Spatial memory is not like a „map in the head“

How do we store the spatial information of our surrounding?

October 10, 2018

When reading this text, you are probably sitting in front of your computer or looking at your phone. Now, from your current position, try to point in a straight line directly to the bathroom closest to you as if the walls around you would be made of glass. How did you solve this task? You need to have built up spatial memory about your surrounding in order to estimate the locations of places that are currently not in sight. It is commonly assumed that for solving such tasks we revert to a cognitive map, a metric mental version of our surrounding. Similar to a real paper map each place, each street, each building we visit is assigned a clear (maybe not 100% accurate) position on this cognitive map and can be accessed immediately from this mental paper map. A new study by Marianne Strickrodt, Tobias Meilinger and Heinrich H. Bülthoff aimed to ascertain whether this understanding of spatial memory is actually correct.

Participants learned a virtual environment, eight corridors strung together. Half of these interconnected corridors belonged to the blue region containing animals as landmarks and the other half belonged to the red region containing tools as landmarks. The environment was presented to the participants via virtual reality glasses while they were freely walking in a large motion tracking hall. After intensive learning participants were teleported to different locations within the environment. From there they had to point towards previously learned landmarks in the environment from memory. Target landmarks could either be located in the neighbouring corridor, in the second next corridor, the corridor after the second next and so on. Also, target landmarks could either be located in the same region as the participant (e.g. standing at the cow in the blue corridor the task was to point to the giraffe located in another blue corridor) or in the other region (e.g. standing at the cow in the blue corridor the participant had to point to the hammer located in one of the red corridors of the other region).

Marianne Strickrodt from the Max Planck Institute for Biological Cybernetics explains: “The results of the study indicate that participants did not simply read out information from a single cognitive map. Instead, results allow for the conclusion that memory for navigable space is manifold.” She assumes that “participants seem to have built up local, regional and global cognitive maps, hence, cognitive mini-maps which are confined to a single corridor only, to a region containing multiple corridors, and a cognitive map which is covering the entire environment.” This range of spatial memory content is not used comprehensively all the time. Instead, depending on one’s current location and the target of interest only the relevant memory content seems to be selected. This flexible use implies that our memory for navigable space might be hierarchical. Importantly, the direction estimation process was eventually bound to the corridor-to-corridor sequence experienced during learning. This is a process different from what would be expected when reading out relational information from place A and place B from a pure map-like memory structure.

In sum, the idea that we memorize a map-like, mental birds-eye picture of the environment does not seem to capture the factual memory content that we store in our brains. Locally confined places such as rooms and corridors seem to play a major role, maybe as unique memory units, like pieces of a puzzle. To come up with a direction estimate these pieces seem to be strung together mentally, step-by-step until reaching the target. Strickrodt acclaims, that “more research is needed to understand whether and how these units are enriched with additional information about regional belonging or maybe a fictive “mental north” that could be propagated across multiple places to facilitate the understanding of where they are relative to each other.”

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