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The task we chose to test working memory in tamarins is one that has been used across a broad range of species for more than 30 years, so using it to replicate studies across and within species is very easy! It is called delayed matching-to-sample. Basically, an animal is shown a sample visual item for some period of time (typically seconds) and then the sample disappears (delay) for some period of time. Following the delay, there is a test, typically presenting 2 images, side by side. The animal must choose which one of the two it saw before as the sample in order to get rewarded. This tests an animal’s ability to remember a single item, or set of items, over a delay period. The test is a recognition test, in that the animal must just recognize the correct item as remembered, or just seen, or familiar, to respond. We use the same items multiple times across sessions so familiarity would lead to incorrect responses quite often. Guessing leads to 50% accuracy since the animal guesses to select one of two items.

People with Alzheimer’s Disease (AD) show significantly reduced capacity to keep items in working memory. If given a list of 10 – 16 words, the average remembered is between 1 – 2 words after only a few minutes in AD patients. The difference between AD and elderly matched control humans is so marked and consistent that working memory tasks are often used to predict AD in patients and have been reported to have an 85-90% prediction accuracy.

Here is Haagen Dasz at age 20, learning how to match the sample, a red square, with the test item, a red square (left video), and a blue circle with a blue circle (right video). In perceptual matching, we leave the sample on so that the monkey can just match it exactly. We also start by placing a virtual “cheerio” on the correct choice because the monkeys are motivated to touch a cheerio to get a real one. Later, we remove the virtual cheerio visual cue so that the monkey has to match the test item with the sample. Then, we add a delay between the sample and the 2-item test and that is when we are starting to test their memory for items they’ve seen.

Neiworth has also studied memory processing in adult humans in past work (see JEP: Learning, Memory, and Cognition (1990)). Sensitivities to diversity in the stimulus set, interstimulus interval effects in lists, and rehearsal styles were variables that we are sensitive to in testing in the lab.

CITATION: Wright, A. A., Cook, R. G., Rivera, J. J., Shyan, M. R., Neiworth, J. J., & Jitsumori, M. (1990). Naming, rehearsal, and interstimulus interval effects in memory processing. Journal of experimental psychology. Learning, memory, and cognition, 16(6), 1043–1059.

Here is Haagen Dasz being tested in a delayed matching-to-sample task. This is one trial. She would receive 12 trials in a daily session. 

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