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Stroop effect

Lab 2 introduces you to the nuts and bolts of another classic experimental psychology paradigm, the Stroop
effect. Data collection will occur on the computers. Each student will complete a 5-10 minute Stroop experiment.
The data will be analyzed and reported in a full APA style research report.
The main goal of this experiment is provide a concrete example of a 2×2 Factorial Design. As well, we will learn to relate theory and data.You will be taught about the horse-race model of Stroop, and you will use this model to predict the data from the class experiment.
The class experiment has two goals. First, to replicate the Stroop effect. Second, to test a manipulation that will reduce the size of the Stroop effect. In this case, the manipulation will be task. For half of the trials, you will identify the color, and for the other half of the trials you will identify the word.
In your research paper you will be required to introduce the Stroop effect, and explain the horse race model.
You will explain how the horse race model can be used to predict which task will lead to the largest Stroop
effect. You will describe the methods and results. The results will be reported in a figure or table (your
choice).
NOTE: when you report the results you MUST report all main effects, the interaction, and any
necessary post-hoc tests.
Things you will learn:
Using reaction time as a dependent measure
2×2 Factorial designs
Reading and citing primary source material
Predicting data based on a theory
Control in experimental design
Background on the Stroop paradigm:
The Stroop paradigm involves the identification of a bi-valent stimulus. For example, you could be presented
with a word, that is written in a particular color. Dimension 1 is the word (e.g., BLUE), and dimension 2 is the
color (e.g., RED). The resulting stimulus would look like this: BLUE. In this case the word and color do not
match, this is called an incongruent stimulus. A congruent stimulus occurs when the word and color dimension
match (e.g., BLUE). In a standard Stroop experiment you would be presented with these kinds of congruent
and incongruent items. The task usually involves identifying the color dimension as quickly as possible, while
ignoring the word. The Stroop effect itself is the finding that reaction times to identify the color dimension are
faster for congruent trials (when the word matches) than incongruent trials (when the word mismatches). The
effect is interesting because people are unable to ignore the word dimension even though it is not part of their
task. The Stroop effect is usually used to measure your ability to selectively attend to information in your
environment. The review paper by Macleod (1990) demonstrates the popularity of Stroop research, and the
many different ways that this task has already been studied.
Background readings:
Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental
Psychology, 18, 643-662.
Macleod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review.
Psychological Bulletin, 109, 163-203.
-Pages 187-188 describe the horse-race model (it is termed the relative speed of processing account).

Writing the paper
Refer to the lab manual for more resources on writing APA style research-reports.
1. Use the same general APA formatting rules that you learned in lab 1.
2. Create a suitable title for the paper
3. Write the abstract :
-no more than 250 words (between 150-250 words)
-The aim is to very briefly describe the main experimental aims, how they address the theory at hand,
and the basic pattern of results.
The introduction (around 2 double-spaced pages)
The goal of the introduction is to put the research into a broader context, and then narrow the focus to describe
the specific research aims.
A. Opening section: (starting broad) – about 1 paragraph
-Define the general problem of selective attention.
-Give an anecdote that describes a real-world situation involving the need to select task-relevant
from irrelevant information
-Link this real world situation to the Stroop paradigm (this provides an argument that the Stroop
paradigm can be used to understand how selective attention works
B. Middle section: (discussing prior work)
-Define the Stroop paradigm (1-2 paragraphs)
-cite the original paper
-describe the basic features of a Stroop experiment
-Describe the assumptions of the Horse-Race model (1-2 paragraphs)
-e.g., the model assumes color and word information have different processing times –
Mention that the purpose of the experiment is to test predictions of the model.
C. Final section: (narrowing down to the aims of the experiment)
-Explain that the specific aim of the experiment is to further test the horse-race model of the Stroop
effect.
-Briefly describe the independent variables that will be manipulated –
Congruency (congruent vs. incongruent
-Task (name color vs. name word)
-Does the model predict a main effect of Congruency?
-Does the model predict a main effect of Task?
-Does the model predict an interaction between Congruency & Task?
-Briefly explain what participants will do in your experiment.
Methods (1-2 pages)
The methods section should be a complete recipe that anyone could follow to replicate your
experiment. At the same time, you should be as brief as possible.
-Participants
-how many people? where did they come from?
– Materials
-How many words, how many colors
-How were they combined to make congruent and incongruent items
How many congruent items
How many incongruent items
-Procedure
-What was the design, IVS, DVs, within or between?
-Describe the trial-sequence
Results
The result section is used to report the patterns in the data, and the statistical support for those patterns.
Refer to the lab manual for help on reporting statistics from a factorial design. – Describe the statistical
analysis
e.g., mean RTs from each condition were submitted to a 2(Task:name word vs. color) x 2
(congruency: congruent vs. incongruent) within-subjects ANOVA. -Tell the reader where they can see
the data.
-e.g., the results of experiment 1 are presented in table 1, or in figure 1
-you will have to make a table or figure to display the data in your paper –
Describe the pattern of each main effect
-The main effect of Task was …
-The main effect of Congruency was
-Describe the Congruency X Task interaction
-You will report the interaction the same way as a main effect.
Discussion
The discussion can be used to briefly restate verbally the pattern of the most important results, and then to
relate the results to theory and ideas developed in the introduction.
a.Introduction to the discussion
Summarize the results (the main effect of task, the main effect of congruency, the interaction effect between
task and congruency) in everyday, easy-to-understand, language.
(No statistics, no numerical values! Just a summary of the main findings)
b. Interpretation of the results
Discuss how the data can be explained by the Horse Race Model.
Discuss whether or not the model accurately predicted the patterns of data.
Discuss whether the results have been interpreted with respect to the hypothesis
Explain whether the present findings are consistent with the previous studies (Macleod, 1990; Stroop, 1935).
Compare your findings with the previous research findings. Explain how your results are similar to
the previous research findings (e.g. the original paper) and how they differ from them! If they are
different from the original paper we replicated explain in what way they are different and why.
c. Further discussion
Discuss the possible limitations, potential problems with the current research (e.g., order effect, other
potential confounds).
Discuss the shortcomings of your study.
Were there problems with the stimuli, testing conditions, participant previous experience that could have
affected the outcome?
Does this finding create new questions?
References
-include citations used in the paper
Figures and Tables