The two main theories behind the Stroop effect are the speed of processing theory and the selective attention theory. Other theories include the automaticity hypothesis, bottleneck theory and parallel distributed processing theory.
The Stroop effect is the interference in the brain when it receives conflicting information. The effect is demonstrated by asking subjects to read color words written in different colors. When subjects are asked to name the color rather than read the word, the Stroop effect demonstrates that reaction time decreases.
The speed of processing theory states that humans read words faster than they recognize colors. The theory is that humans learn that words are more important than color identification, so the brain automatically reads the word first. When subjects are asked to name the color instead, there is a delay in response.
The selective attention theory states that the brain needs more information to identify a color than it does to read a word. This theory hypothesizes that reading words is automatic, so the brain naturally does it first.
The automaticity hypothesis, which is similar to the selective attention theory, theorizes that reading words is automated but color identity is not. The bottleneck theory proposes the brain processes types of information automatically. When subjects are asked to identify the color, it disrupts that flow of automatic processing. Parallel distributed processing theory asserts different information is processed through different streams in the brain. If two streams are activated simultaneously, the stronger stream, reading, processes before the weaker stream.