Fig. 5
From: Mothers’ pupillary responses to infant facial expressions
Grayscale (bitmap) intensity values of the stimuli. Pair-wise comparisons between means of different stimulus categories indicate higher intensity (and, hence, luminance) for face stimuli with “strong positive” vs. “negative” emotional expressions. SN strong negative, MN mild negative, SP strong positive, MP mild positive. Horizontal line indicates the mean grayscale intensity across all stimuli