Hello all,

Thanks in advance for any and all advice. I'm new to lmm and glmm and have
learned much from reading this forumn.

I am attempting to construct psychometric curves using glmm. Here is the
experimental setup.

Rats (n=8) are trained to discriminate between two stimuli (A,B).
Each rat is tested on four (4) different stimulus pairs (
(A1,B1),(A2,B2),...).
Each rat is tested on each pair for three days. The stimulus pair
presentation order is randomly selected.
Each day consists of ~300 trials evenly split between the two stimuli.

I would like to construct a psychometric curve of performance against
sampling duration. The rats select their own 'sampling duration' for each
presentation on each trial. I am interested in knowing if there is a
general effect where stimulus sampling duration predicts performance (I
expect a sigmoidal relationship). I also want to model the effects of the
stimulus set, the stimulus (A,B), and day when accounting for the random
effects (Subject, StimulusSet, Day).

Normally, in my literature, persons do 1) pool all trials across all
subjects and then fit a logistic curve, or 2) for each subject (or each
subject's session) fit a curve. I've never been satisfied with either
approach.

>From what I've been reading, it seems like glmm is a better way. Therefore,
oh wise denizens of this list, I ask for your thoughts.

My current model is:

glmer(Correct ~
SampleDuration+StimulusSet+Stimulus+Day+(StimulusSet:Day|Subject),
family=binomial(link="logit"), data=g)


When I run this, my results are not unexpected, but I'm always leery of
this. I *think* that this model fits the fixed effects of (SampleDuration,
StimulusSet,Stimulus, and Day). Additionally, I fit a random intercept for
each subject and a random slope for each subject that varies by
StimulusSet:Day.

I expect that there are some individual differences between the Subjects. I
also expect that there will be differences between StimulusSets and Days.
Specifically, some StimulusSets are easier than others and there is
learning from Day 1 to Day 3.

Does this all make sense, or, have I ventured down a terrible path?

Thanks

Donald

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