Tracking the temporal dynamics of the face-like inversion effect as revealed by Chinese characters using magnetoencephalography.

The neural basis of configural processing has been extensively studied by exploiting face inversion during recognition, and growing evidence has revealed that word inversion also involves changes in configuration. However, the neural dynamics of face-like inversion effects remain unclear. Here, we tracked the temporal dynamics of neural responses that were sensitive to inversion during Chinese character recognition as they occurred during face recognition using multivariate decoding and temporal generalization analyses. We recorded magnetoencephalography while participants performed a one-back task for faces, compound characters, and simple characters with upright and inverted orientations. We showed that the inversion effect (inverted versus upright) can be decoded at occipitotemporal sensors for all stimulus types over and across time points, with a stronger impact on faces and compound characters than on simple characters. The inversion effect occurred earlier and lasted longer for faces than for characters, and the effect was also stronger for compound characters than for simple characters. Finally, we demonstrated inversion effects in the event-related field for all stimulus types and identified their sources in the ventral occipitotemporal areas. Overall, this study provides novel evidence for the temporal dynamics of the face-like inversion effect occurring during Chinese character recognition.

Alpha oscillations track content-specific working memory capacity.

Though the neural basis of working memory (WM) capacity is often studied by exploiting inter-individual differences, capacity may also differ across memory materials within a given individual. Here, we exploit the content-dependence of WM capacity as a novel approach to investigate the oscillatory correlates of WM capacity, focusing on posterior 9-12 Hz alpha activity during retention. We recorded scalp electroencephalography (EEG) while male and female human participants performed WM tasks with varying memory loads (2 vs. 4 items) and materials (English letters vs. regular shapes vs. abstract shapes). First, behavioural data confirmed that memory capacity was fundamentally content-dependent: capacity for abstract shapes plateaued at around two, while the participants could remember more letters and regular shapes. Critically, content-specific capacity was paralleled in the degree of attenuation of EEG-alpha activity that plateaued in a similar, content-specific, manner. While we observed greater alpha attenuation for higher loads for all materials, we found larger load effects for letters and regular shapes than for abstract shapes - consistent with our behavioural data showing a lower capacity plateau for abstract shapes. Moreover, when only considering 2-item trials, alpha attenuation was greater for abstract shapes - where 2-items were close to the capacity plateau - than for other materials. Multivariate decoding of alpha-activity patterns reinforced these findings. Finally, for each material, load effects on capacity (K) and alpha attenuation were correlated across individuals. Our results demonstrate that alpha oscillations track memory capacity in a content-specific manner and track not just the number of items, but also their complexity.SIGNIFICANCE STATEMENTWorking memory (WM) is limited in its capacity. We show that capacity is not fixed for an individual but is rather memory-content dependent. Moreover, we used this as a novel approach to investigate the neural basis of WM capacity with EEG. We found that both behavioural capacity estimates and neural oscillations in the alpha band varied with memory loads and materials. The critical finding is a capacity plateau of approximately two items only for the more complex materials, accompanied by a similar plateau in the EEG alpha attenuation. The load effects on capacity and alpha attenuation were furthermore correlated across individuals for each of the materials. Our results demonstrate that alpha oscillations track the content-specific nature of WM capacity.

Temporal expectation based on the duration variability modulates alpha oscillations during working memory retention.

While maintaining information over a delay of time, working memory (WM) also allows individuals to prepare the mnemonic contents for prospective utilisation. However, it remains unclear whether the expectation of the time of WM test could modulate neural responses during the retention interval of WM and subsequent performance. Here, we investigated whether temporal expectations based on the variability of delay duration can modulate 9-13 Hz alpha oscillations during WM retention and whether the expectation-induced alpha activity was associated with WM performance. Participants performed a retro-cueing WM task with magnetoencephalography (MEG) (Experiment 1) and a standard WM task with electroencephalography (EEG) (Experiment 2). The expectation of the timing of the WM test was manipulated by the temporal structure of the tasks with small or large variability in the delay durations. We showed that alpha oscillations during retention interval and WM performance varied with duration variability in both of the MEG and EEG experiments. The novel finding was greater alpha-power attenuation over the left frontal and parietal regions during WM retention when the duration variability was small and the test onset was predictable, compared to when the duration variability was large and the test onset was less predictable. Importantly, we observed a positive relationship in variability difference between the response benefit and alpha-power attenuation in the left posterior parietal regions at both MEG-source and EEG-electrode levels. Finally, we confirmed the behavioural benefit when a condition with a fixed delay-duration was included in a behavioural experiment (Experiment 3). When conjoined, the delay duration enables individuals to anticipate when the relevant information would be put to work, and alpha oscillations track the anticipatory states during WM maintenance.

Spatially Specific Attention Mechanisms Are Sensitive to Competition during Visual Search.

Extensive studies have focused on selection mechanisms during visual search. One important influence on these mechanisms is the perceptual characteristics of the stimuli. We investigated the impact of perceptual similarity between targets and nontargets (T-N similarity) in a visual search task using EEG. Participants searched for a predefined target letter among five nontargets. The T-N similarity was manipulated with three levels: high, middle, and low. We tested for the influences of T-N similarity on an ERP (e.g., N2pc) and alpha oscillations. We observed a significant N2pc effect across all levels of similarity. The N2pc amplitude was reduced and occurred later for high similarity relative to low and middle similarities. We also showed that the N2pc amplitude was inversely correlated with the RTs across all similarities. Importantly, we found a significant alpha phase adjustment about the same time as the N2pc for high similarity; by contrast, no such effect was observed for middle and low similarities. Finally, we showed a positive correlation between the phase-locking value and the N2pc-the stronger the alpha phase-locking value, the larger the N2pc, when the T-N similarity was high. In conclusion, our results provide novel evidence for multiple competitive mechanisms during visual search.

Top-Down Activation of Spatiotopic Sensory Codes in Perceptual and Working Memory Search.

A critical requirement of an efficient cognitive system is the selection and prioritization of relevant information. This occurs when selecting specific items from our sensory inputs, which then receive preferential status at subsequent levels of processing. Many everyday tasks also require us to select internal representations, such as a relevant item from memory. We show that both of these types of search are underpinned by the spatiotopic activation of sensory codes, using both fMRI and MEG data. When individuals searched for perceived and remembered targets, the MEG data highlighted a sensor level electrophysiological effect that reflects the contralateral organization of the visual system-namely, the N2pc. The fMRI data were used to identify a network of frontoparietal areas common to both types of search, as well as the early visual areas activated by the search display. We then combined fMRI and MEG data to explore the temporal dynamics of functional connections between the frontoparietal network and the early visual areas. Searching for a target item resulted in significantly enhanced phase-phase coupling between the frontoparietal network and the visual areas contralateral to the perceived or remembered location of that target. This enhancement of spatially specific phase-phase coupling occurred before the N2pc effect and was significantly associated with it on a trial-by-trial basis. The combination of these two imaging modalities suggests that perceptual and working memory search are underpinned by the synchronization of a frontoparietal network and the relevant sensory cortices.

The Neural Dynamics of Fronto-Parietal Networks in Childhood Revealed using Magnetoencephalography.

Our ability to hold information in mind is limited, requires a high degree of cognitive control, and is necessary for many subsequent cognitive processes. Children, in particular, are highly variable in how, trial-by-trial, they manage to recruit cognitive control in service of memory. Fronto-parietal networks, typically recruited under conditions where this cognitive control is needed, undergo protracted development. We explored, for the first time, whether dynamic changes in fronto-parietal activity could account for children's variability in tests of visual short-term memory (VSTM). We recorded oscillatory brain activity using magnetoencephalography (MEG) as 9- to 12-year-old children and adults performed a VSTM task. We combined temporal independent component analysis (ICA) with general linear modeling to test whether the strength of fronto-parietal activity correlated with VSTM performance on a trial-by-trial basis. In children, but not adults, slow frequency theta (4-7 Hz) activity within a right lateralized fronto-parietal network in anticipation of the memoranda predicted the accuracy with which those memory items were subsequently retrieved. These findings suggest that inconsistent use of anticipatory control mechanism contributes significantly to trial-to-trial variability in VSTM maintenance performance.

Age group and individual differences in attentional orienting dissociate neural mechanisms of encoding and maintenance in visual STM.

Selective attention biases the encoding and maintenance of representations in visual STM (VSTM). However, precise attentional mechanisms gating encoding and maintenance in VSTM and across development remain less well understood. We recorded EEG while adults and 10-year-olds used cues to guide attention before encoding or while maintaining items in VSTM. Known neural markers of spatial orienting to incoming percepts, that is, Early Directing Attention Negativity, Anterior Directing Attention Negativity, and Late Directing Attention Positivity, were examined in the context of orienting within VSTM. Adults elicited a set of neural markers that were broadly similar in preparation for encoding and during maintenance. In contrast, in children these processes dissociated. Furthermore, in children, individual differences in the amplitude of neural markers of prospective orienting related to individual differences in VSTM capacity, suggesting that children with high capacity are more efficient at selecting information for encoding into VSTM. Finally, retrospective, but not prospective, orienting in both age groups elicited the well-known marker of visual search (N2pc), indicating the recruitment of additional neural circuits when orienting during maintenance. Developmental and individual differences differentiate seemingly similar processes of orienting to perceptually available representations and to representations held in VSTM.

Attention biases visual activity in visual short-term memory.

In the current study, we tested whether representations in visual STM (VSTM) can be biased via top-down attentional modulation of visual activity in retinotopically specific locations. We manipulated attention using retrospective cues presented during the retention interval of a VSTM task. Retrospective cues triggered activity in a large-scale network implicated in attentional control and led to retinotopically specific modulation of activity in early visual areas V1-V4. Importantly, shifts of attention during VSTM maintenance were associated with changes in functional connectivity between pFC and retinotopic regions within V4. Our findings provide new insights into top-down control mechanisms that modulate VSTM representations for flexible and goal-directed maintenance of the most relevant memoranda.

Temporal profiles of cortical oscillations in novice performers for goal-directed aiming in a shooting task.

Goal-directed aiming relies on the ability to control attention and visuomotor movements while preparing for motor execution. Research in precision sports has investigated cortical oscillations for supporting expert performance. However, the results may be influenced by adaptive and strategic behaviors after intensive training. Whether and at what time points distinctive oscillations support goal-directed aiming without such training remains elusive. In this electroencephalographic (EEG) study, we investigated how the theta, alpha and beta oscillations change to support accurate aiming before novices took an action. We first conducted a model-based analysis to examine the correlation of cortical oscillations with accurate shooting on a trial-by-trial basis in a within-individual manner. The results showed that alpha and beta oscillations at different time points during the aiming period were better predictors of aiming accuracy. We then compared the oscillatory power for good versus poor performance. The results showed decreases in the alpha and beta power across distributed cortical areas and an increase in the frontal theta power successively before shot release. Moreover, greater intertrial phase coherence was observed for good performance than for poor performance in posterior alpha activity and anterior beta activity during the aiming period. In conclusion, these results advance our understanding of the temporal dynamics of theta, alpha and beta oscillations in orchestrating goal setting, motor preparation and focused attention to monitoring both external and internal states for accurate aiming. Among the three, alpha and beta oscillations are critical for predicting aiming performance and theta oscillations reflect effortful cognitive control.

Attention modulates maintenance of representations in visual short-term memory.

Recent studies have shown that selective attention is of considerable importance for encoding task-relevant items into visual short-term memory (VSTM) according to our behavioral goals. However, it is not known whether top-down attentional biases can continue to operate during the maintenance period of VSTM. We used ERPs to investigate this question across two experiments. Specifically, we tested whether orienting attention to a given spatial location within a VSTM representation resulted in modulation of the contralateral delay activity (CDA), a lateralized ERP marker of VSTM maintenance generated when participants selectively encode memory items from one hemifield. In both experiments, retrospective cues during the maintenance period could predict a specific item (spatial retrocue) or multiple items (neutral retrocue) that would be probed at the end of the memory delay. Our results revealed that VSTM performance is significantly improved by orienting attention to the location of a task-relevant item. The behavioral benefit was accompanied by modulation of neural activity involved in VSTM maintenance. Spatial retrocues reduced the magnitude of the CDA, consistent with a reduction in memory load. Our results provide direct evidence that top-down control modulates neural activity associated with maintenance in VSTM, biasing competition in favor of the task-relevant information.

The effects of stimulus inversion on the neural representations of Chinese character and face recognition.

This study investigates whether stimulus inversion influences neural responses of Chinese character recognition similarly to its effect on face recognition in category-selective and object-related brain areas using functional magnetic resonance imaging. Participants performed a one-back matching task for simple (one radical) and compound (two radicals) Chinese characters and faces with upright and inverted orientations. Inverted stimuli produced slower response times with stronger activity within the fusiform gyrus (FG) than upright stimuli for faces and Chinese characters. While common inversion-related activation was identified in the left FG among stimulus types, we observed a significant inter-regional correlation between the left FG and the intraparietal sulcus for face inversion. Importantly, analyses of region-of-interest (ROI) multivariate pattern classification showed that classifiers trained on face inversion can decode the representations of character inversion in the character-selective ROI. However, this was not true for face inversion in face-selective ROIs when the classifiers were trained on characters. Similar activity patterns for character and face inversion were observed in the object-related ROIs. We also showed higher decoding accuracy for upright stimuli in the face-selective ROI than in the character-selective ROI but this was not true for inverted ones or when patterns were examined in the object-related ROIs. Together, our results support shared and distinct configural representations for character and face recognition in category-selective and object-related brain areas.

Attentional modulation of perceptual comparison for feature binding.

We investigated the neural correlates of attentional modulation in the perceptual comparison process for detecting feature-binding changes in an event-related functional magnetic resonance imaging (fMRI) experiment. Participants performed a variant of a cued change detection task. They viewed a memory array, a spatial retro-cue, and later a probe array. Their task was to judge whether the cued item had changed between the two arrays. Change type was manipulated to be a color-location binding or a color feature change. The retro-cue onset time in the retention interval was manipulated to be early or late. As a consequence of strong inter-item competition, we found strong prefrontal activation for late cues when contrasting the binding-change with the color-change condition. In contrast, we observed a comparable behavioral and neural effect between the two types of change detection when retro-cue was presented early. More importantly, we demonstrated a significant inter-regional correlation between the prefrontal and parietal regions in both binding- and color-change conditions for late cues. In addition, extensive prefrontal-parietal-visual functional connectivity was showed for detecting binding changes in the late-cueing condition. These results support the critical role in prefrontal-parietal-visual functional coupling for resolving strong inter-item competition during the comparison process in the binding-change condition. We provide direct evidence that attention modulates neural activity associated with perceptual comparison, biasing competition in favour of the task-relevant information in order to detect binding changes.

Chinese characters elicit face-like N170 inversion effects.

Recognition of both faces and Chinese characters is commonly believed to rely on configural information. While faces typically exhibit behavioral and N170 inversion effects that differ from non-face stimuli (Rossion, Joyce, Cottrell, & Tarr, 2003), the current study examined whether a similar reliance on configural processing may result in similar inversion effects for faces and Chinese characters. Participants were engaged in an orientation judgment task (Experiment 1) and a one-back identity matching task (Experiment 2). Across two experiments, the N170 was delayed and enhanced in magnitude for upside-down faces and compound Chinese characters, compared to upright stimuli. The inversion effects for these two stimulus categories were bilateral for latency and right-lateralized for amplitudes. For simple Chinese characters, only the latency inversion effects were significant. Moreover, the size of the right-hemisphere inversion effects in N170 amplitude was larger for faces than Chinese characters. These findings show the N170 inversion effects from non-face stimuli closely parallel effects seen with faces. Face-like N170 inversion effects elicited by Chinese compound characters were attributed to the difficulty of part-whole integration as well as the disrupted regularity in relational information due to inversion. Hemispheric difference in Chinese character processing is also discussed.

Searching for targets within the spatial layout of visual short-term memory.

Recent studies have revealed that the internal representations that we construct from the environment and maintain in visual short-term memory (VSTM) to guide behavior are highly flexible and can be selectively modulated according to our task goals and expectations. In the current study, we conducted two experiments to compare and contrast neural mechanisms of selective attention related to searching for target items within perceptual versus VSTM representations. We used event-related potentials to investigate whether searching for relevant target items from within VSTM representations involves spatially specific biasing of neural activity in a manner analogous to that which occurs during visual search for target items in perceptual arrays. The results, replicated across the two experiments, revealed that selection of a target object within a search array maintained in VSTM proceeds through a similar mechanism as that in the perceptual domain. In line with previous results, N2pc potentials were obtained when targets were identified within a perceptual visual-search array. Interestingly, equivalent N2pcs, with similar time courses and scalp distributions, were also elicited when target items were identified within a VSTM representation. The findings reinforce the notion of highly flexible VSTM representations that can be modulated according to task goals and suggest a large degree of overlap in the spatially specific neural mechanisms of target selection across the perceptual and VSTM domains.

Think Hard or Think Smart: Network Reconfigurations After Divergent Thinking Associate With Creativity Performance.

Evidence suggests divergent thinking is the cognitive basis of creative thoughts. Neuroimaging literature using resting-state functional connectivity (RSFC) has revealed network reorganizations during divergent thinking. Recent studies have revealed the changes of network organizations when performing creativity tasks, but such brain reconfigurations may be prolonged after task and be modulated by the trait of creativity. To investigate the dynamic reconfiguration, 40 young participants were recruited to perform consecutive Alternative Uses Tasks (AUTs) for divergent thinking and two resting-state scans (before and after AUT) were used for mapping the brain reorganizations after AUT. We split participants into high- and low-creative groups based on creative achievement questionnaire (CAQ) and targeted on reconfigurations of the two brain networks: (1) default-mode network (DMN) and (2) the network seeded at the left inferior frontal gyrus (IFG) because the between-group difference of AUT-induced brain activation located at the left IFG. The changes of post-AUT RSFCs (DMN and IFGN) indicated the prolonged effect of divergent thinking. More specifically, the alterations of RSFCIFG-AG and RSFCIFG-IPL (AG: angular gyrus, IPG: inferior parietal lobule) in the high-creative group had positive relationship with their AUT performances (originality and fluency), but not found in the low-creative group. Furthermore, the RSFC changes of DMN did not present significant relationships with AUT performances. The findings not only confirmed the possibility of brain dynamic reconfiguration following divergent thinking, but also suggested the distinct IFGN reconfiguration between individuals with different creativity levels.

The capacity constraint in the prefrontal and parietal regions for coordinating dual arithmetic tasks.

Using a dual-serial-arithmetic paradigm, we examined whether a capacity limitation constrains the neural activation that underlies dual-task performance. Six conditions were run in the experiment (the baseline, single-addition, single-subtraction, dual-addition, dual-subtraction, and the dual-operation condition). In the baseline condition, participants were asked to remember the initial pair of numbers and ignore subsequent stimuli. In the single-addition and single-subtraction conditions, participants had to calculate a running total over a series of stimuli. In the dual-addition and dual-subtraction conditions, they had to do two arithmetic tasks involving the same operand (e.g., + 2 and + 7, - 3 and - 5). Participants performed one addition and one subtraction task (e.g., + 2 and - 7, - 3 and + 5) in the dual-operation condition. The functional magnetic resonance imaging results showed strict left prefrontal and parietal regions in the single-addition condition and bilateral activation in the single-subtraction condition. Greater activation in the prefrontal and parietal regions was observed in both the dual-operation condition and the dual-addition condition in comparison to the single-addition condition. No greater activation was observed in either the dual-operation condition or dual-subtraction condition in comparison to the single-subtraction condition. These results suggest a constraint imposed by a limit in capacity for the neural activity subserving dual-task performance when one of the tasks places high resource demands on the executive network.

Functional interplay of top-down attention with affective codes during visual short-term memory maintenance.

Visual short-term memory (VSTM) allows individuals to briefly maintain information over time for guiding behaviours. Because the contents of VSTM can be neutral or emotional, top-down influence in VSTM may vary with the affective codes of maintained representations. Here we investigated the neural mechanisms underlying the functional interplay of top-down attention with affective codes in VSTM using functional magnetic resonance imaging. Participants were instructed to remember both threatening and neutral objects in a cued VSTM task. Retrospective cues (retro-cues) were presented to direct attention to the hemifield of a threatening object (i.e., cue-to-threat) or a neutral object (i.e., cue-to-neutral) during VSTM maintenance. We showed stronger activity in the ventral occipitotemporal cortex and amygdala for attending threatening relative to neutral representations. Using multivoxel pattern analysis, we found better classification performance for cue-to-threat versus cue-to-neutral objects in early visual areas and in the amygdala. Importantly, retro-cues modulated the strength of functional connectivity between the frontoparietal and early visual areas. Activity in the frontoparietal areas became strongly correlated with the activity in V3a-V4 coding the threatening representations instructed to be relevant for the task. Together, these findings provide the first demonstration of top-down modulation of activation patterns in early visual areas and functional connectivity between the frontoparietal network and early visual areas for regulating threatening representations during VSTM maintenance.

The neural correlates of attention orienting in visuospatial working memory for detecting feature and conjunction changes.

The neural mechanisms of attentional orienting in visuospatial working memory for change detection were investigated. A spatial cue was provided with the onset time manipulated to allow more effective top-down control with an early cue than with a late cue. The change type was also manipulated so that accurate detection depended on color or the binding of color and location. The results showed that both the frontal and parietal regions subserved the change detection task without cueing. When data were collapsed over the two change types, early cueing increased activation in the right inferior frontal gyrus (IFG) and middle frontal gyrus (MFG) while late cueing increased activation in the right inferior parietal lobule (IPL) and temporoparietal junction (TPJ) as compared with the no-cue condition. The cue onset time led to different levels of enhancement in the frontal and posterior cortices related to top-down control and stimulus-driven orienting. For feature detection, early cueing increased activation in the right MFG and late cueing increased activation in the bilateral precuneus (PCu), right TPJ, and right cuneus. The neural correlates of conjunction detection involved the right PCu and cerebellum without cueing, were associated with the anterior MFG, left IFG, and the left STG with early cueing, and involved the right MFG, left IFG, and right IPL with late cueing. The left IFG was correlated with memory retrieval of the cued representation for conjunction detection, and the right posterior PCu was associated with maintenance and memory retrieval among competing stimuli.

Top-down modulation of alpha power and pattern similarity for threatening representations in visual short-term memory.

Recent studies have shown that top-down attention biases task-relevant representations in visual short-term memory (VSTM). Accumulating evidence has also revealed the modulatory effects of emotional arousal on attentional processing. However, it remains unclear how top-down attention interacts with emotional memoranda in VSTM. In this study, we investigated the mechanisms of alpha oscillations and their spatiotemporal characteristics that underlie top-down attention to threatening representations during VSTM maintenance with electroencephalography. Participants were instructed to remember a threatening object and a neutral object in a cued variant delayed response task. Retrospective cues (retro-cues) were presented to direct attention to the hemifield of a threatening object (i.e., cue-to-threat trials) or a neutral object (i.e., cue-to-neutral trials) during a retention interval prior to the probe test. We found a significant retro-cue-related alpha lateralisation over posterior regions during VSTM maintenance. The novel finding was that the magnitude of alpha lateralisation was greater for cue-to-threat objects compared to cue-to-neutral ones. These results indicated that directing attention towards threatening representations compared to neutral representations could result in greater regulation of alpha activity contralateral to the cued hemifield. Importantly, we estimated the spatiotemporal pattern similarity in alpha activity and found significantly higher similarity indexes for the posterior regions relative to the anterior regions and for the cue-to-threat objects relative to cue-to-neutral objects over the posterior regions. Together, our findings provided the oscillatory evidence of greater top-down modulations of alpha lateralisation and spatiotemporal pattern similarity for attending to threatening representations in VSTM.

Selection History Modulates Working Memory Capacity.

Recent studies have shown that past selection history affects the allocation of attention on target selection. However, it is unclear whether context-driven selection history can modulate the efficacy of attention allocation on working memory (WM) representations. This study tests the influences of selection history on WM capacity. A display of one item (low load) or three/four items (high load) was shown for the participants to hold in WM in a delayed response task. Participants then judged whether a probe item was in the memory display or not. Selection history was defined as the number of items attended across trials in the task context within a block, manipulated by the stimulus set-size in the contexts with fewer possible stimuli (4-item or 5-item context) or more possible stimuli (8-item or 9-item context) from which the memorized content was selected. The capacity measure (i.e., the K measure) was estimated to reflect the number of items that can be held in WM. Across four behavioral experiments, the results revealed that the capacity was significantly reduced in the context with more possible stimuli relative to the context with fewer possible stimuli. Moreover, the reduction in capacity was significant for high WM load and not observed when the focus was on only a single item. Together, these findings indicate that context-driven selection history and focused attention influence WM capacity.