A classic psychological experiment is that of Stroop (1935) who wanted to test if the brain processed certain types of information faster than others, i.e., if certain information is processed automatically while other information is processed deliberately. He set up an experiment to see if reading was faster than naming. He presented participants with lists of words written in various coloured ink and asked them to name the colour of the ink. One list contained colour words (e.g., red, blue, etc) and the other nonsense syllables. He found that it took longer for participants to name the colour words than the nonsense syllables when the print colour was incongruent to the colour name. For example, the reaction time was longer for participants to name the ink colour of the word "blue" written in red ink than a nonsense syllable in red ink. He believed that this delay in reaction time was due to interference of automatic processes (reading) on deliberate processes (naming). While there is some controversy over the exact explanation of this effect, the "Stroop effect" is a highly reliable one.

The experiment you will be conducting is a modification of the classic Stroop experiment, using numbers rather than letters, designed by Elmes, Kantowitz, and Roediger (1989). Our question is: Are reading and naming deliberate processes or do they occur automatically? You will be using a repeated measures design (the same participants will be tested on all levels of the independent variable). There are three levels of the independent variable (type of list), (colour words, non colour words, and xxx's) The dependent variable is the time it takes to read a list (in seconds) while making as few errors as possible.

The means of the these three groups will be compared in the statistical analysis. By now you know that if we want to look at means from three or more groups or conditions, we use an Analysis of Variance (ANOVA). An ANOVA answers the question "Is the variation among the means of the groups significantly greater than that expected by chance?" Think about the order in which participants will be tested. What is your hypothesis? For example, you may predict that it will take longer to complete the number of digits list than the numbers list because the numbers in the digits list interfere with counting the digits. You may formulate a similar hypothesis with the variation of the stroop that you are using.  Would this support the theory that some aspects of reading and naming are automatic? Do you have any other hypotheses? What about counting the plus signs? Remember to formulate your hypothesis(es) before you begin to recruit participants.

Participants

Chose a convenient sample of 12 participants (e.g., people in the SUB or in your dorm). Be sure to include how you obtained your sample (i.e.: volunteered, participated of their own free will, received credit, were paid, etc) in your report and include descriptors such as gender, age, etc. that you feel relevant. Before recruiting participants you should consider how subject factors might affect your results. Consider factors such as gender (will you use all males, all females, or some of each sex), age (will you any age or only those between 19 and 24), and will it matter if the subject is a known to the experiment(s) or not. If you decide to only use people in their 20's how will you determine how old they are? Can you and will you control for these factors? Are there other factors you should be considering? Note that other Psyc 2023 students cannot be used. Do you know why?

Apparatus or Materials

Stopwatch

The three lists (describe)

Procedure

When you are approaching and running participants, you need to tell all participants:

1) the purpose of your study (not the expected results)

2) that it is part of a course requirement

3) that participation is voluntary and subjects can stop at any time throughout the experiment

4) that you do not need names - assuring their confidentiality

5) that the data will be analyzed as a group

Participants must first read the instructions on the top of each list carefully and let the experimenters know when they are ready to begin. Experimenters need to accurately record the time needed for each subject to complete each of the three lists. One of the experimenters should say start and immediately start the stopwatch (or whatever is being used) and stop it as soon as each subject has completed each list. The same experimenter should record the time for every subject. Each experimenter should understand their tasks and conduct these tasks identically for each and every subject.

It is important for you to record the times for each subject according to the list that he or she is reading. You will need to counterbalance the order in which the lists are presented so that you do not get an order or practice effect. Therefore, participants will not be doing the lists in the same order. For example, subject 1 may require 28, 23, and 17 seconds to complete the lists while subject 2 may require 18, 22, and 26 seconds. However, subject 1 did list 3, then 2, and then 1 while subject 2 did list 1, then 2, and then 3. The reaction times should be recorded into the table below.

For complete counterbalancing each of the following combinations would be given to two participants, 123, 132, 213, 231, 312, 321.

 Once the procedure is completed, you need to:

1) thank the participants for their participation

2) debrief the participants - tell them

a) your hypotheses

b) where they can obtain more information

c) how to obtain the results if they so desire

You will run a one-way ANOVA to test if there is a difference in the reaction times between the three groups. If you find significance (p<.05) with the 1x3 ANOVA, then you will need to probe the data using paired t-tests to determine between which groups the significance occurred. You should also include a figure illustrating the three means. The SPSSwin commands on included at the end of this section.

If you find significance, what does it mean? If you do not find significance what does it mean? How does this information help us? What factors may have influenced the findings? How might you improve on this study; either through controls, by expanding the design, or changing the design? How does this relate to the original Stroop effect? Do you think the use of a convenient sample was a problem here? Why or why not?

Elmes, D.G., Kantowitz, B.H., and Roediger, H.L. (1989). Research Methods in Psychology,  (3rd Ed.) New York: West Publishing Company.

 MacLeod, C.M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163-203.

 Stroop, J.R., (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662.

 NOTE: A full APA style report is required. You need to obtain at least two recent relevant articles in addition to the above. Remember PsycLIT. Use these articles in the introduction and discussion sections of your paper to strengthen your ideas.

Note: record time in seconds for the following conditions: Be careful to record all "numbers" times in column 1, "pluses" in column 2 and "digits" in column 3, as presentation order will vary
 

Note:  To get your data to display to 2 decimal places,  when you open SPSS 8.0,  go under the Edit menu and choose Options,  then click on the Data tab,  on the left in the middle there is a box to display decimal places, change from 0 to 2.  This must be done before entering data to take effect.

Once in SPSSwin, enter the data in the Data Editor window. Name the 3 variables. To do this click on the var1 cell, or click on define variable under the data menu at the top. A variable name dialog box will open, name the first variable or column numbers, click on OK, click at the top of the second column and name it pluses, repeat and name the third column digits

Enter the scores for each of the subjects for list 1 , list2 and list3 .

To begin entering scores, click on the first cell of variable 1, enter the number and press enter or use your arrow keys

After all scores are entered, save your data file, choose File on the top menu bar, and click on Save data. Type stroop.sav in the "file name" box and make sure it is being saved in the correct directory. Click on ok.

Print your data file. Choose printer setup from the file menu, to ensure the correct printer has been selected. Then, choose print from the file menu.

To get descriptives (means, standard deviations, etc.) Choose Statistics on the menu bar. Highlight Summarize, then Descriptives. This information will be presented in your output window.

To run a repeated-measures anova:

Under Statistics, choose General Linear Model, choose GLM- Repeated Measures. A Repeated Measures Define Factors dialog box will open. Enter "list" in the Within Factor Name box. Enter "3" in the Numbers of levels box. Click on Add then Define.

-A Repeated Measures ANOVA dialog box will open. Highlight "numbers" in the left column . Click on the Ø to specify it as variable 1, highlight "pluses" Ø variable 2, "digits" Ø variable 3. Now click on the Model button at the bottom of the dialog box. Click on the Multivariate tests box so that the box does not have an X in it. Click on Continue. Click OK.

You will now want to save and print your output file.  In terms of the information needed for this lab, much of the output given by the anova command is not needed for our purposes. You need only the last block of output: tests involving lists within-subjects effect. The tests of between-subjects effects and Mauchly to epsilon figures can be deleted.

To save output choose Save Output from the File menu.

Print output.

Now you want to create a graph. Click on the Graph menu at the top. Choose Bar . A dialog box will open, click on Simple and also choose Summaries of Separate Variables. Click on Define. Highlight all 3 variables and click on the Ø to move them to the right box Bars Represent. They will appear as MEAN (numbers), etc. Click on OK.

A chart carousel will appear. The graph requires some edits before saving and printing. Click on the Edit button. Choose the * button . Change the size to medium. Double click on the scale axis "mean" or choose "axis" under the Chart menu. Center justify the axis.

Save the chart; File, Save Chart.

Print the chart: File, print

Note: the chart will be included as a figure in your lab report. Both the SPSSwin data and output printouts should be stapled to the back of your report, just before the grading sheet.

Extra Analysis:

If you find that a significant difference exists between groups, (ie. A significant F), then you should conduct t-tests to determine where the significant difference lies. The planned comparisons (t-tests) you perform, (maximum of 2) will depend on what you hypothesized in terms of your results. If your F was significant, markers will expect that t-tests be conducted and included in your lab report.

To do the t-tests, under the Statistics menu, choose Compare Means; Paired samples t test. Highlight the 2 variables you want to examine, they will appear in the Current Selection dialog box. Click on the _ to list them in the right column and click on OK. Determine whether they are significant at the .05 level. Make sure you print out this output as well and include in lab report.