Final answer:
People are slower on incongruent trials in the Stroop task because the brain has to resolve interference between the meaning of the word and the color of the ink, requiring more cognitive effort.
Step-by-step explanation:
The most commonly accepted explanation for why most people are slower on incongruent trials than on congruent trials in the Stroop task is due to the interference between different information (what the words say and the color of the words), which the brain has to process. This conflict of information requires the brain to engage in more cognitive effort and suppress the automatic tendency to read the word rather than name the ink color, which takes more time. This phenomenon is related to cognitive control and attentional processes in the brain.