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Randomized Controlled Trial
. 2014 May;26(5):1021-38.
doi: 10.1162/jocn_a_00542. Epub 2013 Dec 17.

The Dynamics of Proactive and Reactive Cognitive Control Processes in the Human Brain

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Free PMC article
Randomized Controlled Trial

The Dynamics of Proactive and Reactive Cognitive Control Processes in the Human Brain

L Gregory Appelbaum et al. J Cogn Neurosci. .
Free PMC article

Abstract

In this study, we leveraged the high temporal resolution of EEG to examine the neural mechanisms underlying the flexible regulation of cognitive control that unfolds over different timescales. We measured behavioral and neural effects of color-word incongruency, as different groups of participants performed three different versions of color-word Stroop tasks in which the relative timing of the color and word features varied from trial to trial. For this purpose, we used a standard Stroop color identification task with equal congruent-to-incongruent proportions (50%/50%), along with two versions of the "Reverse Stroop" word identification tasks, for which we manipulated the incongruency proportion (50%/50% and 80%/20%). Two canonical ERP markers of neural processing of stimulus incongruency, the frontocentral negative polarity incongruency wave (NINC) and the late positive component (LPC), were evoked across the various conditions. Results indicated that color-word incongruency interacted with the relative feature timing, producing greater neural and behavioral effects when the task-irrelevant stimulus preceded the target, but still significant effects when it followed. Additionally, both behavioral and neural incongruency effects were reduced by nearly half in the word identification task (Reverse Stroop 50/50) relative to the color identification task (Stroop 50/50), with these effects essentially fully recovering when incongruent trials appeared only infrequently (Reverse Stroop 80/20). Across the conditions, NINC amplitudes closely paralleled RTs, indicating this component is sensitive to the overall level of stimulus conflict. In contrast, LPC amplitudes were largest with infrequent incongruent trials, suggesting a possible readjustment role when proactive control is reduced. These findings thus unveil distinct control mechanisms that unfold over time in response to conflicting stimulus input under different contexts.

Figures

Figure 1
Figure 1
SOA Design and Tasks. (A) In these SOA variants of the Stroop and Reverse Stroop tasks, color-word stimuli were presented with five levels of relative onset timing. As depicted schematically, the target stimulus component (aligned here at 0 ms), could be preceded by, presented simultaneously with, or followed by the irrelevant stimulus component. Here each of the temporal separations (−200, −100, 0, +100, and +200ms) are shown on a separate row indicating the relative timing onsets between the target and distracter elements. Once both stimulus components were presented, they remained on the screen for an additional 1000 ms for all conditions. In the Stroop task (top) the participants’ task was to report the physical color of the stimulus while ignoring the meaning of the written word. In the Reverse Stroop task (bottom) the participants were to report the written word, while ignoring the physical color. (B) Schematic illustration showing the three Tasks. These were comprised of two possible ‘Attentional Goals’ (color or word identification) and two relative ‘Incongruency Proportions’ (50/50% or 80/20%, Congruent/Incongruent).
Figure 2
Figure 2
Reaction times (RTs) and incongruency RT differences (incongruent minus congruent) for the three tasks. (A) In all three tasks incongruent trials (red) are slower than congruent (blue) trials. (B) Incongruent minus congruent RT differences (black) are largest at negative SOAs and decline monotonically at later SOAs for all tasks. Overall, the effect sizes across SOAs were greatly reduced (nearly 2 to 1) in the ReverseStroop-50/50 task relative to either of the other two tasks (Stroop-50/50 and ReverseStroop-80/20), which did not significantly differ from each other.
Figure 3
Figure 3
ERP results for the 0 ms SOA conditions. (A) Grand average waveforms computed in the 6-channel ROI are shown for incongruent (red) and congruent (blue) trials of the 0 ms SOA condition of the three Attentional Goals. (B) Incongruent minus congruent difference waveforms reveal prominent negative (NINC) and positive (LPC) deflections for each task. (C) Spline-interpolated topographic maps computed over the significant NINC and LPC latency ranges (highlighted in gray in (A) and (B) and specified below each map in (C) are shown for each task.
Figure 4
Figure 4
Incongruency difference waves averaged over the 6-channel ROI are shown for all SOAs in the three tasks. All waveforms are shown time-locked to the onset of the relevant target component of the stimulus for the different tasks. NINC and LPC effects are indicated by the dark and light grey shading, respectively.
Figure 5
Figure 5
ERP latencies and amplitudes for three Attentional Goals. (A) Latency ranges of significant within-SOA effects are shown by the dark grey bars for the NINC and light grey bars for the LPC for each SOA and task. (B) Mean ERP amplitudes for the NINC (negative amplitudes plotted upward) and LPC (positive amplitudes plotted downwards) are shown for the 5 SOAs and three tasks. Hashed outlines for the +200 ms SOA LPC component indicate that these values were estimated from the local peak window and that these responses did not reach permutation significance. Error bars indicate +/− 1 standard deviation.
Figure 6
Figure 6
ERP latencies and amplitudes for three Attentional Goals. (A) Latency ranges of significant within-SOA effects are shown by the dark grey bars for the NINC and light grey bars for the LPC for each SOA and task. (B) Mean ERP amplitudes for the NINC (negative amplitudes plotted upward) and LPC (positive amplitudes plotted downwards) are shown for the 5 SOAs and three tasks. Hashed outlines for the +200 ms SOA LPC component indicate that these values were estimated from the local peak window and that these responses did not reach permutation significance. Error bars indicate +/− 1 standard deviation.

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