It is involved in the perception of where others are gazing (joint attention) and is thus important in determining where others' emotions are being directed. It is also involved in the perception of biological motion. In individuals without autism, the superior temporal sulcus also activates when hearing human voices 
↑Campbell, R., Heywood, C.A., Cowey, A., Regard, M., and Landis, T. (1990). Sensitivity to eye gaze in prosopagnosic patients and monkeys with superior temporal sulcus ablation. Neuropsychologia, 28(11), 1123-1142.
↑Grossman, E. D. & Blake, R. (2001). Brain activity evoked by inverted and imagined biological motion. Vision Research, 41, 1475-1482.