An interesting commentary in the latest issue of PNAS (on a paper that appears in the same issue):
R M Seyfarth and D L Cheney
Imagine that you’re working in your office and you hear two voices outside in the hallway. Both are familiar. You immediately picture the individuals involved. You walk out to join them and there they are, looking exactly as you’d imagined. Effortlessly and unconsciously you have just performed two actions of great interest to cognitive scientists: cross-modal perception (in this case, by using auditory information to create a visual image) and individual recognition (the identification of a specific person according to a rich, multimodal, and individually distinct set of cues, and the placement of that individual in a society of many others). An article in this issue of PNAS by Proops, McComb, and Reby (1) shows that horses do it, too, and just as routinely, without any special training. The result, although not surprising, is nonetheless the first clear demonstration that a non-human animal recognizes members of its own species across sensory modalities. It raises intriguing questions about the origins of conceptual knowledge and the extent to which brain mechanisms in many species—birds, mammals, as well as humans—are essentially multisensory.