Exercise 2: The stroop effect

Accept the exercise

In this exercise we’ll put some of what we’ve learned so far together into an simple experiment demonstrating the The Stroop Effect. Then we’ll gradually build this codebase out into a full experiment and implement some snazzy things like speech recognition.

import time
import sys
import random
from psychopy import visual,event,core,gui

stimuli = ['red', 'orange', 'yellow', 'green', 'blue']

win = visual.Window([800,600],color="gray", units='pix')
placeholder = visual.Rect(win,width=180,height=80, fillColor="lightgray",lineColor="black", lineWidth=6,pos=[0,0])
word_stim = visual.TextStim(win,text="", height=40, color="black",pos=[0,0])
instruction = visual.TextStim(win,text="Press the first letter of the ink color", height=20, color="black",pos=[0,-200])
while True:
    cur_stim = random.choice(stimuli)
    word_stim.setText(cur_stim)
    word_stim.setColor(cur_stim)
    placeholder.draw()
    instruction.draw()
    word_stim.draw()
    win.flip()
    core.wait(1.0)
    placeholder.draw()
    instruction.draw()    
    win.flip()
    core.wait(.15)

    if event.getKeys(['q']):
        win.close()
        core.quit()

Once you’ve successfully run this code and understand what all the lines do, proceed to the following exercises.

Exercise 2 parts

1. Create a fixation cross using a TextStim object visual.TextStim set text to “+” and color to “black” and height to 15. Make the fixation cross appear for 500 ms before each color word, and disappear right before the color word appears.

2. Rather than cycling throught the colors, use event.waitKeys() to wait for a response (e.g., “o” for “orange”). Your script should only accept ‘r’, ‘o’, ‘y’, ‘g’, ‘b’ (the first letter of each color) and – to make testing easier for you – ‘q’ for quit.

   Tip

   Make sure your code has just the functionality it needs, e.g., for part 2, you don’t need event.getKeys(['q'])

3. Compute the reaction times – the time it takes to respond from when the color word appears, to when the user presses a key, in milleconds (e.g., .8 secs should show up as 800). Store these in a list called RTs. (Use psychopy timers)

   Tip

   Append each reaction time to the RTs list after every response

   Print the list to verify that the reaction times are correct (e.g., if you take approx 1 second to respond, is it recording 1000?). Your submitted code should have this print statement.

4. Now let’s implement some feedback. If the user responded correctly, do nothing. If the user responded incorrectly, show “Incorrect” in black letters and add a 1s time delay before going on to the next trial.

5. Now, instead of waiting for a response forever, let’s implement a timeout. Show accuracy feedback as before, show “Too slow” if the user takes more than 1.5 secs to respond.

6. Introduce incongruent trials by showing words in the “wrong” color, e.g., “yellow” printed in green. To do this, define a function called make_incongruent() which takes in a color as an argument and returns one of the other colors in stimuli that’s different from the one being passed in. Then set the color word’s color to this new value, thereby creating an incongruent trial.