Fig 1.
In the beginning of each trial, an instructional cue consisting of either “word” for word-reading or “color” for color-naming was presented which was followed by a 1,3 or 5 second cue-target interval and an imperative color word stimulus (“red”, “blue” or “green”) written in colored letters. Any response would trigger a 3 second inter trial interval prior to the next cue. The time period of interest in this study was -500ms to 1500ms with 0ms indicating cue onset.
Table 1.
Stroop task performance by task type, transition type and congruency.
Fig 2.
Task-related ERPs and their associations with reaction time.
(A) Topography of the ERP difference from the contrast of color-naming versus word-reading trials. Blue color indicates larger ERPs for word-reading trials. Red color indicates larger ERPs for color-naming trials. The value that was used to compute the difference was the mean ERP amplitude within the period of 250–800 ms after the cue onset. The electrodes with significant ERP difference across subjects were marked by stars (p < 0.05). (B) Cue-evoked ERP waveforms from electrodes in the left-frontotemporal, the midline-frontal and the centroparietal scalp regions for color-naming trials and word-reading trials. Time zero is the cue onset. The time periods with significant ERP difference across subjects were shaded by gray color (p < 0.05). (C) ERP amplitudes for different RT groups by task type. Significant differences between RT groups were marked (** p < 0.01, * p < 0.05).
Fig 3.
Switch-related ERPs and their association with reaction time.
(A) Topography of the ERP difference from the contrast of task-switch versus task-repeat trials. Red color indicates larger ERPs for switch trials. Blue color indicates larger ERPs for repeat trials. The value used to compute the difference was the mean ERP amplitude within the period of 450–800 ms after the cue onset. The difference was computed for each subject and the grand-average was plotted in the figure. The electrodes with significant ERP difference across subjects were marked by stars (p < 0.05). (B) Cue-evoked ERP waveforms from electrodes in the left-frontal and the centroparietal scalp regions for task-switch trials and task-repeat trials. Time zero is the cue onset. The time periods with significant ERP difference were shaded by gray color (p < 0.05). (C) ERP amplitudes for different RT groups by transition type. Significant differences between RT groups were marked (** p < 0.01, * p < 0.05).
Fig 4.
Task-related ERPs and their association with RT by congruency.
ERP amplitudes are plotted for different RT groups by task and stimulus type (congruous vs. incongruous) for (A) the left-frontotemporal negativity (FT7, 250–700 ms), (B) the midline-frontal negativity (Fz, 450–800 ms), and (C) the centroparietal positivity (CP2, 450–800 ms). Significant differences of ERP amplitudes between RT groups were marked (** p < 0.01, * p < 0.05). Because of the small number of trials available for analysis two RT groups (fast and slow) instead of three RT groups were used.
Fig 5.
Switch-related ERPs and their association with RT by congruency.
ERP amplitudes are presented for different RT groups by switch and stimulus type (congruous vs incongruous) for (A) the left-frontal negativity (F3, 450–800 ms), and (B) the centroparietal positivity (Pz, 450–800 ms). Significant differences of ERP amplitudes between RT groups were marked (** p < 0.01, * p < 0.05). Because of the small number of trials available for analysis two RT groups (fast and slow) instead of three RT groups were used.
Table 2.
ERP components, their correlations with behavioral performance, and their proposed functional roles.