Re-appreciating the why of cognition: 35 years after Marr and Poggio

Marr and Poggio's levels of description are one of the most well-known theoretical constructs of 20th century cognitive science. It entails that behavior can and should be considered at three different levels: computation, algorithm, and implementation. In this contribution focus is on the top level in Marr and Poggio's scheme: the computational level of description, the level that describes the 'why' of cognition. I argue that the computational level should be taken as a starting point in devising experiments in cognitive science. Instead, the starting point in empirical practice often is a focus on the stimulus or on some capacity of the cognitive system. The 'why' of cognition tends to be ignored when designing research, and is not considered in subsequent inference from experimental results. The overall aim of this manuscript is to show how re-appreciation of the computational level of description as a starting point for experiments can lead to more informative experimentation