UCLA

Perceptual decision-making, evaluating the sensory world in order to choose an action, is often done in conditions of uncertainty. People can implicitly learn from past experiences in order to help the decision-making process but the conditions in which this happens and how metacognition impacts this is unknown. Furthermore, how this ability to implicitly learn priors changes with healthy aging has not been studied. In these three studies, participants performed a perceptual decision-making task in which different colored stimuli were associated with different prior biases (e.g., 75% of the red trials go leftward). In Study 1, we examined the differences between learning priors implicitly through experience versus explicit instruction and how that affects performance and metacognition with two computational models, Linear Ballistic Accumulator Model (LBA) and a Hierarchical Bayesian Estimation of metacognition (H-Meta- d’). Participants were able to learn priors implicitly and used them to guide decision-making. Bias primarily influenced decisions with the least sensory information, but not for stimuli with more robust information. Those who were instructed of the priors were more confident for prior- consistent (vs. inconsistent) stimuli while this was not seen in participants who experienced the priors implicitly. However, there were no differences in metacognitive efficiency between the two instruction groups. Our results suggest that implicitly learned priors can influence decision-making when sensory information is unreliable, but do not contribute when sensory information is more robust. In Study 2, older and younger adults performed the same decision-making task with prior instruction manipulation but with different prior conditions. Instead of opposite-oriented priors, one prior was biased towards a side while the other prior was equally likely to go left or right. When participants were instructed of priors, younger adults were faster and more accurate compared to older adults. Younger adults were more confident for Positive prior (biased) trials while older adults’ confidence was unaffected by prior condition. In contrast, in the implicit “experience” group, younger and older adults largely matched on speed and accuracy, but younger adults were more confident than older adults overall. LBA parameter estimates largely align with past research that suggests that older adults have a slower information processing rate, greater response caution and require more evidence before making a decision (Garton et al., 2019). In Study 3, I present preliminary results of functional magnetic resonance imaging to examine the neural correlates of implicit learning and decision-making. Activation in the putamen and thalamus was observed during prior-consistent Equal prior trials with little sensory information. Motor and visual areas, as well as frontal gyri were primarily activated for the Positive Prior trials that were prior-consistent. Findings from these studies may augment understanding of the decision-making mechanisms in healthy aging as well as in clinical patient populations and may provide insight into novel therapies or rehabilitation.