Fig. 2

Trial structure in the experimental paradigm used to examine pupillary responses to infant facial expressions. Trial events consisted of (1) a black screen (duration = 1000 ms, a sound alarm was presented 500 ms prior to the next visual stimulus), (2) pre-stimulus display consisting of randomized pixels from the face images with stimulus-matched luminance (duration = 2000 ms), (3) face stimulus (duration = 5000 ms), and (4) a white border added to the face stimulus to signal the end of the trial. Pupil data were analyzed from the period starting from the pre-stimulus interval (displaying randomized pixels) and ending 5 s after the onset of the face stimulus