Introduction: (Initial Observation)
Learning or memorizing is sometimes a challenge for many people. On the other hand some others got a grip on learning and know how to learn or memorize easily. The amount of information that you can memorize in your short memory is called memory span. The length of time that information will remain in your mind is memory retention.
In this project you will perform experiments to test memory span and memory retention on yourself and a few other test subjects. Learning about how we learn and the factors that may affect our memory can actually help us to learn easier. So we also try to perform some tests to learn about the factors that affect our learning ability.
Find out about memory span and memory retention. Read books, magazines or ask professionals who might know in order to learn about the methods that you can test memory span and memory retention. Keep track of where you got your information from.
Overview of Memory Processes
Memory is more than a single process.
Memory allows us to acquire, retain and recall information.
The corresponding processes are encoding, storage and retrieval.
encoding = the process of converting information into a form that can be entered and stored in memory
storage = the process whereby an encoded memory is held for future use
retrieval = the process whereby a stored memory is brought into consciousness
Memory is currently thought to have three stages: very short, short and long.
These vary in type of info, function, duration and capacity (see table).
|Type of Info||Sense Data||Info from Sensory or Long-Term Memory||Encoded Info from Working Memory|
|Function||Register Immediate Sensations||Process Input from Sensory Memory & Retrieve Long-Term Memories||Store Lasting Memories|
|Duration||0.25 to 3 seconds||About 30 seconds||Potentially Lifelong|
Sensory memory briefly holds the tremendous amount of information coming in from the senses. Unless you focus your attention on some part of that information, the memory disappears in about one second.
Short-term memory or working memory holds your current thoughts.
Short-term memory can contain input from two sources:
- The contents sensory memory that you are paying attention to may enter short-term memory.
- Information recalled from long-term memory is processed in short-term memory.
Short-term or working memory is the problem-solving area of the mind. This is where you remember, imagine or figure things out. Most of the contents of working memory are lost after about 30 seconds, but some is converted to long-term memories.
Long-term memory holds what we usually think of as our memories. Encoded info from working memory is stored here. Previously stored material can be retrieved from long-term memory into working memory.
The capacity of short term memory is about 7 chunks of information, whether each bit is a single number or a more complex set of things.
The capacity of short-term memory can be increased by chunking:
F A U E C P S D A I W T
E P A F D I C T W A U S
New material seems to bump existing material out.
The contents of short-term memory disappear in about 30 seconds, unless you repeat them to yourself over and over.
Maintenance rehearsal is the conscious repetition of the contents to short-term memory. If you are prevented from doing this (5 3 9 6 9)(6 9 12 4 3 5 1 6 7 2 3…) the contents disappear.
Long-term memory is apparently limitless in capacity and duration.
LTM is limited by encoding and retrieval.
Encoding is the process whereby information is put into long-term memory.
Simple repetition (maintenance rehearsal) may help keep things in STM, but it does not work especially well at getting things into LTM.
More effective is to repeat the information in some new meaningful way. This is called elaborative rehearsal because you elaborate on the material.
This is especially useful if you apply the information to yourself (the self-reference effect) and use visual imagery.
This strategy can be useful. To improve your recall of things you are learning:
- Ask questions about the material.
- Think about where the information leads.
- Put the new information into the context of your existing information.
- Come up with examples of the ideas, especially from your own personal experience.
- Consider the evidence for or against an idea.
Memories are not isolated bits of info.
Everything that is encoded is added to a semantic network. In other words, what you memorize is added to what you already know.
Organization and Retrieval in the Long Term Memory
When does Wednesday come after Thursday?
Items recalled from long-term memory are clustered or grouped.
The clustering is based on some logical association between the items.
What is the first word that comes into your mind when you hear the word “red”?
Collins & Loftus (1975) proposed the well-known semantic network model.
In this model, each concept is linked with a set of others, which are in turn linked to still others.
A specific item can be linked with a category (rose® bush) or vice-versa (flower® daisy).
An object can be linked with a characteristic (knife® sharp), and vice-versa.
A place can be linked with an activity (classroom® sleep), and so forth.
The concepts and their links form a network.
Some linkages are stronger than others.
When a concept is activated, the activation can spread to linked concepts, activating them.
The shorter and stronger the chain of linkages, the more quickly one concept leads to another.
Retrieval is the process of putting the contents of long-term memory into working memory.
Retrieval often depends on a retrieval cue, a hint or prompt that triggers the memory.
When you are unable to recall information due to missing, inadequate or inappropriate cues you are experiencing retrieval cue failure.
Very often the unrecalled information is in fact in LTM.
Have you ever had something on the tip of your tongue? The tip-of-the-tongue phenomenon occurs when you have the feeling that you know a piece of information but you can’t quite recall it at the moment. These experiences have been studied by a number of memory researchers. Usually some part of the information can be recalled.
About half the time, people can recall the first letter of the word or name they are looking for and often they know the length of the word (in syllables).
Often people produce similar sounding, looking or meaning words.
The recalled bits may serve as cues to retrieve the missing piece.
The missing word usually comes to mind some time after you stop trying to think of it.
Tip-of-tongue experiences highlight that retrieval is not a simple all-or-none process.
There are different types of recall:
Recall or free recall is the retrieval of information with no cues.
Cued recall is the retrieval of information in response to a cue (complete the sentence).
Recognition is simply identifying a piece of retrieved information (as on a multiple choice test).
Serial recall is the retrieval of information in order.
It doesn’t do you much good to remember the directions to a friends house unless you remember them in order: “I know how to get there. You take six lefts and four rights.”
Sometimes each list item cues recall of the next: I remember students more easily in alphabetical order.
The serial position effect refers to the relative ease of recalling items at different positions on a list.
primacy effect: items at the beginning of the list are more easily recalled
recency effect: items at the end of the list are more easily recalled
The Encoding Specificity Principle
Recreating the original learning conditions improves retrieval.
I remember students names more easily if they don’t move around in the room.
The Context Effect
An encoded memory may include more than the specific piece of info that was being learned, such as environmental stimuli present at the time of learning.
These stimuli can serve as cues to aid in the retrieval of the learned information.
I have an easier time remembering students’ names in class than in the grocery store.
There seems to be a hierarchy of contexts: the closer the context to the original, the easier it is to recall (I recently saw a student on Block Island, although he looked familiar, it took me several minutes to realize that he was a student; I couldn’t recall his name for about a half hour).
Students do better on exams when tested in the room where they learned.
A memory may include not only external cues (as in the context effect) but also internal cues.
Free recall of things learned while intoxicated is slightly better when done intoxicated (though overall, learning and recall is worse when you are intoxicated).
When you feel good, you have happy memories; when you are blue, you have sad memories.
Where were you when you heard that OJ Simpson had been found not guilty?
A flashbulb memory is proposed to involve the retrieval of a number of details surrounding a rare and striking event.
Neisser & Harsch (1992) carried out an experiment on flashbulb memories:
Immediately after the Challenger disaster, students wrote down what they had been doing when they heard the news. Three years later, they were asked to recall the same things.
Most of the students were very confident of their recollections, but about a third were wrong. Seeing the proof of their errors, these students still felt confident that their memories were correct.
Improve your Studying
- Take enough time
- Spread out your study sessions
- Organize as you go
- Use visual imagery
- Explain it to someone
- Compare and contrast to reduce interference
- Spend more time on the middle
- Use contextual cues
Memory: Encoding, Storage, Retention, and Retrieval
Informally, memory is retention of information over long periods of time.Ebbinghaus studied memories by teaching himself lists of nonsense words and then studying his retention of these lists over periods of hours to days. This was one of the earliest studies of memory in psychology.
- Short Term Memory
- Working Memory
- Long Term Memory
- Spreading Activation Model
- Practice and Strength
- Depth of Processing
- Elaborative Processing and Text
- Forgetting: Gone or Inaccessible?
- Forgetting: Decay or Interference?
- Retrieval and Inference
- Other Facts about Memory
Let’s start by testing our memory span …
Contrast this with your ABC’s!
Short Term Memory
While Ebbinghaus studied retention over long intervals, later experiments studied forgetting over periods of seconds to minutes …
Short term memory was postulated to explain short term forgetting effects (as distinct from longer term effects).
- Between sensory and long term memory.
- Place to rehearse new information from sensory buffers.
- Limited capacity (Miller’s 7 plus or minus 2).
- Probability of encoding in LTM directly related to time in STM.
However, it is now believed that short term forgetting has the same character as long term forgetting. It just happens quicker because it involves information that is not learned as well. The shape of the forgetting curves are the same. Hence we don’t need to postulate a special type of memory.
Instead, we need a theory of
- Why we can rehearse only a limited amount of information at a time.
- How different memories get different strengths (and so are forgotten at different rates).
Long Term Memory
A simple observation: we often need to recall information that we learned long ago.
How quickly and reliably we recall it depends on:
- Activation: How long since we last used the information.
- Strength: How well we have practiced it.
Experimental Evidence: (Anderson 1976)
- Subjects learn some sentences. Some sentences are studied twice as long as others.
- Subjects must discriminate sentences they learned from distracters. They are tested for each sentence more than once, with varying intervening sentences.
- Both amount of study and how recently the information was accessed affect speed of response.
- However amount of study matters only if the information was not recently accessed (an interaction effect).
Delay (number of intervening items): Degree of Study: Short (0-2) Long (3 or more) Less Study 1.11 seconds 1.53 seconds More Study 1.10 seconds 1.38 seconds
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to test and report memory span and memory retention on some test subjects and study some of the factors that may affect memory span or memory retention.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variables are factors that you want to study. For example if you want to study the effect of time to learn on memory retention, then time to learn is an independent variable. Memory retention will then be a dependent variable.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Sample hypothesis for the above variables:
My hypothesis is that more time to learn results a higher memory retention
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Memory Span Experiments
Human short-term memory has a limited span. We will do a series of experiments to determine what that span is.
Memory span can be tested in many different ways, but they are all based on the number of bits of information that a person can recall almost immediately after receiving such information. Following is another example.
Usually a short list of words is presented, after which the participant is asked to repeat them. Dependent measure (the ‘memory span’) is the longest list a participant can reliably repeat. For most words and most people, this is about 7.
Generally, you should find your memory span is “longer” (i.e., can hold more items) for shorter words, letters that sound different and digits, than for longer words or letters that sound the same. Most find their span is 7-9 items for the former type, and 5-7 for the latter. (Again, lack of differences between the item types may just reflect too few trials.)
Experiment 1: Kim’s Game
Gather together an assortment of objects – pens, pencils, paper-clips, books, PostIt notes, etc. The stranger the object, the better! You need a large number of them – at least 10 or more. Place them in some compact arrangement on your desk, so that all items are visible. Find a few test subjects (Someone who you are testing his memory span). Ask him/ her to look at objects for 30 seconds and go back and try to write down all the items in the pile.
Compare each list with what you actually have in your pile. Compare the number of things each test subject remembered. Your results table may look like this:
|Test Subject||Number Of objects||Number of objects remembered||Number of objects remembered because of a relation.|
Now think or ask the subjects: what helped them remember certain things? Did they recognize things in your pile that they had themselves? Did that help? How many objects were remembered because of some relations? Do not pack the things away just yet.
Calculate the average score for your test subjects.
Questions: What conclusions can you draw from this experiment? What does this indicate about the capacity of short-term memory? What does it indicate that helps improve the capacity of short-term memory?
Experiment 2: “I went to market…..”
Gather your friends and make a group for this experiment. One person starts off with “I went to market and I bought a fish” (or some other product, or whatever!). The next person has to say “I went to market and I bought a fish and I bought a bread roll as well”. The process continues, with each person adding some item to the list each time. Keep going around the group until you cannot remember the list accurately. Make a note of the first time someone gets it wrong, and then record the number of items that you can successfully remember. Some of you will find it hard to remember more that a few, others will fare much better. Do this a few more times with different lists, and then calculate your average score, and your group’s average score.
Questions: What does this tell you about short-term memory? What do you do that helps you remember? What do you estimate is the typical capacity of human short-term memory? Is this a good test for short-term memory?
Experiment 3: Improving your memory
Many people can perform astonishing feats of memory; recalling the sequence of cards in a pack, or recounting pi to 1000 decimal places, for example. There are also adverts for `Improved memory’ (usually leading to success, or wealth, or other such inducement), and so the question arises, can you improve your memory abilities? This experiment shows you one technique. Experiment this on yourself and your friends (test subjects). Report the results.
Procedure: Look at the list below of numbers and associated words:
1 bun 2 shoe 3 tree 4 door 5 hive 6 sticks 7 heaven 8 gate 9 whine 10 hen
Notice that the words sound similar to the numbers. Now think about the words one at a time and visualize them, in as much detail as possible. For example, for `1′, think of a large, sticky iced bun, the based spiraled round and round with raisons in, covered in sweet white gooey icing. Got an image of that? Good! Now do the rest, using as much visualization as you can muster: imagine how things would look, smell, taste, sound, etc.
This is your reference list, and you and your test subjects need to know it off by heart.
Having learnt it, look back at another pile of items, as used in the Experiment 1. Mentally pick one (say, for example, a paper clip), and call it number one. Now visualize it interacting with the bun. It can get stuck into the icing on the top of the bun, and make your fingers all gooey and sticky when you try to remove it. If you ate the bun without noticing, you’d get a crunched tooth when you bit into it – imagine how that would feel. When you’ve really got a graphic scenario developed, move onto the next item, call it number two, and again visualize it interacting with the reference item, shoe. Continue down your list, until you have done ten things. This should take you about the 30 seconds allowed. Then return to your desk and try and recall the numbers in order, the associated reference word, and then the image associated with that word.
After all test subjects have repeated this experiment, your results table may look like this:
|Test Subject||Number Of objects||Number of objects remembered|
See the average number of items remembered. Compare it with the average number of items remembered in experiment number 1. Has your recall ability improved? What does this show you about memory?
Experiment 4: Menu design
Introduction: If our brains relate or group the materials in a certain logical order, then such logical order may also be used to simplify the memorization process.
Group the following functions under an appropriate heading, assuming that they were to form the basis for a menu-driven word-processing system – the heading you choose would become the menu title, with the functions appearing under the appropriate one. You can choose as many or as few menu headings as you wish. You may also alter the wordings of the functions slightly if you wish.
save, save as, new, delete, open mail, send mail, quit, undo, table, glossary, preferences, character style, format paragraph, lay out document, position on page, plain text, bold text, italic text, underline, open file, close file, open copy of file, increase point size, decrease point size, change font, add footnote, cut, copy, paste, clear, repaginate, add page break, insert graphic, insert index entry, print, print preview, page setup, view page, find word, change word, go to, go back, check spelling, view index, see table of contents, count words, renumber pages, repeat edit, show alternative document, help.
Optional: Once you have done this, try to recall the last list of items that you bought from market! How did you do? Did you find that you could remember as many as earlier? If not, why is this so? Is it any harder to remember the order of things as well as what they actually are? If so, why?
Return to your menu designs.
Show others all your headings, and ask them to group the functions under your headings. Compare their groupings with yours. You should find that there are areas of great similarity, and some places where the odd function is misplaced. Discuss the similarities and discrepancies.
Record your results in a table like this:
|Test Subject||Total number of functions||Common Groupings||Rate of common grouping|
Common groupings is the number of functions that a test subject placed in the same group as you did. To calculate the rate of common grouping divide the common grouping for each test subject by the total number of functions.
Questions: Why do some functions always seem to be grouped together? Why do some groups of functions always get categorized correctly? Why are some less easy to place under the `correct’ heading? Why is this important?
Count the number of items in your menus. What is the average? What is the disadvantage of putting all the functions on the screen at once? What is the problem with using lots of menu headings? What is the problem of using very few menu headings?
Consider the following: I can group my functions either into 3 menus, with lots of functions in each one, or I can put them into 8 menus with less in each. Which will be easier to use? Why?
(Optionally) Design an experiment to test your answers. Perform the experiment and report on your results.
Memory retention experiment
|Following is an experiment report for factors affecting memory retention. This study is focusing on two factors that are chunking data and time to learn. This information is only a sample for you to use and design your own experiments. You may want to focus on other factors that may affect memory retention. Factors such as age, education, gender, time of the day, food and nutrients and many other factors can be tested individually or in a group.|
For our experiment, we wanted to test two factors and their effects on memory retention. We believed that chunking data into acronyms and also the time allowed to memorize the data were significant factors when dealing with memory retention. In our experiment, we came up with 4 lines of 25 characters each; 2 of the lines had random letters, while the other 2 lines had well-established acronyms. We then allowed our test subjects to memorize one of the random lines and one of the acronym lines for 15 seconds each and write down as many of the letters as they could in sequence. Then we allowed the subject to memorize the other random line and other acronym line for 30 seconds and had them write down as many letters from that sequence. We then analyzed the data and created plots of the residuals and interactions. From our experiment, we were able to see that the chunking of data from recognizable acronyms was a large factor in memory retention, but the time allowed to memorize the sequence had little effect on the ability to retain memory information.
In the book Human Factors in Engineering and Design, by Sanders and McCormick, it is stated that the maximum number of bits that can be held in working memory is seven, with a plus or minus of two. A bit is an item of information, which could be a letter, digit, or word that is recognizable as a whole item on its own. A good example of this chunking of information is the letters HATEARDOOR. These 10 letters would be considered 10 bits of information if themselves, i.e. memorizing the H, and then the A, and memorize everything after that in order. However, if we chunked that sequence of letters into three groups: HAT, EAR, DOOR, we could memorize the whole sequence quite easily. This type of chunking helps increase our ability to memorize bits of information.
Using this as our basis, we want to test the factors of time and chunking on the capacity of working memory. We believe that the amount of time given to memorize a group of letters and whether or not the sequence of letters could be chunked into more familiar groupings of letters has a significant effect on the subject’s ability to remember the sequence of letters.
The experimental design used for this experiment was a two-factor factorial design, with the two factors being the time given to memorize the sequence and the arrangement of the sequence into recognizable chunks or not. We allowed the subjects a time limit of 15 seconds for one set of non-chunk-able and chunk-able lines, and 30 seconds for a second set. We counted a run when the subject had completed both sets, a total of four lines to memorize. The data was collected and tabulated below:
The Number of Letters Recalled for Each of the Thirty Subjects Tested
Time Given to Complete (Seconds)
|7 5 9 10 8 9 9 6 5 9||15 6 6 15 10 12 12 15 18 18|
|5 2 4 7 4 10 9 9 9 7||10 6 12 15 15 21 15 12 18 10|
The subjects that we used ranged from all age groups and we were not selective about whether we would test strictly males or females. We collected a total of 10 samples, and it was our goal of detecting a difference of at least two letters in memorizing the sequence. One issue that we came up with during the design of this experiment was that we did not know the variance of our population and therefore did not know the sample size that we should have collected for this experiment.
Another issue that we came up with was that we were concerned that the subjects would be able to memorize the sequences and so when we gave the second set of lines, we changed the starting point of the sequence of the letters and chunks, but left the actual sequence intact. We believe that this would eliminate the issue of subjects being able to have a portion of the sequence already memorized, while also not changing the difficulty level of the two sets by using different chunks or letters. Below are the lines that were used to test the subjects:
- Fifteen-seconds – Random Order: MBFQCITATMITBCSBNCCKPNQAB
- Fifteen-seconds – Chunked Order: QFCIBMATTMITCBSNBCKCPQNBA
- Thirty-seconds – Random Order: CKPNQABMBFQCTIMTATIBSCBN
- Thirty-seconds – Chunked Order: CBSNBCKCPQNBAATTIBMQFCMIT
It was our initial hypothesis that the ability to chunk the letters into groups and also the more time allowed to memorize the sequence of letters would both increase the subjects ability to memorize more of the sequence of letters. From the results and the table, we discovered that the ability to chunk the information into recognizable groups had a large significance on the subject’s ability to remember, but the greater time allowed to memorize the sequence actually had very little significance on the ability to remember. From this information, we were able to show that one of our initial hypotheses was correct, but the fact that the amount of time did not matter in the subject’s ability to remember seems a bit disturbing. It is just hard to believe that time does not play a role in one’s ability to memorize things, and there might have been a nuisance factor in our procedure that we did not account for.
One possible area for error in our experimental design might have been the fact that we were unable to calculate the correct sample size for our experiment, and therefore with a greater number of subjects, we would have been able to reduce the possible error in our data analysis. Another possible area of error might have been our subject sampling. It is a widely held belief that the age and sex of the subjects play a large role in the ability to memorize things, and in our experiment, we used a whole range of subjects. Perhaps if we narrowed our subjects down to a specific age range and sex, the data collected could be analyzed with a greater degree of freedom. The last possible area of error that we thought of was that since time was not a factor in our experiment, perhaps the amount of time used was insufficient to detect a significant factor. If we changed the time so that there was either a greater time difference than the 15-30 seconds time range that was used, we probably would have had a greater significant factor.
Analyzing the table results, there appears to be little to no interaction between the factors, time used to memorize and chunking of the information, and therefore we left the interactions of the factors out of our discussion.
For our experiment, we had hoped to prove that both the amount of time given to memorize a line of letters and the ability of the subject to chunk that line of letters into recognizable groups would play a large factor in the ability of the subject to memorize the line. We tested 10 subjects and asked them to view a line of non-sequenced letters for 15 seconds and see how much they could remember, then asked them to view a line of chunk-able letters for 15 seconds and see how many of those letters they could remember. We then repeated this procedure but using a new string of letters and 30 seconds instead of 15. After collecting and analyzing the data, it is our discovery that the amount of data a subject was able to remember was largely affected by their ability to chunk the information into recognizable groups, but that the amount of time, either 15 or 30 seconds, had very little affect on the subject’s ability to memorize the sequence of letters.
Montgomery, Douglas C. Design and Analysis of Experiments. Fourth Edition. 1997 John Wiley & Sons, Inc. Pg: 234-252, 667-674.
Sanders, Mark S. and McCormick, Ernest J. Human Factors in Engineering and Design.
1997, McGraw-Hill, Inc. Pg 67.
Sanders and McCormick, Human Factors in Engineering Design, 1997, pg 67.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
If you do any calculations for this project, write your calculations in this part of your report.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
List of References
Introduction to Psychology
James W. Kalat
Wadsworth Publishing Co. 1999
Dr. Daniel Suthers
Learning Research & Development Center
University of Pittsburgh
3939 O’Hara Street
Pittsburgh, PA 15260