Positive Interpretation of Emotional Ambiguity Across Development: LC-dlPFC Circuitry
Emotionally ambiguous facial expressions provide a tractable model for studying how uncertain affective information is resolved into categorical judgments. Here we tested whether developmental differences in this process are reflected in locus coeruleus (LC) circuitry and how these neural effects relate to behavioral and decision-process indices of interpretive bias. Participants from late childhood through middle-aged adulthood completed an angry-to-happy facial morph task during fMRI. Behavioral responses were analyzed using signal detection theory, and drift-diffusion modeling, and fMRI data were analyzed using LC-seeded generalized psychophysiological interaction and trial-level neural models. Positive bias increased systematically across development. Drift-diffusion analyses showed that this shift was captured specifically by drift intercept, a stimulus-independent evaluative component of evidence accumulation, rather than by perceptual sensitivity, starting point, or response caution. At the neural level, the association between LC-dlPFC coupling and positive bias was strongest in middle-aged adults. Trial-level analyses further indicated that dlPFC carried the clearer moment-to-moment evaluative signal, whereas LC contributed through slower temporal properties, indexed by the Hurst exponent, that shaped bias-related cortical coupling. Importantly, higher LC structural integrity (contrast-to-noise ratio) was associated with lower LC temporal persistence and, in turn, more negative LC-dlPFC coupling. Together, these findings suggest that age-related differences in positive interpretation are not simply differences in perceptual sensitivity or response tendency, but reflect age-graded variation in evaluative evidence accumulation supported by LC-dlPFC circuitry. This work extends recent evidence implicating LC-prefrontal connectivity in ambiguity processing and identifies evaluative drift bias as an age-graded circuit-level signature of emotional ambiguity resolution. Significance StatementHow the brain resolves emotionally ambiguous faces across development is poorly understood. Using psychometric, drift-diffusion, and fMRI analyses in youth, emerging adults, and middle-aged adults, we show that age-related increases in positive interpretation are explained by drift intercept, a stimulus-independent evaluative component of evidence accumulation, rather than by perceptual sensitivity or starting-point bias. LC-dlPFC coupling tracked this same bias dimension. Trial-level analyses suggested that dlPFC carried the clearer moment-to-moment evaluative signal, whereas LC contributed through slower temporal properties of bias-related coupling. These findings identify evaluative drift bias as a measurable circuit-linked mechanism of emotional ambiguity resolution.