Toronto: Alzheimer's not only steals people's memories but also their ability to recognise faces, which widens the gulf between those with the neurodegenerative disease and their loved ones, according to a new study.
Face perception plays a fundamental role in human communication, which is why humans have evolved into experts at quickly detecting and identifying faces. This faculty is thought to depend on the ability to perceive a face as a whole, researchers said.
Also known as "holistic perception," this ability is in contrast to the detailed analysis required to perceive individual facial features, such as the eyes, nose or mouth.
For the study, researchers from Montreal University in Canada recruited people with Alzheimer's along with healthy seniors to study their ability to perceive faces and cars in photos that were either upright or upside down.
They found that the results for people with Alzheimer's were similar to those in the control group in terms of answer accuracy and the time to process the upside-down faces and cars.
"To perform these tasks, the brain must perform a local analysis of the various image components perceived by the eye," said Sven Joubert from Montreal University.
"However, with the upright faces, people with Alzheimer's were much slower and made more mistakes than the healthy individuals. This leads us to believe that holistic face recognition in particular becomes impaired," Mr Joubert said.
Subjects with Alzheimer's disease also demonstrated normal recognition of the upright cars, a task that in theory does not require holistic processing. This suggests that Alzheimer's leads to visual perception problems specifically with faces, researchers said.
The study explains the mechanism involved in the problem that people with Alzheimer's have with recognising the faces of family members or celebrities, they said.
The findings were published in the Journal of Alzheimer's Disease.
