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Rhesus Macaques Used Working Memory to Remember the Order of Images

Adult rhesus macaque in a natural setting
Research · Behaviour

Six eight-year-old male rhesus macaques (Macaca mulatta) were tested on whether they used working memory to remember the order of images in a short sequence. Working memory is a limited-capacity system that actively keeps information available for a short period. When the monkeys had to perform another mental task during the memory interval, their memory for image order deteriorated far more than their ability to recognise images.

The monkeys first saw five images one after another on a touchscreen. At test, they were shown two of those images and had to choose which had appeared earlier. The task had been developed to study the “when” component of episodic-like memory — memory for elements of a particular past event, including what happened and in what order. Earlier work had found that hippocampal damage did not impair monkeys on this task in the way it impaired comparable order memory in rodents, raising the possibility that the monkeys were relying on short-term working memory instead.

A competing task tested the role of working memory

To test that idea, the researchers inserted a perceptual classification task during the delay between the image sequence and the memory test. This competing task occupied cognitive resources that would otherwise be available for actively maintaining the sequence. The researchers also ran recognition tests in which the monkeys judged whether an image had appeared in the studied list. Recognition can often be solved through familiarity — the sense that an image has been seen before — and is much less dependent on actively keeping the full sequence in working memory.

Order memory depended more on working memory than recognition did

The competing cognitive load strongly reduced accuracy in the order task, while recognition performance was much less affected. The authors therefore conclude that the macaques relied on working memory to solve this particular image-order task. That makes the task a poor model of long-term episodic memory, while also showing that memory for order and familiarity-based recognition can rely on different memory processes.

Sources and image credit

  1. Singhal, P., Templer, V. L., & Hampton, R. R. (2026). Dissociation of memory for order and memory for items by concurrent cognitive load in rhesus monkeys (Macaca mulatta). Hippocampus, 36(5), e70123. https://doi.org/10.1002/hipo.70123Primary research article first published online 21 August 2026. Rhesus macaques saw five images in sequence and later judged which of two images had appeared first. Concurrent cognitive load attenuated memory for order much more than recognition memory. The authors conclude that the image-order task depended on working memory and is a poor model of long-term episodic memory.

Image: Anagha devi — adult rhesus macaque (Macaca mulatta), photographed 17 November 2019; Wikimedia Commons. Representative species image, not one of the animals in the memory study. CC BY-SA 4.0. · CC BY-SA 4.0 · Source

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