Why do Alzheimer's patients stop recognising loved ones?

Human communication relies on the ability to detect and identify the faces of others as a whole. Before analysing individual features like the nose or mouth, facial perception is "holistic," allowing us to identify others quickly and easily. A recent study from the University of Montreal's geriatric institute suggests that it's this faculty for "holistic" facial perception that's impaired in patients suffering from Alzheimer's disease.

Until now, Alzheimer's patients' inability to recognise loved ones was attributed to memory loss. In other words, if a mother or father no longer recognises their child, it's because they've forgotten the child exists.

The researchers tested Alzheimer's patients and healthy seniors on their ability to perceive faces and cars in photos that were either upright or upside down.

They found no real difference in terms of accuracy or time required to process upside-down faces or cars in the two groups. To achieve these tasks, the brain carries out a local analysis of the different components of the image perceived by the eye.

However, when given photos of faces the right way round, the Alzheimer's patients were much slower and made more errors than the group of healthy seniors. For the researchers, this difference in behaviour shows that holistic facial recognition -- requiring an overall perception of faces -- is impaired by the disease, even from its early stages. What's more, the Alzheimer's patients had no trouble recognising upright cars.

To help patients recognise loved ones for longer, the study's authors suggest several different future strategies, based on the recognition of particular facial traits or voices, for example.