How does the brain work when under the stroop effect?

Answer 1

A friend of mine recently sent me this link for the "color test."I get this or a similar link every now and then. It is a fun little neurological game, and I am always intrigued by the pop-neuro explanations that come along with it.

Go ahead - take the test, then come back….

This color test is an old neuro-psychological test known as the Stroop test, and the effect is known as the Stroop Effect after John Ridley Stroop who first published about the effect in English in 1935. As is common, the effect was first described as a neuro-psychological phenomenon and then efforts were made to explain the effect as a consequence of neuroanatomy - how the brain is hardwired and how the different parts of the brain work together.

That is where the pop-neuro comes into play. All the sites I found that used the effect as a party game gave the same wrong explanation for the effect - that it is a demonstration of the right-brain/left-brain "struggle" or interaction.

This site explains the effect this way:

Actually, this test is checking your brains ability to separate the left brain functions and right brain functions. The problem is that the left side of your brain is trying to tell you to read the word, while at the same time, the right side of your brain is trying to tell you to identify the color!!!

This makes me wonder if the author copied this explanation from another site, or just made it up because it sounds good.

The Stroop Effect does indeed represent processing that is occurring in the brain to rectify different imperatives, but it has nothing to do with the left-brain/right-brain thing. The effect, as it is currently understood, is a matter of attention. A better paradigm for understanding this effect rather than left/right is top-down, or the hierarchical organization of the brain.

Our brains mostly function subconsciously - you don't have to pay attention in order to breath, walk, or process visual input. At the same time the highest brain functions allow us to attend to a subset of the sensory information coming in, our internal thought, and even many of our automatic functions. You can voluntary control your breathing if you attend to it, otherwise your primitive brainstem will happily breathe on its own without your conscious control.

What is happening with the Stroop Effect is a phenomenon called interference. You are being asked to attend to the color of the "ink" of the words, and not to the words themselves. However, it is actually impossible to turn off the reading of words once you learn how to read. The process of translating letters into words becomes so automatic that we cannot stop that part of our language center from doing it. It is thought, in fact, that most people do not even have the pathways in the brain that would enable us to inhibit that part of language function - it is literally impossible.

This is supported by experimental evidence that the Stroop Effect - which specifically refers to the delay in naming or clicking the "ink"color for color words - is always present. There are no experimental conditions that make it go away.

(As an aside, I was told by Terrence Hines that he found a small number of people who can be hypnotized to make the Stroop Effect go away - the first time this has been described - and he surmises they have a variant of hardwiring that allows this. However, I do not have the reference for this - so take it as hearsay for now.)

In fact this effect is so reliable that it has been used to catch spies. If a Russian agent is pretending to be American they can be tested to see if they exhibit the Stroop Effect for Russian words. If you cannot read a language, there will be no delay; if you can then you cannot avoid the delay.

What is happening then is that we are being confronted with conflicting stimuli - the color and the word. We then have to consciously suppress the word and respond to the color. But this takes an attentional effort and requires a finite amount of processing time that is unavoidable - hence the Stroop Effect.

What the test is really measuring (assuming literacy in the language tested) is attention, or mental effort - the highest order mental function in our brain hierarchy.

That this effect is wrongly explained on popular sites as a left-brain/right-brain conflict reflects the popularity of this concept. It is a highly overused concept, and is simply wrong in this case. Language is indeed typically encoded in the left temporal lobe (although about 5% of people are dominant for language on the right side and this is more common in left-handers). But color is not a right-brain process. Both hemispheres (the occipital lobes specifically) are able to see and process color information.

This common error also reflects the fact the we tend to explain phenomena with the explanatory models we have at hand. We are always, in fact, limited by our current repertoire of explanatory models or paradigms, because our understanding of the universe will never be complete.

The history of scientific progress reflects a tendency to explain as much as possible within current paradigms. If, however, those paradigms or insufficient eventually they will reach their limits. New modes of explanation will then have to be created - and this is the most creative and difficult aspect of science.

The most dramatic example of this of which I am aware was the crisis of classical physics that required Einstein and others to develop the new paradigms of relativity and quantum mechanics to solve.

Often, however, explanatory models are incrementally expanded, without the drama of a crisis of impasse and a bold new theory to smash old ideas. Also - sometimes the evidence suggests new modes of explanation before anyone realizes the inadequacy of the old modes. For example, Mendel discovered that heredity was digital rather than analog - meaning that some genetic traits were inherited in an all-or-none fashion (through genes), rather than an infinite blending of the traits from both parents.

The left-brain/right-brain notion is stuck in popular culture, but is mostly wrong. The real interaction among various brain structures is far more complex and interesting. But it is common for scientific concepts to trickle down to the popular culture through various imperfect media, where they are distorted and over-simplified into mostly wrong soundbites.

I have therefore come to believe, through my own experience and by observing others, that for any complex topic (whether scientific, some other academic speciality, or any other developed set of knowledge) which I have not studied from primary sources or experts, that whatever knowledge I have gleaned from the popular culture is almost certainly mostly wrong.

Answer 2

During the Stroop effect, the brain experiences interference between reading and identifying the color of the ink used to print words. This conflict requires the brain to quickly suppress the automatic response of reading the word in favor of focusing on the color. The prefrontal cortex is particularly involved in resolving this conflict and inhibiting the automatic response.