Manually adding a trial to a PAL_AMPM object?

[Matt J Dunn]

The Psi method (via PAL_AMPM<...> functions) provide an intensity value (.xCurrent) at which the current trial must be presented. As far as I can tell, this isn't a suggestion but a requirement (i.e. you can't then present at a different intensity, since the function PAL_AMPM_updatePM() doesn't allow you to input an alternative intensity.

Is there no way to manually add the results of trials presented at other intensities to the PAL_AMPM object? For example, I could manually add an entry to the .x and .response fields of the MATLAB object (known as PM in the demos), but I wonder if this workaround could upset the Psi procedure in other ways.

The reason I ask is that in some patient populations it helps to be able to include occasional trials at high intensity, for encouragement. And since I am presenting at these intensities, it makes sense to incorporate the response data into the Psi object, rather than simply throw it away. After all, more data can surely only help to improve the model fit?

[Nick Prins]

This has now been added as an option (version 1.11.3; 24 February, 2023). Use the 'xIndex' argument in PAL_AMPM_updatePM to specify which stimulus intensity was presented on the trial. Note that the forced intensity must be one of the stimulus intensities included in the PM.stimRange vector. We make this explicit by asking to specify the index of the desired intensity in the PM.stimRange vector, not the stimulus intensity itself. For example, if

Code: Select all

PM.stimRange = [0.1 0.2 0.3 0.4 0.5];

and the method suggests to use 0.2 (by setting PM.xCurrent to 0.2) but you wish to override and present a stimulus at intensity 0.4 then let the method know that you used 0.4 like this:

Code: Select all

PM = PAL_AMPM_updatePM(PM,response,'xIndex',4);

Note that the 'xIndex' argument is optional: If you use the suggested stimulus intensity, you can leave out the 'xIndex' argument:

Code: Select all

PM = PAL_AMPM_updatePM(PM, response);

Type 'help PAL_AMPM_updatePM' for more information on how to use this feature. Basic usage is demonstrated in PAL_AMPM_Override_Demo.m in the PalamedesDemos folder.