Alzheimer’s patients demonstrate difficulty recognizing familiar scenes

This prospective study found that patients with very mild Alzheimer's disease showed poorer ability to recognize personally familiar street scenes than normal controls.

Subjects were 20 patients with very mild Alzheimer's disease and 20 normal controls with equal basic visual acuity. The authors prepared pictures of street scenes, including eight personally familiar and eight unfamiliar scenes, and asked patients to judge whether a picture was familiar or not and to describe how they came to that conclusion. Certain pictures had low luminance to simulate foggy or rainy or nighttime conditions and every picture was designated a condition level according to how difficult it was to recognize. Scene recognition accuracy was measured by considering the number of pictures successfully recognized and the condition level.

Compared with control subjects, Alzheimer's patients showed poorer mean accuracy and poorer ability for both familiar and unfamiliar scenes. The authors found that Alzheimer's patients used a global element to help judge when personally familiar scenes were displayed, which was the method controls usually adopted when presented with novel scenes.

The most common type of error Alzheimer's patients made was misidentifying a familiar scene as novel. The authors say patients more often adopted global elements to judge personally familiar scenes probably because of their inability to recognize sufficient local elements to elicit a feeling of familiarity.