Date Published: January 15, 2019
Publisher: Public Library of Science
Author(s): Megan C. Fitzhugh, Peter S. Whitehead, Lisa Johnson, Julia M. Cai, Leslie C. Baxter, Corianne Rogalsky, Maurice Ptito.
The visual color-word Stroop task is widely used in clinical and research settings as a measure of cognitive control. Numerous neuroimaging studies have used color-word Stroop tasks to investigate the neural resources supporting cognitive control, but to our knowledge all have used unimodal (typically visual) Stroop paradigms. Thus, it is possible that this classic measure of cognitive control is not capturing the resources involved in multisensory cognitive control. The audiovisual integration and crossmodal correspondence literatures identify regions sensitive to congruency of auditory and visual stimuli, but it is unclear how these regions relate to the unimodal cognitive control literature. In this study we aimed to identify brain regions engaged by crossmodal cognitive control during an audiovisual color-word Stroop task, and how they relate to previous unimodal Stroop and audiovisual integration findings. First, we replicated previous behavioral audiovisual Stroop findings in an fMRI-adapted audiovisual Stroop paradigm: incongruent visual information increased reaction time towards an auditory stimulus and congruent visual information decreased reaction time. Second, we investigated the brain regions supporting cognitive control during an audiovisual color-word Stroop task using fMRI. Similar to unimodal cognitive control tasks, a left superior parietal region exhibited an interference effect of visual information on the auditory stimulus. This superior parietal region was also identified using a standard audiovisual integration localizing procedure, indicating that audiovisual integration resources are sensitive to cognitive control demands. Facilitation of the auditory stimulus by congruent visual information was found in posterior superior temporal cortex, including in the posterior STS which has been found to support audiovisual integration. The dorsal anterior cingulate cortex, often implicated in unimodal Stroop tasks, was not modulated by the audiovisual Stroop task. Overall the findings indicate that an audiovisual color-word Stroop task engages overlapping resources with audiovisual integration and overlapping but distinct resources compared to unimodal Stroop tasks.
The human brain is capable of selectively attending to pertinent information, concurrently ignoring or inhibiting irrelevant information, overriding automatic responses, and correcting errors. Collectively, these specific abilities are referred to as cognitive control and have been the focus of dozens of research studies over the last several decades (for reviews see [1–4]).
The aim of the present study was to characterize the brain regions that support cognitive control during an audiovisual (AV) color-word Stroop task. The neurobiology of single-modality cognitive control (typically within either the visual or auditory domains) has been well studied in color-word Stroop tasks and other similar paradigms, as has audiovisual control and integration for sounds and objects. But to our knowledge, no previous neuroimaging study has investigated AV cognitive control using a color-word Stroop task. Thus, it was unclear how the brain regions recruited during the widely-used visual color-word Stroop task are dependent upon it being a unimodal task, and how color-word Stroop task results relate to AV integration and crossmodal correspondence findings. The present AV color-word Stroop fMRI study fills these gaps in the literature and provides an intersection between the fields of cognitive control and audiovisual integration. Specifically, the present study (1) characterizes how traditionally-defined AV integration regions are modulated in a classic cognitive control paradigm, and (2) identifies the neural correlates of conflict resolution in an AV color-word Stroop task, for comparison to the neural correlates of previous unimodal color-word Stroop tasks. We replicated previous behavioral AV Stroop task findings [44,45], in that congruent visual information facilitated auditory speech perception and incongruent visual information interfered with auditory speech perception (as measured by reaction time differences between congruent or incongruent trials and audio-only trials). We then implemented our fMRI-adapted version of Donohue et al.’s  AV Stroop task during fMRI acquisition. Our findings are discussed in detail below. Briefly, our results indicate that some AV integration regions are sensitive to AV interference while others are sensitive to facilitation in a color-word Stroop task, and that our AV color-word Stroop task engages regions distinct from those modulated by unimodal color-word Stroop tasks in previous studies.
In the present study we used fMRI to investigate the neural resources engaged during an audiovisual color-word Stroop task. Superior parietal regions frequently implicated in unimodal Stroop tasks and attention more generally were more responsive to AV stimuli than unimodal stimuli and exhibited an interference effect when incongruent visual information was presented alongside the auditory stimulus. Posterior STG/STS regions previously implicated in AV integration and more anterior STG auditory regions also were found to be more responsive to AV than auditory stimuli alone, but unlike the superior parietal region, these temporal regions exhibited facilitation effects (i.e. reduced activation for AV congruent stimuli than unimodal stimuli), suggesting that helpful visual information was reducing the demands of these primarily auditory regions. The dorsal ACC, which is reliably implicated in conflict resolution by unimodal Stroop tasks, was not found to be modulated by task condition in the present AV Stroop study. This null finding in the dorsal ACC may be driven by the equal distribution of congruent and incongruent trials which has been found to diminish interference effects in the ACC, but future studies are needed to clarify the role of the ACC in multimodal conflict processing. Altogether, the present study indicates that regions implicated in audiovisual integration also are sensitive to conflict resolution in a color-word Stroop task; and that an AV color-word Stroop task implicates distinct but overlapping cognitive control resources identified by previous unimodal Stroop studies. These findings suggest that AV cognitive control and AV integration rely upon overlapping resources (particularly in the superior parietal lobe). Furthermore, the visual color-word Stroop task that is widely-used as both a clinical and research measure of cognitive control, may not be capturing all of the neural resources engaged in the conflict resolution that occurs in everyday life, due to the tight connection between auditory and visual information in the real world .