in a step-wise fashion, to predict startle responses. All predictors were initially entered as fixed-effect predictors. To assess whether the slopes characterizing the relationship between lower-level predictors (e.g., stimulus valence and session) and startle responses varied among sessions and/or among participants, we added the random slope coefficients for stimulus valence and session to the model one at a time. We used a log likelihood ratio test to evaluate whether adding a random slope coefficient significantly improved the goodness-of-fit of a model over one without the coefficient.
