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QuestHandler Staircaise with 75% correct threshold

Hello,

we’re using the staircase procedure to calculate a threshold for a visual yes-no detection task. Participants are supposed to have a 75% threshold of answering correctly. We set up the QuestHandler as described in the documentation, but when trying out the titration, we get around 100% correct instead of the desired 75%. What are we doing wrong?

Thanks in advance!

staircase = QuestHandler(
                                startVal=0.5,
                                startValSd=0.2,
                                pThreshold=0.63,  #because it is a one up one down staircase
                                gamma=0.01,
                                nTrials=100,
                                minVal=0,
                                maxVal=1
                                )
    for contrast in staircase:
        key = []
        stimulus.opacity = contrast #update the difficulty or contrast from the staircase
        while not key:
            draw_stim(noise, stimulus, reddot, annulus) # draw the stimulus
            window.flip()
            key = kb.getKeys(keyList=keys)
        if keys[1] in key: # if they didn't see it
            print("no")
            response = 0
            staircase_means.append(staircase.mean())
        else:
            response = 1
            print("yes")
            staircase_means.append(staircase.mean())
        staircase.addResponse(response)
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