The positivity effect reflects preserved perceptual sensitivity: a signal detection theory analysis of facial emotion recognition in ageing

Older adults typically show reduced recognition of negative facial emotions alongside relative preservation of happiness-the positivity effect. Whether this pattern reflects differences in perceptual sensitivity, response strategy, or both has not been tested with Signal Detection Theory (SDT). SDT decomposes performance into perceptual sensitivity (d') and response criterion (c), allowing us to determine whether age-related changes operate at the perceptual or decisional level. Seventy-six older adults and sixty-four young adults completed a six-alternative forced-choice identification task with 24 computer-generated facial expressions spanning six basic emotions. Older adults showed markedly lower global sensitivity, confirmed by bootstrap. A significant Group × Emotion interaction qualified this main effect: the sensitivity deficit was substantially smaller for happiness than for all other emotions. Group differences in criterion were confined to sadness, anger and surprise and were largely accounted for by the coupling between c and d' inherent to the task; for happiness, older adults showed a small, non-significant trend towards a more liberal criterion. Confusion analysis revealed that errors concentrated on emotion pairs sharing overlapping Action Units. These findings locate the positivity effect primarily at the level of early perceptual encoding, with at most a modest decisional contribution.