Acta Psychologica 58 (1985) 225-235 North-Holland
THE EFFECTS OF EFFORT ON STROOP INTERFERENCE *
David P. MacKINNON, R. Edward GEISELMAN and J. Arthur WOODWARD Unrcwwt~v of California, Los Angeles, USA
Accepted August 1984
Stroop interference was defined as the difference in time needed to name the ink colors of printed color and color-related words versus control plus signs. The effect of effort on Stroop interference was studied using an inter-subject competition procedure designed to manipulate effort. In experiment 1, subjects in the competition group were successful at inhibiting Stroop interference when compared to the performance of subjects in the no-competition group. This result is consistent with theories that postulate attentional effects on Stroop interference. In experiment 2, the significant decrease in Stroop interference was accompanied by a significant reduction in recognition memory for Stroop list items. Therefore. Stroop interference was reduced at a stage during the processing of word meaning. This result is consistent with theories that locate Stroop interference before response output.
The purpose of this research is twofold: first, to investigate the effect of effort on Stroop interference; and second, to study the locus of the mechanism by which effort may influence Stroop interference. Stroop (1935) demonstrated that the time for naming the color of ink with which color words are incongruently written is greater than the time for naming the colors of squares or other color-irrelevant symbols. The difference between the performance times with these two kinds of stimuli is called Stroop interference, or simply the Stroop effect. In the 49 years since the discovery of this phenomenon, the Stroop effect has received considerable attention in cognitive psychology; first of all, in an attempt to understand the effect itself (Seymour 1977; Stirling 1979) and alternatively, in the study of other constructs such as automatic
* This research was supported in part by Grant BNS 7910053, funded jointly by the National Science Foundation and Office of Naval Research.
Mailing address: R.E. Geiselman, Dept. of Psychology, University of California. Los Angeles, CA 90024. USA.
OOOl-6918/85/$3.30 0 1985, Elsevier Science Publishers B.V. (North-Holland)
226 D. P. Mcrc~Kwmm el 01. / Efforr und Swoop mterfrrenc.e
processes (Posner and Snyder 1975) hemispheric dominance (Perret 1974) and cognitive styles (Broverman 1960). Jenson and Rohwer (1966) and Dyer (1973) provide extensive reviews of the Stroop effect and its applications.
In this research, we are asking two related questions about the nature of the effect of effort on Stroop interference. First, what happens when subjects expend considerable effort to perform as rapidly as possible on all materials (i.e., on color word items as well as on control plus signs)? Is the performance difference between the types of items (the inter- ference) equal to, greater than, or less than that...