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2 Memories or 1? STMLTM For decades. researchers have debated the question of whether memory is divided into a short-term store and a long-term store.

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Presentation on theme: "2 Memories or 1? STMLTM For decades. researchers have debated the question of whether memory is divided into a short-term store and a long-term store."— Presentation transcript:

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2 2 Memories or 1? STMLTM For decades. researchers have debated the question of whether memory is divided into a short-term store and a long-term store – two memories that function in different ways and operate on different principles. Dual-store theorists make this distinction. They say that a given independent variable may have different effects on recall depending on which memory the individual uses. The Issue This is called “dissociation”: The same variable has different effects in different tasks.

3 2 Memories or 1? STMLTM Single-store theorists say that we have only one memory. A single set of principles can be used to explain performance in any memory task. It’s like having a formula you can use to predict how many items a subject will recall. For each task you enter numbers for such variables as the number of practice trials, the number of items in the list, and the length of the retention interval. The Issue Dual-store theorists would say you need two formulas, not just one.

4 2 Memories or 1? STMLTM An experiment by Peterson and Peterson (1959) aroused a lot of controversy because it seemed to demonstrate the existence of a short-term memory. Classic Experiment Procedure 1. You are read a single nonsense syllable consisting of three consonants, like CHJ. 2. Immediately afterwards, a 3-digit number is stated, like 506. You count backwards from that number continuously until a signal light flashes 3 to 18 seconds later. 3. You then try to recall the three letters in their original order.

5 2 Memories or 1? STMLTM Let’s Try It! Classic Experiment When the top (green) light comes on, you will hear 3 letters and then a number. You should immediately repeat that number to yourself and then start counting BACKWARDS from it by 3’s. When the bottom (red) light comes on, stop counting immediately and try to write down the letters that were given in their original order. s

6 2 Memories or 1? STMLTM Let’s Try It! Classic Experiment The interval between the last letter pronounced and the red light was 18 seconds. At this retention interval, participants were correct only about 10% of the time. However, the percent of the class who got KSG right is probably higher than that. That’s because of a flaw in the original experiment that undermined the Petersons’ conclusions. s K S G The answer... Before discussing the flaw, let’s look at the overall results.

7 2 Memories or 1? STMLTM Classic Experiment Retention Interval (seconds)Probability of Correct Recall At a retention interval of 3 seconds, recall was down to a probability of about.80. At an interval of 18 seconds, recall was down to

8 STMLTM Importance Classic Experiment Such rapid forgetting of a single nonsense syllable over just 18 seconds was surprising. Most studies used retention intervals of hours or days and found less forgetting of whole lists of items. The prevailing theoretical framework was the “interference theory of forgetting.” It said that we forget things because of other things we have learned, not simply because of the passage of time. 2 Memories or 1?

9 STMLTM Importance Classic Experiment It appeared that memory simply “decayed” as time passed. If it wasn’t decay, then what was the source of the interference? Could it be the numbers subjects recited during the retention interval to prevent them from rehearsing the nonsense syllable? Target InformationInterfering Information LettersNumbers 2 Memories or 1?

10 STMLTM Importance Classic Experiment This would be _______________ interference (retroactive or proactive). RI from the numbers to the letters was unlikely. Studies showed that interference was strongest when the interfering and target information were similar. Target InformationInterfering Information LettersNumbers retroactive 2 Memories or 1?

11 STMLTM The Flaw Classic Experiment The Petersons acknowledged another possible source of interference: Each participant got 48 different nonsense syllables during the experiment, 8 at each of 6 retention intervals. What if they remembered some of them? Then we would have... Interfering InformationTarget Information Letters on Previous Trials Letters on Current Trial 2 Memories or 1?

12 STMLTM The Flaw Classic Experiment There could be proactive interference from letters on previous trials to letters on the current trial. This should not happen if those letters disappeared from short-term memory and did not get into long-term memory (since they weren’t rehearsed). Interfering InformationTarget Information Letters on Previous Trials Letters on Current Trial 2 Memories or 1?

13 STMLTM The Flaw Classic Experiment The Petersons tested this by looking at correct recalls in blocks of 12 trials to see if recall went down as the number of preceding trials went up. There was no decrease, no evidence for proactive interference. Interfering InformationTarget Information Letters on Previous Trials Letters on Current Trial 2 Memories or 1?

14 STMLTM The Flaw Classic Experiment But then Keppel and Underwood (1962) looked at recall on every trial, starting with Trial 1. Now there was clear evidence for proactive interference. Interfering InformationTarget Information Letters on Previous Trials Letters on Current Trial Here is what they found for subjects’ very first nonsense syllable. 2 Memories or 1?

15 STMLTM Classic Experiment Retention Interval (seconds)Probability of Correct Recall Peterson & Peterson Recall on Trial 1 (Keppel & Underwood, 1962) Caused by PI from previous items

16 STMLTM Interference Effects Classic Experiment Keppel and Underwood (1962) found that as the number of trials increased, recall of the current item decreased. The previous trials were a source of PI. An additional source of interference is the letters within the nonsense syllable (“intraitem interference”.) Recall of a single consonant is almost 100% at an interval of 12 seconds, and it gets lower and lower as you go from 1 to 5 consonants (Melton, 1963). 2 Memories or 1?

17 STMLTM Interference Effects Classic Experiment To reduce intraitem interference, you can present a simple word instead of unrelated letters. Murdock (1961) found that after 18 seconds, recall of a single, monosyllabic word was almost 100%. Recall of 3 words was as low as 3 consonants. Such interference effects should not occur if subjects recalled the items from short-term memory. 2 Memories or 1?

18 STMLTM Dissociation or Continuity? Classic Experiment Short-term memory implies information disappears rapidly as time passes. That’s why it’s called “short- term”. In contrast, the passage of time is considered to be a minor factor in long-term memory... 2 Memories or 1? Recall Jenkins & Dallenbach’s experiment on sleep and memory: Subjects forgot relatively few nonsense syllables when they were asleep during an 8-hour retention interval. They forgot a lot more if they were awake and susceptible to interference.

19 STMLTM Dissociation or Continuity? Classic Experiment Did Peterson & Peterson demonstrate that time was an important factor in forgetting? This would represent a dissociation of the effects of time in different kinds of memory tasks and support the dual- store approach. 2 Memories or 1?

20 STMLTM Dissociation or Continuity? Classic Experiment Characteristics of Long-Term Tasks: 1. Multiple practice trials 2. Long lists — at least 10 items. 3. Long retention intervals — hours or days Characteristics of Short-Term Tasks: 1. 1 presentation of the item(s) 2. Short lists — less than 10 (within memory span) 3. Brief retention interval — less than 30 seconds 2 Memories or 1?

21 STMLTM Dissociation or Continuity? Classic Experiment Interference variables, not time, caused forgetting, so the Petersons’ task was not fundamentally different from conventional long-term tasks. 2 Memories or 1? This famous experiment on short-term memory did not even support the dual-store theory!

22 STMLTM Short-Term Memory vs. Short-Term Store Classic Experiment Some researchers (like Atkinson and Shiffrin) distinguish between these terms. “Short-Term Store” refers to a theoretical concept. “Short-Term Memory” refers to performance in short-term tasks, like the Petersons’. This performance may or may not be explainable in terms of a short-term store. 2 Memories or 1? It’s important to distinguish between observation and interpretation. However, short-term memory usually refers to a theoretical construct.

23 STMLTM Evidence for Short-Term Memory Free Recall Some of the strongest evidence for the dual-store theory comes from the free recall procedure. 2 Memories or 1? You are most likely to remember the beginning words (primacy effect) and the end words (recency effect). This is where you are presented with a series of words just once and immediately afterwards you try to recall the words in any order.

24 STMLTM Evidence for Short-Term Memory Free Recall According to the Atkinson-Shiffrin model, the more times you repeat something, the more likely it is you will transfer it from short-term to long-term memory. 2 Memories or 1? In free-recall experiments, subjects usually repeat words as the list is presented. Rundus (1971) asked subjects to rehearse aloud so he could tape record them and count how many times each word was said. Effects of Repetition

25 STMLTM Evidence for Short-Term Memory Free Recall 2 Memories or 1? Effects of Repetition Probability of Correct RecallMean Number of Repetitions Serial Position in List Recall showed a typical serial position curve... Earlier items were repeated more times than later items.

26 STMLTM Evidence for Short-Term Memory Free Recall 2 Memories or 1? Effects of Repetition Probability of Correct RecallMean Number of Repetitions Serial Position in List Repetition went in the same direction as recall for beginning and middle items. It went opposite to recall for the end items.

27 STMLTM Evidence for Short-Term Memory Free Recall Dual-store theorists would say that subjects had to use LTM to recall the beginning and middle items. These words wouldn’t last long enough in STM until the recall test was given. 2 Memories or 1? Repetition helped put these words into LTM: the more repetitions, the higher the recall. Effects of Repetition

28 STMLTM Evidence for Short-Term Memory Free Recall What about the end items? Recall went up as repetitions went down, so recall of end items did not depend on repetition. 2 Memories or 1? Dual-store theorists would say that it depended on time: The closer a word was to the test, the less it would decay, and the better were the chances of recalling it. Effects of Repetition

29 STMLTM Evidence for Short-Term Memory Free Recall 2 Memories or 1? The bottom line? Effects of Repetition D I S S O C I A T I O N s The effects of repetition were dissociated according to a word’s position in the list. This is evidence that the words came from different memories that functioned in different ways.

30 STMLTM Evidence for Short-Term Memory Free Recall The retention interval is the time between presentation of the last word and the signal to recall the list. 2 Memories or 1? Suppose you had to wait 30 seconds before recalling the list. Which words would be most affected? Effects of Retention Interval

31 STMLTM Evidence for Short-Term Memory Free Recall Dual-store theorists say the beginning and middle words are recalled from LTM. This holds information for years; 30 seconds shouldn’t matter. 2 Memories or 1? Effects of Retention Interval End items come from STM, which only holds information up to 30 seconds without rehearsal. So waiting 30 seconds should erase these words.

32 STMLTM Evidence for Short-Term Memory Free Recall Glanzer and Cunitz (1966) presented a 15-word list and gave a free-recall test either immediately after the last word or after a 30-second delay. 2 Memories or 1? Effects of Retention Interval During the delay, subjects counted backwards from a number so they couldn’t rehearse the words. The results...

33 STMLTM Evidence for Short-Term Memory Free Recall 2 Memories or 1? Effects of Retention Interval Probability of Correct Recall Serial Position in List Immediate Test 30-second delay Recency Effect eliminated by delay Primacy Effect unaffected by delay

34 STMLTM Evidence for Short-Term Memory Free Recall The fact that retention interval had different effects on different parts of the list is another example of...? 2 Memories or 1? Effects of Retention Interval It’s another reason to dissociate short-term from long-term memory. D I S S O C I A T I O N s


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