Cognitive test batteries in animal cognition research: evaluating the past, present and future of comparative psychometrics.

For the past two decades, behavioural ecologists have documented consistent individual differences in behavioural traits within species and found evidence for animal "personality". It is only relatively recently, however, that increasing numbers of researchers have begun to investigate individual differences in cognitive ability within species. It has been suggested that cognitive test batteries may provide an ideal tool for this growing research endeavour. In fact, cognitive test batteries have now been used to examine the causes, consequences and underlying structure of cognitive performance within and between many species. In this review, we document the existing attempts to develop cognitive test batteries for non-human animals and review the claims that these studies have made in terms of the structure and evolution of cognition. We argue that our current test battery methods could be improved on multiple fronts, from the design of tasks, to the domains targeted and the species tested. Refining and optimising test battery design will provide many benefits. In future, we envisage that well-designed cognitive test batteries may provide answers to a range of exciting questions, including giving us greater insight into the evolution and structure of cognition.