Brain Aging & Cognition: Fluid vs Crystallized (2D)

This companion simulator plots two of the most replicated findings in cognitive-aging research on one chart. Dragging the age slider does not just relabel a number — it drives a fluid-ability curve that declines roughly linearly from young adulthood onward (mirroring documented slowing in processing speed, working-memory span and simple/choice reaction time of about 1–2 ms per year past the mid-20s) alongside a crystallized-ability curve built from vocabulary and accumulated-knowledge studies, which holds flat or keeps climbing into the 60s before leveling off. The two curves visibly cross and diverge as the slider moves, which is the textbook signature of the fluid/crystallized dissociation: raw speed erodes while acquired knowledge is preserved or still growing. To make the effect concrete rather than abstract, a real playable reaction-time task sits underneath the chart — click to arm it, wait for the box to turn green, then click again as fast as you can — and your measured time is compared directly against the model's predicted reaction time for whatever age you set, so you can see where your own reflexes land relative to a simulated 25-, 55- or 85-year-old.