Reduced N400 Amplitudes Research Articles

Effects of predictability on visual and linguistic narrative comprehension in autistic and non-autistic adults

ABSTRACT Autistic individuals sometimes show differences from non-autistic individuals when understanding stories, regardless of whether those stories are told through words or pictures. In narrative comprehension, predicting upcoming words or events in a story may facilitate understanding. In studies measuring event-related potentials (ERPs) with non-autistic adults, more predictable words in a linguistic narrative or panels in a visual narrative typically elicit reduced N400 amplitudes compared to less predictable words/panels. However, the predictive processes used by autistic individuals may differ from those used by non-autistic individuals, which could contribute to differences in narrative comprehension. Here, we report two studies examining predictive processing in linguistic and visual narrative comprehension among autistic and non-autistic adults. Autistic adults showed earlier N400 modulations by cloze compared to non-autistic adults in both linguistic and visual modalities, which may reflect a more bottom-up processing style that relies less on active prediction of upcoming words or events.

Overt and Covert Effects of Mental Fatigue on Attention Networks: Evidence from Event-Related Potentials during the Attention Network Test.

Mental fatigue is a variation in the psychophysiological state that subjects encounter during or after prolonged cognitive activity periods, affecting top-down attention and cognitive control. The present study aimed to investigate the effects of mental fatigue on attention in the context of the three attention networks according to the Posnerian model (alerting, orienting, and executive networks) by combining the Attentional Network Test (ANT) and event-related potentials technique. Thirty healthy subjects were enrolled in the study. A continuous arithmetic task lasting one hour induced mental fatigue, and EEG recordings were conducted before and after the task while subjects were performing the ANT. The efficiencies of three networks were comparable between groups, while RTs shortened only in the control group and the accuracy related to the alerting and conflict networks declined only after mental effort. Mental fatigue reduced N1 amplitude during alerting network engagement and p3 amplitude during orienting. It also reduced N2 and P3 amplitude during the conflict, particularly the incongruent target-locked response. These findings underscore the covert effects of mental fatigue on attention, suggesting that even in healthy young subjects, compensatory mechanisms may maintain adequate overt performances, but fatigue still has a detrimental effect on top-down attentional mechanisms.

Electrophysiological Measures of Listening-in-Noise With and Without Remote Microphone System Use in Autistic and Non-Autistic Youth.

This study examined the neural mechanisms by which remote microphone (RM) systems might lead to improved behavioral performance on listening-in-noise tasks in autistic and non-autistic youth. Cortical auditory evoked potentials (CAEPs) were recorded in autistic (n = 25) and non-autistic (n = 22) youth who were matched at the group level on chronological age ( M = 14.21 ± 3.39 years) and biological sex. Potentials were recorded during an active syllable identification task completed in quiet and in multi-talker babble noise with and without the use of an RM system. The effects of noise and RM system use on speech-sound-evoked P1-N1-P2 responses and the associations between the cortical responses and behavioral performance on syllable identification were examined. No group differences were observed for behavioral or CAEP measures of speech processing in quiet or in noise. In the combined sample, syllable identification in noise was less accurate and slower than in the quiet condition. The addition of the RM system to the noise condition restored accuracy, but not the response speed, to the levels observed in quiet. The CAEP analyses noted amplitude reductions and latency delays in the noise compared with the quiet condition. The RM system use increased the N1 amplitude as well as reduced and delayed the P2 response relative to the quiet and noise conditions. Exploratory brain-behavior correlations revealed that larger N1 amplitudes in the RM condition were associated with greater behavioral accuracy of syllable identification. Reduced N1 amplitude and accelerated P2 response were associated with shorter syllable identification response times when listening with the RM system. Findings suggest that although listening-in-noise with an RM system might remain effortful, the improved signal to noise ratio facilitates attention to the sensory features of the stimuli and increases speech sound identification accuracy.

Changes in Taste Perception in Patients with Minor and Major Cognitive Impairment Linked to Alzheimer's Disease Recorded by Gustatory Evoked Potentials.

The need for early diagnosis biomarkers in Alzheimer's disease (AD) is growing. Only few studies have reported gustatory dysfunctions in AD using subjective taste tests. The main purpose of the study was to explore gustatory functions using subjective taste tests and recordings of gustatory evoked potentials (GEPs) for sucrose solution in patients with minor or major cognitive impairment (CI) linked to AD, and to compare them with healthy controls. The secondary objective was to evaluate the relationships between GEPs and the results of cognitive assessments and fasting blood samples. A total of 45 subjects (15 healthy subjects, 15 minor CI patients, 15 major CI patients) were included to compare their gustatory functions and brain activity by recording GEPs in response to a sucrose stimulation. CI groups were combined in second analyses in order to keep a high power in the study. Correlations were made with cognitive scores and hormone levels (ghrelin, leptin, insulin, serotonin). Increased P1 latencies and reduced N1 amplitudes were observed in minor or major patients compared to controls. GEPs were undetectable in 6 major and 4 minor CI patients. Thresholds for sucrose detection were significantly higher in the major CI group than in controls or the minor CI group. No correlation was found with hormone levels. The cortical processing of sensory taste information seems to be altered in patients with minor or major CI linked to AD. This disturbance was identifiable with subjective taste tests only later, at the major CI stage.

Electrophysiological signatures of visual temporal processing deficits in developmental dyslexia.

Developmental dyslexia (DD) is a common neurodevelopmental disorder that affects reading ability despite normal intelligence and education. In search of core deficits, previous evidence has linked DD with impairments in temporal aspects of perceptual processing, which might underlie phonological deficits as well as inefficient graphemic parsing during reading. However, electrophysiological evidence for atypical temporal processing in DD is still scarce in the visual modality. Here, we investigated the efficiency of both temporal segregation and integration of visual information by means of event-related potentials (ERPs). We confirmed previous evidence of a selective segregation deficit in dyslexia for stimuli presented in rapid succession (<80 ms), despite unaffected integration performance. Importantly, we found a reduced N1 amplitude in DD, a component related to the allocation of attentional resources, which was independent of task demands (i.e., evident in both segregation and integration). In addition, the P3 amplitude, linked to working memory and processing load, was modulated by task demands in controls but not in individuals with DD. These results suggest that atypical attentional sampling in dyslexia might weaken the quality of information stored in visual working memory, leading to behavioral and electrophysiological signatures of atypical temporal segregation. These results are consistent with some existing theories of dyslexia, such as the magnocellular theory and the "Sluggish Attentional Shifting" framework, and represent novel evidence for neural correlates of decreased visual temporal resolution in DD.

Nuances of knowing: Brain potentials reveal implicit effects of domain knowledge on word processing in the absence of sentence-level knowledge.

In previous work investigating the relationship between domain knowledge (of the fictional world of Harry Potter) and sentence comprehension, domain knowledge had a greater impact on electrical brain potentials to words which completed sentences about fictional "facts" participants reported they did not know compared to facts they did. This suggests that individuals use domain knowledge continuously to activate relevant/related concepts as they process sentences, even with only partial knowledge. As that study relied on subjective reports, it may have resulted in response bias related to an individual's overall domain knowledge. In the present study, we therefore asked participants with varying degrees of domain knowledge to complete sentences describing fictional "facts" as an objective measure of sentence-level knowledge. We then recorded EEG as the same individuals (re-)read the same sentences, including their appropriate final words, and sorted these according to their objective knowledge scores. Replicating and extending Troyer et al., domain knowledge immediately facilitated access to meaning for unknown words; greater domain knowledge was associated with reduced N400 amplitudes for unknown words. These findings constitute novel evidence for graded preactivation of conceptual knowledge (e.g., at the level of semantic features and/or relations) in the absence of lexical prediction. Knowledge also influenced post-N400 memory/integration processes for these same unknown words; greater domain knowledge was associated with enhanced late positive components (LPCs), suggesting that deeper encoding during language processing may be engendered when knowledgeable individuals encounter an apparent gap in their knowledge.

Exploring the internal forward model: action-effect prediction and attention in sensorimotor processing.

Action-effect predictions are believed to facilitate movement based on its association with sensory objectives and suppress the neurophysiological response to self- versus externally generated stimuli (i.e. sensory attenuation). However, research is needed to explore theorized differences in the use of action-effect prediction based on whether movement is uncued (i.e. volitional) or in response to external cues (i.e. stimulus-driven). While much of the sensory attenuation literature has examined effects involving the auditory N1, evidence is also conflicted regarding this component's sensitivity to action-effect prediction. In this study (n = 64), we explored the influence of action-effect contingency on event-related potentials associated with visually cued and uncued movement, as well as resultant stimuli. Our findings replicate recent evidence demonstrating reduced N1 amplitude for tones produced by stimulus-driven movement. Despite influencing motor preparation, action-effect contingency was not found to affect N1 amplitudes. Instead, we explore electrophysiological markers suggesting that attentional mechanisms may suppress the neurophysiological response to sound produced by stimulus-driven movement. Our findings demonstrate lateralized parieto-occipital activity that coincides with the auditory N1, corresponds to a reduction in its amplitude, and is topographically consistent with documented effects of attentional suppression. These results provide new insights into sensorimotor coordination and potential mechanisms underlying sensory attenuation.

Exploratory Study on Chemosensory Event-Related Potentials in Long COVID-19 and Mild Cognitive Impairment: A Common Pathway?

People affected by the Long COVID-19 (LC) syndrome often show clinical manifestations that are similar to those observed in patients with mild cognitive impairments (MCI), such as olfactory dysfunction (OD), brain fog, and cognitive and attentional diseases. This study aimed to investigate the chemosensory-evoked related potentials (CSERP) in LC and MCI to understand if there is a common pathway for the similarity of symptoms associated with these disorders. Eighteen LC patients (mean age 53; s.d. = 7), 12 patients diagnosed with MCI (mean age 67; s.d. = 6), and 10 healthy control subjects (mean age 66; s.d. = 5, 7) were recruited for this exploratory study. All of them performed a chemosensory event-related potentials (CSERP) task with the administration of trigeminal stimulations (e.g., the odorants cinnamaldehyde and eucalyptus). Study results highlighted that MCI and LC showed reduced N1 amplitude, particularly in the left frontoparietal network, involved in working memory and attentional deficits, and a reduction of P3 latency in LC. This study lays the foundations for evaluating aspects of LC as a process that could trigger long-term functional alterations, and CSERPs could be considered valid biomarkers for assessing the progress of OD and an indicator of other impairments (e.g., attentional and cognitive impairments), as they occur in MCI.

Readers scrutinize lexical familiarity only in the absence of expectations: Evidence from lexicality effects on event-related potentials

Readers generate predictions about the meaning of upcoming words while reading constraining sentences. These predictions feed down to predictions about orthographic form. For example, orthographic neighbors of predicted words yield reduced N400 amplitudes compared to non-neighbors regardless of lexical status (Laszlo & Federmeier, 2009). We investigated whether readers are sensitive to lexicality in low constraint sentences when they must scrutinize the perceptual input more closely for word recognition. In a replication and extension of Laszlo and Federmeier (2009), we observed similar patterns as the original study in high constraint sentences, but found a lexicality effect in low constraint sentences that was not present when the sentence was highly constraining. This suggests that, in the absence of strong expectations, readers adopt a different reading strategy to scrutinize the structure of words more in depth to make sense of what they have read compared to when they encounter a supportive sentence context.

Neural correlates of understanding emotional words in late childhood.

Prior studies involving adults have shown that words can elicit emotional processing, with emotion-label (e.g., happiness) and emotion-laden words (e.g., gift) having distinct processes. However, limited studies have explored the developmental changes in these processes in relation to emotional valence. To address this question, this exploratory study measured event-related potentials (ERPs) in 11-14-year-old children/adolescents (N=25) and adults (N=23) while performing an emotional categorization task. The stimuli used were two-character Chinese words, with factors for word type (emotion-label versus emotion-laden) and valence (positive versus negative). To confirm word emotionality, neutral words were also included and compared with all emotional words. The results showed that adults exhibited reduced N400 amplitudes to emotion-label words compared to emotion-laden ones in both positive and negative valence contexts. The differentiation was only sustained for negative valence in the late positive component (LPC). Similar scalp distributions of the effects of word type were found in children/adolescents; however, they exhibited a more prolonged processing of all emotional words than adults. These results suggest that the processing of emotion-label and emotion-laden words are distinct in late childhood, and this discrepancy varies with emotional valence and increasing age.

Benefits and costs of predictive processing: How sentential constraint and word expectedness affect memory formation

This study investigated how the strength of schema support provided by strongly (SC) and weakly constraining (WC) sentences affects the encoding of expected and unexpected words, and how this is reflected in event-related potentials (ERPs). In a surprise recognition memory test, words studied on the previous day were presented together with new words and lures that were expected but not presented in the study phase. ERPs recorded in the study phase were compared for subsequently remembered and forgotten words. Better memory performance for expected over unexpected words was electrophysiologically supported by a parietal subsequent memory effect (SME) reflecting enhanced item-specific encoding of contextually expected words. SC sentences not only facilitated the semantic integration of sentence-ending words, as reflected in reduced N400 amplitudes, but also enabled the rapid successful encoding of these words into memory, which is evidenced by an SC > WC pattern in memory performance and correlations between pre- and post-stimulus SMEs for SC sentences. In contrast, words processed in WC sentence contexts necessitated sustained elaborative encoding processes as reflected in a late frontal slow wave SME. Expected but not presented words were associated with high rates of false positive memory decisions, indicating that these words remained in a state of high accessibility in memory even one day after the study phase. These mnemonic costs of predictive processing were more pronounced for expected words from SC sentences than from WC sentences and could reflect the lingering of strong semantic predictions which were associated with the pre-updating of sentence representations.

The time course of emotional authenticity detection in nonverbal vocalizations

Previous research has documented perceptual and brain differences between spontaneous and volitional emotional vocalizations. However, the time course of emotional authenticity processing remains unclear. We used event-related potentials (ERPs) to address this question, and we focused on the processing of laughter and crying. We additionally tested whether the neural encoding of authenticity is influenced by attention, by manipulating task focus (authenticity versus emotional category) and visual condition (with versus without visual deprivation). ERPs were recorded from 43 participants while they listened to vocalizations and evaluated their authenticity (volitional versus spontaneous) or emotional meaning (sad versus amused). Twenty-two of the participants were blindfolded and tested in a dark room, and 21 were tested in standard visual conditions. As compared to volitional vocalizations, spontaneous ones were associated with reduced N1 amplitude in the case of laughter, and increased P2 in the case of crying. At later cognitive processing stages, more positive amplitudes were observed for spontaneous (versus volitional) laughs and cries (1000–1400 msec), with earlier effects for laughs (700–1000 msec). Visual condition affected brain responses to emotional authenticity at early (P2 range) and late processing stages (middle and late LPP ranges). Task focus did not influence neural responses to authenticity. Our findings suggest that authenticity information is encoded early and automatically during vocal emotional processing. They also point to a potentially faster encoding of authenticity in laughter compared to crying.

Early evoked brain activity underlies auditory and audiovisual speech recognition deficits in schizophrenia

ObjectivesPeople with Schizophrenia (SZ) show deficits in auditory and audiovisual speech recognition. It is possible that these deficits are related to aberrant early sensory processing, combined with an impaired ability to utilize visual cues to improve speech recognition. In this electroencephalography study we tested this by having SZ and healthy controls (HC) identify different unisensory auditory and bisensory audiovisual syllables at different auditory noise levels. MethodsSZ (N = 24) and HC (N = 21) identified one of three different syllables (/da/, /ga/, /ta/) at three different noise levels (no, low, high). Half the trials were unisensory auditory and the other half provided additional visual input of moving lips. Task-evoked mediofrontal N1 and P2 brain potentials triggered to the onset of the auditory syllables were derived and related to behavioral performance. ResultsIn comparison to HC, SZ showed speech recognition deficits for unisensory and bisensory stimuli. These deficits were primarily found in the no noise condition. Paralleling these observations, reduced N1 amplitudes to unisensory and bisensory stimuli in SZ were found in the no noise condition. In HC the N1 amplitudes were positively related to the speech recognition performance, whereas no such relationships were found in SZ. Moreover, no group differences in multisensory speech recognition benefits and N1 suppression effects for bisensory stimuli were observed. ConclusionOur study suggests that reduced N1 amplitudes reflect early auditory and audiovisual speech processing deficits in SZ. The findings that the amplitude effects were confined to salient speech stimuli and the attenuated relationship with behavioral performance in patients compared to HC, indicates a diminished decoding of the auditory speech signals in SZs. Our study also revealed relatively intact multisensory benefits in SZs, which implies that the observed auditory and audiovisual speech recognition deficits were primarily related to aberrant processing of the auditory syllables.

Sensory attenuation is modulated by the contrasting effects of predictability and control

Self-generated stimuli have been found to elicit a reduced sensory response compared with externally-generated stimuli. However, much of the literature has not adequately controlled for differences in the temporal predictability and temporal control of stimuli. In two experiments, we compared the N1 (and P2) components of the auditory-evoked potential to self- and externally-generated tones that differed with respect to these two factors. In Experiment 1 (n = 42), we found that increasing temporal predictability reduced N1 amplitude in a manner that may often account for the observed reduction in sensory response to self-generated sounds. We also observed that reducing temporal control over the tones resulted in a reduction in N1 amplitude. The contrasting effects of temporal predictability and temporal control on N1 amplitude meant that sensory attenuation prevailed when controlling for each. Experiment 2 (n = 38) explored the potential effect of selective attention on the results of Experiment 1 by modifying task requirements such that similar levels of attention were allocated to the visual stimuli across conditions. The results of Experiment 2 replicated those of Experiment 1, and suggested that the observed effects of temporal control and sensory attenuation were not driven by differences in attention. Given that self- and externally-generated sensations commonly differ with respect to both temporal predictability and temporal control, findings of the present study may necessitate a re-evaluation of the experimental paradigms used to study sensory attenuation.

Similarities and Differences between Performers and Observers in Processing Auditory Action Consequences: Evidence from Simultaneous EEG Acquisition.

In our social environment, we easily distinguish stimuli caused by our own actions (e.g., water splashing when I fill my glass) from stimuli that have an external source (e.g., water splashing in a fountain). Accumulating evidence suggests that processing the auditory consequences of self-performed actions elicits N1 and P2 ERPs of reduced amplitude compared to physically identical but externally generated sounds, with such reductions being ascribed to neural predictive mechanisms. It is unexplored, however, whether the sensory processing of action outcomes is similarly modulated by action observation (e.g., water splashing when I observe you filling my glass). We tested 40 healthy participants by applying a methodological approach for the simultaneous EEG recording of two persons: An observer observed button presses executed by a performer in real time. For the performers, we replicated previous findings of a reduced N1 amplitude for self- versus externally generated sounds. This pattern differed significantly from the one in observers, whose N1 for sounds generated by observed button presses was not attenuated. In turn, the P2 amplitude was reduced for processing action- versus externally generated sounds for both performers and observers. These findings show that both action performance and observation affect the processing of action-generated sounds. There are, however, important differences between the two in the timing of the effects, probably related to differences in the predictability of the actions and thus also the associated stimuli. We discuss how these differences might contribute to recognizing the stimulus as caused by self versus others.

The N400 indexes acquisition of novel emotion concepts via conceptual combination.

The ability to learn new emotion concepts is adaptive and socially valuable as it communicates culturally held understandings about values, goals, and experiences. Yet, little work has examined the underlying mechanisms that allow for new emotion concepts and words to be integrated into the conceptual system. One such mechanism may be conceptual combination, or the ability to form novel concepts by dynamically combining previously acquired conceptual knowledge. In this study, we used event-related potentials (ERPs) to investigate the electrophysiological correlates of novel emotion concept acquisition via conceptual combination. Participants were briefly trained on 30 novel emotion combinations, each consisting of two English emotion words (the components; e.g., "sadness+fatigue") and a pseudoword (the target; e.g., "despip"). Participants then completed a semantic congruency task while ERPs were recorded. On each trial, two components were presented serially, followed by a target; participants judged whether the target was a valid combination of the preceding components. Targets could be correct or incorrect trained pseudowords, or new untrained pseudowords. Furthermore, components could be presented in reversed order (e.g., "fatigue" then "sadness") or as synonyms (e.g., "exhaustion" for "fatigue"). Consistent with our main hypotheses, we found a main effect of target, such that the correct combinations showed reduced N400 amplitudes when compared to both incorrect and untrained pseudowords. Critically, this effect held regardless of how the preceding components were presented, suggesting deeper semantic learning. These results extend prior findings on conceptual combination and novel word learning, and are congruent with predictive processing accounts of brain function.

Engineering creativity: Prior experience modulates electrophysiological responses to novel metaphors

Novel metaphorical language use exemplifies human creativity through production and comprehension of meaningful linguistic expressions that may have never been heard before. Available electrophysiological research demonstrates, however, that novel metaphor comprehension is cognitively costly, as it requires integrating information from distantly related concepts. Herein, we investigate if such cognitive cost may be reduced as a factor of prior domain knowledge. To this end, we asked engineering and nonengineering students to read for comprehension literal, novel metaphorical, and anomalous sentences related to engineering or general knowledge, while undergoing EEG recording. Upon reading each sentence, participants were asked to judge whether or not the sentence was original in meaning (novelty judgment) and whether or not it made sense (sensicality judgment). When collapsed across groups, our findings demonstrate a gradual N400 modulation with N400 being maximal in response to anomalous, followed by metaphorical, and literal sentences. Between‐group comparisons revealed a mirror effect on the N400 to novel metaphorical sentences, with attenuated N400 in engineers and enhanced N400 in non‐engineers. Critically, planned comparisons demonstrated reduced N400 amplitudes to engineering novel metaphors in engineers relative to non‐engineers, pointing to an effect of prior knowledge on metaphor processing. This reduction, however, was observed in the absence of a sentence type × knowledge × group interaction. Altogether, our study provides novel evidence suggesting that prior domain knowledge may have a direct impact on creative language comprehension.

Activating words beyond the unfolding sentence: Contributions of event simulation and word associations to discourse reading

Previous studies have shown that during comprehension readers activate words beyond the unfolding sentence. An open question concerns the mechanisms underlying this behavior. One proposal is that readers mentally simulate the described event and activate related words that might be referred to as the discourse further unfolds. Another proposal is that activation between words spreads in an automatic, associative fashion. The empirical support for these proposals is mixed. Therefore, theoretical accounts differ with regard to how much weight they place on the contributions of these sources to sentence comprehension. In the present study, we attempted to assess the contributions of event simulation and lexical associations to discourse reading, using event-related brain potentials (ERPs). Participants read target words, which were preceded by associatively related words either appearing in a coherent discourse event (Experiment 1) or in sentences that did not form a coherent discourse event (Experiment 2). Contextually unexpected target words that were associatively related to the described events elicited a reduced N400 amplitude compared to contextually unexpected target words that were unrelated to the events (Experiment 1). In Experiment 2, a similar but reduced effect was observed. These findings support the notion that during discourse reading event simulation and simple word associations jointly contribute to language comprehension by activating words that are beyond contextually congruent sentence continuations.

Reward Modulates Affective Priming Effect in Cognitive Conflict Processing: Electrophysiological Evidence.

Previous research demonstrated that cognitive conflict could induce an affective priming effect, and the stage (detection/resolution) of conflict processing led to different directions (positive/negative) of the affective priming effect. We suggested that rewards play a critical role in the affective priming effect on conflict resolution. The present study used event-related potentials (ERPs), using the arrow flanker task as primes and choosing specific affective words as targets to investigate the affective priming effect induced by cognitive conflict during the resolution stage. Our question was whether rewards created a modulating effect. Participants were asked to judge the congruency of the prime stimuli and then evaluate the valence of the target words. For behavioral results, the conflict effect was significant, and the reward promoted the behavioral performance of participants. For ERP results, enhanced N2 amplitudes for incongruent primes indicated a significant conflict effect. More importantly, as expected, in the rewarded condition, the enhanced N400 amplitudes for positive targets following incongruent primes were found, indicating a positive priming effect. However, in the unrewarded condition, the reduced N400 amplitudes for positive targets following incongruent primes were found, indicating conflict resolution hindered the processing of positive stimuli. These findings suggested that cognitive conflict-induced the positive priming effect during the resolution stage and that rewards had a moderating effect on the positive priming effect.

The neurocognitive basis of metamemory: Using the N400 to study the contribution of fluency to judgments of learning.

Metamemory is crucial for monitoring, evaluating, and optimizing memory performance. The basis of metamemory, however, is a matter of considerable debate. In the present study, we examined the contribution of processing fluency-the ease of processing information during learning-to metamemory judgments. We recorded event-related potentials (ERPs) while participants studied related and unrelated word pairs across two study-test cycles in a judgment of learning (JOL) task. In the first study-test cycle, related pairs were associated with better cued recall, higher JOLs, and a reduced N400 amplitude than unrelated pairs. Crucially, between- and within subject correlational analyses indicated that reduced N400 amplitudes, indexing more fluent processing, were associated with higher JOLs. Furthermore, single-trial N400 mediated a small but significant portion of the relatedness effect on JOLs. In the second study-test cycle, relatedness still increased recall and JOLs. However, related and unrelated pairs did not differ in N400 amplitude. Rather, unrelated pairs elicited a parietal positivity in a later time window that partially mediated the relatedness effect on JOLs. Together, these results suggest that processing fluency, indexed by the N400, contributes to the relatedness effect on JOLs when novel word pairs are learned, but not when previously studied pairs are relearned. Our results also imply that aspects of fluency not captured by the N400 and/or explicit beliefs about memory contribute to JOLs. This study demonstrates the utility of ERPs in gaining new insights into the neurocognitive mechanisms of metamemory.