Final answer:
The Seattle Longitudinal Study showed that in middle age, information processing abilities and memory were the two mental abilities that start to decline. Engagement in mental and physical activities can help in delaying this cognitive decline.
Step-by-step explanation:
In the Seattle Longitudinal Study, the research indicated that while many cognitive abilities remain steady throughout early and middle adulthood, there are declines in certain areas of cognitive functioning as we transition into late adulthood, specifically with our fluid intelligence. The study found that the two mental abilities that showed decline during middle age were related to information processing abilities and memory. As these cognitive abilities decline, the speed at which new information is processed and remembered tends to slow down. Despite this natural progression, engaging in mental and physical activities can help delay the onset of cognitive decline and the incidence of associated conditions like mild cognitive impairment and dementia. Therefore, sustaining an active lifestyle and continuing cognitive activities such as puzzles, reading, or playing strategic games can be beneficial for maintaining cognitive health.