Landmark Agnosia: Evaluating the Definition of Landmark-based Navigation Impairment.

Objective: Landmark agnosia is a rare type of navigation impairment, for which various definitions have been presented. From a clinical as well as theoretical perspective, consensus on the characteristics of landmark agnosia would be valuable. In the current study we review the literature concerning landmark agnosia and present a new case study. Existing literature highlights the importance of examining familiar as well as novel landmark processing and substantial variation in performance patterns of individual patients. Method: We performed a case study with patient KS, a 53-year-old male, suffering from landmark agnosia, making use of elaborate neuropsychological screening and virtual reality-based tests of navigation ability. Results: Our extensive examination of his impairment shows that landmark agnosia can be very narrow; in KS it is restricted to recognition of newly learned landmarks only. Also, he has no trouble recognizing familiar landmarks that are not part of a navigated route. Conclusions: The literature review shows that the right temporal lobe, and the right hippocampus in particular are the main lesion sites for landmark agnosia. Furthermore, our case study substantiates that this disorder can occur for both familiar and novel landmarks, and can affect novel landmarks in isolation from familiar landmarks. Moreover, it can occur in isolation from problems with processing route information.