Simplicity and validity in infant research

Infancy researchers often use highly simplified, animated, or otherwise artificial stimuli to study infant's understanding of abstract concepts including “causality” or even “prosociality”. The use of these simplified stimuli have led to questions about the validity of the resulting empirical findings. Do simplified stimuli effectively communicate abstract concepts to infants? Even if they do, why not use stimuli more like what infants encounter in their everyday lives? Here we make explicit the underlying logic of using simplified stimuli in studies with infants: Simplified stimuli allow for stronger experimental control and therefore more precise inferences compared to more complex, uncontrolled, naturally occurring events. We discuss the inherent tradeoff between measurement validity and ecological validity, offer three strategies for assessing the validity of simplified stimuli, and then apply those strategies to the increasingly common use of simplified stimuli to assess the development of complex social concepts in the infant mind. Ultimately, we conclude that while concerns about the validity of experiments using simplified stimuli are founded, results from such studies should not be dismissed purely on ecological grounds.