STROOP TASK:
A TEST OF CAPACITY TO DIRECT ATTENTION

Introduction

To understand the mental process involved try this experiment. Look at the following letters on the screen: tree. If you are like most people it is difficult for you not to quickly read the word "tree."  Most humans are so proficient at reading printed words that they cannot easily ignore them. In fact it takes considerable attentional effort to ignore them. This tendency to quickly read a word is used in the Stroop Task.

The Stroop Task is a psychological test of our mental (attentional) vitality and flexibility. The task takes advantage of our ability to read words more quickly and automatically than we can name colors. If a word is printed or displayed in a color different from the color it actually names; for example, if the word "green" is written in blue ink (as shown in the figure to the left) we will say the word "green" more readily than we can name the color in which it is displayed, which in this case is "blue." 

The cognitive mechanism involved in this task is called directed attention, you have to manage your attention, inhibit or stop one response in order to say or do something else. 

The Neurophysiology

John Ridley Stroop first reported this effect in his Ph.D. thesis published in 1935. Current research on the Stroop effect emphasizes the interference that automatic processing of words has on the more mentally "effortful" task of just naming the colors. The task of making an appropriate response -- when given two conflicting signals -- has tentatively been located in a part of the brain called the anterior cingulate. This is a region that lies between the right and left halves of the frontal portion of the brain. It is involved in a wide range of thought processes and emotional responses.

Although the functions of the anterior cingulate are very complex, broadly speaking it acts as a conduit between lower, somewhat more impulse-driven brain regions and higher, somewhat more thought-driven behaviors. The Stroop effect's sensitivity to changes in brain function may be related to its association with the anterior cingulate.

The Stroop Test provides insight into cognitive effects that are experienced as a result of attentional fatigue.

For a discussion of the capacity to direct attention and its fatigue see Kaplan, S. (1995). The restorative benefits of nature: Toward an integrative framework. Journal of Environmental Psychology, 15, 169-182  and  Kaplan, S. (2001). Meditation, restoration and the management of mental fatigue. Environment and Behavior, 33, 480-506.