“…First, in many studies, the encoding is assumed to optimize the mutual information between the external stimulus and the internal representations 19–21,23 , but it is seldom the case that this is actually the objective that an observer needs to optimize. An alternative possibility is that the encoding optimizes the observer’s current objective, which may vary depending on the task at hand 25,27 . Second, the nature of the resource that constrains the encoding is also unclear, and several possible limiting quantities are suggested in the literature (e.g., the expected spike rate, the number of neurons 17,18,21 , or a functional on the Fisher information, a statistical measure of the encoding precision 19,20,22,24,25 ).…”