I want to make a model including interaction term of factor 1 and factor 2.
But i don't understand difference of models like
m <- lmer(RT ~ fac1 * fac2 + (1+fac1*fac2|subject), data = df)
m<- lmer(RT ~ fac1 : fac2 + (1|subject) + (fac1:subject) + (fac2:subject), data = df)
which one is right for making interaction term and what is difference between them ?
thanks for reading !