Stroop effect: interference and facilitation with verbal and manual responses.

Two groups of 12 volunteers manually (button pushing) or verbally identified the ink color of 5, randomly ordered and tachistoscopically presented, kinds of stimulus conditons, specified by the nature of the noncolor information and the relationship between color and noncolor information: Congruent Color Words, Noncolor Words, Scrambled Color Words, Nonword Geometric Shapes, and Noncongruent Color Words. With verbal response, facilitation of reaction time occurred for Congruent Color Words compared to Scrambled Color Words and Noncolor Words but not when compared to the Nonword Control, while with manual response facilitation appeared for all comparisons. Interference appeared for both groups, with Noncongruent Color Words having the slowest reaction time. The present design corrected for inadequacies in previous studies and more firmly established the conclusion of parallel perceptual processing of color and noncolor information, with facilitation/interference effects being localized in postperceptual decision operations of signal summation and response competition.