Measuring and understanding individual differences in cognition

This is the author accepted manuscript.Individuals vary in their cognitive performance. While this variation forms the foundation of the study of human psychometrics, its broader importance is only recently being recognized. Explicitly acknowledging this individual variation found in both humans and non-human animals provides a novel opportunity to understand the mechanisms, development and evolution of cognition. The papers in this special issue highlight the growing emphasis on individual cognitive differences from fields as diverse as neurobiology, experimental psychology and evolutionary biology. Here, we synthesize this body of work. We consider the distinct challenges in quantifying individual differences in cognition and provide concrete methodological recommendations. In particular, future studies would benefit from using multiple task variants to ensure they target specific, clearly defined cognitive traits and from conducting repeated testing to assess individual consistency. We then consider how neural, genetic, developmental and behavioural factors may generate individual differences in cognition. Finally, we discuss the potential fitness consequences of individual cognitive variation and place these into an evolutionary framework with testable hypotheses. We intend for this special issue to stimulate researchers to position individual variation at the centre of the cognitive sciences.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.We thank all participants of the workshop on Causes and Consequences of Individual Differences in Cognition, October 2017. NJB is funded by a Royal Society Dorothy Hodgkin Fellowship. AT is funded by a Human Frontiers Research Program grant (RGP00049). JRM is funded by an ERC Consolidator Award (616474). JMF is funded by a HFSP grant (RGP0006) and a Natural Sciences and Engineering Research Council of Canada Discovery Grant (435596). JMF would like to thank Gabrielle Davidson for discussions on hypothesis testing during the workshop. John Quinn and one anonymous reviewer provided helpful comments on this manuscript