Which of the following is least likely to improve with age in terms of cognitive function?

Cognitive functions are known to change as individuals age, and some functions improve while others decline. Notably, speed of processing is understood to be least likely to improve with age. Older adults often experience a decline in the speed at which they can process information, which can affect various cognitive tasks and daily activities. This slowdown can be attributed to several factors, including changes in the brain's neural connectivity and processing efficiency.

In contrast, abstract reasoning skills, memory recall, and problem-solving capabilities may show a more nuanced pattern. While some aspects of these functions can be maintained or even improved through experience and continued mental engagement, speed of processing tends to decline more consistently as age increases. This decline in processing speed can significantly impact the overall efficiency with which other cognitive tasks are performed.

Thus, the recognition that speed of processing is typically least likely to improve—highlighting age-related changes in cognitive function—is well-supported in the study of cognitive aging.