Macaque monkeys categorize images by their ordinal number

Area of Science:

• Cognitive science
• Neuroscience
• Animal behavior

Background:

• Serial order recall is a fundamental cognitive function.
• The strategies underlying serial recall (sequential associations vs. ordinal position) remain unclear.
• Nonverbal memory strategies in non-human primates offer insights into basic mnemonic principles.

Purpose of the Study:

• To investigate the nonverbal mnemonic strategies employed by macaque monkeys in a delayed sequence recall task.
• To determine whether monkeys prioritize sequential item associations or item-to-ordinal position associations for memory recall.
• To explore the flexibility and hierarchy of mnemonic strategies in primates.

Main Methods:

• Three macaque monkeys were trained on a delayed sequence recall task involving abstract images.
• Stimuli consisted of 30 abstract images presented in fixed temporal order within triplets.
• Monkeys identified sequentially presented images while avoiding a distractor, testing their recall accuracy and error patterns.

Main Results:

• The most frequent error involved mistaking a distractor image with the same ordinal number within its triplet as a correct sample image.
• This suggests a primary reliance on categorizing images by their ordinal position.
• Secondary strategies, including working memory for sample images and associations between triplet members, were also observed.

Conclusions:

• Macaque monkeys utilize multiple mnemonic strategies for serial recall, with a primary tendency to associate items with their ordinal positions.
• Working memory and inter-item associations serve as secondary strategies, employed to refine recall accuracy and avoid errors.
• These findings highlight the adaptive nature of mnemonic strategies, influenced by innate predispositions and task demands.