Until the middle of the 20th century, it was thought that intelligence peaked in adolescence and then began to decline, and continued its descent over the remainder of a person 's life. However, psychological researchers, particularly the work of K. Warner Schaie and his 1956 study called the Seattle Longitudinal Study, have proven that hypothesis incorrect, proving that some aspects of intelligence, such as vocabulary skills, actually increase until about age 60. Middle adulthood is a time when many people have acquired a particular vocational expertise that makes them uniquely more qualified and capable than younger adults. This means that many in midlife are at the height of their careers, which also means increased job responsibilities. …show more content…
Interindividual variability, means some people allow themselves to be in “ruts” which they gain little if any new knowledge. Other people are hungry for new knowledge, they would travel, read, and visit museum. Plasticity, refers to the people’s intellectual abilities which are not absolutely fixed but can be modified under certain conditions at almost any time of in life. Two forms of intelligence which are the main focus of middle adulthood are crystalized and fluid intelligence. Crystallized intelligence is dependent upon accumulated knowledge and experience. This kind of intelligence tends to hold steady as we age, in fact, it may even improve. For example, adults shows relatively stable increasing scores on intelligence test until their mid-30s to mid-50s. Fluid intelligence, on the other hand, is more dependent on basic information-processing skills and start to decline even prior to middle adulthood. Cognitive processing speed slows down, same as to the ability to solve problems and divided attention. However, practical-problem skills tend to increase, which is important to solve real-world problems in