QuestHandler: pTreshold & StartValSd

[MaudBeeckmans]

Hi,

I am trying to construct my first experiment using the QuestHandler and ran into some problems. A simple description of the experiment is as followed: participants have to detect a small target inside a grating. A staircase procedure (using the questhandler) is used to adapt the opacity of the target. The goal is to make sure participants have an accuracy of 70%. I wanted to use the QuestHandler implemented in psychopy, however when testing the effects of adapting the pTreshold & StartValSd I ran into some problems. I thought the pTreshold defined the goal-accuracy, however this seems not to be the case: I wrote a short script that uses a fixed response-array to test first the difference in the staircase._nextIntensity with different pTresholds, next with different StartValSds. Weirdly, the staircase output is exactly the same when using different pTresholds.
Is it not correct that the pTreshold defines the goal-accuracy and how can I create an accuracy of 70%? The test-script is added below. And how could I make sure the opacity of the target is adapted in such a way that the accuracy is 70%: what parameters of the QuestHandler define the accuracy, what output of the questhandler should I use (mean, mode or quantile) and is the QuestHandler appropriate for the goal of my script?

Thanks in advance.

Test-script:

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from psychopy import visual, data, event, core, gui import numpy as np   n_trials = 84 n_blocks = 2 Opa_array = np.empty([n_blocks, int(n_trials/2)])   responses = np.concatenate([np.ones(35), np.zeros(42-35)]) responses = responses.astype(int) np.random.shuffle(responses)   #%%Test differences in Tresholds Tresholds = np.array([0.60, 0.70]) for block in range(n_blocks): Tres = Tresholds[block] staircase1 = data.QuestHandler(startVal = 0.25, startValSd = 0.15, nTrials = n_trials/2, pTreshold = Tres) for i in range(int(n_trials/2)): Opa_array[block, i] = staircase1._nextIntensity resp = responses[i] staircase1.addResponse(resp) print(‘The staircase output with pTreshold = {}’.format(Tres)) print(staircase1.mode(), staircase1.quantile())   print(‘StartValSd = {0}; pTreshold = {1}’.format(staircase1.startValSd, Tresholds)) print(‘Difference between the 2 created intensity_arrays’) print(Opa_array[0] - Opa_array[1])   #%% Test differences in StartValSd StartVals = np.array([0.15, 0.25]) for block in range(n_blocks): Tres = 0.7 StartVal = StartVals[block] staircase1 = data.QuestHandler(startVal = 0.25, startValSd = StartVal, nTrials = n_trials/2, pTreshold = Tres) for i in range(int(n_trials/2)): Opa_array[block, i] = staircase1._nextIntensity resp = responses[i] staircase1.addResponse(resp) print(‘The staircase output with StartValSD = {}’.format(StartVal)) print(staircase1.mode(), staircase1.quantile())   print(‘StartValSd = {0}; pTreshold = {1}’.format(StartVals, Tres)) print(‘Difference between the 2 created intensity_arrays’) print(Opa_array[1] - Opa_array[0])

buran write Nov-29-2020, 03:07 PM:
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