Data Variables

In the previous example, we created a derived parameter that determined the correct key based on the color of the Stroop stimulus. We can now create a data variable that determines whether the participant pressed the correct key. We can then use this data variable to create feedback for the participant.

Assume the same timeline as before and the same derived parameter:

from sweetbean.variable import (
    DataVariable,
    FunctionVariable,
    TimelineVariable,
)
from sweetbean import Block, Experiment
from sweetbean.stimulus import Text

timeline = [
    {"color": "red", "word": "RED"},
    {"color": "green", "word": "GREEN"},
    {"color": "green", "word": "RED"},
    {"color": "red", "word": "GREEN"},
]

# EVENT SEQUENCE

color = TimelineVariable("color", ["red", "green"])
word = TimelineVariable("word", ["RED", "GREEN"])


def correct_key_fct(col):
    if col == "red":
        return "f"
    elif col == "green":
        return "j"


correct_key = FunctionVariable("correct", correct_key_fct, [color])

Now we can create a DataVariable that determines whether the participant pressed the correct key. The 1 in the declaration indicates from which stimulus to get the variable (1 = previous, 2 = second previous, etc.). We can use the DataVariable directly as parameter in stimuli, or we can us it as input for a FunctionVariable to create the feedback text:

correct = DataVariable("correct", 1)

# Predicates
def feedback_text_fct(was_correct):
    if was_correct:
        return "That was correct!"
    else:
        return "That was false!"


feedback_text = feedback_text_fct("feedback_text", feedback_txt_fct, [correct])

Again, we can use this in a feedback stimulus.

fixation = FixationStimulus(500)
stroop = TextStimulus(2000, word, color, ["j", "f"], correct_key)
feedback = TextStimulus(800, feedback_text)

event_sequence = [fixation, stroop, feedback]


train_block = Block(event_sequence, timeline)
experiment = Experiment([train_block])

experiment.to_html("stroop.html")

There is one additional variable type, that we can use: The shared variable. It is a special variable that can be shared across different trials and can be updated via side effects: Shared Variables And Side Effects