Spatial direction comprehension in images, arrows, and words in two patients with posterior cortical atrophy.

To successfully move through the world, the brain constructs spatial representations that situate the body within the environment. Communicating spatial directions poses specific challenges to this process, in part because the format through which the information is communicated must be interpreted to match the visual scene the navigator is viewing while traversing that space. For example, if a navigator needs to turn left to reach a goal, the information may be presented in the form of words ("turn left"), schemas (arrows pointing left), or images of the specific left turn. Previous research has suggested unique representations exist for spatial directions within and across modalities. Behavioral data reveal, for instance, that interpreting images seems to require spatial information, whereas words or schemas can be processed using a visual-matching strategy. In the current pre-registered study, we tested two patients with posterior cortical atrophy, who did not have spatial neglect, to determine whether they had general impairments interpreting spatial directions across formats, or specific impairments in particular formats. Our results are consistent with the specific impairment prediction, supporting the idea that interpreting spatial directions in images requires action-relevant spatial processing. We conducted single-case analyses for the patients we tested in comparison to a group of non-clinically diagnosed older adults. Of the two patients, one showed a classical dissociation between a color control task and spatial directions across all modalities. This patient also showed a classical dissociation between images (most impaired) and schemas, and between schemas and words (least impaired). Our findings lend support for a hypothesized hub in the spatial navigation network, which converts format-specific information into actionable spatial directions, and has implications for designing the built environment to optimize for spatial behavior.