The Bivalency effect in task switching: Event‐related potentials

Grundy, John G.; Benarroch, Miriam F.F.; Woodward, Todd S.; Metzak, Paul D.; Whitman, Jennifer C.; Shedden, Judith M. · 2011 · OpenAlex-citations

DOI: 10.1002/hbm.21488

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Summary

This study investigates the neural time course of the "bivalency effect" in task switching, a phenomenon where the occasional presence of stimuli cueing multiple tasks (bivalent stimuli) causes response slowing on all other trials within that block. While previous functional MRI (fMRI) research identified the dorsal anterior cingulate cortex (dACC) as critical for this effect, the temporal dynamics of ACC involvement remained unclear due to fMRI's limited temporal resolution. The authors aimed to provide the first high-temporal-resolution account of this effect using event-related potentials (ERPs) and to determine if the effect dissipates with extended practice. Twenty-five participants performed three alternating tasks: color judgment of shapes, parity judgment of digits, and case judgment of letters. The experiment consisted of six experimental blocks alternating between purely univalent blocks and bivalent blocks, where 20% of case-judgment trials featured colored letters (bivalent stimuli). EEG data were recorded from 128 electrodes. The researchers analyzed reaction times (RTs) and ERPs, focusing on univalent trials in bivalent blocks ("uni–biv") versus univalent trials in univalent blocks ("uni–uni"). They employed partial least squares (PLS) analysis to identify spatiotemporal patterns in the ERP data without a priori biases, followed by conventional statistical tests and dipole source localization. Behavioral results confirmed the bivalency effect: RTs for uni–biv trials were significantly slower than for uni–uni trials. This slowing effect was most pronounced in the early experimental blocks but dissipated with extended practice, as the RT difference between block pairs decreased significantly from the first pair (blocks 1–2) to the last pair (blocks 5–6). Electrophysiologically, frontal electrode sites showed significant amplitude differences associated with the bivalency effect in three specific time windows: 100–120 ms, 375–450 ms, and 500–550 ms. The early window likely reflects additional extraction of visual features, while the later windows reflect the suppression of processing carried over from irrelevant cues. Dipole source analysis localized these frontal ERP differences to the dACC, supporting previous fMRI findings. Crucially, the ERP differences also diminished with practice, mirroring the behavioral data. The findings demonstrate that the bivalency effect involves a controlled response style mediated by the dACC, characterized by specific neural processing stages for feature extraction and conflict suppression. The study establishes that the ACC is recruited to adjust control when bivalent stimuli introduce conflict, even on univalent trials. Furthermore, the dissipation of both behavioral and electrophysiological effects with practice suggests that participants learn to process bivalent stimuli more efficiently, reducing the need for ACC-mediated control adjustments. This provides a detailed temporal map of the neural mechanisms underlying cognitive flexibility and conflict monitoring in task switching.

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• task switching