The representation of space is more than space : evidence from an environment learned through navigation

Abstract

The cognitive map theory suggests that the brain has a representation of space in the hippocampal-entorhinal system that supports memory for locations and spatial layout. This spatial representation was initially assumed to encode only geometric properties. However, studies about the function of hippocampus have shown that it also plays a critical role in supporting declarative memory, and recent theories have hypothesized the encoding of space is a sub-process of a memory system. If space is not represented independently, memory for spatial and non-spatial properties might interact. This study tested whether connections between non-spatial properties can distort judgments about spatial distance. In virtual reality, subjects navigated through a virtual environment to learn the locations of a set of target houses, and then were tested on their ability to judge the distances between houses and reconstruct a map of the environment. The maps were constructed to have pairs of houses that had the same spatial distance but were either similar or different in their non-spatial properties. Color similarity, event similarity, and social distance of house owners were varied in different experiments. If memory for spatial and non-spatial properties interact, similar houses would be expected to be judged as closer than the different houses. Such biases were observed in both estimates of pairwise distances and reconstructed maps. To rule out a hierarchical clustering explanation, we also tested whether social proximity and spatial proximity could interact in the reverse direction. We manipulated the spatial distance between houses and found that pairs of houses with owners of the same social distances were judged to have a closer social relationship when their houses were closer in space. These results are difficult to reconcile with the cognitive map theory, and cannot fully be explained by hierarchal organization of space. Our results support theories that space is represented with other properties, and are consistent with the idea that the mechanisms for encoding space in the hippocampal-entorhinal system have a broader function.