The Default Mode of Primate Vocal Communication and Its Neural Correlates

It’s been argued that the integration of the visual and auditory channels during human speech perception is the default mode of speech processing (Rosenblum, 2005). That is, speech perception is not a capacity that is ‘piggybacked’ on to auditory-only speech perception. Visual information from the mouth and other parts of the face is used by all perceivers and readily integrates with auditory speech. This integration is ubiquitous and automatic (McGurk and MacDonald, 1976) and is similar across all sighted individuals across all cultures (Rosenblum, 2008). The two modalities seem to be integrated even at the earliest stages of human cognitive development (Gogate et al., 2001; Patterson and Werker, 2003). If multisensory speech is the default mode of perception, then this should be reflected both in the evolution of vocal communication and in the organization of neural processes related to communication. The purpose of this chapter is (1) to briefly describe the data that reveal that human speech is not uniquely multisensory, that in fact, the default mode of communication is multisensory in nonhuman primates as well and (2) to suggest that this mode of communication is reflected in the organization of the neocortex. By focusing on the properties of a presumptive unisensory region – the auditory cortex – I will argue that multisensory associations are not mediated solely through association areas, but are instead mediated through large-scale networks that include both ‘lower’ and ‘higher’ sensory areas.