I am trying to use the staircase to find the JND for a phonetic feature (degree of nasality, without nasality being contrastive in the language, so this is a degree perception, not a category perception).
I have already used the staircase in PsychoPy and it’s working great, but I’ve always used it to find the 50/50 threshold between two categories. For this new experiment, I’ll need to use a 2AFC in which the subject will hear a standard and then assess which of the 2 following sounds had more nasality.
My first question is this - if I’m going to use the built-in PsychoPy analysis functions, can I simply use a 1-up/1-down procedure like I do with my previous yes/no staircase procedures? Or do I need to use 1-up/3-down (or something else). Since PsychoPy uses all of the data (rather than just the reversals) to build the pyschometric function, then it should be fine to use 1-up/1-down, but I’m certainly not sure on that.
My second question is this: In the analysis of the resulting data, am I using the formula correctly (modified from my use of it in a 50/50 threshold):
fit2 = data.FitWeibull(levelsList, responseList, expectedMin = 0.5) MyJND = fit2.inverse(0.80)
My understanding is that this will give the 80% detect a difference threshold for the continuum of nasality I’m using. Is that right? Is there a reason to use 80% detection as the marker of JND rather than 75% or 60%?
Thanks for your help,