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Working Memory and Fluid Reasoning: Same or Different?

The views expressed are those of the author and are not necessarily those of Scientific American.

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In 1990, researchers Patrick Kyllonen and Raymond Christal found a striking correlation.

They gave large groups of American Air Force recruits various tests of working memory, in which participants performed simple operations on a single letter. For instance, in the “alphabet recoding” task, the computer briefly displayed three letters:

H, N, C

Followed by an instruction, such as:

Add 4

In which the answer would be:

L, R, G

Of course, adding four letters is a piece of cake. The difficult part is remembering the letter while performing the next mental operation, and holding both of those in mind while operating on the third. This can get increasingly difficult with more complex instructions and more letters to transform in your head.

Across four different studies, they found extremely high correlations—ranging from .80 to .90 — between their measures of working memory and various measures of reasoning. In fact, the correlations were so high they titled their paper: “Reasoning ability is (little more than) working memory capacity?!

Many studies since then have confirmed that working memory is an important contributor to fluid reasoning. Out of all the cognitive abilities ever measured by intelligence researchers, fluid reasoning is the most general cognitive ability of them all, explaining the most amount of variance in all of the other cognitive abilities. The ability to infer relations and spot patterns on problems that draw on minimal prior knowledge and expertise plays a role– in varying degrees– across virtually all areas of human intellectual functioning.

But just how strong is the relationship between working memory and fluid reasoning? As is often the case with science, the strength of the correlation between working memory and fluid reasoning has been all over the map, making the true relationship between working memory and fluid reasoning difficult to determine.

There are many reasons for the inconsistencies. Different studies include a different selection of tests, a different number of tests, and a different range of cognitive abilities among the participants. These sort of methodological details matter.

A new study suggests an additional factor at play: the timing of the tests. Adam Chuderski reviewed 26 studies that administered measures of working memory and the Raven’s Progressive Matrices test, which is the most widely used measure of fluid reasoning.*

On each Raven’s question, you are presented with a 3×3 matrix and you have to identify the missing piece that completes the pattern:

What does it take to do well on this test? It turns out there are only a handful of rules required to solve all the items on this test. The easier problems require you to apply a single rule— such as adding or subtracting a single attribute (such as a line). But the harder ones require combining multiple rules, and juggling multiple attributes (such as shapes, sizes, and colors). The difficulty in solving the Raven’s items is that you have to sort out the relevant attributes from the irrelevant attributes and hold the rules in your mind while testing them. And when some rules don’t work out, you have to know when to stop going down that path and start over. Since this task requires the ability to discover the abstract relations among novel stimuli, it is a good measure of nonverbal fluid reasoning.

Chuderski found that the studies that increased the time pressure of the Raven’s test significantly increased the correlation between working memory and fluid reasoning. In other words, when people were given more time to reason, working memory capacity wasn’t as strong a contributor to fluid reasoning.

He found this finding intriguing, so across two studies, he decided to dig deeper.

In his first study, he administered multiple tests of working memory and fluid reasoning to 1,377 people with an age range of 15-46. Using a statistical technique called confirmatory factor analysis, he confirmed that the time pressure of the fluid reasoning tests impact the strength of the correlation between working memory and fluid reasoning.

In the case of the “highly speeded group” (20 minutes), working memory explained all of the variance in fluid reasoning, whereas in the “unspeeded group” (60 minutes), working memory accounted for only 38% of the variance in fluid reasoning:

Chuderski replicated this finding in a second study, finding that under no time pressure during fluid reasoning, working memory only explained about a third of the differences in reasoning performance. Also, he found that a measure of “relational learning”– the ability to learn from prior letter relations to increase efficiency of subsequent processing of number relations– independently contributed to the amount of variation in fluid reasoning.

Why does this matter?

These results suggest we may be seriously underestimating fluid reasoning ability in people by imposing strict time pressures. This study is consistent with other recent research suggesting that “fast intelligence” can be distinguished from “slow intelligence”.

Researchers, educators, and business leaders attempting to assess a person’s level of fluid reasoning face a dilemma: Do you measure the person’s fluid reasoning ability through a highly speed task or do you give the individual more of an opportunity to display his or her reasoning power? As Chuderski notes,

“The former testing method [highly speeded tests] will measure the ability to cope with complexity in a dynamic environment, thus having a high real-world validity, as the technological and informational pressure of the world increases rapidly, but it may underestimate people who regardless of their limited capacity would work out good solutions in less dynamic environments. The latter method [more relaxed time pressures] will give a more comprehensive account of reasoning ability, including the contribution of intellectual faculties that lay beyond WM, and seem to be complementary to it, but it could also include a lot of noise (e.g., learned task-dependent strategies) negatively influencing the evaluation of future effectiveness of an individual in demanding, timed, and completely novel tasks.”

This is important, because given more time, people can compensate for their working memory capacity limitations. For instance, people show large improvements in fluid reasoning after learning how to draw diagrams to represent a problem. When Kenneth Gilhooly and his colleagues presented syllogisms orally, it placed a higher demand on working memory as participants had to store the premises in their head. But when the syllogisms were presented with all the premises remaining on the projector screen, people performed better because they could unload the premises from their working memory and free up limited resources to construct an efficient mental model of the problem.

Over the past decade, John Sweller and colleagues have designed instructional techniques that relieve working memory burdens on students and increase learning and interest. Drawing on both the expertise and working memory literatures, they match the complexity of learning situations to the learner, attempting to reduce unnecessary working memory loads that may interfere with reasoning and learning, and optimize cognitive processes most relevant to learning.

There are also implications for brain training interventions. As I’ve mentioned in an earlier article, the cognitive training literature is a swamp. While some studies find that improving working memory improves fluid reasoning, others studies find a lack of transfer.

A potential cause for the inconsistencies in the cognitive training literature may be the timing of the tasks. For instance, Susanne Jaeggi and colleagues administered their fluid reasoning tests under extreme time constraints (e.g., 10-11 minutes for 18 Raven’s items), and found that working memory training showed an increase in fluid reasoning performance. In contrast, Roberto Colom and colleagues administered fluid reasoning tests under standard time pressures and found no effect of working memory training on fluid reasoning.

These contradictory findings make sense in light of Chuderski’s study: when fluid reasoning tasks have strict time limits, they are essentially tests of working memory. So you would expect more of a transfer from working memory to fluid reasoning under such conditions. But when fluid reasoning tasks have more relaxed time pressures, working memory is more weakly associated with fluid reasoning, and other cognitive mechanisms come into play, such as relational learning and associative learning. Also, external aids can be employed, such as the use of diagrams to facilitate the construction of more elaborate and efficient mental models.


Working memory and fluid reasoning: same or different? It depends. Imposing extreme time pressures on an IQ test forces people to draw almost exclusively on their limited capacity working memory capacity, whereas giving people more time to think and reason gives them more of a chance to bring to the table other cognitive functions that contribute to their intellectual brilliance.

© 2014 Scott Barry Kaufman, All Rights Reserved.

* Win cash prizes and co-authorship of a scientific paper by creating your very own Raven’s items!

Note: Portions of this article were excerpted from Ungifted: Intelligence Redefined.

image credit #1: istockphoto; image credit #2: George Doutsiopoulos; image credit #3: Chuderski study

Scott Barry Kaufman About the Author: Scott Barry Kaufman is Scientific Director of The Imagination Institute in the Positive Psychology Center at the University of Pennsylvania. Follow on Twitter @sbkaufman.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. nicholasjh1 1:56 pm 01/22/2014

    I find this very interesting since my working memory IQ is approximately 107, however my IQ average is 147.

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  2. 2. jtdwyer 2:22 pm 01/22/2014

    Unfortunately I could not access the full research report, but following computational models, suggesting that memory and instruction logic are the same thing is nonsensical. More appropriately, it should be considered here that reasoning ability/performance is functionally constrained by limitations in working memory capacity.
    That presumes that the ‘measurement’ of working memory capacity and reasoning ability are not simply measuring the same things. In computers, after all, discrete memory capacities can be physically measured – this is not the case for ‘working memory capacity’ in the human brain – I suspect it can only be indirectly inferred from other measures.

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  3. 3. pinetree 7:54 pm 01/22/2014

    I suggest out of self interest there is another bias often overlooked. “Of course, adding four letters is a piece of cake.” No it isn’t for those of us with order impairments typical of dyslexia. I bet you could have messed Steve Jobs up with that three letter test due to the massive about of ordering it requires which includes going through all letters before and after in sequence. Basic memorization with order is excoriating. For instance I can not recite poetry or songs for more than a line or two but I can paraphrase many obscure things that I read long ago.

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  4. 4. stargene 3:06 am 01/23/2014

    This research may help explain the consistently different scores I have achieved in the past. When taking the classic and timed Wechsler Adult Intelligence Scale
    test, I twice scored 134. But when taking any purported intelligence test which was untimed, e.g.: when I could take all the time in the world, such as the Terman-McNemar 200 test developed for Terman’s mentally
    gifted group and an early version of the famous Mega
    Test*, published in Omni Magazine in April, 1985, I scored at roughly 156 to 160.


    Clearly, for those higher, untimed scores, my ‘working memory’, never wonderful under pressure, was supple-
    mented by something more going on in the old brainpan. For lack of a more detailed explanation, I’ve considered the ‘something more’ to be associated with sheer creativity or some other form of divergent thinking.

    Tangentially, since some psychologists posit that,
    above an IQ of maybe 115, general intelligence and general creativity tend to sort independently of one another, I once made a very rough estimate that
    Albert Einstein, arguably a transcendent genius having statistically nearly the best of both convergent and
    divergent thinking for his time, may have had an IQ
    of not much less than 180 but not much more than 190,
    and a commensurately high creativity score, working together to great effect. My reasoning was very crude and certainly excluded many other factors… but I pretended that Einstein’s IQ was roughly at least 1
    in 38,000 or so, which pool, with respect to creativity, would also be a randomly selected group of about
    38,000, given the hypothetical independence of
    general intelligence and general creativity. This
    would follow naively from the fact that the square
    root of ~ 1.5 billion (the world’s human population at his birth date) is just above 38,000. This also
    hugely depends on the impossible total sampling of the entire world’s population of the day of course and the unlikeliness of Einstein having had truly the highest plausible IQ and the highest plausible creativity
    index (whatever that means.) :-)

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  5. 5. m 5:41 am 01/23/2014

    at nichlasjh1

    This is well known by anyone with a high iq and not only that it is obvious.

    Intelligence has never been about a quick answer, real intelligence is about being able to fit “a square peg to a round hole”.

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  6. 6. nicholasjh1 12:18 pm 01/23/2014


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  7. 7. truthseeker33 10:50 am 01/24/2014

    EQ, IQ, memorization, retention, recall, all of this is learned behavior associated with having gravitated through some kind of formalized education process, at some point. If you REALLY want to conduct an intelligence test, put an Air Force officer out in the boonies someplace, where all the residents have learned how to live off the land, generally, and make the officer survive without his/her computer, cellphone, and other modern niceties. Who’s the dummy NOW??!?!?!! If you joined the military, in one way you already failed the Mother Of All Intelligence Tests anyway.

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  8. 8. shaunogrady 10:35 am 01/26/2014

    Stress from the time crunch may be influencing the use of working memory. Working memory, in the form measured by these tasks, is a deliberate act, and stress reduces our mind’s ability to react deliberately. I would like to see more on the effects of general stress on working memory and reasoning. A study comparing different levels of social stress (performing a memory task alone, one on one, and in front of an audience) may show the same differential influence of working memory on reasoning abilities.

    We know the cortisol stress response results in temporary and permanent changes in different regions of the brain and under different forms of environmental stress. Intuitively, these changes would result in different (but environmentally adaptive) information processing styles and reasoning abilities under different forms of stress.

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  9. 9. evelyn haskins 7:21 pm 05/24/2014

    Why is the ‘obvious answer’ L,R,G?.

    To me there is no obvious answer but a new question/

    Add four WHAT?

    My initial reaction would be to say “L,R,G +4″

    If you instructed “add four letters” then I would think any random letters would do.

    If you instructed ‘complete the sequence” I would ask what sequence? Those three letters do not form a sequence in any way I can perceive.

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  10. 10. ztech1979 12:30 pm 06/3/2014

    High IQ socieites have known about these results about a decade ago, and thus allow take home, ‘IEQ’ tests for admission. More time, allows a problem to be attacked from long-term memory which, in certain individuals, allows for faster loading (thus, with more information per time) into working memory. Associative memory also becomes important in un-timed conditions. Under truly untimed conditions (interday), scores can increase between 1-2 sd, in certain people.

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