Many patients with Alzheimer’s disease – and even some healthy elderly – demonstrate conceptual errors that are characteristic of healthy preschool children (saying, for example, that the sun or the wind is alive). At Massachusetts General Hospital (Psychiatry/Gerontology), I investigate the mechanisms underlying these phenomena in adults, while running parallel studies with young children at Harvard. In both sets of studies, I focus on the effect of individual differences in Executive Function on the acquisition and loss of conceptual understanding.