[R-sig-ME] lmer - individual slopes

[Cátia Ferreira De Oliveira]

Hello,

I hope you had a lovely winter break.
I am interested in extracting the individual slopes for an experimental
design where individuals are asked to do a task with two conditions -
congruent and incongruent. These participants are also divided into groups
- sleep or awake. Should I consider group allocation in the model? The
individual slopes are extracted so that we can check whether the rate of
learning is stable across sessions.
Should we use:

a) lmer(Response times ~ Congruency + Group + (Congruency| Participant)

Or is it ok to just have it as:

b) lmer(Response times ~ Congruency + (Congruency| Participant)

Thanks

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