Distinct ERP profiles of stimulus-stimulus and stimulus-response compatibility effects Kai Wang, Qi Li and Xun Liu Institute of Psychology, Chinese Academy of Sciences, Beijing, China
RESULTS
ABSTRACT From perspective of the dimensional overlap framework, the present study aimed to investigate the possible distinct event-related potential (ERP) correlates of stimulus-stimulus (S-S) and stimulusresponse (S-R) compatibility effects. Two parallel tasks, Simoncolor-Stroop (SCS) task and Simon-spatial-Stroop (SSS) task, each incorporating two classical stimulus-response-compatibility (SRC) paradigms, Stroop task and Simon task, were performed. For both tasks, in the earliest time window of interest (200~250 ms for the SCS task, 230~280 ms for the SSS task) S-S compatibility effect were significant while S-R effects were not. However ERP correlates of SRC effects of both type were essentially of the same pattern in later periods. During an early period (100~200ms) of lateralized readiness potentials (LRPs) in both S-S and S-R conditions, waveforms for compatible trials were more positive than those of incompatible trials reflecting a common motor-related electrophysiological processing of these compatibility effects. These findings revealed both common and distinct mechanisms of S-S and S-R conflict processing.
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According to the dimensional overlap (DO) theory (Kornblum et al., 1990), stimulus response compatibility (SRC) effects (Proctor and Reeve, 1990) can be categorized and attributed to DO ( similarity of properties) between stimulus-stimulus (S-S) sets or between stimulus-response (S-R) sets in experimental context. Based on this account, we can examine the modular organization of the cognitive control network and test whether there is a common conflict monitoring (CM) module and a common executive control (EC) module responsible for both S-S and S-R conflicts (1CM1EC model), or these two types of SRC effects are sub-served by distinct CM and EC modules (2CM2EC model) (Egner, 2008). However, our hypothesis is that CM modules are distinct for S-S and S-R conflicts, but both conflicts are modulated by a common EC module (2CM1EC model), which was supported by our previous behavioral and brain imaging studies have provided evidences for the 2CM1EC model (Liu et al., 2004, Liu et al., 2010). The present work aimed to provide electrophysiological evidence to this topic.
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Figure 2. ERP results with difference waveforms. S-S compatibility effects were significant while S-R were not in areas marked by vertical grey lines. Simon-color-Stroop task
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Participants. Twenty six college students (13 female) performed both tasks. A signed informed consent was obtained from each participant prior to the experiment. Experimental Design. By modifying and integrating Stroop task and Simon task, we developed two tasks (Simon-color-Stroop and Simon-spatial-Stroop task, see Figure 1), each of which can induce both S-S or S-R type of conflict separately. Data Analysis. EEG were recorded using a 64-channel system (Neuroscan, Neuroscan Inc.). Mean amplitudes of four middle-line electrodes (FCz, Fz, Cz, Pz, Oz) of five time windows were chosen for analysis with repeated measurement analysis of variance (ANOVA). The first three windows were 50-ms ones, starting 200 ms (SCS task) or 230 ms (SSS task) after target onset, and the last two windows lasted for 100 ms each, 420~620 ms for SCS; 430~630 ms for SSS task. Lateralized readiness potentials (LRPs) were calculated, over the motor cortex, by subtracting potentials contralateral to the responding hand from ipsilateral potentials. An early time window (100-200ms), which may reflect covert motor activation (Hartmut, 2011), were chosen for statistical analysis. Simon-color-Stroop task
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Figure 3. LRP results calculated for C3-C4 electrode pairs In both tasks, conflicts caused by both S-S and S-R compatibility effects modulated ERP amplitudes of multiple time windows. However, S-S and S-R compatibility effects showed distinct ERP profiles in temporal onset and latency of difference-wave peaks (Figure 2): S-S compatibility effect occurred at an earlier time window as compared to S-R compatibility effect. During an early period (110~210 ms) of LRPs in S-S conditions of both tasks, waveforms for incompatible trials were more positive than those of compatible trials, reflecting motor-related electrophysiological correlates of these compatibility effects (Figure 4). Because of lateralized stimulus display in S-R conditions of both tasks, compatibility effects of LRP in S-R conditions were further facilitated by lateralized conduction of visual sensory information.
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1) ERP correlates of S-S compatibility effects had earlier onset time and peaked earlier in difference waveforms than those of S-R compatibility effects. 2) Both S-S and S-R congruence effects was related to automatic response activation; classic S-R congruence (induced by Simon like tasks) was further affected by lateralized conduction of visual sensory information.
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These electrophysiological evidences indicated that both common and distinct mechanisms were responsible for S-S and SR type of conflict processing supporting a 2CM1EC structure of human cognitive control functions.
REFERENCES Egner, T. (2008). 'Multiple conflict-driven control mechanisms in the hum an brain'. Trends in Cognitive Sciences, vol. 12, no. 10, pp. 374380. Leuthold, H. (2011). 'The Simon effect in cognitive electrophysiology: A short review'. Acta Psychologica, vol. 136, no. 2, pp. 203-211. Kornblum, S. (1990). 'Dimensional overlap: cognitive basis for stimulus-response compatibility--a model and taxonomy'. Psychological Review, vol. 97, no. 2, pp. 253-270. Liu, X. (2004). 'Common and distinct neural substrates of attentional control in an integrated Simon and spatial Stroop task as assessed by event-related fMRI'. Neuroimage, vol. 22, no. 3, pp. 1097-1106. Liu, X. (2010). 'Dimensional overlap accounts for independence and integration of stimulus-response compatibility effects', Attention, Perception, & Psychophysics, vol. 72, no. 6, pp. 1710-1720. Proctor, R.W. (1990). 'Stimulus-response compatibility: An integrated perspective' (Vol. 65): North Holland.
Figure 1. Task designs (A, B) and procedures (C, D) of the two tasks. To request a copy of the poster, please send an email to
[email protected].
