A new perspective on the role of the frontoparietal regions in Stroop-like conflicts

Abstract

Humans are goal-directed; however, goal-unrelated information still affects us, but how? The Stroop task is often used to answer this question, relying on conflict (incongruency) between attributes, one targeted by the task and another irrelevant to the task. The frontal regions of the brain are known to play a crucial role in processing such conflict, as they show increased activity when we encounter incongruent stimuli. Notably, the Stroop stimuli also consist of conceptual dimensions, such as semantic or emotional content, that are independent of the attributes that define the conflict. Since the non-targeted attribute usually refers to the same conceptual dimension as the targeted-attribute, it is relevant to the task at hand. For example, when naming the emotion of an emotional face superimposed by an emotional word, both the targeted-attribute and the non-targeted attribute refer to the conceptual dimension "emotion". We designed an fMRI paradigm to investigate how conflicts between different conceptual dimensions impact us. Even though the conflict was task-irrelevant, incongruent stimuli resulted in longer reaction times, indicating a behavioral congruency effect. When examining the neural mechanisms that underlie this effect, we found that the frontal regions exhibited repetition suppression, while the bilateral intraparietal sulcus (IPS) showed a congruency effect linked to the behavioral effect. Taken together, these findings suggest that individuals are unable to completely ignore task-irrelevant information, and that the IPS plays a crucial role in processing such information.

Keywords: attention; conflict adaptation; conflict monitoring; congruency effect; intraparietal sulcus; repetition suppression.

FIGURE 1

Paradigm. (a) Uncoupling the conflict from the task: The current study breaks the coupling between the conflict and the task by asking participants to make an animacy judgment, thus making the conflict task‐irrelevant. Note that in the figure, the term dimension refers to the conceptual dimension, defined as the semantic field. (b) The event‐related fMRI paradigm presented three types of stimuli: color‐word, picture‐word, and emotional picture‐word. Each stimulus was either congruent or incongruent, depending on the relationship between its attributes. Every word (in the color‐word type) and picture (in the picture‐word types) appeared at least twice, once in a congruent and once in an incongruent stimulus. The second appearance was always in a different run than the first appearance. In the figure, this is represented by the three dots in the timeline.

FIGURE 2

Regions of interest (ROI) and activations. (a) Four ROIs were used for the analysis based on Xu et al. (2016). Each ROI is composed of several spheres because overlapping and homologous spheres were united and are presented in the same color. (b) The difference (Δ) in PSC between the incongruent and congruent conditions (incongruent—congruent). In the bilateral IPS activation was significantly higher in the incongruent than the congruent condition, manifested by a positive Δ. (c) The difference in PSC between the first and non‐first conditions (first—non‐first). In all regions, except the bilateral IPS, activation was significantly lower for the non‐first than the first condition, manifested by a positive Δ. The ROIs showed different sensitivity to congruency and repetition in the parietal and frontal regions. For each effect, correction for multiple comparisons across the four regions was carried out using the Holm‐Bonferroni method. Error bars are standard errors. IFG, inferior frontal gyrus; IPS, intraparietal sulcus; L, left; MFG, middle frontal gyrus; R, right; SMA, supplementary motor area; Δ, difference (incongruent—congruent) or (first—non‐first).

FIGURE 3

Relationship between IPS activation and behavior. (a) The calculation procedure. For each stimulus, the difference (Δ) between incongruent and congruent conditions (Δ = incongruent—congruent) was calculated in terms of the RT and PSC of the IPS. The averaged ΔPSC of the IPS was computed for each participant for stimuli with positive ΔRT (incongruent RT > congruent RT) and negative ΔRT (incongruent RT < congruent RT). (b) A bar graph presenting the result of the ΔPSC comparison between the positive and negative ΔRT. Across participants, a higher ΔPSC was evident for stimuli with positive ΔRT than negative ΔRT, implying a functional significance of the bilateral IPS activation in the congruency effect. PSC, percent signal change; RT, reaction time; Δ, difference (incongruent—congruent); *p < .05.