A recent study finds that motivation is a key component of performance on standardized IQ test. Researchers compared IQ scores with and without a material incentive to perform well. They found that everyone performs better with the incentive, but those with lower baseline IQ scored have a larger effect. They conclude from this that performing well on an IQ test requires both intelligence and motivation, but that those who score poorly may lack either one or both – and some simply lack motivation.

These results reflect a broader theme I often point out to students – when we examine the nervous system we are mostly asking people to perform specific tasks and then we infer how well the system is working based upon their performance. We cannot (with few exceptions) directly interrogate the nervous system to see how well certain components are functioning. So we design tasks that are meant to isolate, as much as possible, one function and to also maximally stress that function.

But it is impossible to completely isolate one subsystem within the brain, and so other functions can interfere with our testing, and we have to tease this out by using multiple tasks and then triangulating to the common element that seems to be causing trouble. This is most true for cognitive function.

For example, if I want to test Wernicke’s area (in the superior posterior temporal lobe) I will give the patient several verbal commands (without non-verbal cues) and see if they can interpret them. Wernicke’s area translates ideas into words and words into ideas, and so we test its function by testing verbal comprehension. However, in order to test this one piece of the brain, the patient also needs to be able to attend to the exam (they need to be alert and attentive), then need to be able to hear and get that information to Wernicke’s area, they need to have the general cognitive ability to understand what is happening and that they are expected to do something, and they need to be able to move to execute whatever command I gave them. And they may decide just to be uncooperative with the exam, for whatever reason. So many parts of the brain and nervous system need to work together to perform even a simple task.

We isolate Wernicke’s function, and other functions, by controlling for variables. So I will give the patient many commands, some easier for Wernicke’s area to interpret, and others more challenging – but with all other variables being equal. If commands that are difficult from a language comprehension point of view are what give the patient the most difficulty, then that is probably the part of the brain that is not working.

IQ testing is not different – it is simply a task that involves multiple neurological functions, only one of which is general intelligence (which itself is a tricky concept, as there are many components to what we would think of as intelligence, and many different kinds of intelligence). We need to think of IQ as a measure of how people perform on IQ tests, and not necessarily of any one specific neurological function. Since IQ is measuring many variables at once (memory, fund of knowledge, judgment, perception, cognitive processing speed, attention, language, test-taking endurance, and yes – even motivation) it’s difficult to separate out these variables. It can be done to some extent, and the most elaborate battery of IQ tests (called neuropsychological testing) is designed to separate out at least several components of intelligence, like verbal-IQ from memory IQ.

This does not mean that IQ testing is worthless, we just need to have a nuanced and realistic view of what it is and what it is not. This new data on motivation is not surprising at all, and adds to our ability to properly interpret IQ testing.

Also, another way to look at IQ testing, or any type of testing, is not what it is actually measuring but what it predicts. If a test is predictive of some outcome, then it has utility, regardless of how messy a measure it is. The BBC quotes Dr James Thompson, senior honorary lecturer in psychology at University College London, who said:

“Life is an IQ test and a personality test and an IQ result contains elements of both (but mostly intelligence). “If an IQ test doesn’t motivate someone then that is a good predictor in itself.”

I agree – if someone possesses the raw cognitive ability, but lacks the motivation to apply it, they will perform poorly on IQ tests, and perhaps in life also. For example, IQ testing does predict school performance (if imperfectly). Perhaps both are strongly influenced by motivation. Therefore, despite the fact that IQ testing is messy and complex, it can still tell us something useful. It just should not be viewed as a pristine measure of something innate and immutable about a person.