The effect of base-rate priors on decision-making and confidence in healthy aging

Perceptual decision-making is often done in conditions of uncertainty. Through a process of Bayesian inference, people can combine priors, such as knowledge about base-rates, with available sensory evidence to make perceptual decisions. How this ability changes with aging is not well understood. Here we compare perceptual decision-making in younger (n = 78) and older (n = 56) adults, using a two-alternative-forced-choice task in which participants judged the orientation of dots in dynamic Glass pattern stimuli (rightward or leftward) that varied in coherence in one direction. In one condition, participants were explicitly told that for one color, the stimuli would occur more frequently in one orientation than the other while stimuli in the other color were equally likely to occur in both orientations. In the other condition, participants implicitly learned this prior through experience with the task. When explicit knowledge of the prior was given, younger adults performed more accurately than older adults with both groups showing more accuracy for items in the color with an unequal base rate. When the prior was implicitly learned, there was no overall age difference in accuracy and older adults showed a greater benefit of the unequal prior in accuracy than younger adults. In both conditions, participants were more confident in decisions about stimuli that were consistent with the prior. Older adults were generally less confident in their decisions in the implicit condition despite the fact that their performance was not significantly different than that of the younger adults. These results suggest that older and younger adults can incorporate a prior in perceptual decision-making, and that older adults may particularly benefit from implicit learning of the base-rate prior. For both older and younger adults, judgements that were consistent with the prior, even when no diagnostic sensory information was present, were more confident than judgements that were inconsistent with the prior. These results suggest that a base-rate prior can influence confidence even in the absence of evidence. Linear Ballistic Accumulator model 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. These results suggest that older adults may be negatively impacted by explicit presentation of multiple sources of information during decision-making.