Correct use of StopInterval in QuestHandler

Hi everybody,

I’m trying to use the questHandler with the stopInterval termination rules. I read the doc of the QuestHandler class but I can’t understand what does it mean :

stopInterval: None or a number
The minimum 5-95% confidence interval required in the threshold estimate before stopping. If both this and nTrials is specified, whichever happens first will determine when Quest will stop.

In my current test I have images with a level of noise between 0 and 1 and I use the QuestHandler object like this :

``````staircase = data.QuestHandler(0.5, 0.5, pThreshold=0.51, stopInterval=0.01, delta=0.01, beta=3.5, gamma=0.1, minVal=0.0025, maxVal=1, nTrials=30)

``````

In this line I choose `stopInterval` randomly and it stop in 30 trials. I don’t now how to calculate the correct value in order to have a 95% confidence level.

I also checked the code of the questHandler class and I saw that they compare the result of the `confInterval()` function and the value of `stopInterval`. The experience stop if `confInterval() < stopInterval`.
So I print my values of `confInterval()` during my experience and the values are between 0.22 at the beginning and 0.13 after 30 trials.

Do you have any ideas how to calculate stopInterval in order to have a 95% confidence level?

Apologies for resurrecting an old post - I’m also trying to figure this out. Am I correct in believing that stopInterval = 0.05 is requiring a confidence interval of at least 95%?

As I do my trials (spatial 2AFC contrast discrimination), the figure reported by stairs.confInterval(True) reduces. Is this the expected behaviour?

Kind regards,

Martin

I am in the same boat. I cannot find a clarification regarding the proper usage of stopInterval. I am assuming it is related to the certainty regarding QUEST’s estimate: a large value of stopInterval would allow QUEST to end sooner, whereas a small value would force QUEST to continue until the CI is very small.

However, it is not clear what units stopInterval should be specified in:

• Is the value specified by stopInterval in units of the staircased variable (e.g., intensity)? For example, if the confidence interval surrounding the estimate ranges from 2 to 3, then a stopInterval of 1 would terminate the staircase.

• Alternatively, is stopInterval specified in internal grain (i.e., arbitrary) units? For example, if the confidence interval surrounding the estimate ranges from 0.2 to 0.25 on the internal grain, then a stopInterval of 0.05 would terminate the staircase.

Martin and Cynthia-- the level of significance associated with the estimated confidence interval (e.g., 95%) is separate from the size of the confidence interval (e.g., in intensity or arbitrary units). I could have a confidence interval ranging between 3.50 and 9.00 or between 10.00 and 10.01, both could have a 95% level significance. That just means that there is a 95% chance that the estimate lies between 3.5 and 9 or between 10 and 10.01 for both CI’s. The size of each CI is 5.50 and 0.01, respectively. I think this is what stopInterval is defining…

Clarification would be much appreciated.