Is a purple banana as much a banana as a yellow one? People with Alzheimer's disease may think so, since they focus more on shape than color when remembering objects, suggests a recent study in APA's Neuropsychology (Vol. 19, No. 1).

To see how healthy older adults and Alzheimer's patients encode and retrieve memories of items, Toby J. Lloyd-Jones, PhD, of the University of Kent in England, showed pictures of common objects--such as fruits, animals and insects--to 12 healthy older adults and 12 adults diagnosed with Alzheimer's.

Then, Lloyd-Jones presented participants with a mix of 96 new and previously viewed images. Each original image, such as a yellow banana, had an incorrectly colored counterpart, such as a purple banana. Whether correctly colored or not, some objects were the same color as before and others were different.

Participants had to name which objects they already had seen and which were new objects. Alzheimer's patients remembered previously seen objects as well as healthy older adult participants. There was no effect of changing object color from their study period to the test.

The healthy participants and Alzheimer's patients performed equally well on the test, including on identifying previously seen objects whose color had changed. The results suggest that both groups effectively used shape, not color, to remember previously encountered items.

But in a second test of 12 Alzheimer's patients and 12 older adults, after participants went through the same conditions as in the first experiment, Lloyd-Jones asked participants to decide if an item was colored correctly--for example, if a yellow banana should be yellow. This time, Alzheimer's participants' performance differed from that of healthy older adults. They were less accurate and slower to respond. They also were more likely to remember a banana they had seen before that had changed color, as compared with a different shape that had not changed color. In contrast, healthy older adults performed better with items that remained the same color from their initial study to the test.

The results suggest that Alzheimer's patients may lack the mental ability to combine an object's different elements, such as shape and color, into a distinct object in their minds, Lloyd-Jones explains.

"Remembering an object may benefit from combining together different attributes," he says. "It seems Alzheimer's patients lack this ability to glue different kinds of information together."

Rather, Lloyd-Jones says, the Alzheimer's patients in his study seemed to focus on the object shape and disregard color information even when it was useful for remembering objects.