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People with Alzheimer’s Disease (AD) typically perform more poorly than do elderly age-matched controls on tasks involving visual search in which one has to find a target among a sea of distractors. An experiment using visual search is testing one’s ability to attend to unique features when there are a lot of distractors present which might also be processed. As we age, distractors are harder to ignore and this is one way in which items may not be processed in memory very well. If one is overwhelmed with distractors drawing attention, then it will be hard to remember the important stimulus in a sea of unimportant ones (like, when one has to find one’s car parked in a lot, especially if we are distracted by other tasks during or soon after the parking process). AD patients are worse at this than controls, but there is a challenge in aging with lack of ability to inhibit less important details generally

We use a typical visual search task originally developed for humans more than 30 years ago and tested hundreds of times with people. In it, a target set of items is presented in one of 4 quadrants on an iPad. The task for the monkeys is to touch the quadrant that shows the target. Monkeys will guess if they cannot determine the target, so accuracy is one way we can tell if they can do it. Another is reaction time — in people and in monkeys, targets that share features with distractors are harder to find and thus take longer to respond to identify.

Here is Haagen Dasz, age 20, selecting a quadrant with a target that is very easy to spot. This is called a disjunctive target because it has a unique feature which is not shared with any of the distractors in the other quadrants, so it should “pop out” visually.

In this trial, Haagen Dasz is confronted with a conjunctive feature task, and this is one that AD patients have difficulty with. Here the distractors share the colors (green and orange) and the shapes (stars and circles) with the target quadrant. The target just contains a different combination of the features which is unique. Play it several times if you can’t see the difference — it takes anyone longer to see the target in a conjunctive feature task.

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