Manual Responses Are Verbally Mediated in Stroop Identification Tasks

Abstract

In a typical Stroop experiment, participants view a color word written in a color that is either congruent or incongruent with the word’s meaning and identify either the target’s color (Stroop condition) or meaning (reverse Stroop condition). Incongruent words generally interfere with identifying the target color more than incongruent colors interfere with identifying the target word. A common explanation for this classic asymmetry asserts that vocally identifying the target’s color or meaning relies on a verbal code, which biases attention to the target’s meaning over its color. However, the asymmetry also occurs with nonverbal keypress responses, so participants may covertly map verbal codes onto keys to remember which key represents each color. To verify this verbal mediation hypothesis, we presented Stroop color-word targets along with 4 cues to help participants remember which key represented each color. In one condition the cues were color words, and in the other the cues were color patches. We hypothesized that the word cues would elicit the classic asymmetry and color cues would abolish this asymmetry. The results supported our hypotheses; for word cues the Stroop effect was larger than the reverse Stroop effect, p < .001, ηp = .64, and color cues abolished this difference, p < .001, ηp = .31. This study is the first to provide direct confirmation of the verbal mediation hypothesis and suggests that task demands are more important than the response modality (vocal versus manual) for biasing processing toward one of the Stroop target’s features.