Hierarchical structures: chunking by food type facilitates spatial memory.

Three experiments assessed the ability of male Sprague-Dawley rats to organize the spatial locations of different food types in a hierarchical manner to maximize the efficiency of working memory. Independent groups were exposed, on a 12-arm radial maze, to baiting arrangements varying in the stability of the pattern and type of food used as bait. Training rats with stable, differentiable baiting arrangements produced increased accuracy in choice performance, hierarchically ordered patterns of choice selection, slower growth of proactive interference when trials were massed, and the learning of the geometrical relations among food types independent of other extramaze cues. Such findings are strong evidence of the rat's ability to encode and use local cues for navigation, based on properties of the reinforcer. The application of a chunking strategy may provide for more efficient use of working memory by facilitating information storage, recall, or resetting mechanisms.