Name:
Candidate Number: 15
Date of Submission: 3/30/12
Subject: Psychology- standard level
The effect of interference on Short Term
Memory(STM)
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The idea of the study is to measure the effect of inhibiting rehearsal on the duration of Short
Term Memory (STM). This study is primarily conducted by Peterson and Peterson in 1959. Each of 24 participants had read the same six different trigram (meaningless three-consonant syllables, e.g. TGH). Participants were asked to recall trigrams after intervals of 3, 6, 9, 12, 15 or 18 seconds. The study found that Short-term memory has a limited duration when rehearsal is prevented. For a further investigation, this study will be the manipulation of the original study but the method used will be different. If this study will be identical to the primary study, then there is one conclusion that is the intervention has indeed play a major role short term memory.
Introduction
The duration of short term memory experiment was first studied by Peterson-Peterson in
1959. In 1885, Hermann Ebbinghaus (1885) found that memory deteriorated over time. He found that forgetting is fastest in the first hour after learning which supports the argument of trace decay operating on short term memory. Short term memory refers to memories which last for a few minutes. It only last up to 30 seconds and have a capacity of 7 +/- 2 items. Peterson and
Peterson (1959) at Indiana University raised the theory of what contributes to forgetting: Decay or interference? He found that participants recalled fewer items the longer the delay before recall. The decay theory states that information is lost spontaneously over time, even when there is no interference from other materials (Reed, 2004, p. 72 [4]). But it is possible that other factors such as interference or lack of available cues may have an effect on forgetting rather than trace decay. If recall was poor after a period of time then it could be said that decay has occurred.
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To Study how long short term memory lasts, rehearsal must not be allowed to refresh information in short term memory or to transfer to long-term memory. The participant receives trigrams to remember, say three separate words, like ODC, KCO, and UMB. Immediately afterward the participant receives a 3- digit number and starts counting backwards by 3's (378,
375, 372, 369, . . . ) until the experimenter asks the participant to report the three words. The
Peterson and Peterson procedure minimizes rehearsal and recoding by tying up active processes in short term memory during the retention interval. They are tied up by having participants count backwards by 3’s. Counting backwards requires mental computation and speaking, so it leaves little chance for rehearsal and recoding (Peterson, 1966). The original study result is that the participants were able to recall 80% of trigrams after a 3 seconds delay. Nevertheless, after 18 seconds less than 10% of trigrams were recalled correctly.
The aim of the study is to investigate how long information remains in short term memory. The study of duration of short term memory is very beneficial because it allow us to understand not only about ourselves, it can also be used to improve our brain. Suppose I forgot everything that happens last night during party, for that reason I might blame my brain as not functioning well.
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Method
The main concept is to test the duration of short term memory. To carry out the experiment, at least 20 participants will be used to get more reliable information. In this experiment, the participant's personal properties will not be offended whether it's of materials or informative. They have the right to choose to go on or withdraw. But the participant will not be compelled to do without his or her consent or s/he may leave during the experiment. Any person, regardless of gender, race or sex variation, with the capacity of understanding of how to count the number can be used.
To carry out the experiment repeated measure is best fit method to use because the same subject can be used under different condition. There are some variables that cannot be studied using a repeated measures design, but in this study it can be used. There are two major reasons to used repeated measure: first, to increase statistical power; and second, to learn something about the form of the response over time or across situation. And then we can come to a conclusion to
"how much do the interferences within time interval affect the short term memory?” Each participant will carry out two different but the same type of tests: the first one will be counting the number backward by one; the second test will be without any number. And at the end of each test, we will see the variation with same subject.
The participants will be used individually in a quiet environment. In doing so, each participant can focus their mind on the experiment. The outside noises can interfere the participant’s concentration and ruin data. The participants will be informed about the experiment and gave them a practice test that similar to the actual experiment. Either slideshow or note card
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may be used in this experiment. The participant will have to remember 4 meaningless syllables, e.g. YJGD, by reading out loud. Then they will be asked to count 3 digit numbers backward by
4’s out loud. Participants will be asked to recall four words that they recorded after interval of 4,
8, 12, 16, 20, 24 seconds.
The sampling method that will be used in this test is Opportunity. The reason for using this method is that we can't use the population as the participant, it's impossible; instead a few random people will be selected to represent as a whole.The independent variable is the letter that each participants must memorized. The dependent variable is the individual's ability to recall the letter.
Materials:
1.
Computer
2.
PowerPoint
3.
Subjects
4.
Pen or pencil
5.
Procedure
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This graph is the presentation of the present of trigram recalled correctly every three second passed. According to the graph, the trend line goes down steadily, but there is a little hill like camel’s hump at the interval of 9 second. 80% of the participants had recalled the letters correctly after nine second interval although 73% of the subjects recalled another letters shown to them after six second. In another word, 12 out of 15 participants were able to recall the trigram. It could be the result from the trigram being easier to remember. At the interval of 24 second, the chance of recalling the trigram might reach below 2 percent.
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The true purpose of the study is to investigate how the intervention can affect the short term memory. To be able to find out the solution, the participants were asked to read the three letters (trigram) shown on the screen. In the next slide, they were inquired to count the three digit number backward by one. At interval of every three second, different trigrams were presented to them to read to see whether the interference play a major role in short term memory. Just as expected, the result was stunning, they could not recall as the time was expanded. Most of them got right the first trigram, but they were likely to miss one or two letter, or they switched the order the letters. Although, this experiment required logical operation, to make easier for all individual, the participants were required to count the three digits only by one. Some of them might have difficulty with logical thing, but subtracting one out of ten is not a hard thing to do.
As far as each individual’s difference is concerned, a subject who is more focused on task in task is likely to recall more letters. Moreover, they understood the procedure and follow it accurately throughout the experiment.
The research of Peterson and Peterson found that the longer the interval delays the less trigram were recalled. In order to be true, it must work all the time for all people. To confirm it to be true, I investigated further and the outcome was very much identical to the primary studies, alike enough to prove that the interference erases the short term memory. The strength of the research method is the results have replicability and they have been reproduced many times. The
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weakness is that remembering trigrams is not an every day occurrence, and so it is questionable how much ecological validity these findings have.
Suggestion
The reason why this study is not reliable is that it required a lot more participants to consider the theory to be factual. And before conducting the experiment, each subject must be able to follow the procedure and not start before they are ready. One major suggestion I have in mind is that it’s best to conduct in quiet place where the room is empty. For most people, the procedure is hard to understand, so they need further explanation and practice test.
Conclusion
They result of the study reveal that the short term memory is different form long term memory in term of duration. The longer the interval delay with counting the numbers backward, chance of recalling the trigram or any particular letters is limited or decreased. Without interference, each participant was able to recollect the letters. So, we can make a conclusion that the short term memory is affected only when interference step in.
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Appendix
Trial 1 What were the letters that you read? Trail 2 What were the letters that you read?
1 MJI 1 IYJ
2 LIW
3 PKQ
2 BNX
3 VPL
4 JNS
5 YGL
6 ZFJ
4 TLJ
5 HVY
6 QIF
Result Data:
Trial 1-Subject 1 What were the letters you read? Trail 2
1 MJI
2 LIW
3 PKQ
4 JNS
5 PKL
6 JLK
Subject 2 Subject 2
1 MJI
2 LWI
3 PKQ
4 LWP
5 YGL
6 ZFJ
Subject 3 Subject 3
1 MJI
2 MIL
3 PIQ
4 PQR
5 YGL
6 ZIL
Subject 4 Subject 4
1 MJI
2 JIW
3 PKQ
4 JNS
5 YGL
6 PNY
What were the letters you read?
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
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Subject 5
Subject 6
Subject 7
Subject 8
Subject 9
1 MJI
2 LIW
3 PKQ
4 JNS
5 YGT
6 JFN
1 JIM
2 LIM
3 PKQ
4 JNS
5 NNT
6 ZJI
1 MJI
2 LWJ
3 PQK
4 NQI
5 YKR
6 ZIJ
1 ABC
2 LIY
3 PQK
4 JNS
5 YIL
6 SNC
1 MJI
2 MIJ
3 POW
4 JNS
5 YGL
6 ZYJ
10
Subject 5
Subject 6
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 7
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 8
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 9
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF

Subject 10
Subject 11
Subject 12
Subject 13
Subject 14
1 MJI
2 ILW
3 PKQ
4 IKL
5 PIK
6 ZFJ
1 MJI
2 LIW
3 KIJ
4 JNS
5 YNW
6 ZFJ
1 NJI
2 NWG
3 PKQ
4 JNS
5 YGL
6 ZGO
1 MJI
2 ABC
3 PKQ
4 JNS
5 YKL
6 ZLJ
1 MJI
2 LIW
3 PKQ
4 JNP
5 JGN
6 ZFJ
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Subject 10
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 11
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 12
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 13
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Subject 14
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF

Subject 15
1 MJI
2 JIW
3 PKQ
4 JNI
5 YGL
6 ZQJ
Subject 15
1 IYJ
2 BNX
3 VPL
4 TLJ
5 HVY
6 QIF
Reference
Peterson, L.R., & Peterson, M.J. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology , 58, 193-198
McLeod, S. A. (2008).
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