Retrospective attention enhances visual working memory in the young but not the old: An ERP study

Behavioral evidence from the young suggests spatial cues that orient attention toward task‐relevant items in visual working memory (VWM) enhance memory capacity. Whether older adults can also use retrospective cues (“retro‐cues”) to enhance VWM capacity is unknown. In the current event‐related potential (ERP) study, young and old adults performed a VWM task in which spatially informative retro‐cues were presented during maintenance. Young but not older adults' VWM capacity benefited from retro‐cueing. The contralateral delay activity (CDA) ERP index of VWM maintenance was attenuated after the retro‐cue, which effectively reduced the impact of memory load. CDA amplitudes were reduced prior to retro‐cue onset in the old only. Despite a preserved ability to delete items from VWM, older adults may be less able to use retrospective attention to enhance memory capacity when expectancy of impending spatial cues disrupts effective VWM maintenance.     

Orienting to external versus internal regions of space: consequences of attending in advance versus after the fact

We examined effects of knowing where to attend to-be-remembered information in advance versus after the fact. Participants performed a visuospatial short-term memory task with orienting cues that appeared before or after a memory display and reported whether a probe item had appeared on the cued side. Event-related potentials (ERPs) were recorded for cues, memory displays, and probes. Performance was better in precued versus postcued conditions. ERPs to orienting cues and memory displays were lateralized in relation to the direction of attention in precued but not postcued conditions. ERPs to recognition probes were lateralized, but this was similar between pre- and postcued conditions. Results suggest that we can orient visuospatial attention outwardly to external events and inwardly to remembered events alike, but knowing where to attend information in advance gives a bigger boost to brain and behavior.     

High working memory load impairs selective attention: EEG signatures

According to the load theory of attention, increased working memory load impairs selective attention, resulting in greater distractor interference during inhibitory control processing. However, the EEG signatures correlated with this modulation effect of working memory on inhibitory control remain unclear. In present study, 25 healthy human participants performed a flanker task in a low and high working memory load conditions, while behavioral and electroencephalography (EEG) data were recorded. The results showed a larger reaction time interference effect while increasing working memory load, and this was accompanied by a larger N2 amplitude and a smaller P3 amplitude for incongruent trials. Time–frequency analysis revealed that, increased working memory load had no significant modulation effect on flanker related theta-ERS magnitude. Incongruent trials evoked smaller alpha-ERD magnitude than congruent trials in both low and high working memory load conditions. Increased working memory load was associated with larger flanker related alpha-ERD magnitude. Taken together, these results suggested that increased working memory load can impair top-down cognitive control processes, impairing inhibitory control processes during performance of the flanker task.     

The impact of salience and visual working memory on the monitoring and control of saccadic behavior: An eye‐tracking and EEG study

In a concurrent eye‐tracking and EEG study, we investigated the impact of salience on the monitoring and control of eye movement behavior and the role of visual working memory (VWM) capacity in mediating this effect. Participants made eye movements to a unique line‐segment target embedded in a search display also containing a unique distractor. Target and distractor salience was manipulated by varying degree of orientation offset from a homogenous background. VWM capacity was measured using a change‐detection task. Results showed greater likelihood of incorrect saccades when the distractor was relatively more salient than when the target was salient. Misdirected saccades to salient distractors were strongly represented in the error‐monitoring system by rapid and robust error‐related negativity (ERN), which predicted a significant adjustment of oculomotor behavior. Misdirected saccades to less‐salient distractors, while arguably representing larger errors, were not as well detected or utilized by the error/performance‐monitoring system. This system was instead better engaged in tasks requiring greater cognitive control and by individuals with higher VWM capacity. Our findings show that relative salience of task‐relevant and task‐irrelevant stimuli can define situations where an increase in cognitive control is necessary, with individual differences in VWM capacity explaining significant variance in the degree of monitoring and control of goal‐directed eye movement behavior. The present study supports a conflict‐monitoring interpretation of the ERN, whereby the level of competition between different responses, and the stimuli that define these responses, was more important in the generation of an enhanced ERN than the error commission itself.     

Motivation enhances visual working memory capacity through the modulation of central cognitive processes

Motivation is well known to enhance working memory (WM) capacity, but the mechanism underlying this effect remains unclear. The WM process can be divided into encoding, maintenance, and retrieval, and in a change detection visual WM paradigm, the encoding and retrieval processes can be subdivided into perceptual and central processing. To clarify which of these segments are most influenced by motivation, we measured ERPs in a change detection task with differential monetary rewards. The results showed that the enhancement of WM capacity under high motivation was accompanied by modulations of late central components but not those reflecting attentional control on perceptual inputs across all stages of WM. We conclude that the “state‐dependent” shift of motivation impacted the central, rather than the perceptual functions in order to achieve better behavioral performances.     

Event‐related potentials reveal the effect of prior knowledge on competition for representation and attentional capture

Objects compete for representation in our limited capacity visual system. We examined how this competition is influenced by top‐down knowledge using event‐related potentials. Competition was manipulated by presenting visual search arrays in which the target or distractor was the only color singleton compared to displays in which both singletons were presented. Experiments 1 and 2 manipulated whether the observer knew the color of the target in advance. Experiment 3 ruled out low‐level sensory explanations. Results show that, under conditions of competition, the distractor does not elicit an N2pc when the target color is known. However, the N2pc elicited by the target is reduced in the presence of a distractor. These findings suggest that top‐down knowledge can prevent the capture of attention by distracting information, but this prior knowledge does not eliminate the competitive influence of the distractor on the target.     

Never mind the spider: Late positive potentials to phobic threat at fixation are unaffected by perceptual load

Research suggests that processing of emotional stimuli may be eliminated if a concurrent task places sufficient demands on attentional resources. To test whether this holds for stimuli with strong emotional significance, pictures of spiders as well as mushrooms were presented at fixation to spider‐fearful and non‐fearful participants. Concurrently, perceptual load was manipulated in two levels with a peripheral letter discrimination task. Results of event‐related potentials showed that, compared with non‐fearful participants, spider‐fearful participants showed greater late positive potentials (LPP) to spiders than mushrooms, which provides a manipulation check that spiders were emotionally meaningful to spider‐fearful participants. Critically, this effect was not affected by level of perceptual load. These findings suggest that strong emotional stimuli at fixation may resist manipulations of perceptual load.     

Multisensory processing and oscillatory gamma responses: effects of spatial selective attention

Here we describe an EEG study investigating the interactions between multisensory (audio-visual) integration and spatial attention, using oscillatory gamma-band responses (GBRs). The results include a comparison with previously reported event-related potential (ERP) findings from the same paradigm. Unisensory-auditory (A), unisensory-visual (V), and multisensory (AV) stimuli were presented to the left and right hemispaces while subjects attended to a designated side to detect deviant target stimuli in either sensory modality. For attended multisensory stimuli we observed larger evoked GBRs approximately 40–50 ms post-stimulus over medial-frontal brain areas compared with those same multisensory stimuli when unattended. Further analysis indicated that the integration effect and its attentional enhancement may be caused in part by a stimulus-triggered phase resetting of ongoing gamma-band responses. Interestingly, no such early interaction effects (<90 ms) could be found in the ERP waveforms, suggesting that oscillatory GBRs may be more sensitive than ERPs to these early latency attention effects. Moreover, no GBR attention effects could be found for the unisensory auditory or unisensory visual stimuli, suggesting that attention particularly affects the integrative processing of audiovisual stimuli at these early latencies.     

Neurobehavioral correlates of the rapid formation of the symbolic control of visuospatial attention

Prior research suggests that nonpredictive symbolic central cues can produce nonvoluntary shifts of endogenous attention when associations between cues and spatial locations are overlearned during cognitive development. The present ERP study extends this research by first showing that overlearned cue-spatial location associations necessary to support nonvoluntary attentional orienting can be rapidly formed in adult humans. A second experiment indicates that the nonvoluntary orienting formed by such rapid learning is semireflexive (amenable to top-down influence) rather than reflexive (resistant to top-down influence). A third experiment suggests that the rapid formation of endogenous nonvoluntary orienting requires explicit rather than implicit learning of cue-location associations. These findings provide further support for a strong connection between neurocognitive representations of space, symbol meaning, and attentional control.     

Brain oscillation and connectivity during a chemistry visual working memory task

Many studies have reported that frontal theta and posterior alpha activities are associated with working memory tasks. However, fewer studies have focused on examining whether or not the frontal alpha or posterior theta can play a role in the working memory task. This study investigates electroencephalography (EEG) dynamics and connectivity among different brain regions' theta and alpha oscillations. The EEG was collected from undergraduate students (n = 64) while they were performing a Sternberg-like working memory task involving chemistry concepts. The results showed that the frontal midline cluster exhibited sustained theta augmentation across the periods of stimulus presentations, maintenance, and probe presentation, suggesting that the frontal midline theta might associate with facilitating the central execute function to maintain information in the working memory. Study of the central parietal and the occipital clusters revealed a sequence of theta augmentation followed by alpha suppression at constant intervals after the onset of stimulus and probe presentations, suggesting that the posterior theta might be associated with sensory processing, theta gating, or stimulus selection. It further suggests that the posterior alpha event-related de-synchronization (ERD) might be linked to direct information flow into and out of the long-term memory (LTM) and precede stimulus recognition. An alternating phasic alpha event-related synchronization (ERS) and ERD following the 1st stimulus and probe presentations were observed at the occipital cluster, in which alpha ERS might be linked to the inhibition of irrelevant information.     

Regulation of cognitive resources during sustained attention and working memory in 10-year-olds and adults

We examined differences between 10-year-olds and young adults in resource recruitment and regulation during tasks of sustained attention and spatial working memory. We administered participants spatial 0- and 1-back tasks and used pupillary dilation as a measure of resource recruitment. Repeated administration of 0-back led to smaller pupillary dilations and greater response time (RT) variability, revealing a vigilance decrement. Effects of repeated administration of 0-back and differences between 0- and 1-back in d' and RTs were similar between ages. Results further suggested that the children may not have been as effective as adults in extracting frequency information. Thus, on simple tasks of sustained attention and working memory, children recruit resources in a manner similar to adults. Finally, d' was correlated with RT variability on both tasks at both ages, highlighting the role of attentional fluctuations on both tasks.     

ERP effects of methylphenidate and working memory load in healthy adults during a serial visual working memory task

The objective of the study was to investigate neuronal processing during the encoding, retention and retrieval phases of a serial visual working memory task. Particularly, we were interested in how these phases are affected by working memory load and how processing is modulated by methylphenidate. Healthy adults were asked to memorize the order of four, five or six pictures under methylphenidate (20 mg) and under placebo while brain electrical activity was recorded. On the performance level, the number of correct responses decreased with increasing working memory load. Concerning brain electrical activity, in the encoding phase P3 amplitudes increased at midline electrodes with increasing memory load while load had no effect in the retention and retrieval phase. Medication neither influenced performance nor the different processing stages significantly. Our data provide evidence that during the encoding phase more attentional resources are allocated in trials with higher load as reflected by larger P3 amplitudes.     

The effect of selective attention on the gamma-band auditory steady-state response

Studies have demonstrated that selective attention can modulate the steady-state evoked potential to repetitive visual and tactile stimulation. However, examinations of the effect of attention on the auditory steady-state response (ASSR) have proven equivocal. The current experiment therefore utilized EEG to examine the effect of attention on the ASSR in healthy humans (n = 15). Auditory click trains in the beta (20 Hz) and gamma (40 Hz) ranges were randomly presented binaurally in an oddball discrimination paradigm (each frequency served as the oddball (target) in each of two blocks). A Fast Fourier Transform was used to assess the effect of attention on the ASSR (signal power), and phase consistency across trials was assessed using the phase-locking factor (PLF). As expected, both 20 and 40 Hz targets elicited a robust P300 response, with maximal amplitudes over parietal regions. For the ASSR, it was found that EEG signal power was larger to 40 Hz targets compared to 40 Hz frequent stimuli across all frontocentral electrodes. No differences in signal power were observed during 20 Hz stimulation. Finally, increased PLF values were observed for 40 Hz targets compared to frequent trials. These results provide evidence that selective attention can enhance signal power and phase-locking of the ASSR, particularly to auditory stimulation in the gamma range.     

Impaired semantic processing during task‐set switching: Evidence from the N400 in rapid serial visual presentation

The cognitive system is able to reconfigure mental resources flexibly to adapt to new a task. While task‐set switching is known to be detrimental to behavioral performance, less is known about the precise loci of these effects on stimulus processing. We measured event‐related potentials to explore the neural consequences of task‐set switching on semantic processing. We examined the context‐sensitive N400 component evoked by the second of two target words embedded in a rapid serial visual presentation under conditions that involved either a task‐set switch or no switching. Whereas the N400 was unaffected by the lag separating the targets in the absence of switching, it was delayed and attenuated in the switch condition when the targets were adjacent in the sequence. These findings indicate that task‐set reconfiguration temporarily prevents semantic activation and provide evidence for the nonautomaticity of semantic processing of words.     

Atypical visual change processing in children with autism: An electrophysiological Study

Children with Autism Spectrum Disorder (ASD) may display atypical behaviors in reaction to unattended changes that occur in all sensory modalities. Atypical automatic auditory change processing has been highlighted in ASD via the analysis of mismatch negativity (MMN). The present study investigated visual deviancy detection in children with ASD in order to determine whether unusual reactions to change operate in other sensory modalities. Twelve children with ASD were presented with a passive visual oddball paradigm using dynamic stimuli. Compared to controls, children with ASD showed an earlier visual mismatch response, suggesting a hypersensitivity to visual deviancy. This study is thus consistent with the hypothesis of the existence of “general” atypical change detection processing in children with ASD that might contribute to their intolerance of change.     

Guidance of visual attention from working memory contents depends on stimulus attributes

Recent work shows that items maintained in working memory could guide the orienting of attention in visual search, demonstrating an interesting interaction between working memory and attention. For such guidance effect, some studies emphasize the importance of search task type: for fixed-target search, task-irrelevant memory items stay inside the attentional focus and guides attention; for varied-target search, these items stay outside attentional focus and do not guide attention. With two experiments, we showed that stimulus attribute of items held in working memory can play an important role in attentional guidance. The first behavioral experiment duplicated a previous fixed-target search paradigm demonstrating robust guidance effect but failed to find such effect when the stimuli was simply changed from colored shapes to complex artificial shapes. The second event-related potential experiment duplicated a previous varied-target search paradigm that used complex shapes but did not observe any guidance effect. A clear guidance effect was found when we changed the stimuli to colored shapes. The results suggest that attentional guidance from working memory depends on stimulus attributes of the items held in working memory. When effective attribute is used, task-irrelevant items that stay outside the attentional focus are still able to guide attention.     

When flanker meets the n‐back: What EEG and pupil dilation data reveal about the interplay between the two central‐executive working memory functions inhibition and updating

We investigated the interplay between inhibition and updating, two executive working memory (WM) functions. We applied a novel task paradigm consisting of flanker stimuli presented within an n‐back task and studied the interaction between inhibitory demands and load on WM updating using behavioral measures, EEG, and pupil dilation. In contrast to studies that examine the interaction between inhibitory demands and load on WM storage components, the current task paradigm allowed testing the interaction between the executive WM components updating and inhibition. We found a reduced flanker interference effect for the highest (2‐back) updating load condition compared to lower updating load conditions on most measures. We interpret these findings as indicating that inhibitory control and WM updating are closely intertwined executive functions. Increased load on updating seemed to result in an overall more activated attentional network thus enhancing inhibitory control, such that task performance is less susceptible to distracting information.     

FN400 potentials are functionally identical to N400 potentials and reflect semantic processing during recognition testing

The “F” in FN400 denotes a more frontal scalp distribution relative to the morphologically similar N400 component—a distinction consistent with the hypothesized distinct roles of FN400 in familiarity memory versus N400 in language. However, no direct comparisons have substantiated these assumed dissimilarities. To this end, we manipulated short‐term semantic priming during a recognition test. Semantic priming effects on N400 were indistinguishable from memory effects at the same latency, and semantic priming strongly modulated the “FN400,” despite having no influence on familiarity memory. Thus, no evidence suggested either electrophysiological or functional differences between the N400 and FN400, and findings were contrary to the linking of the “FN400” to familiarity. Instead, it appears that semantic/conceptual priming (reflected in the N400) occurs during recognition tests and is frequently (mis)labeled as FN400 and attributed to familiarity.     

Electrophysiological evidence for different effects of working memory load on interference control in adolescents than adults

The present study investigated how the development of interference control is influenced by the development of working memory (WM) capacity during adolescence. In a dual-task, 17 adolescents (12-16 years) and 19 adults (18-48 years) performed a gender word-face Stroop task, while WM-capacity was manipulated by a concurrently performed N-back task. Behavior (reaction times, % errors and % misses) and event-related potentials associated with the detection (N450) of the Stroop conflict and response selection (sustained positivity; SP) were measured without or with a concurrent WM load. Adolescents had lower accuracy on N-back and Stroop trials than adults. N450 results showed Stroop conflict above temporal-occipital cortex which was suggested to be caused by processing of distracter faces. This N450 conflict response was smaller in adults and only present when holding a simultaneous WM-load, whereas adolescents' N450 conflict responses were already present without a concurrent WM-load and did not further increase with load. These N450 results indicate poorer distracter suppression in adolescence which is suggested to be due to insufficient attentional resources for top-down control. Irrespective of WM-load, adolescents also had larger parietal SP conflict responses than adults, suggesting inefficient response selection in case of activation of two conflicting responses. The main conclusion is that adolescents have worse distracter suppression than adults, caused by lower availability of resources for top-down control.     

Probing the sensory effects of involuntary attention change by ERPs to auditory transients

An auditory selective attention set allows one to enhance the processing of goal‐relevant sound events, which is reflected by the enhancement of the N1 event‐related potential (ERP). The present study investigated whether the sensory consequences of distraction (i.e., involuntary attention changes triggered by infrequent sensory events) can be revealed as the removal of this attentional ERP enhancement. Continuous tones featuring occasional gaps were presented, and participants performed a gap‐detection task. Independently from gaps, abrupt pitch changes (glides) were introduced, either rarely or frequently, in separate conditions. Whereas rare glides preceding gaps by 150 ms strongly impacted gap‐detection performance and gap‐related N1 amplitudes, their impact on gaps following rare glides by 650 ms was significantly smaller in both measures. This result demonstrates the utility of N1 in probing the sensory impact of auditory distraction.