The Stroop Effect
-- PY01 Lab One
Date: 09/21/04
TA: Jan Benjamin Engelmann
Email: jbe@Brown.edu
Office: R383, Hunter Lab
Office Hours: Friday 2-3
Agenda
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Outline of Experimental Procedure
Run the experiment
What does the experiment show us?
Exploratory Data Analysis (EXCEL)
– Frequency Histograms
– Mean and Standard Deviation
– Bar Graphs
• Next Lab
– More on Data Analysis
– How to write a Lab Report
Experimental Procedure
• Work in pairs of 2
• Experimenters’ Task
– Start timer
– Record time and errors of participant
– For 4 stimulus cards
• Participants’ Task
– Say aloud the color of the ink
– As fast as possible!
– As accurately as possible!
– From top left to bottom right
Experimenter’s Task
present stimuli
start timer
record errors (answer key)
stop timer
record time
reset timer
start next card (according to specific order)
Check list
• Every booth should have:
– One set (4 pieces) of cards;
– One piece of answer key;
– One timer
• Every person should have:
– One sheet for your results
– Four sheets for class results
• Are all items present?
• Start the experiment!
Automaticity
• What does the experiment tell us?
• Routine behaviors become automatic
– Driving
– Reading
– Cycling
• That’s a good thing!
– Frees mental resources.
• Trade-off: Obligatory processing
– Can cause interferences
• Sources of interference:
– Semantic inconsistency
– Lexical priming
Descriptive Statistics
• How to interpret data?
• What is the Mean?
– Measure of Central Tendency.
– Most representative value in the data
set.
• Arithmetic Average.
• X bar = ∑X/N
• How about the Standard Deviation?
– Variability – deviation from CT
– Deviations of each observation from the
mean
– √[(X-Xbar)2/N]
Standard Error of the Mean
• One measure of variability.
• SEM = Standard Deviation / √ N
• Better reflection of inferential
statistics.
– You can estimate whether groups differ
significantly.
Exploratory Data Analysis
• Frequency histograms
– Reflects underlying distribution of
observations.
• Bar graph
– Displays Mean Reaction Time across
Conditions.
– Include Measure of Variability.
• Scatter plot
– Shows relationship between 2 variables.
– Correlation.
Creating Graphs in Excel
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Frequency Histograms
How many bins/intervals?
Rule of thumb: 10-12 (depends on data).
Reflects # of observations in each interval.
Is data normally distributed? Where is the
middle? How wide is the distribution?
• IN EXCEL:
• Size of interval = difference between
largest and smallest value and divide by
#bins-1.
• Use graph wizard.
Frequency Histogram
4.5
4
# of Bins = 10
Bin Size 45 units
# of Observations
3.5
3
2.5
2
1.5
1
0.5
0
75-115 115-155 155-195 195-235 235-275 275-315 315-355 355-395 395-435 >435
Bins (Intervals)
Bar Graph
Reaction Time as a Function of Condition
500
Reaction Time (ms)
450
400
350
300
250
200
150
100
50
0
A
B
C
Condition
D
Time Accuracy Trade-off
• Create Scatterplot.
• Relationship between the two
variables?
• What does that tell us about the RTAccuracy trade-off?
Scatterplot
600
Reaction Time (ms)
500
400
300
200
100
0
0
2
4
6
Errors
8
10
12
For Next Week
• Create Graphs:
– 4 HISTOGRAMS
• Card A time; Card A error
• Card C time; Card C error
– 2 Bar Graphs
• mean time and number of errors
– Scatterplot
• Mean Time and Error for each participant
• Plot Mean Time (y) vs. Mean Error (x)
• Label your axes clearly!!!
• Think about the data and what it means.
• Questions in hand out.
Appendix
Gaussian/Normal Distribution
Mean = 100
Central
Tendency
Dispersion/
Spread
Std Deviation = 16