Anatomic bases of event-related potentials and their relationship to novelty detection in humans

Native language advantage in electrical brain responses to speech sound changes in passive and active listening condition

It is not clear whether the brain can detect changes in native and non-native speech sounds in both unattended and attended conditions, but this information would be important to understand the nature of potential native language advantage in speech perception. We recorded event-related potentials (ERPs) for changes in duration and in Chinese lexical tone in a repeated vowel /a/ in native speakers of Finnish and Chinese in passive and active listening conditions. ERP amplitudes reflecting deviance detection (mismatch negativity; MMN and N2b) and attentional shifts towards changes in speech sounds (P3a and P3b) were investigated. In the passive listening condition, duration changes elicited increased amplitude in the MMN latency window for both standard and deviant sounds in the Finnish speakers compared to the Chinese speakers, but no group differences were observed for P3a. In passive listening to lexical tones, P3a was increased in amplitude for both standard and deviant stimuli in Chinese speakers compared to Finnish speakers, but the groups did not differ in MMN. In active listening, both tone and duration changes elicited N2b and P3b, but the groups differed only in pattern of results for the deviant type. The results thus suggest an overall increased sensitivity to native speech sounds, especially in passive listening, while the mechanisms of change detection and attentional shifting seem to work well for both native and non-native speech sounds in the attentive mode.

Comparing auditory distance perception in real and virtual environments and the role of the loudness cue: A study based on event-related potentials

The perception of the distance to a sound source is relevant in many everyday situations, not only in real spaces, but also in virtual reality (VR) environments. Where real rooms often reach their limits, VR offers far-reaching possibilities to simulate a wide range of acoustic scenarios. However, in virtual room acoustics a plausible reproduction of distance-related cues can be challenging. In the present study, we compared the detection of changes of the distance to a sound source and its neurocognitive correlates in a real and a virtual reverberant environment, using an active auditory oddball paradigm and EEG measures. The main goal was to test whether the experiments in the virtual and real environments produced equivalent behavioral and EEG results. Three loudspeakers were placed at ego-centric distances of 2 m (near), 4 m (center), and 8 m (far) in front of the participants (N = 20), each 66 cm below their ear level. Sequences of 500 ms noise stimuli were presented either from the center position (standards, 80 % of trials) or from the near or far position (targets, 10 % each). The participants had to indicate a target position via a joystick response ("near" or "far"). Sounds were emitted either by real loudspeakers in the real environment or rendered and played back for the corresponding positions via headphones in the virtual environment. In addition, within both environments, loudness of the auditory stimuli was either unaltered (natural loudness) or the loudness cue was manipulated, so that all three loudspeakers were perceived equally loud at the listener's position (matched loudness). The EEG analysis focused on the mismatch negativity (MMN), P3a, and P3b as correlates of deviance detection, attentional orientation, and context-updating/stimulus evaluation, respectively. Overall, behavioral data showed that detection of the target positions was reduced within the virtual environment, and especially when loudness was matched. Except for slight latency shifts in the virtual environment, EEG analysis indicated comparable patterns within both environments and independent of loudness settings. Thus, while the neurocognitive processing of changes in distance appears to be similar in virtual and real spaces, a proper representation of loudness appears to be crucial to achieve a good task performance in virtual acoustic environments.

A multimodal cortical network of sensory expectation violation revealed by fMRI

The brain is subjected to multi-modal sensory information in an environment governed by statistical dependencies. Mismatch responses (MMRs), classically recorded with EEG, have provided valuable insights into the brain's processing of regularities and the generation of corresponding sensory predictions. Only few studies allow for comparisons of MMRs across multiple modalities in a simultaneous sensory stream and their corresponding cross-modal context sensitivity remains unknown. Here, we used a tri-modal version of the roving stimulus paradigm in fMRI to elicit MMRs in the auditory, somatosensory and visual modality. Participants (N = 29) were simultaneously presented with sequences of low and high intensity stimuli in each of the three senses while actively observing the tri-modal input stream and occasionally reporting the intensity of the previous stimulus in a prompted modality. The sequences were based on a probabilistic model, defining transition probabilities such that, for each modality, stimuli were more likely to repeat (p = .825) than change (p = .175) and stimulus intensities were equiprobable (p = .5). Moreover, each transition was conditional on the configuration of the other two modalities comprising global (cross-modal) predictive properties of the sequences. We identified a shared mismatch network of modality general inferior frontal and temporo-parietal areas as well as sensory areas, where the connectivity (psychophysiological interaction) between these regions was modulated during mismatch processing. Further, we found deviant responses within the network to be modulated by local stimulus repetition, which suggests highly comparable processing of expectation violation across modalities. Moreover, hierarchically higher regions of the mismatch network in the temporo-parietal area around the intraparietal sulcus were identified to signal cross-modal expectation violation. With the consistency of MMRs across audition, somatosensation and vision, our study provides insights into a shared cortical network of uni- and multi-modal expectation violation in response to sequence regularities.

The cost of attentional reorienting on conscious visual perception: an MEG study

How do attentional networks influence conscious perception? To answer this question, we used magnetoencephalography in human participants and assessed the effects of spatially nonpredictive or predictive supra-threshold peripheral cues on the conscious perception of near-threshold Gabors. Three main results emerged. (i) As compared with invalid cues, both nonpredictive and predictive valid cues increased conscious detection. Yet, only predictive cues shifted the response criterion toward a more liberal decision (i.e. willingness to report the presence of a target under conditions of greater perceptual uncertainty) and affected target contrast leading to 50% detections. (ii) Conscious perception following valid predictive cues was associated to enhanced activity in frontoparietal networks. These responses were lateralized to the left hemisphere during attentional orienting and to the right hemisphere during target processing. The involvement of frontoparietal networks occurred earlier in valid than in invalid trials, a possible neural marker of the cost of re-orienting attention. (iii) When detected targets were preceded by invalid predictive cues, and thus reorienting to the target was required, neural responses occurred in left hemisphere temporo-occipital regions during attentional orienting, and in right hemisphere anterior insular and temporo-occipital regions during target processing. These results confirm and specify the role of frontoparietal networks in modulating conscious processing and detail how invalid orienting of spatial attention disrupts conscious processing.

A simple model of the electrosensory electromotor loop in Gymnotus omarorum

This article introduces and tests a simple model that describes a neural network found in nature, the electrosensory control of an electromotor pacemaker. The cornerstone of the model is an early-stage filter based on the subtraction of a feedforward integrated version of the recent sensory past from the present input signal. The output of this filter governs the modulation of a premotor pacemaker command driving the sensory signal carrier generation and, in consequence, the timing of subsequent electrosensory input. This early filter has a biological parallel in the known connectivity of the first electrosensory relay within the brain stem of the weakly electric fish Gymnotus omarorum. Our biomimetic model of this active, perception-driven action-sensation cycle was contrasted with previously published and here provided new data. When the amplitude of the electrosensory input was manipulated to mimic previous experiments on the novelty detection characteristics, the model reproduces them rather faithfully. In addition, when we applied continuous variations to the input it shows that increases in stimulus amplitudes are followed by increases in the EOD rate, but decreases do not cause rate modulation suggesting a rectification in some stage of the loop. These behavioral experiments confirmed results generated the simulations suggesting that beyond explaining the novelty detection process this simple model is a good description of the electrosensory -electromotor loop in pulse weakly electric fish.

Auditory event-related potentials in separating patients with depressive disorders and non-depressed controls: A narrative review

This narrative review brings together the findings regarding the differences in the auditory event-related potentials (ERPs) between patients with depressive disorder and non-depressed control subjects. These studies' results can inform us of the possible alterations in sensory-cognitive processing in depressive disorders and the potential of using these ERPs in clinical applications. Auditory P3, mismatch negativity (MMN) and loudness dependence of auditory evoked potentials (LDAEP) were the subjects of the investigation. A search in PubMed yielded 84 studies. The findings of the reviewed studies were not highly consistent, but some patterns could be identified. For auditory P3b, the common findings were attenuated amplitude and prolonged latency among depressed patients. Regarding auditory MMN, especially the amplitude of duration deviance MMN was commonly attenuated, and the amplitude of frequency deviance MMN was increased in depressed patients. In LDAEP studies, generally, no differences between depressed patients and non-depressed controls were reported, although some group differences concerning specific depression subtypes were found. This review posits that future research should investigate whether certain stimulus conditions are particularly efficient at separating depressed and non-depressed participant groups. Future studies should contrast responses in different subpopulations of depressed patients, as well as different clinical groups (e.g., depressive disorder and anxiety disorder patients), to investigate the specificity of the auditory ERP alterations for depressive disorders.

P3b Does Not Reflect Perceived Contrasts

It has been shown that P3b is not a signature of perceptual awareness per se but is instead more closely associated with postperceptual processing (Cohen et al., 2020). Here, we seek to investigate whether human participants’ attentional states are different in the report and the no-report conditions. This difference in attentional states, if exists, may lead to degraded consciousness of the stimuli in the no-report condition, and it therefore remains unknown whether the disappearance of P3b is because of a lack of reportability or degraded consciousness. Results of our experiment 1 showed that participants did experience degraded contents of consciousness in the no-report condition. However, results of experiment 2 showed that the degraded contents of consciousness did not influence the amplitude of P3b. These findings strengthen the claim that P3b is not a signature of perceptual awareness but is associated with postperceptual processing.

Suggested visual blockade during hypnosis: Top-down modulation of stimulus processing in a visual oddball task

Several theories of hypnosis assume that responses to hypnotic suggestions are implemented through top-down modulations via a frontoparietal network that is involved in monitoring and cognitive control. The current study addressed this issue re-analyzing previously published event-related-potentials (ERP) (N1, P2, and P3b amplitudes) and combined it with source reconstruction and connectivity analysis methods. ERP data were obtained from participants engaged in a visual oddball paradigm composed of target, standard, and distractor stimuli during a hypnosis (HYP) and a control (CON) condition. In both conditions, participants were asked to count the rare targets presented on a video screen. During HYP participants received suggestions that a wooden board in front of their eyes would obstruct their view of the screen. The results showed that participants’ counting accuracy was significantly impaired during HYP compared to CON. ERP components in the N1 and P2 window revealed no amplitude differences between CON and HYP at sensor-level. In contrast, P3b amplitudes in response to target stimuli were significantly reduced during HYP compared to CON. Source analysis of the P3b amplitudes in response to targets indicated that HYP was associated with reduced source activities in occipital and parietal brain areas related to stimulus categorization and attention. We further explored how these brain sources interacted by computing time-frequency effective connectivity between electrodes that best represented frontal, parietal, and occipital sources. This analysis revealed reduced directed information flow from parietal attentional to frontal executive sources during processing of target stimuli. These results provide preliminary evidence that hypnotic suggestions of a visual blockade are associated with a disruption of the coupling within the frontoparietal network implicated in top-down control.

Electrophysiological Screening for Children With Suspected Auditory Processing Disorder: A Systematic Review

Objective: This research aimed to provide evidence for the early identification and intervention of children at risk for auditory processing disorder (APD). Electrophysiological studies on children with suspected APDs were systematically reviewed to understand the different electrophysiological characteristics of children with suspected APDs. Methods: Computerized databases such as PubMed, Cochrane, MEDLINE, Web of Science, and EMBASE were searched for retrieval of articles since the establishment of the database through May 18, 2020. Cohort, case-control, and cross-sectional studies that evaluated the literature for the electrophysiological assessment of children with suspected APD were independently reviewed by two researchers for literature screening, literature quality assessment, and data extraction. The Newcastle-Ottawa Scale and 11 entries recommended by the Agency for Healthcare Research and Quality were used to evaluate the quality of the literature. Results: In accordance with the inclusion criteria, 14 articles were included. These articles involved 7 electrophysiological testing techniques: click-evoked auditory brainstem responses, frequency-following responses, the binaural interaction component of the auditory brainstem responses, the middle-latency response, cortical auditory evoked potential, mismatch negativity, and P300. The literature quality was considered moderate. Conclusions: Auditory electrophysiological testing can be used for the characteristic identification of children with suspected APD; however, the value of various electrophysiological testing methods for screening children with suspected APD requires further study.

Somatosensory Deviance Detection ERPs and Their Relationship to Analogous Auditory ERPs and Interoceptive Accuracy

Abstract. Automatic deviance detection has been widely explored in terms of mismatch responses (mismatch negativity or mismatch response) and P3a components of event-related potentials (ERPs) under a predictive coding framework; however, the somatosensory mismatch response has been investigated less often regarding the different types of changes than its auditory counterpart. It is not known whether the deviance detection responses from different modalities correlate, reflecting a general prediction error mechanism of the central nervous system. Furthermore, interoceptive functions have been associated with predictive coding theory, but whether interoceptive accuracy correlates with deviance detection brain responses has rarely been investigated. Here, we measured ERPs to changes in somatosensory stimuli’s location and intensity and in sound intensity in healthy adults ( n = 34). Interoceptive accuracy was measured with a heartbeat discrimination task, where participants indicated whether their heartbeats were simultaneous or non-simultaneous with sound stimuli. We found a mismatch response and a P3a response to somatosensory location and auditory intensity changes, but for somatosensory intensity changes, only a P3a response was found. Unexpectedly, there were neither correlations between the somatosensory location deviance and intensity deviance brain responses nor between auditory and somatosensory brain responses. In addition, the brain responses did not correlate with interoceptive accuracy. The results suggest that although deviance detection in the auditory and somatosensory modalities are likely based on similar neural mechanisms at a cellular level, their ERP indexes do not indicate a linear association in sensitivity for deviance detection between the modalities. Furthermore, although sensory deviance detection and interoceptive detection are both associated with predictive coding functions, under these experimental settings, functional relationships were not observed. These results should be taken into account in the future development of theories related to human sensory functions and in extensions of the predictive coding theory in particular.

The Effect of Prior Knowledge of Color on Behavioral Responses and Event-Related Potentials During Go/No-go Task

In daily life, the meaning of color plays an important role in execution and inhibition of a motor response. For example, the symbolism of traffic light can help pedestrians and drivers to control their behavior, with the color green/blue meaning go and red meaning stop. However, we don't always stop with a red light and sometimes start a movement with it in such a situation as drivers start pressing the brake pedal when a traffic light turns red. In this regard, we investigated how the prior knowledge of traffic light signals impacts reaction times (RTs) and event-related potentials (ERPs) in a Go/No-go task. We set up Blue Go/Red No-go and Red Go/Blue No-go tasks with three different go signal (Go) probabilities (30, 50, and 70%), resulting in six different conditions. The participants were told which color to respond (Blue or Red) just before each condition session but didn't know the Go probability. Neural responses to Go and No-go signals were recorded at Fz, Cz, and Oz (international 10-20 system). We computed RTs for Go signal and N2 and P3 amplitudes from the ERP data. We found that RT was faster when responding to blue than red light signal and also was slower with lower Go probability. Overall, N2 amplitude was larger in Red Go than Blue Go trial and in Red No-go than Blue No-go trial. Furthermore, P3 amplitude was larger in Red No-go than Blue No-go trial. Our findings of RT and N2 amplitude for Go ERPs could indicate the presence of Stroop-like interference, that is a conflict between prior knowledge about traffic light signals and the meaning of presented signal. Meanwhile, the larger N2 and P3 amplitudes in Red No-go trial as compared to Blue No-go trial may be due to years of experience in stopping an action in response to a red signal and/or attention. This study provides the better understanding of the effect of prior knowledge of color on behavioral responses and its underlying neural mechanisms.

EEG, MEG and neuromodulatory approaches to explore cognition: Current status and future directions

Neural oscillations and their association with brain states and cognitive functions have been object of extensive investigation over the last decades. Several electroencephalography (EEG) and magnetoencephalography (MEG) analysis approaches have been explored and oscillatory properties have been identified, in parallel with the technical and computational advancement. This review provides an up-to-date account of how EEG/MEG oscillations have contributed to the understanding of cognition. Methodological challenges, recent developments and translational potential, along with future research avenues, are discussed.

Updating Emotional Stimuli in Heroin Abstainers' Working Memory: An Event-Related Potential Investigation

BACKGROUND

It is well-documented that heroin users demonstrate aberrant emotion-processing abilities. However, the mechanism by which heroin users process emotional information after it has captured their attention and entered their working memory is unclear.

OBJECTIVES

A modified emotional 2-back task was used to examine whether heroin abstainers demonstrate specific bias patterns in updating emotional stimuli in their working memory.

METHODS

In total, 26 male heroin abstainers and 29 healthy controls were asked to identify whether the current picture was the same as a picture that had appeared two trials earlier, while behavioral data and electroencephalogram data were collected.

RESULTS

Contrary to predictions, the heroin abstainers and healthy controls demonstrated a similar pattern of P300 activity in response to emotional stimuli with no between-group differences in accuracy or reaction time. More specifically, the P300 amplitudes were larger for negative pictures than for positive and neutral pictures. Surprisingly, we found larger P300 amplitudes at Fz electrodes than at Cz and Pz electrodes in the control group, whereas there was no significant difference at midline electrodes in the heroin abstainers.

CONCLUSIONS/IMPORTANCE

Although subtle differences may exist in attentional engagement toward incoming emotional stimulus between two groups, the similar P300 pattern may indicate partial preservation of emotional working memory capacity associated with adaptive emotion regulation in heroin abstainers. These results deepen our understanding of the emotion regulation impairments associated with chronic drug use.

Cortical responses to auditory novelty across task conditions: An intracranial electrophysiology study

Elucidating changes in sensory processing across attentional and arousal states is a major focus in neuroscience. The local/global deviant (LGD) stimulus paradigm engages auditory predictive coding over short (local deviance, LD) and long (global deviance, GD) time scales, and has been used to assay disruption of auditory predictive coding upon loss of consciousness. Our previous work (Nourski et al., 2018, J Neurosci 38:8441-52) examined effects of general anesthesia on short- and long-term novelty detection. GD effects were suppressed at subhypnotic doses of propofol, suggesting that they may be more related to task engagement than consciousness per se. The present study addressed this hypothesis by comparing cortical responses to auditory novelty during passive versus active listening conditions in awake listeners. Subjects were seven adult neurosurgical patients undergoing chronic invasive monitoring for medically intractable epilepsy. LGD stimuli were sequences of four identical vowels followed by a fifth identical or different vowel. In the passive condition, the stimuli were presented to subjects as they watched a silent TV program and were instructed to attend to its content. In the active condition, stimuli were presented in the absence of a TV program, and subjects were instructed to press a button in response to GD target stimuli. Intracranial recordings were made from multiple brain regions, including core and non-core auditory, auditory-related, prefrontal and sensorimotor cortex. Metrics of task performance included hit rate, sensitivity index, and reaction times. Cortical activity was measured as averaged auditory evoked potentials (AEPs) and event-related band power in high gamma (70-150 Hz) and alpha (8-14 Hz) frequency bands. The vowel stimuli and LD elicited robust AEPs in all studied brain areas in both passive and active conditions. High gamma responses to stimulus onset and LD were localized predominantly to the auditory cortex in the superior temporal plane and had a comparable prevalence and spatial extent between the two conditions. In contrast, GD effects (AEPs, high gamma and alpha suppression) were greatly enhanced during the active condition in all studied brain areas. The prevalence of high gamma GD effects was positively correlated with individual subjects' task performance. The data demonstrate distinct task engagement-related effects on responses to auditory novelty across the auditory cortical processing hierarchy. The results motivate a closer examination of effective connectivity underlying attentional modulation of cortical sensory responses, and serve as a foundation for examining changes in sensory processing associated with general anesthesia, sleep and disorders of consciousness.

Neural correlates of the Dunning-Kruger effect

The Dunning-Kruger effect (DKE) is a metacognitive phenomenon of illusory superiority in which individuals who perform poorly on a task believe they performed better than others, yet individuals who performed very well believe they under-performed compared to others. This phenomenon has yet to be directly explored in episodic memory, nor explored for physiological correlates or reaction times. We designed a novel method to elicit the DKE via a test of item recognition while electroencephalography (EEG) was recorded. Throughout the task, participants were asked to estimate the percentile in which they performed compared to others. Results revealed participants in the bottom 25th percentile over-estimated their percentile, while participants in the top 75th percentile under-estimated their percentile, exhibiting the classic DKE. Reaction time measures revealed a condition-by-group interaction whereby over-estimators responded faster than under-estimators when estimating being in the top percentile and responded slower when estimating being in the bottom percentile. Between-group EEG differences were evident between over-estimators and under-estimators during Dunning-Kruger responses, which revealed FN400-like effects of familiarity supporting differences for over-estimators, whereas "old-new" memory event-related potential effects revealed a late parietal component associated with recollection-based processing for under-estimators that was not evident for over-estimators. Findings suggest over- and under-estimators use differing cognitive processes when assessing their performance, such that under-estimators may rely on recollection during memory while over-estimators may draw upon excess familiarity when over-estimating their performance. Episodic memory thus appears to play a contributory role in metacognitive judgements of illusory superiority.

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.

Central auditory processing in adults with chronic stroke without hearing loss: A magnetoencephalography study

OBJECTIVE

Stroke lesions in non-auditory areas may affect higher-order central auditory processing. We sought to characterize auditory functions in chronic stroke survivors with unilateral arm/hand impairment using auditory evoked responses (AERs) with lesion and perception metrics.

METHODS

The AERs in 29 stroke survivors and 14 controls were recorded with single tones, active and passive frequency-oddballs, and a dual-oddball with pitch-contour and time-interval deviants. Performance in speech-in-noise, mistuning detection, and moving-sound detection was assessed. Relationships between AERs, behaviour, and lesion overlap with functional networks, were examined.

RESULTS

Despite their normal hearing, eight patients showed unilateral AER in the hemisphere ipsilateral to the affected hand with reduced amplitude compared to those with bilateral AERs. Both groups showed increasing attenuation of later components. Hemispheric asymmetry of AER sources was reduced in bilateral-AER patients. The N1 wave (100 ms latency) and P2 (200 ms) were delayed in individuals with lesions in the basal-ganglia and white-matter, while lesions in the attention network reduced the frequency-MMN (mismatch negativity) responses and increased the pitch-contour P3a response. Patients' impaired speech-in-noise perception was explained by AER measures and frequency-deviant detection performance with multiple regression.

CONCLUSION

AERs reflect disruption of auditory functions due to damage outside of temporal lobe, and further explain complexity of neural mechanisms underlying higher-order auditory perception.

SIGNIFICANCE

Stroke survivors without obvious hearing problems may benefit from rehabilitation for central auditory processing.

Childhood leukemia survivors exhibit deficiencies in sensory and cognitive processes, as reflected by event-related brain potentials after completion of curative chemotherapy: A preliminary investigation

Objective: The purpose of this study was to characterize post-chemotherapy sensory, memory, and attention abilities in childhood survivors of acute lymphoblastic leukemia (ALL) to better understand how treatment affects cognitive functioning. Methods: Eight ALL survivors and eight age-matched, healthy children between the ages of 5-11 years participated in the study. Among the ALL survivors, a median of 63 days (range 22-267 days) elapsed between completion of chemotherapy and this assessment. Sounds were presented in an oddball paradigm while recording the electroencephalogram in separate conditions of passive listening and active task performance. To assess different domains of cognition, we measured event-related brain potentials (ERPs) reflecting sensory processing (P1 component), working memory (mismatch negativity [MMN] component), attentional orienting (P3a), and target detection (P3b component) in response to the sounds. We also measured sound discrimination and response speed performance. Results: Relative to control subjects, ALL survivors had poorer performance on auditory tasks, as well as decreased amplitude of the P1, MMN, P3a, and P3b components. ALL survivors also did not exhibit the amplitude gain typically observed in the sensory P1 component when attending to the sound input compared to when passively listening. Conclusions: Atypical responses were observed in brain processes associated with sensory discrimination, auditory working memory, and attentional control in pediatric ALL survivors indicating deficiencies in all cognitive domains compared to age-matched controls. Significance: ERPs differentiated aspects of cognitive functioning, which may provide a useful tool for assessing recovery and risk of post-chemotherapy cognitive deficiencies in young children. The decreased MMN amplitude in ALL survivors may indicate (N-methyl D-aspartate) NMDA dysfunction induced by methotrexate, and thus provides a potential therapeutic target for chemotherapy-associated cognitive impairments.

A differential role for human hippocampus in novelty and contextual processing: Implications for P300

The role of the hippocampus in P300 has long been debated. Here, we present a theoretical framework that elucidates hippocampal contributions to scalp P300 based on intracranial and lesion research combined with emerging evidence on the role of the hippocampus in rapid statistical learning, memory, and novelty processing. The P300 has been divided in two subcomponents: a fronto-central P3a related to novelty and distractor processing, and a parietal P3b related to target detection. Interest in a role for hippocampus in scalp P300 was sparked by P3-like ERPs measured intracranially in human hippocampus. Subsequent medial temporal lobe lesion studies show intact scalp P3b, indicating that the hippocampus is not critical for P3b. This contrasts with the scalp P3a, which was significantly diminished in human patients with lesions in the posterior hippocampus. This suggests a differential role for hippocampus in P3a and P3b. Our framework purports that the hippocampus plays a central role in distractor processing that leads to P3a generation in cortical regions. We also propose that the hippocampus is involved at the end of the cognitive episode for both P3a and P3b implementing contextual updating. P3-like ERPs measured in hippocampus may reflect input signals from cortical regions implementing updates based on the outcome of cognitive processes underlying scalp P3, enabling a model update of the environment facilitated by the hippocampus. Overall, this framework proposes an active role for the hippocampus in novelty processing leading up to P3a generation, followed by contextual updating of the outcome of both scalp P3a and P3b.

Semantic prediction-errors are context-dependent: An ERP study

The human brain is an efficient, adaptive, and predictive machine, constructing a generative model of the environment that we then perceive and become conscious of. Here, we show that different types of prediction-errors - the discrepancies between top-down expectations and bottom-up sensory input - are integrated across processing levels and sensory modalities of the cortical hierarchy. We designed a novel, hybrid protocol in which five prediction-establishing sounds were played in rapid succession (e.g., "meow", "meow", "meow", etc.), followed by either a standard (e.g., "meow") or a deviant (e.g., "woof") prime sound, then a visual target word that was either congruent or incongruent (e.g., "cat" or "dog") with the prime sound. We found that the deviants elicited a more negative voltage than the standards at about 150 ms - the mismatch negativity (MMN), an event-related potential (ERP) sensitive to low-level perceptual violations - and that the incongruent words elicited a more negative voltage than the congruent words at about 350 ms - the N400, an ERP sensitive to high-level semantic violations. We also found that the N400 was context-dependent: the N400 was larger when the target words were preceded by a standard than a deviant. Our results suggest that perceptual prediction-errors modulate subsequent semantic prediction-errors. We conclude that our results are consistent with one of the most important assumptions of predictive coding theories: hierarchical prediction-error processing.

Impact of putamen stroke on task context updating: Evidence from P300 brain waves

According to the context updating theory, the oddball P300 component indexes brain activities underlying revision of the mental representation induced by incoming stimuli. It involves an attention-driven comparison process that evaluates the representation of the previous event in working memory. Delayed latencies have been reported for various types of stroke such as unilateral thalamic stroke. We investigated memory updating effects in patients with putamen stroke. Two groups of patients with putamen and thalamic stroke were recruited along with two control groups of young and old healthy participants. Auditory and visual P300 were elicited respectively in a two-stimulus oddball paradigm. The auditory P300 peak latencies were significantly longer in patients with a putamen lesion than in the aged and young control groups and the same pattern was found in the thalamus-lesioned patient. The delayed auditory P300 component in both patient groups but neither control group suggests impairment of memory updating in patients with putamen stroke comparable with thalamic stroke. Our study illustrates the important role of subcortical structures subserved in context updating.

Assessment of auditory discrimination in hearing-impaired patients

Hearing loss can impair auditory discrimination, especially in noisy environments, requiring greater listening effort, which can impact socio-occupational life. To assess the impact of hearing loss in noisy environments, clinicians may use subjective or objective methods. Subjective methods, such as speech audiometry in noise, are used in clinical practice to assess reported discomfort. Objective methods, such as cortical auditory evoked potentials (CAEPs), are mainly used in research. Subjective methods mainly comprise speech audiometry in noise, in which the signal-to-noise ratio can be varied so as to determine the individual speech recognition threshold, with and without hearing rehabilitation, the aim being to highlight any improvement in auditory performance. Frequency discrimination analysis is also possible. Objective methods assess auditory discrimination without the patient's active participation. One technique used for patients with auditory rehabilitation is the study of auditory responses by CAEPs. This electrophysiological examination studies cortical auditory rehabilitation oddball paradigms, enabling wave recordings such as mismatch negativity, P300 or N400, and analysis of neurophysiological markers according to auditory performance. The present article reviews all these methods, in order to better understand and evaluate the impact of hearing loss in everyday life.

Now you hear it: a predictive coding model for understanding rhythmic incongruity

Rhythmic incongruity in the form of syncopation is a prominent feature of many contemporary musical styles. Syncopations afford incongruity between rhythmic patterns and the meter, giving rise to mental models of differently accented isochronous beats. Syncopations occur either in isolation or as part of rhythmic patterns, so-called grooves. On the basis of the predictive coding framework, we discuss how brain processing of rhythm can be seen as a special case of predictive coding. We present a simple, yet powerful model for how the brain processes rhythmic incongruity: the model for predictive coding of rhythmic incongruity. Our model proposes that a given rhythm's syncopation and its metrical uncertainty (precision) is at the heart of how the brain models rhythm and meter based on priors, predictions, and prediction error. Our minimal model can explain prominent features of brain processing of syncopation: why isolated syncopations lead to stronger prediction error in the brains of musicians, as evidenced by larger event-related potentials to rhythmic incongruity, and why we all experience a stronger urge to move to grooves with a medium level of syncopation compared with low and high levels of syncopation.

Attentional functioning in individuals with 22q11 deletion syndrome: insight from ERPs

The 22q11 deletion syndrome (22q11DS), or DiGeorge syndrome (DG), is one of the most common genetic deletion syndromes. DG also carries a high risk for psychiatric disorders, with learning disabilities frequently being reported. Impairments in specific cognitive domains, such as executive functioning and attention, have also been described. The aim of this study was to investigate attentional functioning in a group of subjects with DG using ERPs, and in particular the P300 and CNV components. We studied ten patients with DG and ten healthy subjects that performed a P300 Novelty task and a CNV motor task. P3b amplitude was significantly lower in patients than in controls, while P3b latency was comparable in patients and controls. The P3a parameters were similar in both groups. All CNV amplitudes were significantly lower in DG patients than in controls. DG patients displayed slower reaction times in the CNV motor task than healthy subjects. These results point to a cognitive dysfunction related above all to executive attentional processing in DG patients. In particular, a specific difficulty emerged in selective attention and in the ability to orient and to sustain the anticipatory attention required for an executive motor response.

Neural Correlates of Selective Attention With Hearing Aid Use Followed by ReadMyQuips Auditory Training Program

OBJECTIVES

The objectives of this study were to investigate the effects of hearing aid use and the effectiveness of ReadMyQuips (RMQ), an auditory training program, on speech perception performance and auditory selective attention using electrophysiological measures. RMQ is an audiovisual training program designed to improve speech perception in everyday noisy listening environments.

DESIGN

Participants were adults with mild to moderate hearing loss who were first-time hearing aid users. After 4 weeks of hearing aid use, the experimental group completed RMQ training in 4 weeks, and the control group received listening practice on audiobooks during the same period. Cortical late event-related potentials (ERPs) and the Hearing in Noise Test (HINT) were administered at prefitting, pretraining, and post-training to assess effects of hearing aid use and RMQ training. An oddball paradigm allowed tracking of changes in P3a and P3b ERPs to distractors and targets, respectively. Behavioral measures were also obtained while ERPs were recorded from participants.

RESULTS

After 4 weeks of hearing aid use but before auditory training, HINT results did not show a statistically significant change, but there was a significant P3a reduction. This reduction in P3a was correlated with improvement in d prime (d') in the selective attention task. Increased P3b amplitudes were also correlated with improvement in d' in the selective attention task. After training, this correlation between P3b and d' remained in the experimental group, but not in the control group. Similarly, HINT testing showed improved speech perception post training only in the experimental group. The criterion calculated in the auditory selective attention task showed a reduction only in the experimental group after training. ERP measures in the auditory selective attention task did not show any changes related to training.

CONCLUSIONS

Hearing aid use was associated with a decrement in involuntary attention switch to distractors in the auditory selective attention task. RMQ training led to gains in speech perception in noise and improved listener confidence in the auditory selective attention task.

The Multiple-Demand System in the Novelty of Musical Improvisation: Evidence from an MRI Study on Composers

The multiple-demand (MD) system has proven to be associated with creating structured mental programs in comprehensive behaviors, but the functional mechanisms of this system have not been clarified in the musical domain. In this study, we explored the hypothesis that the MD system is involved in a comprehensive music-related behavior known as musical improvisation. Under a functional magnetic resonance imaging (fMRI) paradigm, 29 composers were recruited to improvise melodies through visual imagery tasks according to familiar and unfamiliar cues. We found that the main regions of the MD system were significantly activated during both musical improvisation conditions. However, only a greater involvement of the intraparietal sulcus (IPS) within the MD system was shown when improvising with unfamiliar cues. Our results revealed that the MD system strongly participated in musical improvisation through processing the novelty of melodies, working memory, and attention. In particular, improvising with unfamiliar cues required more musical transposition manipulations. Moreover, both functional and structural analyses indicated evidence of neuroplasticity in MD regions that could be associated with musical improvisation training. These findings can help unveil the functional mechanisms of the MD system in musical cognition, as well as improve our understanding of musical improvisation.

ERP Subsequent Memory Effects Differ between Inter-Item and Unitization Encoding Tasks

The "subsequent memory paradigm" is an analysis tool to identify brain activity elicited during episodic encoding that is associated with successful subsequent retrieval. Two commonly observed event-related potential "subsequent memory effects" (SMEs) are the parietal SME in the P300 time window and the frontal slow wave SME, but to date a clear characterization of the circumstances under which each SME is observed is missing. To test the hypothesis that the parietal SME occurs when aspects of an experience are unitized into a single item representation, while inter-item associative encoding is reflected in the frontal slow wave effect, participants were assigned to one of two conditions that emphasized one of the encoding types under otherwise matched study phases of a recognition memory experiment. Word pairs were presented either in the context of a definition that allowed to combine the word pairs into a new concept (unitization or item encoding) or together with a sentence frame (inter-item encoding). Performance on the recognition test did not differ between the groups. The parietal SME was only found in the definition group, supporting the idea that this SME occurs when the components of an association are integrated in a unitized item representation. An early prefrontal negativity also exhibited an SME only in this group, suggesting that the formation of novel units occurs through interactions of multiple brain areas. The frontal slow wave SME was pronounced in both groups and may thus reflect processes generally involved in encoding of associations. Our results provide evidence for a partial dissociation of the eliciting conditions of the two types of SMEs and therefore provide a tool for future studies to characterize the different types of episodic encoding.

Frontal and Posterior Erps Related to Line Bisection

The aim of this study was to investigate the dynamic nature of the cortical visuospatial attention processes during the line bisection test, which is sensitive to perceptual asymmetries. EEGs of 26 normal volunteers were recorded during the administration of a computerized line bisection test, which requires participants mark the midline of lines using a mouse. Two event-related potentials subsequent and time locked to the line presentations, namely, P300 and a positive slow wave, were obtained. Findings suggested that both potentials were related to the test performance, and the right hemisphere was more active. Analysis suggested a right parietotemporal and superior parietal locus for the P300 and right prefrontal activity for the positive slow wave. A dynamic asymmetrical activity was identified, such that after primary visual perception, spatial processing is then initiated in the right parietotemporal cortex and then proceeds to the right prefrontal cortex.

Toward a P300 Based Brain-Computer Interface for Aphasia Rehabilitation after Stroke: Presentation of Theoretical Considerations and a Pilot Feasibility Study

People with post-stroke motor aphasia know what they would like to say but cannot express it through motor pathways due to disruption of cortical circuits. We present a theoretical background for our hypothesized connection between attention and aphasia rehabilitation and suggest why in this context, Brain-Computer Interface (BCI) use might be beneficial for patients diagnosed with aphasia. Not only could BCI technology provide a communication tool, it might support neuronal plasticity by activating language circuits and thereby boost aphasia recovery. However, stroke may lead to heterogeneous symptoms that might hinder BCI use, which is why the feasibility of this approach needs to be investigated first. In this pilot study, we included five participants diagnosed with post-stroke aphasia. Four participants were initially unable to use the visual P300 speller paradigm. By adjusting the paradigm to their needs, participants could successfully learn to use the speller for communication with accuracies up to 100%. We describe necessary adjustments to the paradigm and present future steps to investigate further this approach.

Changes in Neural Activity Underlying Working Memory after Computerized Cognitive Training in Older Adults

Computerized cognitive training (CCT) may counter the impact of aging on cognition, but both the efficacy and neurocognitive mechanisms underlying CCT remain controversial. In this study, 35 older individuals were randomly assigned to Cogmed adaptive working memory (WM) CCT or an active control CCT, featuring five weeks of five ∼40 min sessions per week. Before and after the 5-week intervention, event-related potentials were measured while subjects completed a visual n-back task with three levels of demand (0-back, 1-back, 2-back). The anterior P3a served as an index of directing attention and the posterior P3b as an index of categorization/WM updating. We hypothesized that adaptive CCT would be associated with decreased P3 amplitude at low WM demand and increased P3 amplitude at high WM demand. The adaptive CCT group exhibited a training-related increase in the amplitude of the anterior P3a and posterior P3b in response to target stimuli across n-back tasks, while subjects in the active control CCT group demonstrated a post-training decrease in the anterior P3a. Performance did not differ between groups or sessions. Larger overall P3 amplitudes were strongly associated with better task performance. Increased post-CCT P3 amplitude correlated with improved task performance; this relationship was especially robust at high task load. Our findings suggest that adaptive WM training was associated with increased orienting of attention, as indexed by the P3a, and the enhancement of categorization/WM updating processes, as indexed by the P3b. Increased P3 amplitude was linked to improved performance; however. there was no direct association between adaptive training and improved performance.

Auditory Event-Related Potentials in Parkinson's Disease in Relation to Cognitive Ability

Auditory event-related potentials were evaluated in 45 nondemented patients with mild to moderate Parkinson's disease and 40 matched normal controls. All patients were neuropsychologically assessed by means of the Raven Colored Progressive Matrices, four subtests of the Wechsler Memory Scale (Digit Span Forward, Logical Memory, Visual Memory, Associate Learning), and the Wisconsin Card-sorting Test. The P300 component of the auditory event-related potentials was significantly prolonged in the patients with Parkinson's disease. Correlations between P300 latency and neuropsychological measures showed significant associations with lower performance on the Raven Colored Progressive Matrices and the Wisconsin Card-sorting Test. Our results indicate that for patients with mild to moderate Parkinson's disease subtle changes in cognitive abilities may be reflected as P300 prolongation.

Brain-computer interfaces for patients with disorders of consciousness

The disorders of consciousness refer to clinical conditions that follow a severe head injury. Patients diagnosed as in a vegetative state lack awareness, while patients diagnosed as in a minimally conscious state retain fluctuating awareness. However, it is a challenge to accurately diagnose these disorders with clinical assessments of behavior. To improve diagnostic accuracy, neuroimaging-based approaches have been developed to detect the presence or absence of awareness in patients who lack overt responsiveness. For the small subset of patients who retain awareness, brain-computer interfaces could serve as tools for communication and environmental control. Here we review the existing literature concerning the sensory and cognitive abilities of patients with disorders of consciousness with respect to existing brain-computer interface designs. We highlight the challenges of device development for this special population and address some of the most promising approaches for future investigations.

Creativity, Comprehension, Conversation and the Hippocampal Region: New Data and Theory

Present findings indicate that hippocampal region (HR) damage impairs aspects of everyday language comprehension and production that require creativity ^___ defined as the ability to form new internal representations that satisfy relevant constraints for being useful or valuable in the real world. In two studies, seventeen people participated in extensive face-to-face interviews: sixteen normal individuals and H.M., an amnesic with cerebellar and HR damage but virtually no neocortical damage. Study 1 demonstrated deficits in H.M.'s comprehension of creative but not routine aspects of the interviews ^___ extending to the real world twelve prior demonstrations that H.M. understands routine but not novel aspects of experimentally constructed sentences, deficits that reflected his HR damage, but not his cerebellar damage, his explicit or declarative memory problems, inability to comprehend or recall the instructions, forgetting, poor visual acuity, motoric slowing, time pressure, deficits in visual scanning or attentional allocation, lack of motivation, and excessive memory load in the tasks. Study 2 demonstrated similar deficits in H.M.'s ability to produce creative but not routine aspects of conversational discourse, extending findings in five prior sentence production experiments to real-world creativity. We discuss conceptual frameworks for explaining relations between new-and-useful creativity and the HR.

Development of behavioral parameters and ERPs in a novel-target visual detection paradigm in children, adolescents and young adults

BACKGROUND

The present study analyzes the development of ERPs related to the process of selecting targets based on their novelty.

METHODS

One hundred and sixty-seven subjects from 6 to 26 years old were recorded with 30 electrodes during a visual target novelty paradigm.

RESULTS

Behavioral results showed good performance in children that improved with age: a decrease in RTs and errors and an increase in the d' sensitivity parameter with age were obtained. In addition, the C response bias parameter evolved from a conservative to a neutral bias with age. Fronto-polar Selection Positivity (FSP) was statistically significant in all the age groups when standards and targets were compared. There was a statistically significant difference in the posterior Selection Negativity (SN) between the target and standard conditions in all age groups. The P3a component obtained was statistically significant in the emergent adult (18-21 years) and young adult (22-26 years) groups. The modulation of the P3b component by novel targets was statistically significant in all the age groups, but it decreased in amplitude with age. Peak latencies of the FSP and P3b components decreased with age.

CONCLUSIONS

The results reveal differences in the ERP indexes for the cognitive evaluation of the stimuli presented, depending on the age of the subjects. The ability of the target condition to induce the modulation of the studied components would depend on the posterior-anterior gradient of cortex maturation and on the gradient of maturation of the low to higher order association areas.

The "serendipitous brain": Low expectancy and timing uncertainty of conscious events improve awareness of unconscious ones (evidence from the Attentional Blink)

To anticipate upcoming sensory events, the brain picks-up and exploits statistical regularities in the sensory environment. However, it is untested whether cumulated predictive knowledge about consciously seen stimuli improves the access to awareness of stimuli that usually go unseen. To explore this issue, we exploited the Attentional Blink (AB) effect, where conscious processing of a first visual target (T1) hinders detection of early following targets (T2). We report that timing uncertainty and low expectancy about the occurrence of consciously seen T2s presented outside the AB period, improve detection of early and otherwise often unseen T2s presented inside the AB. Recording of high-resolution Event Related Potentials (ERPs) and the study of their intracranial sources showed that the brain achieves this improvement by initially amplifying and extending the pre-conscious storage of T2s' traces signalled by the N2 wave originating in the extra-striate cortex. This enhancement in the N2 wave is followed by specific changes in the latency and amplitude of later components in the P3 wave (P3a and P3b), signalling access of the sensory trace to the network of parietal and frontal areas modulating conscious processing. These findings show that the interaction between conscious and unconscious processing changes adaptively as a function of the probabilistic properties of the sensory environment and that the combination of an active attentional state with loose probabilistic and temporal expectancies on forthcoming conscious events favors the emergence to awareness of otherwise unnoticed visual events. This likely provides an insight on the attentional conditions that predispose an active observer to unexpected "serendipitous" findings.

Sensory Deviancy Detection Measured Directly Within the Human Nucleus Accumbens

Rapid changes in the environment evoke a comparison between expectancy and actual outcome to inform optimal subsequent behavior. The nucleus accumbens (NAcc), a key interface between the hippocampus and neocortical regions, is a candidate region for mediating this comparison. Here, we report event-related potentials obtained from the NAcc using direct intracranial recordings in 5 human participants while they listened to trains of auditory stimuli differing in their degree of deviation from repetitive background stimuli. NAcc recordings revealed an early mismatch signal (50-220 ms) in response to all deviants. NAcc activity in this time window was also sensitive to the statistics of stimulus deviancy, with larger amplitudes as a function of the level of deviancy. Importantly, this NAcc mismatch signal also predicted generation of longer latency scalp potentials (300-400 ms). The results provide direct human evidence that the NAcc is a key component of a network engaged in encoding statistics of the sensory environmental.

A critical role of the human hippocampus in an electrophysiological measure of implicit memory

The hippocampus has traditionally been thought to be critical for conscious explicit memory but not necessary for unconscious implicit memory processing. In a recent study of a group of mild amnesia patients with evidence of MTL damage limited to the hippocampus, subjects were tested on a direct test of item recognition confidence while electroencephalogram (EEG) was acquired, and revealed intact measures of explicit memory from 400 to 600 ms (mid-frontal old-new effect, FN400). The current investigation re-analyzed this data to study event-related potentials (ERPs) of implicit memory, using a recently developed procedure that eliminated declarative memory differences. Prior ERP findings from this technique were first replicated in two independent matched control groups, which exhibited reliable implicit memory effects in posterior scalp regions from 400 to 600 ms, which were topographically dissociated from the explicit memory effects of familiarity. However, patients were found to be dramatically impaired in implicit memory effects relative to control subjects, as quantified by a reliable condition × group interaction. Several control analyses were conducted to consider alternative factors that could account for the results, including outliers, sample size, age, or contamination by explicit memory, and each of these factors was systematically ruled out. Results suggest that the hippocampus plays a fundamental role in aspects of memory processing that are beyond conscious awareness. The current findings therefore indicate that both memory systems of implicit and explicit memory may rely upon the same neural structures - but function in different physiological ways.

Temporal lobe impairment in West syndrome: event-related potential evidence

Objective

This study investigates auditory processing in infants with West syndrome (WS) using event-related potentials (ERPs).

Methods

ERPs were measured in 25 infants with mainly symptomatic WS (age range = 3–10 months) and 26 healthy term infants (age range = 3–9 months) using an auditory novelty oddball paradigm. The ERP recordings were made during wakefulness and repeated in stage II sleep.

Results

The obligatory components (P150, N250, P350) and novelty response components (P300, Nc) were recordable during both sleep and wakefulness in patients and controls. All ERP latencies decreased with age in controls but not in the WS group (age × group interaction, F = 22.3, p < 0.0001). These ERP latency alterations were not affected by pharmacological treatment for WS.

Interpretation

This study demonstrated a persistently altered ERP signature in patients with a recent history of infantile spasms. The prolongation of auditory obligatory and novelty ERPs in WS patients indicates a severe failure of temporal lobe maturation during infancy. It remains to be investigated whether this predicts long-term cognitive impairments characteristic for this epileptic encephalopathy.

Age-related decline in differentiated neural responses to rare target versus frequent standard stimuli

One mechanism hypothesized to contribute to cognitive aging is the failure to recruit specialized neural modules and generate differentiated neural responses to various classes of stimuli. Here, ERPs were used to examine the extent to which target and standard stimulus types were processed differently by well-matched adults ages 19-99. Subjects responded to designated visual target letters under low and high load conditions. Temporospatial PCA was used to parse the P3b component, an index of categorization/memory updating. The P3b amplitude difference between targets and standards decreased substantially as a function of age. Dedifferentiation began in middle age, and continued into old-old age. The reduced differentiation of neural responses was driven by an age-related decline in the size of the P3b to targets and an age-related increase in the P3b to standards. Larger P3b amplitude to standards among older subjects was associated with higher executive capacity and better task performance. In summary, dedifferentiation begins relatively early in adulthood and progresses in a linear fashion throughout the lifespan. The age-related augmentation of the P3b to standards appears to reflect a compensatory mechanism that helps maintain task performance.

Auditory stream segregation using bandpass noises: evidence from event-related potentials

The current study measured neural responses to investigate auditory stream segregation of noise stimuli with or without clear spectral contrast. Sequences of alternating A and B noise bursts were presented to elicit stream segregation in normal-hearing listeners. The successive B bursts in each sequence maintained an equal amount of temporal separation with manipulations introduced on the last stimulus. The last B burst was either delayed for 50% of the sequences or not delayed for the other 50%. The A bursts were jittered in between every two adjacent B bursts. To study the effects of spectral separation on streaming, the A and B bursts were further manipulated by using either bandpass-filtered noises widely spaced in center frequency or broadband noises. Event-related potentials (ERPs) to the last B bursts were analyzed to compare the neural responses to the delay vs. no-delay trials in both passive and attentive listening conditions. In the passive listening condition, a trend for a possible late mismatch negativity (MMN) or late discriminative negativity (LDN) response was observed only when the A and B bursts were spectrally separate, suggesting that spectral separation in the A and B burst sequences could be conducive to stream segregation at the pre-attentive level. In the attentive condition, a P300 response was consistently elicited regardless of whether there was spectral separation between the A and B bursts, indicating the facilitative role of voluntary attention in stream segregation. The results suggest that reliable ERP measures can be used as indirect indicators for auditory stream segregation in conditions of weak spectral contrast. These findings have important implications for cochlear implant (CI) studies-as spectral information available through a CI device or simulation is substantially degraded, it may require more attention to achieve stream segregation.

Neuro-Behavioral Correlates of Post-Deviance Distraction in Middle-Aged and Old Adults

The presentation of a task-irrelevant deviant (novel) stimulus among otherwise repeated standard stimuli usually reduces performance not only for the deviant stimulus, but also for the standard following that deviant. Here, the so-called post-deviance distraction was investigated in 58 middle-aged and 52 old adults, using an auditory duration discrimination task and event-related potential (ERP) measures. After a deviant stimulus, the participants showed a decrease in performance in the subsequent standard stimulus. This effect was more pronounced in the old, than middle-aged, group. Relative to the standard stimuli preceding the deviant, post-deviant standards triggered a chain of mismatch negativity (MMN), P3a, and reorienting negativity (RON). While MMN and P3a did not differ in old and middle-aged adults, older participants showed a delayed RON. Assuming the RON to reflect processes of general task or feature reconfiguration and updating, these results suggest a delay in orienting-reorienting mechanisms as possible source of increased post-deviance distraction in elderly.

Investigating the age-related "anterior shift" in the scalp distribution of the P3b component using principal component analysis

An age-related "anterior shift" in the distribution of the P3b is often reported. Temporospatial principal component analysis (PCA) was used to investigate the basis of this observation. ERPs were measured in young and old adults during a visual oddball task. PCA revealed two spatially distinct factors in both age groups, identified as the posterior P3b and anterior P3a. Young subjects generated a smaller P3a than P3b, while old subjects generated a P3a that did not differ in amplitude from their P3b. Rather than having a more anteriorly distributed P3b, old subjects produced a large, temporally overlapping P3a. The pattern of the age-related "anterior shift" in the P3 was similar for target and standard stimuli. The increase in the P3a in elderly adults may not represent a failure to habituate the novelty response, but may reflect greater reliance on executive control operations (P3a) to carry out the categorization/updating process (P3b).

Does the age-related "anterior shift" of the P3 reflect an inability to habituate the novelty response?

Old adults often generate larger anterior neural responses than young adults when carrying out task requirements. A common finding in the ERP literature is an "anterior shift" of the P3b to targets. Utilizing principal component analysis (PCA), we recently demonstrated that rather than the P3b moving anteriorly, old adults generate a large P3a that temporally overlaps with their P3b. A dominant hypothesis for the age-related increase in anterior P3 is the failure to habituate the brain's novelty response to rare targets. We tested this hypothesis in young and old adults by comparing the amplitude of the PCA factor representing P3a to targets presented in the first versus last of eight blocks of a visual oddball task. If, unlike young adults, old adults are unable to habituate a novelty response, one would expect (1) the P3a amplitude to decrease between the first and last blocks for young, but not old subjects and (2) the difference in P3a amplitude between young and old subjects to be greater in the last than the first block. Our results indicate the amplitude of the P3a was larger in old adults than young adults. However, this effect was not modulated by block. These findings argue against the hypothesis that an age-related increase in the P3a to targets reflects an inability of old subjects to habituate a novelty response. An alternative hypothesis is that the augmented P3a indexes the increased utilization of frontal executive functions to provide compensatory scaffolding to carry out a task.