Ordered Recall in Rhesus Macaques (Macaca Mulatta): Can Monkeys Recall the Correct Order of Sequentially Presented Images?


Previous research has demonstrated that rhesus monkeys (Macaca mulatta) are capable of identifying sequentially shown images in any order among distractors (i.e. images not part of the list sequence). We investigated ordered recall in rhesus monkeys in which subjects were expected to recognize the correct order of images during a “test” phase (simultaneous presentation of images) after they had seen the images presented sequentially in a “presentation” phase (sequential presentation of images). If subjects were successfully able to execute the ordered recall task, the first trial accuracy data would appear close to 100% accuracy and it would only take one day to learn the list since the lists used were short, 3-item lists. While this study did not conclusively demonstrate monkeys are capable of ordered recall of sequentially presented, trial unique images (i.e. a list sequence presented only once per session), the data suggests that when the stimuli are not trial unique the monkeys treat each sequence as a simultaneous chaining task. A simultaneous chaining paradigm entails simultaneous presentation of all items without any previous sequential presentation of the images. It is unclear whether results resembling simultaneous chaining are seen because these animals have previous experience with simultaneous chaining, if the training procedure needs to be modified for the monkeys to understand the task, or if the task is beyond their cognitive abilities. Further research with serial learning will clarify this finding and also seek to prove whether rhesus monkeys are in fact capable of such ordered recall tasks.