Landmark Recognition and Mental Route Navigation Disorders in Patients with Imagery Neglect and Perceptual Neglect

The complex relationship between perceptual neglect and imagery neglect is still not completely understand because, at least in part, these disorders depend on are associated with, different neural systems and can be dissociated even in the same patient (Beschin, Basso, & Della Sala, 2000). Recent studies show that imagery neglect affects specific mechanisms underlying human orientation. In particular, it impairs the ability to manipulate mental representations of the environment and thus prevents the use of previous navigational experience (see for instance Guariglia et al., 2005; Piccardi, 2009; Guariglia & Piccardi, 2010). In this study, we compared the route learning and delayed recall task performance of imagery neglect patients with pure perceptual neglect patients, patients with no neglect and healthy participants. They had to learn a circular pathway in an unexplored area of the hospital; it included 13 landmarks and five turning points (three on the right and two on the left). During the learning phase, the participants explored the pathway three times with the examiner, who pointed out the landmarks. At the end of this phase, the participants performed two different tasks: a) Landmark Recognition Task and b) Navigational Questions. The first task included 26 pictures of landmarks (13 target pictures and 13 fillers) located along the pathway that the participants had to recognize. Fillers were the same type of stimuli as the target, but with different characteristics (e.g., two different doors). The second, delayed recall task consisted of 30 questions investigating the participants’ ability to recall a learned pathway and the landmarks encountered along the way. We assessed 23 right brain-damaged patients (4 patients with pure perceptual neglect, 8 patients with imagery neglect and 11 patients without neglect) and 17 healthy participants matched for age and education. Our results showed that only patients with imagery neglect had a pervasive disorder in recognizing landmarks met along the route and in mentally navigating the previously learned pathway. Specifically, they were unable to answer navigational questions investigating their mental representation of the pathway. Differently, perceptual neglect patients were able to recognize landmarks as well as answer navigational questions in spite of their exploration disorder. Right brain-damaged patients without neglect showed no deficit on the tasks. In summary, only the imagery neglect patients were unable to build or retrieve a mental representation of the new environment and, thus, failed in performing these tasks. In fact, results showed they were deficient in using a cognitive map of the environment. It is still unknown whether the deficit observed in imagery neglect patients is due to difficulty in building a mental map, recalling it from memory or using it during navigation, leaving unknown the exact point in which the navigational process is compromised.