Global processing deficit in amnestic mild cognitive impairment

Background: Visuo-perceptual and visuo-attentional disorders, such as global processing deficit and simultanagnosia, are not routinely investigated in prodromal forms of typical Alzheimer's disease, as amnestic mild cognitive impairment (MCI). Objective: This study evaluated global processing abilities through Navon's classical paradigm in individuals with amnestic MCI and investigated the related visuo-perceptual and attentional components involved in simultanagnosia. Methods: Sixteen consecutive patients with amnestic MCI (6 single-domain, 10 multiple-domain) and 16 matched controls were requested to identify global and local elements of hierarchical Navon letters, and to name large and small solid letters. Results: While correctly identifying solid letters, patients with multiple-domain amnestic MCI were less accurate in processing the global level of hierarchical stimuli compared to controls. Single-case analyses suggested that global processing may also be impaired in single-domain amnestic MCI. In addition, patients with pathological performance in the Navon task showed perceptual and/or visual focal attention deficits. Conclusions: Early dysfunction of holistic processing can be detected in amnestic MCI. Visuo-perceptual and/or visual focal attention mechanisms, which have been shown to be damaged in Posterior Cortical Atrophy patients with simultanagnosia, may be impaired in individuals with amnestic MCI. Investigation and identification of global processing deficits in MCI could contribute to early diagnosis and longitudinal monitoring of the disease.