Electrophysiologic indices of Stroop and Garner interference reveal linguistic influences on auditory and visual processing.

The purpose of this study was to examine linguistic influences on the auditory and visual processing of words both behaviorally and electrophysiologically. Our task yielded measures of the effect of irrelevant semantic content (Stroop interference) and of the effect of irrelevant linguistic variability (Garner interference). The behavioral results allow us to assess whether the linguistic and nonlinguistic dimensions of verbal stimuli are processed dependently or independently. The electrophysiologic results allow us to determine where any processing interactions are arising, particularly regarding perceptual versus postperceptual underpinnings, and to evaluate the similarity and dissimilarity between the two interference effects. Results show pronounced Stroop and Garner interference both behaviorally and electrophysiologically, indicating linguistic influences on auditory and visual processing. Subjects could not ignore the irrelevant linguistic dimension and attend selectively to the physical dimension of either spoken or written words. The results indicate that the physical and linguistic dimensions of words are not processed independently. With regard to the stage of processing underlying the interference effects, our results suggest that both Stroop and Garner interference involve multiple stages of processing. The two interference effects are not duplicate measures, however, and different electrophysiologic signatures were observed. Stroop interference is characterized by perceptual and postperceptual components. Similar electrophysiologic patterns within the auditory and visual modalities suggest that each interference effect is tapping similar processes for spoken and written stimuli.