Duncan-Johnson and Kopell (1981) found the stroop interference to be a result of the response-competition between ink color and word. A study by Atkinson, Drysdale, and Fulham (2003) found significant stroop and reverse stroop effects. The study determined the stroop effect to be a result of the response-competition phenomenon, not related to the speed of processing of the color or word. Further support of processing traveling through dual pathways in parallel is found in a study using ERP to monitor the brain while subjects took a stroop task (Alain and West, 1999). .
The second theory to explain the stroop phenomenon is known as automaticity. Proposed by LaBerge and Samuels (1974), the theory claims that things that are practiced and repeated often eventually become automatic processes that require little to no attention. Thus, reading the color-word is automatic as one reads very often, but naming the color is not. This theory explains why in an incongruent task subjects are slower and more error prone because they cannot avoid the automatic process of reading. Henik and Tzelgov (1982) found a significant difference between congruent and incongruent trials in a variation of the stroop task. Instead of color and words the task used numbers and number size. It was found that subjects could not ignore the numerical values when asked to judge the size of the numbers. The experimenters concluded that the subjects could not overcome the automatic activation of numerical information. This study provides further support for the automaticity theory. Henek and Rubinsten (2002), using animal names, and physical and semantic sizes in a variation of the stroop task, also found significant effects and determined that a word's meaning is accessed automatically. Using type written responses, a study by Logan and Zbrodoff (1998) found a significant stroop effect interpreting automaticity as an important factor in the occurrence.