The neurocognitive underpinnings of the Simon effect: An integrative review of current research

Published online: 7 October 2020For as long as half a century the Simon task – in which participants respond to a nonspatial stimulus feature while ignoring its position – has represented a very popular tool to study a variety of cognitive functions, such as attention, cognitive control, and response preparation processes. In particular, the task generates two theoretically interesting effects: the Simon effect proper and the sequential modulations of this effect. In the present study, we review the main theoretical explanations of both kinds of effects and the available neuroscientific studies that investigated the neural underpinnings of the cognitive processes underlying the Simon effect proper and its sequential modulation using electroencephalogram (EEG) and event-related brain potentials (ERP), transcranial magnetic stimulation (TMS), and functional magnetic resonance imaging (fMRI). Then, we relate the neurophysiological findings to the main theoretical accounts and evaluate their validity and empirical plausibility, including general implications related to processing interference and cognitive control. Overall, neurophysiological research supports claims that stimulus location triggers the creation of a spatial code, which activates a spatially compatible response that, in incompatible conditions, interferes with the response based on the task instructions. Integration of stimulus-response features plays a major role in the occurrence of the Simon effect (which is manifested in the selection of the response) and its modulation by sequential congruency effects. Additional neural mechanisms are involved in supporting the correct and inhibiting the incorrect response.This research was supported by the Basque Government through the BERC 2018-2021 program and by the Spanish State Research Agency through BCBL Severo Ochoa excellence accreditation SEV-2015-0490 This study was also funded by Juan de la Cierva-Incorporación (Spanish government; JC) and European Commission (Marie Skłodowska-Curie actions 838536_BILINGUALPLAS; JC), by post-doctoral funding of the University of Bremen (DG; ZF 11/876/08), and by an ERC Advanced Grant (BH: ERC-2015-AdG-694722)

Zeitlich-räumliche Charakteristiken von Arbeitsgedächtnis-Prozessen untersucht mit statischen und dynamischen komplexen Stimuli - funktionelle Magnetresonanztomographie, ereigniskorrelierte Potentiale und fMRI-geleitete Quellenanalyse

Experiment 1:In the majority of experiments studying working memory (WM) tasks either delayed match-to-sample (DMTS) or n-back tasks were used to assess WM operations. In n-back tasks, however, a separation of different WM processes is impossible, whereas in DMTS tasks it is usually not required to monitor the WM content.In Experiment 1, a variant of a DMTS task with continuously morphing stimuli was applied, requiring human participants to continuously monitor and compare the currently presented stimulus to the held-in-mind target shape during the retention period. To asses changes caused by cognitive load two different types of stimuli were employed: Complex curved shapes and a simple circle. Furthermore four different delay durations (3, 6, 9, 12 s) have been applied. The goal of the present fMRI study was to characterize brain areas responsible for WM maintenance under continuous monitoring conditions in a WM task with morphing shapes. Moreover, the influence of cognitive load on maintenance activity in motion-sensitive area MT should be investigated. Data from 15 study participants are presented. Conjunction analysis including the contrasts complex versus simple shapes over all delay durations revealed activations in a widespread fronto-parietal network, which has been discussed to be involved in WM by a large body of literature. Area MT showed an association with target complexity, resulting in a significant signal enhancement while monitoring complex shapes (compared with simple circle trials).The present results demonstrate that the level of activation during the maintenance interval might be dependent on target complexity, because complex targets caused a stronger activation than simple circle targets in brain areas associated with WM processes even during similar visual stimulation.Experiment 2:So far, WM retrieval has been investigated only in a few studies. In Experiment 2, a DMTS task using static stimuli was applied to examine differences in the processing of different probe types (targets, non-targets) during the retrieval epoch. Probe stimuli were presented at different positions in the trial (trial position A, B, and C), resulting in parametrically increasing delay durations (3, 7, and 11 seconds) before probe presentation.Twenty individuals completed a similar WM task in an fMRI session as well as in an EEG session.The objective of the present study was to characterize differences in the cognitive processing of target probes and non-target probes by using different methodological approaches (behavioral, fMRI, EEG, and SA data) and to examine the influence of delay duration (cognitive load) on these differences.P3b mean amplitudes showed higher values for target trials compared with non-target trials at electrode position Cz, corroborating old/new effects reported from long-term memory research.The majority of brain regions which showed activation in fMRI in the probe epoch regardless of probe type (probe epoch versus fixation) did also show activation when contrasting target trials with non-target trials. This indicated a specific involvement of these brain areas in the processing of target stimuli. Altogether, behavioral, fMRI and EEG data indicated probe type-related processing differences, which might have been influenced by the ratio of target stimuli to non-target stimuli and also by the presence of distracting probe stimuli during longer delay periods (7, 11 s).Source analysis revealed a sequence of source activities during probe type processing starting with activity in occipital and temporal brain regions. This was presumably linked to the processing of stimulus features, followed by a simultaneous involvement of parietal and frontal brain regions and later processing in superior frontal gyrus (pre-SMA).Differences in source activity between targets and non-targets indicated a specific involvement of left fusiform gyrus in the non-target condition, probably associated with the mental imagination of the target stimulus during non-target probe processing.Furthermore, source activities showed specific engagements in target processing for the regional source in anterior cingulate cortex (ACC) before response execution and also for the regional source in superior frontal gyrus (SFG) before and simultaneously to response execution. These findings might be an indicator for the involvement of both regions in different stages of conflict managing operations because target trials had a lower stimulus frequency compared with non-target trials (at trial positions A and B).Summarized, different WM processes (maintenance, retrieval) were investigated in both experiments, and different methodological approaches were applied. In the general discussion, findings from both experiments are linked to each other, considering brain regions which were involved in the processing of both tasks

Differences and Similarities for Spatial and Feature-Based Selective Attentional Orienting

Using selective attention, we prioritize behaviorally relevant information out of all surrounding stimulation. Attention can be oriented intentionally to spatial and/or non-spatial properties (feature-based attention). When comparing spatial and feature-based attention, previous studies identified a common fronto-parietal network, although some reported specific activation for spatial attention and few found higher activation for feature-based attention. Most studies examining differences between attention types investigated the cueing epoch. We examined reorienting processing (after invalid cueing) and correctly focused attention (after valid cueing) for spatial and feature-based orienting using fMRI in two human samples with 40 participants overall and identical stimuli, stimulus probabilities, and timing for all conditions. A fronto-parietal network including parts of the ventral orienting network was activated for reorienting and focused attention for both attention types. Common activity over validities and attention types was located in bilateral IPL/SMG, bilateral IFG/insula, and the cerebellum. A network of mainly posterior areas showed higher activity for spatial compared to feature-based orienting. Conversely, no specialized areas for spatial focused attention or for feature-based attention (reorienting/focusing) was observed. The posterior clusters specialized for spatial reorienting showed overlapping activity with clusters involved in common spatial and feature-based reorienting as well as focused attention over attention types. Therefore, the results hint at a superordinate fronto-parietal network for both attention types during reorienting and focusing, with a spatial specialization of posterior sub-regions

Temporo-Spatial Characteristics in Working Memory Processes Investigated with Static and Dynamic Complex Stimuli - Functional Magnetic Resonance Imaging, Event-Related Potentials and fMRI-Constrained Source Analysis

Experiment 1:In the majority of experiments studying working memory (WM) tasks either delayed match-to-sample (DMTS) or n-back tasks were used to assess WM operations. In n-back tasks, however, a separation of different WM processes is impossible, whereas in DMTS tasks it is usually not required to monitor the WM content.In Experiment 1, a variant of a DMTS task with continuously morphing stimuli was applied, requiring human participants to continuously monitor and compare the currently presented stimulus to the held-in-mind target shape during the retention period. To asses changes caused by cognitive load two different types of stimuli were employed: Complex curved shapes and a simple circle. Furthermore four different delay durations (3, 6, 9, 12 s) have been applied. The goal of the present fMRI study was to characterize brain areas responsible for WM maintenance under continuous monitoring conditions in a WM task with morphing shapes. Moreover, the influence of cognitive load on maintenance activity in motion-sensitive area MT should be investigated. Data from 15 study participants are presented. Conjunction analysis including the contrasts complex versus simple shapes over all delay durations revealed activations in a widespread fronto-parietal network, which has been discussed to be involved in WM by a large body of literature. Area MT showed an association with target complexity, resulting in a significant signal enhancement while monitoring complex shapes (compared with simple circle trials).The present results demonstrate that the level of activation during the maintenance interval might be dependent on target complexity, because complex targets caused a stronger activation than simple circle targets in brain areas associated with WM processes even during similar visual stimulation.Experiment 2:So far, WM retrieval has been investigated only in a few studies. In Experiment 2, a DMTS task using static stimuli was applied to examine differences in the processing of different probe types (targets, non-targets) during the retrieval epoch. Probe stimuli were presented at different positions in the trial (trial position A, B, and C), resulting in parametrically increasing delay durations (3, 7, and 11 seconds) before probe presentation.Twenty individuals completed a similar WM task in an fMRI session as well as in an EEG session.The objective of the present study was to characterize differences in the cognitive processing of target probes and non-target probes by using different methodological approaches (behavioral, fMRI, EEG, and SA data) and to examine the influence of delay duration (cognitive load) on these differences.P3b mean amplitudes showed higher values for target trials compared with non-target trials at electrode position Cz, corroborating old/new effects reported from long-term memory research.The majority of brain regions which showed activation in fMRI in the probe epoch regardless of probe type (probe epoch versus fixation) did also show activation when contrasting target trials with non-target trials. This indicated a specific involvement of these brain areas in the processing of target stimuli. Altogether, behavioral, fMRI and EEG data indicated probe type-related processing differences, which might have been influenced by the ratio of target stimuli to non-target stimuli and also by the presence of distracting probe stimuli during longer delay periods (7, 11 s).Source analysis revealed a sequence of source activities during probe type processing starting with activity in occipital and temporal brain regions. This was presumably linked to the processing of stimulus features, followed by a simultaneous involvement of parietal and frontal brain regions and later processing in superior frontal gyrus (pre-SMA).Differences in source activity between targets and non-targets indicated a specific involvement of left fusiform gyrus in the non-target condition, probably associated with the mental imagination of the target stimulus during non-target probe processing.Furthermore, source activities showed specific engagements in target processing for the regional source in anterior cingulate cortex (ACC) before response execution and also for the regional source in superior frontal gyrus (SFG) before and simultaneously to response execution. These findings might be an indicator for the involvement of both regions in different stages of conflict managing operations because target trials had a lower stimulus frequency compared with non-target trials (at trial positions A and B).Summarized, different WM processes (maintenance, retrieval) were investigated in both experiments, and different methodological approaches were applied. In the general discussion, findings from both experiments are linked to each other, considering brain regions which were involved in the processing of both tasks