interference theory, the most commonly used procedure has been similar to Stroop's second experiment, in which subjects were tested on naming colors of incompatible words and of control patches. The first experiment in Stroop's study (reading words in black versus incongruent colors) has been discussed less. In both cases, the interference score is expressed as the difference between the times needed to read each of the two types of cards. Instead of naming stimuli, subjects have also been asked to sort stimuli into categories. Different characteristics of the stimulus such as ink colors or direction of words have also been systematically varied. None of all these modifications eliminates the effect of interference. Neuroanatomy Brain imaging techniques including magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), and positron emission tomography (PET) have shown that there are two main areas in the brain that are involved in the processing of the Stroop task. They are the anterior cingulate cortex, and the dorsolateral prefrontal cortex. More specifically, while both are activated when resolving conflicts and catching errors, the dorsolateral prefrontal cortex assists in memory and other executive functions, while the anterior cingulate cortex is used to select an appropriate response and allocate attentional resources. The posterior dorsolateral prefrontal cortex creates the appropriate rules for the brain to accomplish the current goal. For the Stroop effect, this involves activating the areas of the brain involved in color perception, but not those involved in word encoding. It counteracts biases and irrelevant information, for instance, the fact that the semantic perception of the word is more striking than the color in which it is printed. Next, the mid-dorsolateral prefrontal cortex selects the representation that will fulfill the goal. The relevant information must be separated from irrelevant information in the task; thus, the focus is placed on the ink color and not the word. Furthermore, research has suggested that left dorsolateral prefrontal cortex activation during a Stroop task is related to an individual's’ expectation regarding the conflicting nature of the upcoming trial, and not so much on the conflict itself. Conversely, the right dorsolateral prefrontal cortex aims to reduce the attentional conflict and is activated after the conflict is over. Moreover, the posterior dorsal anterior cingulate cortex is responsible for what decision is made (i.e. whether someone will say the written word or the ink color). Following the response, the anterior dorsal anterior cingulate cortex is