According to developmental psychologist k. warner schaie, inductive reasoning, spatial orientation, perceptual speed, and verbal memory begin to gradually decline beginning around age

Inductive reasoning, spatial orientation, perceptual speed, and verbal memory begin to gradually decline beginning around age 25.  This is according to Developmental Psychologist, Dr. K. Warner Schaie, who conducted the Seattle Longitudinal Study (SLS) in 1956. The study shows the psychological development of the participants starting from their 20s to their late 60s. SLS is considered as the most extensive psychological research study about the development and changes of people through adulthood.