Affordances. Motivations, and the World Graph Theory

O’Keefe and Nadel distinguish two paradigms for navigation, the “locale system” for map-based navigation and the “taxon (behavioral orientation) system” for route navigation. This paper models the taxon system, the map-based system, and their interaction; and argues that the map-based system involves the interaction of hippocampus with other systems. We relate taxes to the notion of an affordance. Just as a rat may have basic taxes for approaching food or avoiding a bright light, so does it have a wider repertoire of affordances for possible actions associated with immediate sensing of its environment. We propose that affordances are extracted by the rat posterior parietal cortex, which guides action selection by the premotor cortex and is also influenced by hypothalamic drive information. The Taxon-Affordances Model (TAM) for taxon-based determination of movement direction is based on models of frog detour behavior, with expectations of future reward implemented using reinforcement learning. The specification of the direction of movement is refined by current affordances and motivational information to yield an appropriate course of action. The World Graph (WG) theory expands the idea of a map by developing the hypothesis that cognitive and motivational states interact. This paper describes an implementation of this theory, the WG model. The integrated TAM-WG model then allows us to explain data on the behavior of rats with and without fornix lesions which disconnect the hippocampus from other neural systems.