Hopkins, William D, Taglialatela, J. P. and Leavens, David (2011) Do chimpanzees have voluntary control of their facial expressions and vocalizations? In: Vilain, Anne, Schwartz, Jean-Luc, Abry, Christian and Vauclair, Jacques (eds.) Primate communication and human language : vocalisation, gestures, imitation and deixis in humans and non-humans. John Benjamins Pub, pp. 71-90. ISBN 9789027204547