Individual recognition in horses, monkeys and humans
In the last issue of PNAS (January 20, 2009; 106 (3)), there is an article on "Cross-modal individual recognition in domestic horses (Equus caballus)" by Leanne Proops, Karen McComb and David Reby. Here is the abstract:
"Individual recognition is considered a complex process and, although it is believed to be widespread across animal taxa, the cognitive mechanisms underlying this ability are poorly understood. An essential feature of individual recognition in humans is that it is cross-modal, allowing the matching of current sensory cues to identity with stored information about that specific individual from other modalities. Here, we use a cross-modal expectancy violation paradigm to provide a clear and systematic demonstration of cross-modal individual recognition in a nonhuman animal: the domestic horse. Subjects watched a herd member being led past them before the individual went of view, and a call from that or a different associate was played from a loudspeaker positioned close to the point of disappearance. When horses were shown one associate and then the call of a different associate was played, they responded more quickly and looked significantly longer in the direction of the call than when the call matched the herd member just seen, an indication that the incongruent combination violated their expectations. Thus, horses appear to possess a cross-modal representation of known individuals containing unique auditory and visual/olfactory information. Our paradigm could provide a powerful way to study individual recognition across a wide range of species."
This article is discussed in a comment by Robert M. Seyfarth and Dorothy L. Cheney, "Seeing who we hear and hearing who we see," who begin:
"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 (hows 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."
"Individual recognition, based on auditory, visual, or olfactory cues, is widespread in animals. Its adaptive value is clear. Recognizing others as distinct individuals allows an animal to identify and remember those with whom it may have subtly different competitive or cooperative relations, and to place them in the appropriate social context. Experiments on monkeys, for example, suggest that listeners recognize others individually by voice and make use of this information when responding to calls according to an individual's current mating status, unique dominance rank, membership in a particular kin group, or rank and kinship combined."
In the human case, we take our ability to recognise individuals so much for granted that I wonder how much work has been done on the development of this ability in childhood and whether there is any evidence of cross-cultural variation. Of course there is evidence on the breakdown of this ability in the case of prosopagnosia (as in Oliver Sacks' famous case of the man who mistook his wife for a hat).
There is also some evidence that we may be overconfident in our feeling that we routinely perceive other with attention to their individual traits. Experimental evidence for instance in the article by D. Simons and D. Levin "Failure to detect changes to people during a real-world interaction" (Psychonomic Bulletin & Review 1998, 5 (4), 644-649 available online here) based on an eminently ecologically valid, almost ethnographic experimental design where people continue answering a question asked by a person in the street without showing any awareness of the fact that that person is being replaced by another quite different person in the middle of the conversation! Also anecdotal evidence in the film That Obscure Object of Desire by Buñuel where two quite different actresses, Carole Bouquet and Ángela Molina play the character of Conchita in different scenes without most viewers realizing that there are seeing not one but two individuals.
Carole Bouquet and Ángela Molina
So things may not be as straightforward as they seem, there may well be not only individual but also cultural variability, if not in the existence of an ability to recognise others cross-modally, at least in the way this ability is being put to use, and there may also exist cultural practices, conjuring for instance, where the limits of this ability are being exploited.