Coding across sensory modalities: Integrating the dynamic face with the voice

Primates are social beings. To ensure adequate resources and advance their position in a dominance hierarchy, they must be Machiavellian-ready to exploit social opportunities whenever they appear (Ghazanfar and Santos, 2004; Maestripieri, 2007). Maintenance and the advancement of rank in a social hierarchy entail a range of behaviors such as play, grooming, aggressive attacks, submissive retreats, reconciliations and the formation of coalitions (Cheney and Seyfarth, 1990; Ghazanfar and Santos, 2004; Maestripieri, 2007). Achieving adaptive social behavior requires that primates monitor and accurately perceive the vocal communication signals of conspecifics (Cheney and Seyfarth, 1990; Semple, 1998; Pfefferle et al., 2008). Primate vocalizations are complex-often extended and dynamic with temporal structure on a variety of time scales. Furthermore, these vocalizations are not produced in quiet environments. Instead, they are often embedded in a variety of other biotic and abiotic sounds (Waser and Brown, 1986; Slabbekoorn, 2004; Chandrasekaran et al., 2010b). Therefore, one major task of the primate brain is to extract conspecific vocalizations from these background sounds.