Six-month-old infants' pupil size changes in response to others' affective displays.

<p>In Panel A, functional expression of changes in the 6-month-olds baseline corrected pupil size in response to others' neutral (purple line), positive (black line), and negative (green line) emotional displays. Panel B shows the value of t statistic as a function of time for each pair of stimuli comparison: positive vs. neutral (red line), negative vs. neutral (green line), and negative vs. positive (blue line). The one-tailed critical values of t are represented by the vertical lines with (dotted) and without (solid) Bonferroni correction for three comparisons. The difference is considered to be significant when this line is reached or surpassed. Marked with dark gray are those time windows in which both emotional conditions triggered larger pupil diameters than the neutral one, and the hypothesized negativity bias occurred. Marked with light gray are those time windows where negative emotions triggered larger pupil diameter compared to the emotionally neutral state. (Note that the shaded areas are for illustrative purposes only, marking the time window in which the effect occurred and not the effect duration.)