Common and Specific Loci of Stroop Effects in Vocal and Manual Tasks, Revealed by Event-Related Brain Potentials and Posthypnotic Suggestions

摘要

In the Stroop task color words are shown in various print colors. When print colors are named or classified with button presses, interference occurs if word meaning is color-incongruent and facilitation if it is congruent. Although the Stroop effects in vocal and manual task versions are similar, it is unclear whether the underlying mechanisms are equivalent. We addressed this question by (a) recording event-related brain potentials (ERPs), (b) manipulating the lexicality of neutral stimuli, and (c) giving posthypnotic suggestions (PHS) that written words would lose their meaning. The Stroop effect in the vocal version was twice its manual counterpart. PHS strongly reduced both effects by a similar amount, supporting a common semantic locus during reading. Task- and hypnosis-invariant lexicality effects for neutral words ruled out presemantic reading loci. Articulation-artifact corrected ERPs showed task-invariant Stroop effects in N400 amplitudes, supporting similar semantic loci. However, in the vocal task response-locked ERPs indicated a task-specific Stroop effect over left-inferior frontal and parietal scalp sites, suggesting interference during word production. Interestingly, PHS increased the N1 and decreased the N2 components in ERPs, regardless of congruency, indicating enhanced proactive executive control and diminished demands on conflict-monitoring, respectively. Stroop effects in the N400 were reduced by PHS, confirming their semantic locus. In conclusion, vocal and manual Stroop versions seem to share semantic loci of conflict. The bigger vocal Stroop effect may be attributable to additional loci during word production lexicon. Apparently, PHS diminish Stroop effects by enhancing proactive executive control over lexico-semantic conflicts.