— Cognitive concept
Processing Speed
The cognitive ability index measuring how quickly you can perform simple cognitive operations.
Processing speed is the cognitive ability to perform simple mental operations quickly and accurately under time pressure. It's one of the four major indices on the WAIS-IV (Processing Speed Index, PSI).
What it measures
Processing speed tests typically involve simple symbol-matching or scanning tasks performed under strict time limits. The classic measures are:
- Digit symbol coding — pair symbols with digits as fast as possible
- Symbol search — scan a row of symbols for a target
- Cancellation — cross out target shapes in a field of distractors
How it relates to IQ
Processing speed has a moderate correlation with overall IQ (~0.4-0.5), weaker than the correlation between working memory and IQ. But processing speed is one of the most reliable markers of healthy cognitive aging — slowdown here often precedes broader cognitive decline.
Age and processing speed
Processing speed peaks in the early 20s and declines steadily across adulthood — about 0.5-1 point per decade on standardised measures. This is the main reason older adults perform worse on timed tests despite stable or growing knowledge and judgement.
Related concepts
- Fluid Intelligence
- Crystallised Intelligence
- The g-factor (general intelligence)
- The Flynn Effect
- Verbal IQ