Prestimulus Alpha Activity Research Articles

Altered oscillatory neural dynamics related to word prediction in older adult readers

ABSTRACT The engagement of predictive mechanisms during language comprehension can facilitate processing and modulate neural oscillatory activity. These modulations include alpha-band activity decreases prior to expected words, reflecting anticipatory preparation, and frontal theta-band activity following unexpected words, reflecting engagement of cognitive control. It remains unknown how these oscillatory dynamics are impacted by aging. Here, we re-analysed previously collected EEG data from a sentence reading experiment with older adult participants to examine oscillatory responses to expected and unexpected words. Compared to younger adults, older adults’ frontal theta responses following unexpected words were delayed and reduced in magnitude. Alpha-band decreases prior to expected words were comparable across age groups, but only young adults’ pre-stimulus alpha activity was correlated with the post-stimulus frontal theta response. These results suggest older adults may engage anticipatory neural mechanisms comparably to younger adults, but do not engage the same control mechanisms following prediction errors.

Assessing Trial-by-Trial Electrophysiological and Behavioral Markers of Attentional Control and Sensory Precision in Psychotic and Mood Disorders.

The current study investigated the extent to which changes in attentional control contribute to performance on a visual perceptual discrimination task, on a trial-by-trial basis in a transdiagnostic clinical sample. Participants with schizophrenia (SZ; N = 58), bipolar disorder (N = 42), major depression disorder (N = 51), and psychiatrically healthy controls (N = 92) completed a visual perception task in which stimuli appeared briefly. The design allowed us to estimate the lapse rate and the precision of perceptual representations of the stimuli. Electroencephalograms (EEG) were recorded to examine pre-stimulus activity in the alpha band (8-13 Hz), overall and in relation to behavior performance on the task. We found that the attention lapse rate was elevated in the SZ group compared with all other groups. We also observed group differences in pre-stimulus alpha activity, with control participants showing the highest levels of pre-stimulus alpha when averaging across trials. However, trial-by-trial analyses showed within-participant fluctuations in pre-stimulus alpha activity significantly predicted the likelihood of making an error, in all groups. Interestingly, our analysis demonstrated that aperiodic contributions to the EEG signal (which affect power estimates across frequency bands) serve as a significant predictor of behavior as well. These results confirm the elevated attention lapse rate that has been observed in SZ, validate pre-stimulus EEG markers of attentional control and their use as a predictor of behavior on a trial-by-trial basis, and suggest that aperiodic contributions to the EEG signal are an important target for further research in this area, in addition to alpha-band activity.

Pre-stimulus alpha activity modulates long-lasting unconscious feature integration

Pre-stimulus alpha (α) activity can influence perception of shortly presented, low-contrast stimuli. The underlying mechanisms are often thought to affect perception exactly at the time of presentation. In addition, it is suggested that α cycles determine temporal windows of integration. However, in everyday situations, stimuli are usually presented for periods longer than ∼100 ms and perception is often an integration of information across space and time. Moving objects are just one example. Hence, the question is whether α activity plays a role also in temporal integration, especially when stimuli are integrated over several α cycles. Using electroencephalography (EEG), we investigated the relationship between pre-stimulus brain activity and long-lasting integration in the sequential metacontrast paradigm (SQM), where two opposite vernier offsets, embedded in a stream of lines, are unconsciously integrated into a single percept. We show that increases in α power, even 300 ms before the stimulus, affected the probability of reporting the first offset, shown at the very beginning of the SQM. This effect was mediated by the systematic slowing of the α rhythm that followed the peak in α power. No phase effects were found. Together, our results demonstrate a cascade of neural changes, following spontaneous bursts of α activity and extending beyond a single moment, which influences the sensory representation of visual features for hundreds of milliseconds. Crucially, as feature integration in the SQM occurs before a conscious percept is elicited, this also provides evidence that α activity is linked to mechanisms regulating unconscious processing.

Deep learning-based electroencephalic diagnosis of tinnitus symptom.

Tinnitus is a neuropathological phenomenon caused by the recognition of external sound that does not actually exist. Existing diagnostic methods for tinnitus are rather subjective and complicated medical examination procedures. The present study aimed to diagnose tinnitus using deep learning analysis of electroencephalographic (EEG) signals while patients performed auditory cognitive tasks. We found that, during an active oddball task, patients with tinnitus could be identified with an area under the curve of 0.886 through a deep learning model (EEGNet) using EEG signals. Furthermore, using broadband (0.5 to 50 Hz) EEG signals, an analysis of the EEGNet convolutional kernel feature maps revealed that alpha activity might play a crucial role in identifying patients with tinnitus. A subsequent time-frequency analysis of the EEG signals indicated that the tinnitus group had significantly reduced pre-stimulus alpha activity compared with the healthy group. These differences were observed in both the active and passive oddball tasks. Only the target stimuli during the active oddball task yielded significantly higher evoked theta activity in the healthy group compared with the tinnitus group. Our findings suggest that task-relevant EEG features can be considered as a neural signature of tinnitus symptoms and support the feasibility of EEG-based deep-learning approach for the diagnosis of tinnitus.

Prestimulus oscillatory brain activity interacts with evoked recurrent processing to facilitate conscious visual perception

We investigated whether prestimulus alpha-band oscillatory activity and stimulus-elicited recurrent processing interact to facilitate conscious visual perception. Participants tried to perceive a visual stimulus that was perceptually masked through object substitution masking (OSM). We showed that attenuated prestimulus alpha power was associated with greater negative-polarity stimulus-evoked ERP activity that resembled the visual awareness negativity (VAN), previously argued to reflect recurrent processing related to conscious perception. This effect, however, was not associated with better perception. Instead, when prestimulus alpha power was elevated, a preferred prestimulus alpha phase was associated with a greater VAN-like negativity, which was then associated with better cue perception. Cue perception was worse when prestimulus alpha power was elevated but the stimulus occurred at a nonoptimal prestimulus alpha phase and the VAN-like negativity was low. Our findings suggest that prestimulus alpha activity at a specific phase enables temporally selective recurrent processing that facilitates conscious perception in OSM.

Human visual processing during walking: Dissociable pre- and post-stimulus influences

Walking influences visual processing but the underlying mechanism remains poorly understood. In this study, we investigated the influence of walking on pre-stimulus and stimulus-induced visual neural activity and behavioural performance in a discrimination task while participants were standing or freely walking. The results showed dissociable pre- and post-stimulus influences by the movement state. Walking was associated with a reduced pre-stimulus alpha power, which predicted enhanced N1 and decreased P3 components during walking. This pre-stimulus alpha activity was additionally modulated by time on the task, which was paralleled by a similar behavioural modulation. In contrast, the post-stimulus alpha power was reduced in its modulation due to stimulus onset during walking but showed no evidence of modulation by time on the task. Additionally, stimulus parameters (eccentricity, laterality, distractor presence significantly influenced post-stimulus alpha power, whereas the visually evoked components showed no evidence of such an influence. There was further no evidence of a correlation between pre-stimulus and post stimulus alpha power. We conclude that walking has two dissociable influences on visual processing: while the walking induced reduction in alpha power suggests an attentional state change that relates to visual awareness, the post-stimulus influence on alpha power modulation indicates changed spatial visual processing during walking.

Pre-stimulus Alpha Activity Modulates Face and Object Processing in the Intra-Parietal Sulcus, a MEG Study.

Face perception is crucial in all social animals. Recent studies have shown that pre-stimulus oscillations of brain activity modulate the perceptual performance of face vs. non-face stimuli, specifically under challenging conditions. However, it is unclear if this effect also occurs during simple tasks, and if so in which brain regions. Here we used magnetoencephalography (MEG) and a 1-back task in which participants decided if the two sequentially presented stimuli were the same or not in each trial. The aim of the study was to explore the effect of pre-stimulus alpha oscillation on the perception of face (human and monkey) and non-face stimuli. Our results showed that pre-stimulus activity in the left occipital face area (OFA) modulated responses in the intra-parietal sulcus (IPS) at around 170 ms after the presentation of human face stimuli. This effect was also found after participants were shown images of motorcycles. In this case, the IPS was modulated by pre-stimulus activity in the right OFA and the right fusiform face area (FFA). We conclude that pre-stimulus modulation of post-stimulus response also occurs during simple tasks and is therefore independent of behavioral responses.

Measuring visual electrophysiological responses in individuals with low-functioning autism: a feasibility and pilot study

BackgroundAlthough visual abnormalities are considered common in individuals with autism spectrum disorders, the associated electrophysiological markers have remained elusive. One impediment has been that methodological challenges often preclude testing individuals with low-functioning autism (LFA).MethodsIn this feasibility and pilot study, we tested a hybrid visual evoked potential paradigm tailored to individuals with LFA that combines passively presented visual stimuli to elicit scalp-recorded evoked responses with a behavioral paradigm to maintain visual attention. We conducted a pilot study to explore differences in visual evoked response patterns across three groups: individuals with LFA, with high-functioning autism (HFA), and with typical development.ResultsAll participants with LFA met criteria for study feasibility by completing the recordings and producing measurable cortical evoked waveform responses. The LFA group had longer (delayed) cortical response latencies on average as compared with the HFA and typical development groups. We also observed group differences in visually induced alpha spectral power: the LFA group showed little to no prestimulus alpha activity in contrast to the HFA and typical development groups that showed increased prestimulus alpha activity. This observation was confirmed by the bootstrapped confidence intervals, suggesting that the absence of prestimulus alpha power may be a potential electrophysiological marker of LFA.ConclusionOur results confirm the utility of tailoring visual electrophysiology paradigms to individuals with LFA in order to facilitate inclusion of individuals across the autism spectrum in studies of visual processing.

Pre-stimulus alpha oscillation and post-stimulus cortical activity differ in localization between consciously perceived and missed near-threshold somatosensory stimuli.

Conscious perception of a near‐threshold (NT) stimulus is characterized by the pre‐ and post‐stimulus brain state. However, the power of pre‐stimulus neural oscillations and strength of post‐stimulus cortical activity that lead to conscious perception have rarely been examined in individual cortical areas. This is because most previous electro‐ and magnetoencephalography (EEG and MEG, respectively) studies involved scalp‐ and sensor‐level analyses. Therefore, we recorded MEG during a continuous NT somatosensory stimulus detection task and applied the reconstructed source data in order to identify cortical areas where the post‐stimulus cortical activity and pre‐stimulus alpha oscillation predict the conscious perception of NT somatosensory stimuli. We found that the somatosensory hierarchical processing areas, prefrontal areas and cortical areas belonging to the default mode network showed stronger cortical activity for consciously perceived trials in the post‐stimulus period, but the cortical activity in primary somatosensory area (SI) is independent of conscious perception during the early stage of NT stimulus processing. In addition, we revealed that the pre‐stimulus alpha oscillation only in SI is predictive of conscious perception. These findings suggest that the bottom‐up stream of somatosensory information flow following SI and pre‐stimulus alpha activity fluctuation in SI as a top‐down modulation are crucial constituents of conscious perception.

Reduced alpha amplitudes predict perceptual suppression

The amplitude of prestimulus alpha oscillations over parieto-occipital cortex has been shown to predict visual detection of masked and threshold-level stimuli. Whether alpha activity similarly predicts target visibility in perceptual suppression paradigms, another type of illusion commonly used to investigate visual awareness, is presently unclear. Here, we examined prestimulus alpha activity in the electroencephalogram (EEG) of healthy participants in the context of a generalized flash suppression (GFS) task during which salient target stimuli are rendered subjectively invisible in a subset of trials following the onset of a full-field motion stimulus. Unlike for masking or threshold paradigms, alpha (8–12 Hz) amplitude prior to motion onset was significantly higher when targets remained subjectively visible compared to trials during which the targets became perceptually suppressed. Furthermore, individual prestimulus alpha amplitudes strongly correlated with the individual trial-to-trial variability quenching following motion stimulus onset, indicating that variability quenching in visual cortex is closely linked to prestimulus alpha activity. We conclude that predictive correlates of conscious perception derived from perceptual suppression paradigms differ substantially from those obtained with “near threshold paradigms”, possibly reflecting the effectiveness of the suppressor stimulus.

Deconstructing Reorienting of Attention: Cue Predictiveness Modulates the Inhibition of the No-target Side and the Hemispheric Distribution of the P1 Response to Invalid Targets.

Orienting of attention produces a "sensory gain" in the processing of visual targets at attended locations and an increase in the amplitude of target-related P1 and N1 ERPs. P1 marks gain reduction at unattended locations; N1 marks gain enhancement at attended ones. Lateral targets that are preceded by valid cues also evoke a larger P1 over the hemisphere contralateral to the no-target side, which reflects inhibition of this side of space [Slagter, H. A., Prinssen, S., Reteig, L. C., & Mazaheri, A. Facilitation and inhibition in attention: Functional dissociation of pre-stimulus alpha activity, P1, and N1 components. Neuroimage, 125, 25-35, 2016]. To clarify the relationships among cue predictiveness, sensory gain, and the inhibitory P1 response, we compared cue- and target-related ERPs among valid, neutral, and invalid trials with predictive (80% valid/20% invalid) or nonpredictive (50% valid/50% invalid) directional cues. Preparatory facilitation over the visual cortex contralateral to the cued side of space (lateral directing attention positivity component) was reduced during nonpredictive cueing. With predictive cues, the target-related inhibitory P1 was larger over the hemisphere contralateral to the no-target side not only in response to valid but also in response to neutral and invalid targets: This result highlights a default inhibitory hemispheric asymmetry that is independent from cued orienting of attention. With nonpredictive cues, valid targets reduced the amplitude of the inhibitory P1 over the hemisphere contralateral to the no-target side whereas invalid targets enhanced the amplitude of the same inhibitory component. Enhanced inhibition was matched with speeded reorienting to invalid targets and drop in attentional costs. These findings show that reorienting of attention is modulated by the combination of cue-related facilitatory and target-related inhibitory activity.

The Weakened Relationship Between Prestimulus Alpha Oscillations and Response Time in Older Adults With Mild Cognitive Impairment.

Background: Prestimulus alpha oscillations associated with preparatory attention have an impact on response time (RT). However, little is known about whether there is a deficit in the relationship between prestimulus alpha oscillations and RT in older adults with mild cognitive impairment (MCI).Method: We collected electroencephalography (EEG) data from 28 older adults with MCI and 28 demographically matched healthy controls (HCs) when they were performing an Eriksen flanker task. For each participant, single-trial prestimulus alpha power was calculated for combinations of congruency (congruent vs. incongruent) and response speed (fast vs. slow).Result: Statistical analysis indicated that prestimulus alpha power was significantly lower for fast trials than slow trials in HCs but not in older adults with MCI. The Fisher’s z scores of the within-subject correlation coefficients between single-trial prestimulus alpha power and RT were significantly larger in HCs than in older adults with MCI. In addition, machine learning analyses indicated that prestimulus alpha power and its correlation with RT could serve as features to distinguish older adults with MCI from HCs and to predict performance on some neuropsychological tests.Conclusion: The reduced correlation between prestimulus alpha activity and RT suggests that older adults with MCI experience impaired preparatory attention.

"Fast" versus "slow" word integration of visual and olfactory objects: EEG biomarkers of decision speed variability.

In psychological experiments, behavioral speed varies across trials, and this variation is often associated with corresponding fluctuations in cortical activity. Little is known about such cortical variations in semantic priming tasks where target words are matched with preceding sensory object cues. Here, two visually presented target words ("pear" and "lilac") were repeatedly cued by corresponding odors or pictures, and the participants were to indicate matching or nonmatching combinations. Data were split in behaviorally "fast" versus "slow" trials. We hypothesized that slow trials would be associated with higher prestimulus alpha activity and reduced ERP amplitudes, and that response-time differences between odor-cued and picture-cued trials would be especially large in slow behavioral trials. Results confirmed that slow trials showed increased alpha-band activity prior to word target onset, as well as amplitude decreases in the sensory P1 and semantic N400 components. However, no interactions between cue-modality and processing speed were observed. Instead, odor-cue integration responses were uniquely delayed on incongruent trials, a novel behavioral effect that was not observed in EEG measures. The results show that semantic integration speed is reflected in cortical activity before and during stimulus processing. Behavioral interactions with cue modality did not correspond to observed cortical activity changes, perhaps because olfactory circuits are not readily observed in scalp-recorded EEG. We conclude that combining behavioral speed variability and cortical EEG measures is useful in understanding the fluctuating nature of cognitive processing sequences. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Transcranial Alternating Current Stimulation at Alpha Frequency Reduces Pain When the Intensity of Pain is Uncertain

Alpha activity directly before pain onset has been implicated in pain experience with higher prestimulus alpha associated with lower reported pain. However, expectations about pain intensity also seem to affect prestimulus alpha activity. To date, evidence for a relationship between alpha activity and pain experience has been largely correlational. Transcranial alternating current stimulation at alpha frequency (alpha tACS) permits direct manipulation of alpha activity and therefore an examination of the potential causal relationship between alpha activity and pain. We investigated whether somatosensory alpha tACS could reduce pain experience and whether this was influenced by uncertainty about pain intensity. In a within-subjects design, perceived pain intensity and unpleasantness were assessed in 23 participants during alpha tACS and sham stimulation. Visual cues preceding the pain stimulus were used to manipulate uncertainty. A significant tACS × Uncertainty × Stimulus intensity interaction was found for reported pain intensity (F2,44 = 4.50, P = .017, partial η2 = .17) and unpleasantness (F1,22 = 4.78, P = .040, partial η2 = .18). Pain experience during the application of somatosensory alpha tACS was significantly lowered compared with sham stimulation, but only when the intensity of an upcoming stimulus was uncertain. PerspectiveTo our knowledge, this is the first study to suggest that somatosensory alpha tACS might lead to a reduction in pain. Interventions targeting alpha activity may have the potential to alleviate chronic pain. However, a patient's expectation about the intensity of upcoming pain must also be taken into account.

U-shaped Relation between Prestimulus Alpha-band and Poststimulus Gamma-band Power in Temporal Tactile Perception in the Human Somatosensory Cortex.

Neuronal oscillations are a ubiquitous phenomenon in the human nervous system. Alpha-band oscillations (8-12 Hz) have been shown to correlate negatively with attention and performance, whereas gamma-band oscillations (40-150 Hz) correlate positively. Here, we studied the relation between prestimulus alpha-band power and poststimulus gamma-band power in a suprathreshold tactile discrimination task. Participants received two electrical stimuli to their left index finger with different SOAs (0 msec, 100 msec, intermediate SOA, intermediate SOA ± 10 msec). The intermediate SOA was individually determined so that stimulation was bistable, and participants perceived one stimulus in half of the trials and two stimuli in the other half. We measured neuronal activity with magnetoencephalography (MEG). In trials with intermediate SOAs, behavioral performance correlated inversely with prestimulus alpha-band power but did not correlate with poststimulus gamma-band power. Poststimulus gamma-band power was high in trials with low and high prestimulus alpha-band power and low for intermediate prestimulus alpha-band power (i.e., U-shaped). We suggest that prestimulus alpha activity modulates poststimulus gamma activity and subsequent perception: (1) low prestimulus alpha-band power leads to high poststimulus gamma-band power, biasing perception such that two stimuli were perceived; (2) intermediate prestimulus alpha-band power leads to low gamma-band power (interpreted as inefficient stimulus processing), consequently, perception was not biased in either direction; and (3) high prestimulus alpha-band power leads to high poststimulus gamma-band power, biasing perception such that only one stimulus was perceived.

The relationship between the superior frontal cortex and alpha oscillation in a flanker task: Simultaneous recording of electroencephalogram (EEG) and near infrared spectroscopy (NIRS)

Activity in the alpha band of the electroencephalogram (EEG) reflects functional inhibition of the cerebral cortex. The superior frontal cortex (SFC) is known to control alpha activity. Based on this relationship between SFC and alpha, we hypothesized that SFC controlled alpha mediates proactive control over interference. In this study, we examined the relationship between SFC and alpha in the flanker task by simultaneously recording EEG and near infrared spectroscopy (NIRS). Forty participants performed a flanker task with occasional (compatible 75%, incompatible 25%) and successive (incompatible 100%) conditions. In the occasional condition, larger SFC activity was related to pre-stimulus alpha enhancement under occipital electrodes. This is consistent with a model in which SFC enhances pre-stimulus alpha activity, leading to proactive control over interference. However, we could not detect a correlation between SFC activity and alpha activity in the successive condition. Active inhibition may have been reduced by a need to continuously inhibit brain regions associated with the irrelevant information. This may have reduced the role of the SFC in controlling alpha activity. Based on these findings, we postulate that there are two cerebral mechanisms of proactive control over interference.

Facilitation and inhibition in attention: Functional dissociation of pre-stimulus alpha activity, P1, and N1 components

Attention — the ability to attend to some things while ignoring others — can be best described as an emergent property of many neural mechanisms, facilitatory and inhibitory, working together to resolve competition for processing resources and control of behavior. Previous EEG and MEG studies examining the neural mechanisms underlying facilitation and inhibition of stimulus processing typically used paradigms requiring alternating shifts of attention in the spatial domain, with stimuli occurring at both attended and unattended locations. These studies generally observed greater pre-stimulus alpha oscillations over task-irrelevant vs. relevant posterior regions and bilateral attentional modulations of early sensory processing. In contrast, in the current series of experiments, participants continuously attended to only one hemifield and stimuli were only presented at the attended location, affording us an opportunity to elucidate the inhibitory and facilitatory effects of attention in the brain in a context in which spatial relevance was fixed. We found that continuous attention to one hemifield did not modulate prestimulus alpha activity in ipsilateral regions but did result in a perfectly lateralized P1 attention effect to ipsilateral posterior regions. Moreover, we found a bilateral N1 effect. These findings suggest that pre-stimulus alpha activity, the P1 and the N1 reflect qualitatively different aspects of attention; While pre-stimulus alpha-band activity may reflect a top-down inhibitory mechanism that critically depends on functional competition between task-relevant and irrelevant sensory regions, the ipsilateral P1 effect may reflect stimulus-triggered blocking of sensory processing in irrelevant networks, and the N1 effect facilitation of task-relevant processing.

Prestimulus EEG alpha oscillations modulate task-related fMRI BOLD responses to auditory stimuli

EEG alpha-band activity is generally thought to represent an inhibitory state related to decreased attention and play a role in suppression of task-irrelevant stimulus processing, but a competing hypothesis suggests an active role in processing task-relevant information — one in which phase dynamics are involved. Here we used simultaneous EEG–fMRI and a whole-brain analysis to investigate the effects of prestimulus alpha activity on the event-related BOLD response during an auditory oddball task. We separately investigated the effects of the posterior alpha rhythm's power and phase on activity related to task-relevant stimulus processing and also investigated higher-level decision-related processing. We found stronger decision-related BOLD activity in areas late in the processing stream when subjects were in the high alpha power state prior to stimulus onset, but did not detect any effect in primary sensory regions. Our phase analysis revealed correlates in the bilateral thalamus, providing support for a thalamo–cortical loop in attentional modulations and suggesting that the cortical alpha rhythm acts as a cyclic modulator of task-related responses very early in the processing stream. Our results help to reconcile the competing inhibition and active-processing hypotheses for ongoing alpha oscillations and begin to tease apart the distinct roles and mechanisms underlying their power and phase.

Impairments in background and event-related alpha-band oscillatory activity in patients with schizophrenia.

Studies show that patients with schizophrenia exhibit impaired responses to sensory stimuli, especially at the early stages of neural processing. In particular, patients’ alpha-band (8–14 Hz) event-related desynchronization (ERD) and visual P1 event-related potential (ERP) component tend to be significantly reduced, with P1 ERP deficits greater for visual stimuli biased towards the magnocellular system. In healthy controls, studies show that pre-stimulus alpha (background alpha) plays a pivotal role in sensory processing and behavior, largely by shaping the neural responses to incoming stimuli. Here, we address whether patients’ ERD and P1 deficits stem from impairments in pre-stimulus alpha mechanisms. To address this question we recorded electrophysiological activity in patients with schizophrenia and healthy controls while they engaged in a visual discrimination task with low, medium, and high contrast stimuli. The results revealed a significant decrease in patients’ ERDs, which was largely driven by reductions in pre-stimulus alpha. These reductions were most prominent in right-hemispheric areas. We also observed a systematic relationship between pre-stimulus alpha and the P1 component across different contrast levels. However, this relationship was only observed in healthy controls. Taken together, these findings highlight a substantial anomaly in patients’ amplitude-based alpha background activity over visual areas. The results provide further support that pre-stimulus alpha activity plays an active role in perception by modulating the neural responses to incoming sensory inputs, a mechanism that seems to be compromised in schizophrenia.

Bright illumination reduces parietal EEG alpha activity during a sustained attention task

The influence of the illumination condition on our cognitive-performance seems to be more critical in the modern life, wherein, most people work in an office under a specific illumination condition. However, neurophysiological changes in a specific illumination state and their cognitive interpretation still remain unclear. Thereby, in the present study, the effect of different illumination conditions on the same cognitive performance was evaluated particularly by EEG wavelet analyses. During a sustained attention task, we observed that the higher illumination condition yielded significantly lower parietal tonic electroencephalogram (EEG) alpha activity before the presentation of the probe digit and longer reaction times, than that of the other illumination conditions. Although previous studies suggest that lower prestimulus EEG alpha activity is related to higher performance in an upcoming task, the reduced prestimulus alpha activity under higher illumination was associated with delayed reaction times in the present study. Presumably, the higher background illumination condition seems to be too bright for normal attentional processing and distracted participants' attention during a sustained attention task. Such a bottom–up effect by stimulus salience seemed to overwhelm a prestimulus top-down effect reflected in prestimulus alpha power during the bright background condition. This finding might imply a dynamic competition between prestimulus top-down and poststimulus bottom–up processes. Our findings provide compelling evidence that the illumination condition substantially modulates our attentional processing. Further refinement of the illumination parameters and subsequent exploration of cognitive-modulation are necessary to facilitate our cognitive performance.