Is conflict monitoring supramodal? Spatiotemporal dynamics of cognitive control processes in an auditory Stroop task

Abstract

The electrophysiological correlates of conflict processing and cognitive control have been well characterized for the visual modality in paradigms such as the Stroop task. Much less is known about corresponding processes in the auditory modality. Here, electroencephalographic recordings of brain activity were measured during an auditory Stroop task, using three different forms of behavioral response (overt verbal, covert verbal, and manual), that closely paralleled our previous visual Stroop study. As was expected, behavioral responses were slower and less accurate for incongruent than for congruent trials. Neurally, incongruent trials showed an enhanced fronto-central negative polarity wave (N(inc)), similar to the N450 in visual Stroop tasks, with similar variations as a function of behavioral response mode, but peaking ~150 ms earlier, followed by an enhanced positive posterior wave. In addition, sequential behavioral and neural effects were observed that supported the conflict-monitoring and cognitive adjustment hypothesis. Thus, while some aspects of the conflict detection processes, such as timing, may be modality dependent, the general mechanisms would appear to be supramodal.

Figure 1. Response times

A. Slower response times were observed in the Overt condition (i.e., verbal) compared to the Manual, and for both response-mode conditions participants were slower on incongruent than on congruent trials. Error bars represent standard error of the mean (SEM) values.

Figure 2. Early negative-polarity incongruency effect (N_inc)

A. Time-locked ERP waveforms for the incongruent and congruent conditions (Overt congruent: 1644 sums, Overt incongruent: 1751 sums; Covert congruent: 1754 sums, Covert incongruent: 1836 sums; Manual congruent: 1925 sums, Manual incongruent: 1991 sums). The early negative-wave incongruency effects emerged starting at around 200 ms in all conditions. (Each tick mark represents 100 ms for the traces.) B. Topographic distributions for incongruent minus congruent trials for Overt, Covert, and Manual conditions from 200–300 ms and 400–500 ms. In the Covert and Overt conditions, by 400–500 ms the negativity shifted to a more anterior (and somewhat right lateralized) location, while the effect was basically gone in the Manual condition by this time. In addition, the initial negative-polarity effect in the Manual condition was distributed more posteriorally than in the other conditions.

Figure 3. Late posterior-positivity incongruency effect (SP)

Traces showing the late parietal differences between incongruent and congruent trials over site POz for the Overt, Covert, and Manual conditions. (Sums shown here are the same as reported in Figure 2.) Topographic distributions show the difference of incongruent minus congruent trials from 600 to 700 ms.

Figure 4. Sequential behavioral effects

A. Response times in the Manual response condition for the incongruent (I) and congruent (C) trials as a function of the previous trial type. Participants slowed their response times for incongruent trials when they followed a congruent trial as compared to following another incongruent trial. B. A similar sequential slowing pattern was observed in the Overt response condition. Error bars represent SEM values.

Figure 5. Sequential EEG effects

A. Differential responses to incongruent trials when they were preceded by an congruent versus an incongruent trial (_CI versus _II). A greater late (500 – 800 ms) posterior positivity was elicited for the former case, visible in both the main traces and the difference waves (2^nd column).Topographic distributions of the differences between _CI minus _II are shown for 600–700 ms for the Overt (1164 sums), Covert (1292 sums), and Manual (1376 sums) conditions. B. Differential responses to congruent trials (difference waves) when they were preceded by incongruent (_IC) compared to congruent (_CC) trials for the Overt (964 sums), Covert (1142 sums), and Manual (1217 sums) conditions. A greater late (500 – 800 ms) posterior positivity was seen for _IC trials compared to _CC trials, shown in the first column of traces and in the difference waves in the 2^nd column. Topographic differences of _IC minus _CC are shown for 600 to 700 ms. C. Bar graphs for the manual condition comparing differences in RT to differences in neural activity. The left graph shows the differences of the mean amplitude for _IC minus _CC and _CI minus _II from 600 to 700 milliseconds averaged over sites POz and PO1 and PO2. The right graph shows the differences in response time for these conditions, respectively. Here, the neural activity and response times mirrored each other in the relative size of the differences. Error bars represent SEM values.

Figure 6

Brain-behavior correlation, Manual condition. X-axis shows the difference in neural activity I_I minus C_I trials in microvolts averaged across sites POz, Oz, PO1 and PO2 for 500 to 800 ms. Y-axis shows the difference in response time for _II trials minus _CI trials in milliseconds. Differential activity in previous trial correlates with differential response times across subjects in current trial when the current trial is incongruent.