Auditory Conflict Processing: Behavioral and Electrophysiologic Manifestations of the Stroop Effect

Abstract

One of the most extensively studied phenomena in cognitive neuroscience is the Stroop effect. In an enormous corpus of literature, the Stroop task has been used to study conflict processing in the visual modality; however, scarce data exist in the auditory modality. The main goal of the present study was to investigate auditory conflict processing by means of behavioral and electrophysiologic measures elicited during standard and reversed Stroop tasks. A secondary goal was to examine practice-related effects. Event-related potentials (ERPs) were recorded from 16 adults during tasks requiring classification of word meaning or speaker's gender while ignoring the irrelevant (congruent or incongruent) speaker's gender or word meaning, respectively. The behavioral measures, reaction time and performance accuracy, were simultaneously obtained. Results indicated (1) a significant behavioral Stroop effect manifested by prolonged reaction time and reduced performance accuracy. In contrast, ERP latencies were unaffected by the processing of incongruent versus congruent stimuli, supporting postperceptual conflict processing associated with response selection and execution; (2) reduced N1 amplitude while processing incongruent versus congruent stimuli; (3) similar behavioral Stroop effects in both tasks together with nonsignificant task by stimulus type (incongruent, congruent) interactions for N1 and N4; (4) significantly prolonged N4 and reaction time together with reduced N1 amplitude in the speaker's gender task (to both congruent and incongruent stimuli) compared to those found in the word meaning task; and (5) practice-related improvement in processing efficacy based on enhanced N1 amplitude, as well as shorter N4 and reaction time. Auditory conflict processing was predominantly postperceptual and was located at the response selection and execution stages. Alterations in the N1 component, however, provided support for an auditory conflict-processing "signature" at the initial stages of the arrival of information to the auditory cortex. The current data indicate that speaker's gender and word meaning intruded on one another in a similar fashion, supporting symmetry between standard and reversed auditory Stroop effects. Nonetheless, improved processing efficacy was evident while classifying word meaning. Utilization of the present methodology may prove advantageous for studying clinical populations exhibiting auditory and/or linguistic processing deficits.