The timing of cognitive control in partially incongruent categorization

Abstract

We designed a novel task, partially incongruent categorization (PIC), to examine the timing of cognitive control. In the PIC task, participants categorized the probe stimulus according to a specific concept, and the number of features corresponding to the concept was varied. When there was one feature (c1 condition), the probe would elicit only categorization, but when there was more than one feature (c2 and c3 conditions), the probe would also elicit cognitive control. Here, the high temporal resolution of event-related potentials (ERPs) was utilized to investigate the temporal patterns of activity during conflict detection and control. Cognitive control elicited a N2 that was much larger in response to c2 and c3 than c1 in stimulus-locked waveforms, and no difference was evident between c2 and c3. The N2 was followed by a P3 that was much less on c2 and c3 than c1 trials, with no difference between c2 and c3. A dipole source analysis for two difference waves, c2-c1 and c3-c1, further showed that the corresponding dipoles of the N2 and P3 in the cognitive control conditions were in the anterior cingulate cortex (ACC) and prefrontal cortex (PFC), respectively. Taken together, the present findings support that ERP components in response to the PIC task reflect the time course of cognitive control: the N2 responds to conflict information and subsequently activates the P3 to control this conflict. The connection between the ACC and PFC is supported by their sequential activation within trials.

Figure 1

The main cognitive processes in the PIC task. In condition c1 (A), if the feature relevant to the concept were 0° (A, left), then the participants would form anticipation to the “stripe orientation” attribute. After the presentation of the probe, this attribute would be attended, but the “color” and “shape” attributes would be omitted from attention. For trials requiring a positive response (when the probe stimulus has a stripe orientation of 0°; A, right), the stimulus would not elicit conflict and control. In condition c2 (B), if the features relevant to the concept were square and 45° (B, left), then the participants would form anticipation to “shape” and “stripe orientation.” After presentation of the probe, both of these attributes would be attended, but “color” would be omitted from attention. Trials requiring a positive response could have either a square probe or a probe with 45° stripe orientation. For example, it may be a circle with 45° stripe orientation or a square with 135° orientation (B, right). However, only one feature would be congruent with participants' anticipation and the other feature would become an attended incongruent feature, eliciting conflict and control during categorization. Similarly to c2, in condition c3 (C), if the features in the concept were red, circle, and 45° (C, left), but positive response trials only had one congruent feature (C, right), both conflict and control would be elicited, but the number of conflicting features attended to in c3 is more than in c2.

Figure 2

The experimental procedure for one trial in the present study.

Figure 3

The 64‐channel Neuroscan electrode montage. The statistical analysis is based on data recorded by electrodes located within the small circles.

Figure 4

Mean response times for the c1, c2, and c3 conditions in the PIC task (left). Mean accuracies for the same three conditions (right). Error bars indicate the SE.

Figure 5

Grand average (n = 15) of ERPs in response to c1 (gray line), c2 (black line), and c3 (dotted line) at the 12 electrode sites chosen for statistical analysis. Time = 0 ms corresponds to the onset of target stimulus presentation. N1, P2, N2, and P3 are indicated on the waveform plots. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 6

Grand average of ERPs in response to c1, c2, c3, and the difference waves (c2−c1 and c3−c1) at Cz and topographic maps of the difference waves at 280 ms and 370 ms. The two grand averages and c2−c1 difference waves are presented in the upper left panel, and the two grand averages and c3−c1 difference waves are in the lower left panel. The topographic maps of the c2−c1 difference wave at 280 ms and 370 ms are presented in the upper right panel, and those of the c3−c1 difference wave at 280 and 370 ms are presented in the lower right panel.

Figure 7

Dipole source localizations for the difference wave c2−c1 and c3−c1 at peak latencies of the N2 and P3. The top left panel is the fitted dipole within the 240–300 ms window presented in the sagittal, coronal, and transverse sections (Talairach coordinates x = 8.3, y = 11.2, z = 38.7). The top right panel is the fitted dipole within the 340–400 ms window viewed in the sagittal, coronal, and transverse sections (x = 25.7, y = 24.4, z = 35.9). The bottom left panel is the fitted dipole within the 240–300 ms window viewed in the sagittal, coronal, and transverse sections (x = 0.5, y = 8, z = 32.3). The bottom right panel is the fitted dipole within the 340–400 ms window viewed in the sagittal, coronal, and transverse section s (x = 25.7, y = 25, z = 24.9).