Investigating Spatial Memory and Navigation in Developmental Amnesia: Evidence from a Google Street View Paradigm, Mental Navigation Tasks, and Route Descriptions
Herdman, Katherine Anne
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This dissertation examined the integrity of spatial representations of extensively travelled environments in developmental amnesia, thereby elucidating the role of the hippocampus in forming and retrieving spatial memories that enable flexible navigation. Previous research using mental navigation tasks found that developmental amnesic case H.C., an individual with atypical hippocampal development, could accurately estimate distance and direction between landmarks, but her representation of her environment was fragmented, inflexible, and lacked detail (Rosenbaum, Cassidy, & Herdman, 2015). Study 1 of this dissertation examined H.C.s spatial memory of her home environment using an ecologically valid virtual reality paradigm based on Google Street View. H.C. and control participants virtually navigated routes of varying familiarity within their home environment. To examine whether flexible navigation requires the hippocampus, participants also navigated familiar routes that had been mirror-reversed. H.C. performed similarly to control participants on all route conditions, suggesting that spatial learning of frequently travelled environments can occur despite compromised hippocampal system function. H.C.s unexpected ability to successfully navigate mirror-reversed routes might reflect the accumulation of spatial knowledge of her environment over the 6 years since she was first tested with mental navigation tasks. As such, Study 2 investigated how spatial representations of extensively travelled environments change over time in developmental amnesia by re-testing H.C. on mental navigation tasks 8 years later. H.C. continued to draw sketch maps that lacked cohesiveness and detail and had difficulty sequencing landmarks and generating detours on a blocked route task, suggesting that her overall representation of the environment did not improve over 8 years. Study 3 thoroughly examined the integrity of H.C.s detailed representation of the environment using a route description task. H.C. accurately described perceptual features of landmarks along a known route, but provided inaccurate information regarding the spatial relations of landmarks, resulting in a fragmented mental representation of the route. Taken together, these results contribute meaningfully to our current understanding of the integrity of spatial representations of extensively travelled environments in developmental amnesia. Non-spatial factors that could influence performance on navigation and spatial memory tasks are discussed, as is the impact of these results on theories of hippocampal function.