Figure 1.

Rational analysis. Anderson [1] describes a number of key steps used by the rational analysis framework. Here, we illustrate these steps using adaptive memory as an example. (a) First, one must specify the goals of the cognitive system, which, for memory, involves retrieving information based on triggers in the environment. For example, reading the word ‘Reagan’ should trigger memories of the person Ronald Reagan, who was the President of the United States of America. (b) Next, one must measure the structure of the environment. How frequently and recently one encounters an object in the environment (e.g. reading the word ‘Reagan’) strongly predicts the probability of encountering that object again, which is relevant for memory storage and retrieval. (c) Cognitive limitations of the agents must also be considered to constrain the cognitive system. Given the sheer amount of information flowing into cognitive systems, storage capacity is a severe limitation of memory. Humans are estimated to have an 11 billion-fold loss of information from the retina to memory storage (information flow rates from [2]). (d) Finally, one must derive the optimal behavioural response to the environmental structure based on the constraints on the system. For memory, frequency and recency of encounter with objects in the environment should predict the probability of needing information about that object in the future. These steps can be iterated to refine the theory.