument, memory sets that involve many more com-
parisons than six items tend to show self-terminating searches.
Two final points on the issue of searching for information in STS. First,
Clifton & Trask repeated Sternberg's experiment using single-syllable words
rather than letters. They found exactly the same results he did. That is
exactly what we would expect from a claim that STS holds about 7 chunks. In
Sternberg's experiment, the chunks were letters; in Clifton & Trask's experi-
ment, they were words. Thus, this replicates Murdock's finding that single-
syllable words give the same result as single-syllable letters in a Brown-
Peterson task. Second. Schneider & Shiffrin, who had the theory of automati-
city we looked at in the unit on Attention, find that with consistent mapping,
people start doing parallel searches. Thus, while we normally do serial
exhaustive searches of indormation from STS, if we are overloaded or if we
have automated, other types of searches are possible.
4. Long-Term Memory
Finally, we can briefly talk about LTM. Obviously, in terms of characteristics,
LTM has a huge capacity, has a potentially long duration (years & years, we
hope!), and codes in a variety of formats, although Baddeley's experiment
suggests that semantic coding will be a very important format. As for why we
forget information from LTM, it may be because of decay (although most people
don't believe decay is important in LTM), interference, failure to use the
proper retrieval cue, or simply searching for something in all the wrong
places. As for how information is stored in LTM, it is also stored in
chunks, although we tend to call these chunks episodes. Thus, Wickens, Dow, &
Moody decided to redo Sternberg's experiment, but included a condition where
people were sometimes subject to a distractor task after seeing the memory
set, to force them to put it in LTM, and to wipe out their STS. The question
they asked was, would the chunks people use in STS be the same as the chunks
in LTM?
To simplify the experiment, Wickens et al. used a memory set of 2 or 4 items.
And what they found was, for the comparisons involving STS (those without the
distractor task), people in their experiment showed exactly the same comparison
times as Sternberg's subjects. But, when the distractor task was used, people
were generally about one tenth of a second slower. And that was true both for
a memory set of two items and a memory set of four items.
Why was this an important finding? In the STS experiment, it looks like you
store 2 or four chunks depending on the size of the memory set, and it looks
like each chunk is a single letter. If you store single letters in LTM, then
when you have to search a memory set of two items, you will first have to
locate each item in LTM, retrieve it into STS, and then do a normal search.
But when you have four items, you will have to locate and retrieve four items.
In general, the model is: locate the desired information in LTM, copy it to
STS (where we do our active thinking), and then search STS. So, according to
this model, your response times should be as indicated in the chart:
Size of Memory Set
2 4
----------------------------------------------------------------
Number of LTM
Retrievals: 2 4
Number of STS
Comparisons: 2 4
----------------------------------------------------------------
So, if 2 retrievals takes .1 sec, then 4 retrievals from LTM should take
double that amount (.2 sec). But of course, this didn't happen. And the
reason is, apparently people created new chunks/episodes in LTM. Specifically,
the entire list in STS became a single chunk stored in LTM, so that all you
had to do was locate that one chunk (your list of 2 items for the memory set
2 condition, and your list of 4 items for the memory set 4 condition), copy
it to STS, and then search STS normally. In this experiment, the time it
took to locate and retrieve a list from LTM was .1 second. So, STS and LTM
do NOT necessarily chunk information in the same sorts of ways.
Given this, let's briefly close out this section by considering several studies
that involve a very important finding that seems to require both STS and LTM,
the serial position effect.
a. The Serial Position Effect
One of the major findings (for which there really still is no explanation that
we all agree on) is the serial position effect (SPE). This has to do with your
memory for a relatively long list of words, long enough (say 16 or 25 or
something like that) that they can't all possible fit into STS. The SPE is
the finding that memory is best for the first couple of words (the primacy
effect), and the last couple of words (the recency effect), but is so-so for
the words in the middle (asymptote). Specifically, you'll typically show
better memory for the first word than the second, and you'll have better
memory for the second word than for the third, etc. In analogous fashion,
your memory for the last word will usually be better than your memory for the
next-to-last word, which will usually be better than your memory for the word
that came before it.
Why is this important? According to multistore theorists like Glanzer, the SPE
is really two different results that reflect the operation of two different
memory systems. Specifically, primacy and asymptote are thought to be due to
LTM, and recency is thought to be due to STS. So, when the list finishes, you
still have a few words echoing around in your STS, and you tend to dump those
out first (accounting for recency). As for primacy and asymptote, we need to
add in one more wrinkle to the multistore model to explain how they work.
That one more wrinkle is the concept of rehearsal. In Atkinson & Shiffrin's
model, rehearsal is the mechanism necessary for creating permanent memories in
LTM. Specifically, the more you rehearse an item in STS, the greater the
probability of forming a LTM. (This should be a familiar concept to you from
Wagner's model of classical condition: Remember the experiments with post-
trial episodes where Wagner tried to disrupt rehearsal?). So, when we add in
a model of rehearsal, primacy and asymptote start to make sense. Why? Because
when you hear the first word, you start rehearsing it over and over. As it is
the only word in STS, it is getting all the rehearsals and all the attention.
Then, the second word comes in, and it starts getting rehearsed, as well. But,
the rehearsals are now being split two ways, since there are two words in STS.
That means that the second word is going to get fewer rehearsals that the first
word, and that, in turn, means that the first word should have a greater
probability of making it to LTM, or of being stronger in LTM. And of course,
once the third word comes in, you split your rehearsals three ways so that the
third word gets even fewer rehearsals, and is weaker.
By the time you get to the words in the middle, STS is filled up, so that each
word can only get a few rehearsals before you rehearse something else. Thus,
the words in the middle are the baseline probability that stuff has gotten into
LTM; they correspond to the fewest number of rehearsals, which is why they are
referred to as asymptote. Consistent with this explanation of the SPE, asking
subjects for free recall versus serial recall makes a difference. In free
recall, you're allowed to remember the words in whatever order you want. Free
recall typically shows a strong recency effect, and the words that are normally
first written down are the last few words. In serial recall, however, you have
to remember the words in the order in which they were spoken. That means that
STS (which is holding the last few words) has a bit of time to decay. And as
you would expect, we find a weaker recency effect with serial recall.
b. Rundus' study using the overt rehearsal technique
So how good, really, is this explanation of the SPE? Rundus tried to asnwer
this question by using what is called the Overt Rehearsal Technique. He gave
his subjects a long list of words, and told them to rehearse out loud, instead
of silently. What he found was a strong correlation between primacy and asymp-
tote, and the number of repetitions each word got: The first word got the
most repetitions/rehearsals, but after 5 or so words, all the others got only
a few repetitions. So, in his study, rehearsal was related to primacy and
asymptote, as predicted by the theory, but it was not related to recency (a
finding which is also consistent with the theory).
c. Murdock's experiment using fast versus slow rates
A second experiment involved using dissociation logic. In this procedure,
if the SPE is really two different curves due to different systems, you try
to dissociate the curves by manipulating one system, but not the other. So,
something that should influence ONLY STS should also influence the recency
portion of the SPE, but not primacy or asymptote. In contrast, something
that should influence ONLY LTM should affect primacy and asymptote, but not
recency.
Murdock took the approach of finding a factor that would presumably influence
just LTM. Since LTM depends on rate of rehearsals, he presented the same list
of words to two groups. One group heard the words at a fairly fast rate, but
the other group heard the words at a fairly slow rate. Th point, of course,
is that with the slow rate, each word shold get more rehearsals.
Note that with this procedure, there should be no effect on STS: You only
have so much room in STS, and this doesn't really depend on whether you hear
things at a fast rate or a slow rate. So, if you have room for 5 words, for
example, the last 5 words ought to be there in each group, and each group
should thus first spit out these words.
In line with the rpedictions, Murdock found that a fast rate lowered primacy
and asymptote, but didn't affect recency. Thus, he appeared successful in
showing that the primacy and asymptote portion of the SPE is from LTM.
d. Glanzer & Cunitz's experiment using a distractor task
A related approach using dissociation logic was performed by Glanzer & Cunitz.
They also had several groups, but they used the same rates for all. How their
groups differed was that one had to count backwards for 30 seconds before
recalling (a variety of the Brown-Peterson distractor task meant to wipe out
STS), whereas another recalled without being distracted. As you would expect
from the theory, both groups showed the same primacy and asymptote effects,
but the distractor group had no recency effect. This type of procedure has
also been replicated by Postman & Phillips.
C. Problems with the MultiStore Model
So, in summary, there was a lot of evidence consistent with the multistore
model's view of memory. But things were about to change. It didn't take
long for a number of people (including some of the ones who ran the experiments
mentioned above) to find problems with the model. To keep things simple, I'll
focus on STM and LTM (ignoring the sensory memories and the issue of attention).
1. Interference vs. Decay in STM
The Petersons had claimed that STM or STS lost information because of decay,
and that was one of the reasons it was different from LTM (which lost informa-
tion because of interference). Later studies showed that decay was not
terribly important for STS, and that Brown and the Petersons had overlooked
an important intereference possibility.
a. Keppel & Underwood's study on PI
Keppel & Underwood decided to re-open the issue of proactive interference (PI).
If you recall, the Petersons had separated their trials into blocks of 12
trials to check for PI (i.e., interference due to response competition from
previous trials). However, Keppel & Underwood asked whether 12 trials was the
right size to look for PI. Specifically, they claimed that maybe PI built up
very rapidly, within only a few trials. If that is so, then the reason the
Petersons didn't see any PI is because it was already there in full strength in
the first block. So, Keppel & Underwood re-ran a version of the Brown-Peterson
experiment, but with the addition of checking for recall after every single
trial. They arranged their experiment so that on the very first trial, some
people would count backwards for 0 seconds, others for 3 seconds, others for
9 seconds, etc. Same for the second, third, and fourth trials. And what they
found was that there was absolutely NO forgetting on the first trial! Even if
you had counted backwards for 18 seconds, you still knew what the three letters
were with nearly 100% accuracy. On Trial 2, however, there was evidence of some
forgetting with time spent counting backwards, though it was not nearly so
dramatic as in the Petersons' experiment. And by Trial 3, their results were
essentially like the Petersons. So, they found that PI built up very quickly -
within the first three trials. What happens as you count backwards is that
you start getting response competition from letters you had on previous trials:
You get confused about which letters are the ones you heard on the current trial,
and so you are more likely to recall the wrong letters.
b. Waugh & Norman's study on RI
Waugh & Norman took another approach. They asked whether there might not also
be retroactive interference in STS, although they knew that this would not
account for the Petersons' results, since letters and numbers are not similar
enough for the numbers to interfere with the letters. In RI, of course,
something you learn later interferes with stuff you had learned earlier.
Waugh & Norman used a variation of the probe technique we looked at earlier, in
Sternberg's experiment. People got a list of numbers, but they never knew how
long the list was going to be. At some point, they got a probe consisting of
a number they had heard earlier in the list. All they had to do, once they
got the probe, was try to remember the number that had come AFTER that number
in the list.
What Waugh & Norman also did was run a fast group and a slow group. The fast
group heard numbers at the rate of 4 per second, while the slow group just heard
one number per second. Waugh & Norman argued that their procedure allowed
comparing two potential mechanisms of forgetting in STS: RI and decay. The
reason their experiment can lok at decay is that decay is essentially an
explanation that claims forgetting occurs with nothing more than the passage
of time: The longer it's been, the less you remember. So, all things being
equal, the slow group should have heard stuff longer ago than the fast group,
and should have more trouble with that stuff if decay is important.
Since this is a bit abstract, let's look at two sample trials to see what
Waugh & Norman's experiment was capable of. In the first below, we will
deliberately make PI the same in both groups, and we will also make RI the
same. The only thing that differs should thus be decay:
fast group slow group
time (seconds)
1st second 1 4 7 9 1
2nd second 5 8 2 6 4
3rd second 1 7
4th second 9
5th second 5
6th second 8
7th second 2
8th second 6
9th second 1
In the experiment above, 1 is the probe, since 1 is the repeated number. So,
the number both groups are trying to remember is the number 4. Note that PI
is identical: each group had only one item before 4 (the same item, in fact).
Similarly, note that RI is identical: each group has 7 numbers that came after
(including the probe; again, the numbers were identical for these groups).
The ONLY difference is one of time: The fast group heard 4 about 2 seconds
ago, the slow group heard 4 about 7 seconds ago. So, if decay is operating
like Brown and the Petersons and the multistore model claim, the fast group
should have better memory. But in fact, what Waugh & Norman found was equal
memory for the two groups in this type of setup.
Now consider another type of setup:
fast group slow group
time (seconds)
1st second 1 4 7 9 1
2nd second 5 8 2 6 4
3rd second 1 7
4th second 1
As before, both groups have to remember 4. As before, PI is equal for both
groups. Note that decay is now also equal, since each group heard 4 about 2
seconds ago. But, they are no longer equal on RI: The fast group heard 7
numbers after 4, but the slow group heard only 2 numbers after 4. So, if RI
operates in STS, there should be more opportunity for response competition (due
to more potential responses causing confusion) in the fast group. And in fact,
the upshot of Waugh & Norman's experiment was that forgetting seemed to be
strictly a function of RI: The more numbers there were that came after the
one you were trying to remember, the worse your memory was. So, not only
does STS have PI, it also has RI, just like LTM.
c. Reitman's study on decay
The studies we've looked at so far suggest that short-term memory primarily
loses information due to interference and response competition. So, the
question to be asked is whether there is any evidence of decay, as originally
claimed by Brown and the Petersons. The answer is that there is *some*
evidence of decay, but it's not a major source of loss. This involves a study
by Reitman. She gave her subjects a distractor task that shouldn't involve PI
or RI: trying to listen to a series of "DOH" syllables in a staticky back-
ground, and pressing a key whenever a "TOH" would appear. Obviously, as these
aren't real words, response competition should not be a problem. She also
made this a hard task: She arranged the level of static so that people would
be correct in detecting the "TOHs" only half the time. AND, she deliberately
asked her subjects *not* to rehearse. At the end of the experiment, she
checked with them to see whether they had rehearsed or not. Those who said
they were able to rehearse showed no forgetting. However, the non-rehearsers
did show a bit of forgetting, consistent with a decay theory claim. So, there
is some decay operating, but it is not a major factor.
2. Auditory vs. Other Coding in STM
The multistore model claimed that STM coded primarily for sound, and LTM coded
primarily for meaning. A number of studies quickly challenged this:
a. Wickens' study on semantic codes (release from PI)
Wickens had people listen to short lists of words and try to immediately
recall them in order. When the lists all involved items from the same
semantic category, he found that recall got worse with later lists, due to
proactive interference building up (as in Keppel & Underwood). But, when
later lists involved a *change* in semantic category (from names of animals to
flowers, for example), then there was no proactive interference. Since these
lists seemed to be small enough to be kept in short-term memory, he argued
that this result showed that semantic meaning was capable of causing inter-
ference in STM. For that to be the case, STM would also have to hold semantic
codes, and not just acoustic or sound codes.
b. Shulman's study on homonym and synonym probes of the SPE
Shulman did a clever experiment using the serial position effect. If you will
recall, the recency portion of that effect is supposedly due to STM, while
everything else is due to recall from LTM. He reasoned that if STM
specialized in sound codes and LTM specialized in semantic codes, then people
ought to be especially good at processing meanings on primacy and asymptote
words, and sounds on recency words. So, after hearing a long list of words,
his subjects got a probe task. There were three types of probes. *Identity*
probes presented a word, and the subject's task was to say whether it had been
on the list. These showed the normal serial position effect. *Homonym*
probes presented words that were not on the list. However, half of these
sounded like list words, and subjects had to indicate which were the ones that
sounded like the originals. If recency words are coded for sound, people
ought to be particularly good at making homonym judgments for the recency
words. Finally, *synonym* probes were non-list words, but half of these were
words with similar meanings (EVENING versus NIGHT, for example). In this
condition, subjects had to indicate which were the words with similar
meanings. If primacy and asymptote words are coded for meaning, then people
ought to be particularly good at synonym judgments for these two types of
words. The result: There was no evidence that a given probe type was better
for one portion of the serial position curve than for another. This implies
that sound AND meaning information are available for both the primacy words
(in LTM) and the recency words (in STM). Thus, like the work on interference,
this study claimed that STM and LTM held very similar types of codes or
information.
c. Shepard's study on visual-like imagery codes in STM
Another set of experiments that challenged the idea of there being only
auditory codes in STM was done by Shepard and his colleagues. Your text
mentions several of these. In one, Shepard gave people the task of deciding
whether a letter, if presented upright, would be facing the correct
direction. For example, you might see an "R" at different angles from
upright, or you might see the reversed "R" at different angles. What Shepard
found was that the further from upright a letter was, the longer it took to
decide if it was facing to the left or the right. He claimed that this was
evidence of imagery. Why? Because according to his model, you placed the
image of the letter in your STM and you then had to rotate it to upright to
see which way it faced. So, in rotating the letter, you had to make it go
through all intermediate points, which took time. The alternative, according
to Shepard, would have been to form a description of the letter and compare
it to your description of an "R". If that is what you did, all descriptions
of the backwards-facing R should have been identical to one another, and it
should not have made any difference how far from upright the backwards R was.
Similarly, all descriptions of the forward-facing R should have been
identical. So, the finding that distance from upright has an effect seems to
strongly suggest that people are capable of rotating mental images. These
types of studies are referred to as MENTAL ROTATION studies.
d. Kosslyn, Ball, & Reiser's experiment on imagery in STM
Another study that supported the notion of imagery was done by Kosslyn et al.
They had their subjects learn and study a map of an island. The island had
many different locations on it (well, pond, hut, rocks, beach, dunes, etc.).
To prove that you had learned the map, you had to reproduce it accurately in
a drawing. Anyway, once people had learned the map, they were told to imagine
being at a certain spot on the map (like the Well). They were then given a
second location, and timed while they decided whether the second location was
on the map or not. Basically, the finding in this MENTAL SCANNING study was
that it took longer to decide when things were further away. Like Shepard,
Kosslyn et al. claimed that this meant people had to mentally scan along all
the intervening points, so that it took longer when there were more of these.
To give you a feel for this, quickly imagine going from Girard Hall to the
following locations: Martin Hall; Griffith; Cajundome; the Mall. Your sense
ought to be that you mentally 'arrive' at the nearer locations a bit sooner.
The alternative theory is again a descriptions-based theory that claims
that your map basically is stored in STM as a list of spots, so that all
you have to do is look down your list to find whether something is on it or
not. That type of theory doesn't seem to predict this effect, according to
Kosslyn.
e. Kerr's work on motor/spatial codes in STM
Finally, we can ask what it means exactly to have imagery codes in STM.
Does this mean that we carry around something like a picture, a visual scene?
Our own experiences seem to suggest that this is indeed the case, but an
experiment by Kerr suggests otherwise. Basically, Kerr repeated Shepard's
mental rotation experiments. He also got the same results. So, just what
is the problem here? Only something very simple: The people who did his
experiment had been blind from birth! The letters they got were Braille
letters that were at various angles. Clearly, in this case, these subjects
weren't creating visual pictures. But, they do have codes that tell them
about locations and directions in space. Whatever imagery they created, it
apparently involved these types of spatial (your text calls them "motor")
codes rather than visual codes
3. Rehearsal as the means of encoding stuff into LTM
Finally, the Atkinson-Shiffrin model claimed that rehearsal was the primary
mechanism for coding stuff into LTM. A number of studies very quickly
challenged this claim. They showed cases where rehearsal just plain failed
to have an effect, or where other mechanisms proved more important. Your
text lists a bunch of these, but I'll go through a few important studies.
a. Craik & Watkins' study on phoneme monitoring
Craik and Watkins did a clever experiment where they took a group of subjects
and told them they would hear a list of words. Their task was to remember
the last word that started with a certain phoneme or sound -- say, the "g"
sound. So, as a subject, you might hear a list like the following:
girl desk goat gorilla chalk cat pen phone lab gate...
If you ask yourself what you would do in this situation, the answer is
something like the following: As soon as you hear a target word, put it in
STM and start rehearsing it. Listen for the next target word. When you
hear that, stop rehearsing the first, and start rehearsing the second. And
so on, until the experimenter finally asks you what the last word that started
with a "g" was.
Now go back to the list: GOAT will not get very many rehearsals, since a
word starting with "g" came immediately after. GIRL should get more rehearsals
than GOAT, and GORILLA should get many more rehearsals than GIRL, since there
is a long stretch in there without target words (words starting with a "g").
After the subjects had finished the experiment and had started another task,
they got a surprise request to list ALL the g-words. The rehearsal theory
predicts that words that got a lot of rehearsals should be more likely to
be remembered. However, this did not happen. In this experiment where
subjects did NOT think they would have to remember the words, the memories
for the g-words were all at about the same level. So, what this shows is
that it is not rehearsal that causes the LTM to form, it is rehearsal AND
intention to learn! Somehow, the intention to learn is causing something
else to happen that plain rehearsal by itself isn't.
b. Rundus's experiment using the Distractor Recall Paradigm
Another study showing the same finding was by Rundus. He did a variation of
the Brown-Peterson study. Subjects got a list of numbers, and the distractor
task involved repeating several words out loud for a certain amount of time.
Then, they tried to remember the numbers, and went on to the next trial with
a new set of numbers, and a new set of words. However, at the end of it all,
Rundus asked his subjects to try to remember the distractor words. The
rehearsal theory predicts that words that were repeated a lot should have
had a better chance of getting into LTM. However, Rundus found that amount
of time spent repeating a word had no effect. People didn't think they would
have to recall the distractor items, and these simply did not make it into
LTM.
c. Bower's study on interaction
Bower looked directly at the effects of rehearsal instructions. He had
three groups of subjects. Each got the same list. Basically, each knew it
had to learn the list for a later test of memory. On the list were pairs
of words. One group was told that the best way to learn these pairs was by
rehearsing them -- repeating them over and over. A second group was told
that the best way to learn them was by forming an image for each word. The
third group was told that the best way to learn these words was by forming an
image for each PAIR of words -- an image in which the two objects would be
interacting. If your pair was CUP-TIGER, for example, you might have formed
an image of a tiger holding a cup. The results were that the imagery and
rehearsal groups were about equally good. But, the interacting imagery
group was far superior to the other two. So, tieing stuff together has a
stronger effect on remembering than simply repeating individual things.
d. Bower et al.'s study on Organization
Finally, another relevant study by Bower, Clark, Lesgold, and Winzenz looked
at the effects of organization. To give you the short version of this study,
people briefly saw about 112 words. The words appeared on 4 cards. On
average, they would have seen each word for only a few seconds. After
seeing the cards, people tried to remember the words.
In this study, there were two groups of subjects who differed not in which
words they saw, but in how the words were organized. For one group, the
four cards corresponded to four different categories. At the top of the
card was a word naming a category (like MINERALS). The words on that card
would look something like the following:
MINERALS
METALS STONES
RARE COMMON ALLOYS PRECIOUS MASONRY
platinum aluminum bronze sapphire limestone
silver copper steel emerald granite
gold lead brass diamond marble
iron ruby slate
Then, they would get another card representing another category such as
TRANSPORTATION or ANIMALS. The other group got four cards too, and even
the same words. But in their case, the words were all scrambled up across
the four cards. And of course, what you will have noticed about the card
example above is that it is organized in a logical, hierarchical fashion.
As you might have guessed, the basic result is that the organized group
remembered most of the words, but the disorganized group remembered very
little. Thus, how you organize things has a very powerful influence on
how well you will remember them. (One reason why I give you an explicit
outline, in fact!)
SUMMARY
So, the bottom line: There were a lot of studies that suggested the multi-
store model was too simplistic. Rehearsal didn't seem effective, and a lot
of studies started suggesting that how you *encoded* stuff was going to be
more important than how long you rehearsed it. This led to the final batch
of models that we'll talk about in class today - the processing models.
Unlike the store models, they make the claim that you can process or encode
stuff in a variety of ways, and that some of these will lead to longer lasting
or easier retrieved memories than others.
.