Stroop Effect

Try to say the color of each word instead of reading the words themselves. #consciousness

Excerpt from Philosophy for Heroes: Act. You can pre-order it here:

How do we consciously initiate an action?

If it is not a reflex or other non-conscious action (breathing, swallowing, coughing, etc.), the primary motor cortex generates motor programs to achieve a goal. The basal ganglia selects a single motor program and coordinates the final movement program with the cerebellum. The selection process consists of competing neural committees that refine the motor program in several steps and the “best” program is selected. If the motor program is new, this process can take a moment (or could take several physical attempts if the movement is complex, like a child trying to walk for the first time).

The executive functions are provided by the prefrontal cortex. Instead of initiating an action, the main task of the prefrontal cortex core function is to suppress whatever catches your attention if that action does not align with your ego, social rules, or your long-term plans. For example, not eating the candy bar in front of you to fulfill your long-term goal of being healthy requires prefrontal cortex activity. Vice versa, instead of suppressing a single action, the prefrontal cortex can also suppress every activity but one. This can help with focusing on one particular activity. But instead of trying to directly suppress most neural activity in the primary motor cortex, the actual suppression happens in concert with the basal ganglia. Damage to the basal ganglia can lead to a loss of motivation (apathy): while the primary motor cortex still generates several programs, there is no arbiter to select the best one. Even with focus by the prefrontal cortex, this might not be enough to create a strong enough signal to execute an actual physical action. It is like having many brochures of different travel destinations but not taking the time to compare them and select one. No matter how much effort the travel agencies put into the design of their offer, without someone comparing them and selecting one, their work is in vain.

Executive functions: The executive functions represent a series of ways the prefrontal cortex can suppress thought patterns in other parts of the brain. While winners in the neural competition are selected with the help of the basal ganglia, the prefrontal cortex can counteract those decisions in favor of other actions. The prefrontal cortex makes these decisions based on its models. For example, stealing goes against the norms of society, so the prefrontal cortex suppresses the utilization behavior of the parietal lobe to grab someone else’s property.

With a damaged prefrontal cortex, we would tend to show utilization behavior, which means applying action to anything in our environment that catches our attention. What initiates utilization behavior is the parietal lobe, based on what has been provided by the senses and processed in the occipital and temporal lobes. And this is how most animals (and human children) react toward their environments if their prefrontal cortex is not as developed as it is in (adult) humans. When an animal is presented food, the animal eats it. When the animal is shown a toy, it plays with it. If we present a human with a short attention span a smartphone, that human will feel inclined to pick it up and check his messages.

As a compromise between focus, energy usage, and the possibility to quickly react to your environment, the brain actually oscillates between parietal lobe (utilization behavior) and frontal lobe (focus) activity [Misselhorn et al., 2019]. This way, while the frontal cortex focuses on the current action, the neurons in the parietal lobe are not firing and vice versa.

You can also imagine the executive function like a separate group in our neural committees. This new group takes care that, once started, activities are not stopped but brought to a finish. It rewires our past decisions to the present so that we do not forget them. It will reinforce its point to continue with an activity we have started instead of switching back and forth between equally interesting activities. Eating the candy bar might be the most interesting thing, but finishing our math homework might save us some time: interrupting work is often connected with a lot of overhead because you have to start thinking about it from the beginning. In that regard, you can think of the ability to focus as an optimization to reduce costs when having to deal with multiple things at the same time. Instead of going back and forth, we focus on one thing, finish it, then move on to the next.

After an action has been executed, the thought pattern originally causing the action will be suppressed. For example, when standing in front of a sink and seeing a piece of soap, we might be inclined to wash our hands (utilization behavior). If our prefrontal cortex does not intervene, we will wash our hands. Once finished, our prefrontal cortex will then send a signal to suppress washing our hands a second time—it has evaluated our hands as now being “clean” and “safe.” If this signal fails (which it sometimes do, for example in sufferers from OCD), the brain’s internal status of the hands still shows that they are dirty, so we wash them again. Sufferers from phantom limb pain face a similar problem. Without the signal that the limb has been unclenched, the internal status remains unchanged. For both sufferers from OCD and phantom limb pain, one could argue that they could just look at their hands or missing limb. But as we have discovered, the brain requires two sources of information to update its body schema. In the case of the phantom limb pain, it is the visual signal (with the help of a mirror) and the initiation of the muscle movement (unclenching). In the case of OCD, it is the reevaluation of the risk (germs are invisible) together with the act of handwashing.

We can test this suppressive effect and the functioning of the executive function by measuring the “stroop effect” which is the delay in reaction time between congruent (meaning and color of a word are the same) and incongruent (meaning of a word and its color are different) stimuli. To give the correct answer, the prefrontal cortex has to suppress the part of the brain that provides the meaning of a word (in favor of the part of the brain that provides the information about the color of the text). For example, take a look at the image below and try to name the color of each word instead of reading the word.

stroop effect
Try to say the color of each word instead of reading the words themselves (image source: Shutterstock). The delay in your answer is the “stroop effect,” stemming from the need for your prefrontal cortex to suppress the wrong response (reading the words as opposed to saying the color).

We can get a better understanding of consciousness if we take a look at how we initiate actions. In that regard, the prefrontal cortex actually acts as a suppressor, preventing actions that are proposed by the parietal lobe. If there is damage to the prefrontal cortex, this can lead to utilization behavior where you end up using any usable object in your environment. Actually, the brain oscillates between utilization behavior and suppression in order to leave room both for catching new sense data in your environment, as well as focusing on your current activity. Besides suppression, the prefrontal cortex also “deletes” behavior by sending a “safe” signal. Without that signal, people can show OCD behavior like repeatedly washing their hands.

By Clemens Lode

Clemens Lode is a management consultant with focus on agile project management methods (check out He likes to summarize his insights into books, check out his philosophy series "Philosophy for Heroes" here: His core approach to philosophy and management is that people need to be more aware of their limits and ultimately their identity and their vulnerabilities.

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