Palamedes Toolbox Forum

I've been working through some data from a student who is using PAL_AMUD() to run a simple 1-up 3-down staircase. We've noticed an unexpected behaviour in that the function appears to act like a '1-up 1-down' until after the first reversal.

In principle, this behaviour makes sense, since it means ...

When using PAL_AMPM(), can the values supplied for priors (priorAlphaRange, etc.) be weighted according to a distribution? For example, in a temporal order judgement task, I expect threshold to be somewhere around 30 ms. However, I am running the task on a group of people that could include some ...

I'm running an experiment in which an intensity of zero is certainly impossible to perceive. I want to avoid a Psi object choosing to present several trials at zero, since I already know what the outcome of this will be (50% seen for a 2AFC task). Of course there is value in occasionally presenting ...

Thanks for this Nick. Just to check I've understood you – are you saying that although it might be a good idea to refit data collected using Palamedes, this will make very little practical difference? If that's the case, then we will stick to the simpler method of calling PsiObject ...

I notice that Psignifit takes a different approach to defining beta: rather than giving the value for the slope of the function, Psignifit instead defines it in terms of 'width', i.e. the width of the interval over which the psychometric function rises (typically from 0.1 to 0.9). This feels like a ...

In order to better understand this, I have tried plotting data from a PsiObject using PAL_PFML_Fit(), which gives very different values for threshold as compared to the values obtained from PsiObject.threshold(end) or PsiObject.thresholdUniformPrior(end) . So there must be something different about ...

One thing that causes much confusion in my lab is the fact that beta (AKA 'slope') must be defined in logarithmic terms, whereas all other parameters (alpha, gamma and lambda – threshold, guess rate and lapse rate, respectively), are all taken 'as-is'. This means one has to be very careful when ...

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 ...

Following a Psi procedure to collect response data (implemented using the PAL_AMPM<...> functions), I've been told that it is good practice to estimate threshold by manually sending the intensity and response data into a psychometric function fitting procedure. For example, if I used a @PAL ...

In PAL_AMUD (staircase procedure), there is a field .x and another .xStaircase. What is the difference between these two fields? They seem to be identical most (if not all) of the time, so is it safe to use the values from either when constructing a psychometric function?