The science of intelligence
What is processing speed?
Short answer
Processing speed is how quickly you can take in simple information and act on it accurately. It is one of the broad abilities, labeled Gs, in the CHC model of intelligence. It peaks in the late teens and twenties, and its slowing with age is a leading explanation for other age-related changes.
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What processing speed is
Processing speed is the pace at which you can take in simple information and respond to it accurately. The tasks used to measure it are deliberately easy: matching symbols, crossing out targets, copying codes. Given unlimited time nearly everyone would be right, so speed is what separates people. That makes processing speed different from reasoning, where the challenge is figuring out a rule at all.
Speed tasks are short and repetitive, and they measure something narrow on purpose. A person can be quick at symbol matching and still find a hard matrix puzzle slow going, and the reverse is common too.
Where it sits in models of intelligence
In the Cattell-Horn-Carroll (CHC) framework, processing speed (Gs) is one of the broad abilities, alongside fluid reasoning (Gf), comprehension-knowledge (Gc), visual processing (Gv), auditory processing (Ga), short-term working memory (Gwm) and retrieval fluency (Gr). A 2023 network analysis of the Woodcock-Johnson IV norm sample supported these broad abilities (McGrew et al., 2023). Speed is a real and separate part of the picture, but it is one part. The CHC theory page shows how the pieces fit together.
Try one · Pattern Recognition
Which tile comes next?
Tap the option you think is right, or show the answer.
Show the answer
The missing tile shows four solid triangles (option 6).
How to solve it
- Compare neighboring tiles and name what changes each time.
- From tile to tile, one more triangle is added.
- The fill cycles solid, hatched and outline, then starts again.
- Everything else stays the same from tile to tile.
- The last tile shows three outlined triangles. Apply each change once more.
- So the missing tile shows four solid triangles.
That was 1 puzzle. The full test has 25.
Speed and age
Processing speed is the ability that changes most clearly across adulthood. Speed and some reasoning measures peak in the late teens and twenties, while vocabulary and accumulated knowledge keep rising into the sixties (Hartshorne & Germine, 2015) (Salthouse, 2009).
Timothy Salthouse built a theory on this. His processing-speed theory proposes that increased age in adulthood is associated with slower execution of many mental operations, and that this slowing impairs cognitive functioning (Salthouse, 1996). He named two mechanisms:
- Limited time. When processing is slow, some operations cannot be finished in the time available (Salthouse, 1996).
- Simultaneity. The results of early steps may no longer be available by the time later steps finish, so they cannot be combined (Salthouse, 1996).
The second mechanism links speed to working memory: if you are slow, what you worked out a moment ago may have faded before you need it. Salthouse's supporting evidence includes large reductions in age-related differences on cognitive measures once speed is statistically controlled (Salthouse, 1996). That is a correlational argument, and it is a theory rather than settled fact, but it explains why speed gets so much attention in research on aging.
Why slowing does not lower your IQ
Modern IQ scores compare you with people your own age (Wikipedia: Intelligence quotient). A 65-year-old is scored against other 65-year-olds, who have slowed in similar ways, so typical age-related slowing does not by itself lower the score. Your raw speed can drop over decades while your IQ stays steady. The age norms entry and the IQ and age guide explain this in more detail, and intelligence across the lifespan covers how stable rank order is from childhood to old age.
Speed on the IQ Octopus test
The IQ Octopus test is a reasoning test, not a speed test. Most people finish its 25 puzzles in about 12 minutes, with a hard cap of 20. Your estimated IQ is scored with a Rasch model from the puzzles you answer correctly, and the report shows a confidence range. Rushing tends to cost more in mistakes than it saves in time, so steady and careful is the better approach. See how the test works for the details.
Sources
- McGrew, K. S., Schneider, W. J., Decker, S. L., & Bulut, O. (2023). A psychometric network analysis of CHC intelligence measures. Journal of Intelligence, 11(1), 19. doi.org/10.3390/jintelligence11010019
- Hartshorne, J. K., & Germine, L. T. (2015). Psychological Science, 26(4), 433-443. doi.org/10.1177/0956797614567339
- Salthouse, T. A. (2009). Neurobiology of Aging, 30(4), 507-514.
- Salthouse, T. A. (1996). The processing-speed theory of adult age differences in cognition. Psychological Review, 103(3), 403-428. doi.org/10.1037/0033-295X.103.3.403
- Intelligence quotient. Wikipedia. en.wikipedia.org/wiki/Intelligence_quotient