Will monkeys wager differently as a function of stimulus fluency or when making immediate versus delayed judgements of memory?

Nonhuman animals can engage in forms of metacognitive control and monitoring processes. However, very little testing of the relation between fluency and metacognition has been done in animals, and little research has assessed memory performance in relation to animals making immediate versus delayed judgments of their memory. Here, wagers made by monkeys during test trials served as a form of confidence measure of how well they could complete a memory test. These wagers occurred either after the delay interval between the sample presentation and the test (delayed judgments) or after the sample presentation but before the delay interval and the test (immediate judgments). Overall, no significant difference in performance was found between these two conditions. We also manipulated the fluency of stimuli by either contrasting small (low fluency) or large (high fluency) stimuli or by manipulating size and the degree to which stimuli were of similar perceptual classes (low fluency, harder to distinguish stimuli such as triangular shapes) or were dissimilar in color and shape (high fluency, clip art images). Although low fluency stimuli were remembered at lower levels, the monkeys showed no evidence of adjusting wagering behavior as a function of stimulus type. Thus, the present experiment showed no evidence that monkeys benefitted from delay of judgments of memory and no evidence of stimulus fluency affecting their confidence as measured by their wagering. Rather, most monkeys preferred consistent wagers across all trial types. This may indicate a metacognitive limitation or some other form of behavioral satisficing that led to suboptimal performance.