Psychology HL - IA

1
Psychology Internal Assessment
An experiment to investigate the effect of decreasing rehearsal
on the number of words recalled
Candidate name : XXXXXXXX
Candidate number : XXXXXXXX
Subject : Psychology –HL
Date of Submission : 5th April, 2015
Word count : 1998

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Abstract
The following experiment was conducted as a part of the internal assessment of IB
Psychology. The aim of the experiment is to investigate the effect of decreasing
rehearsal on the number of words recalled in the Short Term Store of memory store
(STS). The experimental hypothesis for this experiment is that, as the time available
for rehearsal of words decreases, the number of words that are recalled will also
decrease. Independent measures design was used. The independent variable of this
experiment is the time given to the participants to rehearse the words given to them.
The dependent variable is the number of words recalled after rehearsal.
The particpants were divided into two groups – the control and the experimental. The
experimental group was shown the list of words they have to recall, for several trials
with the time of rehearsal decreasing with each trial. The control group was shown the
list of words with time given for rehearsal, without any decrease. The participants
were made to write down the words they freely recalled after each trial. The
confounding variables such as demand characteristics, copying of words from other
partipants, etc., were controlled. Opportunity sampling was used to select participants.
Mann Whitney U test was used to test the raw data. The results have shown that the
number of words recalled does decrease with the decrease of the rehearsal time. These
findings can explain many real-life situations such as memorising while studying for
examinations, eye-witness testimony, learning music, etc.

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Introduction
Memory is a cognitive process that enables us to encode, store, retain and recall
information and past experiences. We can also call it as the reconstruction of the past
experiences. Memory can include facts, skills, habits and experiences.
Researches on this cognitive process lead to the crafting of different models such as
Multi store model (MSM), Working Model of Memory (WMM) and Levels of
Processing (LOP). According to MSM, the human memory can be divided into three
simple sections or ‘stores’ of memory.
The three stores are: Sensory, Short-term, and Long-term. The short-term memory
(STM) store is the store that acts like a temporary storage. It has the ability to store
information and process it but has a very limited capacity of items (Miller’s magic
number) and duration of < 30 seconds. As the duration of rehearsal decreases, the
memory in this store begins to decay. If the information from the STM is rehearsed, it
is passed on to the long-term memory store (LTM).
Peterson and Peterson, in 1959 conducted an experiment to investigate the decay in
memory in the STM as a result of decreased rehearsal. When a person tries to
memorize words or numbers, they rehearse the item to remember it for a longer time.
In this experiment, rehearsal was prevented leading to decay in memory. The
experiment was done on 24 participants. 1 The participants were shown a list of
trigrams (A three letter word with only consonants), one word at a time and then told
to recall the trigram2 after an interval of 3, 6, 9, 12, 15 and 18 seconds respectively for
each trial. During the interval, the participants were told to count backwards from a
number and freely recal the trigrams. As a result, the participants recalled 80 % of the
1 http://www.human-memory.net/index.html
2 Trigram: A 3-letter word that has little or no meaning.

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words with an interval of 3 seconds and it kept decreasing to 10% of the trigrams.
Peterson and Peterson concluded that when duration for rehearsal is decreased,
information is rapidly decayed from the STM. 3Brown J. did a similar experiment in
1958 and got identical results. 4
The Aim formulated for this experiment is :
To investigate the effect of decreasing rehearsal on the number of words recalled in
the Short Term Store of memory.
Investigating on the this topic will give us an insight of why we as humans tend to
forget certain things when we do not have much time to rehearse it. This can be
applied to preparations for examinations and eyewitness testimony.
The independent variable is the time interval between revealing the words and the
recall. The interval changes in every trial. The first trial has 5 seconds interval, second
trial – 10 seconds, third trial – 15 seconds. The dependent variable is the number of
words recalled by the participants after every trial.
Based of Brown and Peterson and Peterson’s studies,
Experimental hypothesis:
The participants in the experimental group will recall decreasing number of words
(trigrams) as the time interval increases. The participants in the control group are able
to recall more words.
Null hypothesis:
The increasing time interval does not show a significant effect on the number of
words recalled by the participants.
3 Psychology: Pearson baccalaureate
4 http://mindsandmodels.blogspot.in/2012/01/peterson-and-peterson-1959-decay-in-stm.html
http://psychology4a.com/memory%202.htm

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Method
Design
Independent measures design was used to design this experiment instead of repeated
measures design to prevent practice of the words that the participants have read,
restlessness and boredom of participants, demand characteristics (knowing the aim of
the experiment and acting according to it). However, this design makes it hard for the
experimenter to find enough participants meeting the criteria, to brief and debrief the
participants.
The confounding variables to be controlled were:
• Participants copying from their fellow participants.
• Noise that can prevent rehearsal.
• When a participant finishes their job, they start getting distracted or bored.
• Hawthorne effect
The variables were controlled-
• Participants are observed to prevent copying.
• The experiment is conducted in a quiet area.
• The time given to write down the recalled words was decreased.
• The script of instructions, briefing and debriefing was priorly made to sound
the same to every participant.
The two groups (Experimental and control) were given the same trigrams. The time
interval and the filler task were the same. Both the groups had 4 trials. The time of the
intervals was the independent variable while the number of words recalled is the
dependent variable. It was made sure that the ethical guidelines were followed. The
confidentiality of the participants was ensured. They were briefed and debriefed to

6
make them understand the experiment. The participants were debriefed at the end of
the experiment.
Participants
The target population for this experiment is the population of all IB students who are
non-native English speakers, with basic knowledge in mathematics. The number of
students in the target population was 61. Opportunity sampling was used to allocate
24 participants from the 61 students. This technique was used because it was easier to
obtain the participants who were IB students, of my own school, who were available
at the time of the experiment. Random sampling was done to allocate the participants
into the control and experimental groups. The sampling was done in the grades of 11
and 12 of age 16 or 17, both male and female Indians.
Materials
• Computer
• Projector
• Screen
• Instructions paper5
• Stopwatch
• 24 Consent forms6
• Word list7
• Debriefing8
5 Appendix 2
6 Appendix 4
7 Appendix 1
8 Appendix 3

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Procedure
The participants were first briefed about the experiment to avoid any stress or anxiety
before the experiment. Each participant was asked to read and sign the consent form
before beginning the experiment. The participants were given the freedom to leave the
experiment and were ensured of their confidentiality. I used no form of deception;
everything was made clear to the participants.
 After being shown the power point presentation of the 15 words (Trigrams),
the participants were told to write down the words that they freely recalled on
the first page of the papers.
 Each page had two columns, the first column to do the filler task (writing the
multiples of 8) and the second column for writing the words that they recalled.
 At the end of 3 minutes, the participants were instructed to write down the
multiples of 8 (filler task) on the next page for 5 seconds.
 At the end of 5 seconds, they were told to immediately write down the words
on the next page. This was done for 2 more trials with 10 seconds and 15
seconds of the filler task, respectively.
The same procedure was used for the participants of the control group but they did not
have any time intervals or a filler task. They were debriefed about the experiment and
were given a chance to ask me questions.

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Results
Descriptive Statistics
The data is in the form of interval data and the design of the experiment is
independent samples design, so the mean and standard deviation are calculated.
Measuring mean minimizes error in the prediction of values and gives the average
considering all the values. The mean of the values under each trial (both experimental
and control) were calculated using MS Excel.
Table 1: Mean and standard deviation value of experimental and control group
×̅=
∑×
𝑁
This is the formula for calculating mean, where ∑× is the sum of all the values in one
trial and N is the number of participants.
Mean values Standard
Deviation
Trial 1 Trial 2 Trial 3 Trial 4
Experimental 7.25 5.75 5.25 4.75 1.08012345
Control 8.166667 8.5 8.92 9.33 0.50541775

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Graph 1 Shows the decrease in the number of words recalled with increase in time interval by
experimental group participants
0
1
2
3
4
5
6
7
8
0 sec 5 sec 10 sec 15 sec
Meanofwordsrecalled
Interval time
Experimental Group
Mean
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
Trail 1 Trial 2 Trial 3 Trial 4
Meanofwordsrecalled
Trial number
Control group
Mean
Graph 2 Shows the mean number of words recalled by the control group participants

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Fig 1. Calculation of standard deviation of the scores of control group
Fig 2. Calculation of standard deviation of scores of experimental group
Standard deviation for experimental group = 1.08012345
Standard deviation for control group = 0.50541775
0
0.2
0.4
0.6
0.8
1
1.2
Experimental Control
StandardDeviation
Groups
Standard Deviation

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Standard deviation was used as a measure of dispersion as the data is interval data.
The individual values differ from the mean and are capable of influencing the mean
value. Therefore, calculating standard deviation is necessary. Using, the found mean
values, standard deviation values for both experimental and control group were found
using Excel.
Inferential Statistics
The design is an independent samples design, and the data is ordinal and the
experiment tests one difference between two conditions of groups (control and
experimental), so Mann Whitney U Test was used to test the data. An authentic
website was used for calculations. 9
The acquired value of U at the significance level of 0.05 is 33.5. The critical value is
42 for a one-tailed hypothesis. U < 42 at p ≤ 0.05, therefore, the result is significant
at p ≤ 0.05. This shows that there is a signicant difference in the data at 95% or
higher. Hence, the null hypothesis is rejected and the experimental hypothesis is
accepted. This suggests that the decrease in rehearsal did have a significant effect on
the number of words recalled.
9 Appendix vi

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Discussion
There is a significant decrease in the mean of the words recalled as the interval time
increased. The standard deviation between the means of the trials of the experimental
group is higher than that of control group. This shows that the decrease in rehearsal
has caused higher deviation in the means. The standard deviation between the means
of the trials of the control group is relatively less because the change in values are not
affected by any factor. The value of U produced by Mann-Whitney U test was less
than the critical value at p ≤0.05, so the null hypothesis was rejected.
The study used to attempt to replicate was the experiment conducted by Peterson and
Peterson in 1959. The experiment was conducted to investigate the effect of decrease
in rehearsal of items by increasing the interval time and using a filler task. Peterson
and Peterson have also rejected the null hypothesis and suggested from their
experiment that as decrease in rehearsal increases, number of words recalled
decreases. The hypothesis in this experiment is similar, although the numerical results
are different due to differences in samples, list of words and procedure. An
exponential decrease in the recall of words was represented, while my results have no
exponential decrease but the number of words recalled did decrease. The original
study might have gotten more accurate results due the measures they have taken. For
instance, they have experimented each participant personally, 8 times for each
interval. Due to time constriction, I could not do the same.
Nevertheless, the experimental hypothesis is accepted. This could be because the
experiment was conducted in a simple and controlled manner with a proper
procedure. The use of trigrams made it difficult for the participant to associate the

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words to something to help them remember the words. The sheets given to the
participants to write the recalled words were structured and made it easier for the
participants to write than to verbally present the words. Opportunity sampling made it
less-time consuming and also prevented gender bias. All ethical considerations were
made; participants’ consents were taken, their confidentiality was ensured and to
relieve discomfort and anxiety, they were briefed and debriefed. Possible demand
characteristics were prevented to an extent as the design was independent samples
design.
The experiment did have several drawbacks that could have been prevented. Alike
Peterson and Peterson’s experiment, this study could be criticized for having very low
ecological validity due to several reasons:
 The use of trigrams: People generally do not find the necessity to memorise
trigrams, they memorise words that they can associate with. However,
trigrams were used to prevent such association.
 The experiment was conducted in a closed room with an environment of a
laboratory which makes the setting less natural.
Even though trigrams decrease association of words, it should have been further
decreased by finding out the Witmer association value to make these words. The
participants of the control group were able to recall more words with every trial as
there is no interference with the rehearsal. This cannot be controlled because the
control group should not be exposed to the independent variable. I have made the
participants to write the multiples of 8 for every trial as it is easier to instruct the
participants. But as the number of trials increases, the participants have enough

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practice of the multiples of eight and gives them more scope to rehearse the words.
Changing the task with every trial could have given better results. Due to time
constriction, the number of time intervals, words, trials for each time interval were
decreased. If more time was provided, more accurate results could be produced.
However, the participants were restless even with one trial and 15 words, so less
number of trials and words eliminated the possible restlessness. Participants were
restricted to be taken from students in the same school who know each other. Students
from different high schools should have been taken but this was not possible as it was
difficult to acquire their consent.
Even though there are many drawbacks, the descriptive and inferential statistics have
shown that the results are significant and hence the experiment was successful.
Therefore, decrease in rehearsal causes decrease in recall of words.

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Bibliography
 Concept Formation. http://www.sltinfo.com/concept-formation/
 Decrease in gamma-band activity tracks sequence learning.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4300908/
 Demand Characteristic - About.com Psychology.
http://psychology.about.com/od/dindex/g/demanchar.htm
 Frontiers | Rehearsal development as development of iterative recall
processes | Developmental Psychology.
http://journal.frontiersin.org/article/10.3389/fpsyg.2015.00308/full
 Guillermo Campoy, THE QUARTERLY JOURNAL OF EXPERIMENTAL
PSYCHOLOGY 2008, 61 (5), 724 – 734,
o https://www.um.es/guillermocampoy/papers/Campoy2008.pdf
 LLOYD R. PETERSON AND MARGARET JEAN PETERSON, Journal of
Experimental Psychology, September 1959
http://psych.indiana.edu/tradition/Peterson_and_Peterson_1959.pdf -
Original study
 Online calculator-
http://www.socscistatistics.com/tests/mannwhitney/Default2.aspx
 Critical value for U
http://sphweb.bumc.bu.edu/otlt/MPHModules/BS/BS704_Nonparamet
ric/BS704_Nonparametric4.html
 Memory - Psychology4A.com. http://www.psychology4a.com/memory.html
 Peterson and Peterson (1959) - Memory Psychology - Psychologist World.
http://www.psychologistworld.com/memory/peterson_decay.php

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 Peterson and Peterson 1959 | Simply Psychology.
http://www.simplypsychology.org/peterson-peterson.html
 Serial Position Effect | Simply Psychology.
http://www.simplypsychology.org/primacy-recency.html
 Similarities and differences: short and long term memory.
http://www.ukessays.com/essays/psychology/similarities-and-differences-
short-and-long-term-memory-psychology-essay.php
 SparkNotes: Memory: Memory Processes
http://www.sparknotes.com/psychology/psych101/memory/section1.rhtml
 What Is Memory? - The Human Memory. from http://www.human-
memory.net/intro_what.html

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Appendices
Appendix I : The words shown in the presentation
1. SEZ
2. TIK
3. ROP
4. LOM
5. ZAR
6. BAC
7. CEP
8. DIR
9. FOT
10. GUQ
11. HAX
12. JES
13. KIR
14. LUP
15. VOT

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Appendix ii : Instructions
Instructions given for experimental group:
Each of you are given a consent form. Please read the statements in the consent form.
Write your name, grade, email ID and give your signature in the given blanks.
The aim of the experiment is to investigate the effect of rehearsal on free recall in
high school students.
Do not turn to the next pages unless you’re asked to.
• You have all been given a consent form with 4 sheets of white papers attached
to it and a pencil.
• The white sheets are numbered from 1 to 4.
• Please turn to page 1.
• I am going to show you a power point presentation. Each slide of the
presentation will show you one word.
• The word is a three-letter word, which does have any meaning.
• There will be 15 words so therefore 15 slides, one word in each slide. The
word will be big and clear. Each word will be shown for 5 seconds.
• The last slide will show you the word ‘’Go’’. When you see this slide saying
‘’Go’’, start writing the words you remember onto the paper with your pencil.
• You will be given 3 minutes. Try to write as many words as possible.
• Please do NOT try to copy or obtain answers from the other participants.
• When I say “stop”, please turn to page 2.
(End of experiment for control group)
(Experiment continues for experimental group)
• Do NOTturn back to the previous pages. (experimental)
(when 3 minutes are done)

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• Stop and turn to page 2.
• Start writing the multiples of 8 in the first column.
• Stop writing the numbers and start writing the words you saw in the slides, in
column 2.
• Stop writing the numbers and start writing the words in column 2.
• Stop writing the numbers and start writing the words in column 2.
• Stop writing the words. Put your pencils down. Go back to the consent form.
• The experiment is now over.
Instructions given for control group:
Each of you are given a consent form. Please read the statements in the consent form.
Write your name, grade, email ID and give your signature in the given blanks.
The aim of the experiment is to investigate the effect of rehearsal on free recall in
high school students.
Do not turn to the next pages unless you’re asked to.
• You have all been given a consent form with 4 sheets of white papers attached
to it and a pencil.
• The white sheets are numbered from 1 to 4.
• Please turn to page 1.

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• I am going to show you a power point presentation. Each slide of the
presentation will show you one word.
• The word is a three-letter word, which does have any meaning.
• There will be 15 words so therefore 15 slides, one word in each slide. The
word will be big and clear. Each word will be shown for 5 seconds.
• The last slide will show you the word ‘’Go’’. When you see this slide saying
‘’Go’’, start writing the words you remember onto the paper with your pencil.
• You will be given 3 minutes. Try to write as many words as possible.
• Please do NOT try to copy or obtain answers from the other participants.
• When I say “stop”, please turn to page 2.
(End of experiment for control group)
(Experiment continues for experimental group)
• Do NOTturn back to the previous pages. (experimental)
• Stop writing the numbers and start writing the words you saw in the slides.
• Stop writing the numbers and start writing the words.
• Stop writing the numbers and start writing the words.
• Stop writing the words. Put your pencils down. Go back to the consent form.
• The experiment is now over.

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Appendix iii: Debriefing
Peterson and Peterson originally did this experiment in 1959.
The aim of the experiment was to investigate the duration of Short-term memory and
provide evidence for a model of memory called the Multi-store model.
A lab experiment was conducted in which 24 participants had to recall trigrams
(meaningless three-consonant syllables). To prevent rehearsal participants were
asked to count backwards in threes from a specified random number until they saw a
red light appear.
Participants were asked to recall the words after intervals of 3, 6, 9, 12, 15 or 18
seconds. I have used 5, 10 and 15 seconds.
They got the results that, as the time interval was increased between reading the
words and writing them, the lesser the participants recalled the words.

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Appendix iv : Consent form
• I am participating the experiment with my own will, without being
pressurised.
• I have been informed about the nature of the experiment.
• My anonymity will be confidential and will not be identifiable.
• I know and understand that I have the right to withdraw from the experiment
anytime without being demeaned.
• I will not abject in any way through out the experiment.
• I will have the opportunity to find out the results of the experiment.
Name: ………………………………………………………………………..
Grade: ………………………………………………………………………..
Age: ……………………………………………………………………….
Email ID: …………………………………………………………………….....
Signature of the participant

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Appendix v : Raw data
Number of words recalled by Control group:
Student
number. Control -
Trial 1
Control-
Trial 2
Control-
Trial 3
Control-
Trial 4
1 8 8 9 9
2 4 4 5 4
3 4 4 4 4
4 6 6 5 6
5 9 9 9 8
6 6 8 8 9
7 14 14 15 14
8 12 13 12 12
9 9 9 10 10
10 7 8 10 10
11 8 9 9 14
12 11 10 11 12

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Number of words recalled by experimental group:
Student
No.
Trial 1 (0
sec)
Trial 2 (5
sec)
Trial 3 (10
sec)
Trial 4 (15
sec)
1 11 10 10 8
2 6 4 3 3
3 5 3 3 2
4 4 3 2 2
5 7 6 6 5
6 8 6 4 4
7 7 6 6 6
8 4 3 2 2
9 11 11 11 1
10 11 8 8 7
11 7 7 6 6
12 6 2 2 1

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Appendix vi : Calculation of Mann-Whitney U
Online calculator- http://www.socscistatistics.com/tests/mannwhitney/Default2.aspx

Psychology HL - IA

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