Decoding semantic relatedness and prediction from EEG: A classification method comparison.

Machine-learning (ML) decoding methods have become a valuable tool for analyzing information represented in electroencephalogram (EEG) data. However, a systematic quantitative comparison of the performance of major ML classifiers for the decoding of EEG data in neuroscience studies of cognition is lacking. Using EEG data from two visual word-priming experiments examining well-established N400 effects of prediction and semantic relatedness, we compared the performance of three major ML classifiers that each use different algorithms: support vector machine (SVM), linear discriminant analysis (LDA), and random forest (RF). We separately assessed the performance of each classifier in each experiment using EEG data averaged over cross-validation blocks and using single-trial EEG data by comparing them with analyses of raw decoding accuracy, effect size, and feature importance weights. The results of these analyses demonstrated that SVM outperformed the other ML methods on all measures and in both experiments.

Cognitive control mediates age-related changes in flexible anticipatory processing during listening comprehension.

Effective listening comprehension not only requires processing local linguistic input, but also necessitates incorporating contextual cues available in the global communicative environment. Local sentence processing can be facilitated by pre-activation of likely upcoming input, or predictive processing. Recent evidence suggests that young adults can flexibly adapt local predictive processes based on cues provided by the global communicative environment, such as the reliability of specific speakers. Whether older comprehenders can also flexibly adapt to global contextual cues is currently unknown. Moreover, it is unclear whether the underlying mechanisms supporting local predictive processing differ from those supporting adaptation to global contextual cues. Critically, it is unclear whether these mechanisms change as a function of typical aging. We examined the flexibility of prediction in young and older adults by presenting sentences from speakers whose utterances were typically more or less predictable (i.e., reliable speakers who produced expected words 80% of the time, versus unreliable speakers who produced expected words 20% of the time). For young listeners, global speaker reliability cues modulated neural effects of local predictability on the N400. In contrast, older adults, on average, did not show global modulation of local processing. Importantly, however, cognitive control (i.e., Stroop interference effects) mediated age-related reductions in sensitivity to the reliability of the speaker. Both young and older adults with high cognitive control showed greater N400 effects of predictability during sentences produced by a reliable speaker, suggesting that cognitive control is required to regulate the strength of top-down predictions based on global contextual information. Critically, cognitive control predicted sensitivity to global speaker-specific information but not local predictability cues, suggesting that predictive processing in local sentence contexts may be supported by separable neural mechanisms from adaptation of prediction as a function of global context. These results have important implications for interpreting age-related change in predictive processing, and for drawing more generalized conclusions regarding domain-general versus language-specific accounts of prediction.

The use of context in resolving syntactic ambiguity: Structural and semantic influences.

Verb bias facilitates parsing of temporarily ambiguous sentences, but it is unclear when and how comprehenders use probabilistic knowledge about the combinatorial properties of verbs in context. In a self-paced reading experiment, participants read direct object/sentential complement sentences. Reading time in the critical region was investigated as a function of three forms of bias: structural bias (the frequency with which a verb appears in direct object/sentential complement sentences), lexical bias (the simple co-occurrence of verbs and other lexical items), and global bias (obtained from norming data about the use of verbs with specific noun phrases). For reading times at the critical word, structural bias was the only reliable predictor. However, global bias was superior to structural and lexical bias at the post-critical word and for offline acceptability ratings. The results suggest that structural information about verbs is available immediately, but that context-specific, semantic information becomes increasingly informative as processing proceeds.

Flexible predictions during listening comprehension: Speaker reliability affects anticipatory processes.

During listening comprehension, the identification of individual words can be strongly influenced by properties of the preceding context. While sentence context can facilitate both behavioral and neural responses, it is unclear whether these effects can be attributed to the pre-activation of lexico-semantic features or the facilitated integration of contextually congruent words. Moreover, little is known about how statistics of the broader language environment, or information about the current speaker, might shape these facilitation effects. In the present study, we measured neural responses to predictable and unpredictable words as participants listened to sentences for comprehension. Critically, we manipulated the reliability of each speaker's utterances, such that individual speakers either tended to complete sentences with words that were highly predictable (reliable speaker) or with words that were unpredictable but still plausible (unreliable speaker). As expected, the amplitude of the N400 was reduced for locally predictable words, but, critically, these context effects were also modulated by speaker identity. Sentences from a reliable speaker showed larger facilitation effects with an earlier onset, suggesting that listeners engaged in enhanced anticipatory processing when a speaker's behavior was more predictable. This finding suggests that listeners can implicitly track the reliability of predictive cues in their environment and use these statistics to adaptively regulate predictive processing.

Adaptation to Animacy Violations during Listening Comprehension.

The goal of this study was to examine adaptation to various types of animacy violations in cartoon-like stories. We measured the event-related potentials (ERPs) elicited by words at the beginning, middle, and end of four-sentence stories in order to examine adaptation over time to conflicts between stored word knowledge and context-derived meaning (specifically, to inanimate objects serving as main characters, as they might in a cartoon). The fourth and final sentence of each story contained a predicate that required either an animate or an inanimate subject. The results showed that listeners quickly adapted to stories in the Inanimate Noun conditions, consistent with previous research (Filik & Leuthold, 2008; Nieuwland & Van Berkum, 2006). They showed evidence of processing difficulty for animacy-requiring predicates in the Inanimate Noun conditions in Sentence 1, but the effect dissipated in Sentences 2 and 3. In Sentences 2 and 4, we measured ERPs at three critical points where it was possible to observe the influence of both context-based expectations and expectations from prior knowledge on processing. Overall, the pattern of results demonstrates how listeners flexibly adapt to unusual, conflict-ridden input, using previous context to generate expectations about upcoming input, but that current context is weighted appropriately in combination with expectations from background knowledge and prior language experience.

Electrophysiological evidence for preserved primacy of lexical prediction in aging.

Young adults show consistent neural benefits of predictable contexts when processing upcoming words, but these benefits are less clear-cut in older adults. Here we disentangle the neural correlates of prediction accuracy and contextual support during word processing, in order to test current theories that suggest that neural mechanisms underlying predictive processing are specifically impaired in older adults. During a sentence comprehension task, older and younger readers were asked to predict passage-final words and report the accuracy of these predictions. Age-related reductions were observed for N250 and N400 effects of prediction accuracy, as well as for N400 effects of contextual support independent of prediction accuracy. Furthermore, temporal primacy of predictive processing (i.e., earlier facilitation for successful predictions) was preserved across the lifespan, suggesting that predictive mechanisms are unlikely to be uniquely impaired in older adults. In addition, older adults showed prediction effects on frontal post-N400 positivities (PNPs) that were similar in amplitude to PNPs in young adults. Previous research has shown correlations between verbal fluency and lexical prediction in older adult readers, suggesting that the production system may be linked to capacity for lexical prediction, especially in aging. The current study suggests that verbal fluency modulates PNP effects of contextual support, but not prediction accuracy. Taken together, our findings suggest that aging does not result in specific declines in lexical prediction.

Early processing of orthographic language membership information in bilingual visual word recognition: Evidence from ERPs.

For successful language comprehension, bilinguals often must exert top-down control to access and select lexical representations within a single language. These control processes may critically depend on identification of the language to which a word belongs, but it is currently unclear when different sources of such language membership information become available during word recognition. In the present study, we used event-related potentials to investigate the time course of influence of orthographic language membership cues. Using an oddball detection paradigm, we observed early neural effects of orthographic bias (Spanish vs. English orthography) that preceded effects of lexicality (word vs. pseudoword). This early orthographic pop-out effect was observed for both words and pseudowords, suggesting that this cue is available prior to full lexical access. We discuss the role of orthographic bias for models of bilingual word recognition and its potential role in the suppression of nontarget lexical information.

Internal mechanisms underlying anticipatory language processing: Evidence from event-related-potentials and neural oscillations.

Although numerous studies have demonstrated that the language processing system can predict upcoming content during comprehension, there is still no clear picture of the anticipatory stage of predictive processing. This electroencephalograph study examined the cognitive and neural oscillatory mechanisms underlying anticipatory processing during language comprehension, and the consequences of this prediction for bottom-up processing of predicted/unpredicted content. Participants read Mandarin Chinese sentences that were either strongly or weakly constraining and that contained critical nouns that were congruent or incongruent with the sentence contexts. We examined the effects of semantic predictability on anticipatory processing prior to the onset of the critical nouns and on integration of the critical nouns. The results revealed that, at the integration stage, the strong-constraint condition (compared to the weak-constraint condition) elicited a reduced N400 and reduced theta activity (4-7Hz) for the congruent nouns, but induced beta (13-18Hz) and theta (4-7Hz) power decreases for the incongruent nouns, indicating benefits of confirmed predictions and potential costs of disconfirmed predictions. More importantly, at the anticipatory stage, the strongly constraining context elicited an enhanced sustained anterior negativity and beta power decrease (19-25Hz), which indicates that strong prediction places a higher processing load on the anticipatory stage of processing. The differences (in the ease of processing and the underlying neural oscillatory activities) between anticipatory and integration stages of lexical processing were discussed with regard to predictive processing models.

Effects of word predictability and preview lexicality on eye movements during reading: A comparison between young and older adults.

Previous eye-tracking research has characterized older adults' reading patterns as "risky," arguing that compared to young adults, older adults skip more words, have longer saccades, and are more likely to regress to previous portions of the text. In the present eye-tracking study, we reexamined the claim that older adults adopt a risky reading strategy, utilizing the boundary paradigm to manipulate parafoveal preview and contextual predictability of a target word. Results showed that older adults had longer fixation durations compared to young adults; however, there were no age differences in skipping rates, saccade length, or proportion of regressions. In addition, readers showed higher skipping rates of the target word if the preview string was a word than if it was a nonword, regardless of age. Finally, the effect of predictability in reading times on the target word was larger for older adults than for young adults. These results suggest that older adults' reading strategies are not as risky as was previously claimed. Instead, we propose that older adults can effectively combine top-down information from the sentence context with bottom-up information from the parafovea to optimize their reading strategies. (PsycINFO Database Record

Language context processing deficits in schizophrenia: The role of attentional engagement.

Individuals with schizophrenia exhibit problems in language comprehension that are most evident during discourse processing. We hypothesized that deficits in cognitive control contribute to these comprehension deficits during discourse processing, and investigated the underlying cognitive-neural mechanisms using EEG (alpha power) and ERPs (N400). N400 amplitudes to globally supported or unsupported target words near the end of stories were used to index sensitivity to previous context. ERPs showed reduced sensitivity to context in patients versus controls. EEG alpha-band activity was used to index attentional engagement while participants listened to the stories. We found that context effects varied with attentional engagement in both groups, as well as with negative symptom severity in patients. Both groups demonstrated trial-to-trial fluctuations in alpha. Relatively high alpha power was associated with compromised discourse processing in participants with schizophrenia when it occurred during any early portion of the story. In contrast, discourse processing was only compromised in controls when alpha was relatively high for longer segments of the stories. Our results indicate that shifts in attention from the story context may be more detrimental to discourse processing for participants with schizophrenia than for controls, most likely due to an impaired ability to benefit from global context.

Electrophysiological Evidence for Impaired Control of Motor Output in Schizophrenia.

Previous research has demonstrated pervasive deficits in response-related processing in people with schizophrenia (PSZ). The present study used behavioral measures and event-related potentials (ERPs) to test the hypothesis that schizophrenia involves specific impairment in the ability to exert control over response-related processing. Twenty-two PSZ and 22 matched control participants completed a choice response task in counterbalanced testing sessions that emphasized only accuracy (the unspeeded condition) or emphasized speed and accuracy equally (the speeded condition). Control participants successfully modulated behavioral and ERP indices of response-related processing under speed pressure, as evidenced by faster and less variable reaction times (RTs) and an earlier onset and increased amplitude lateralized readiness potential (LRP). By contrast, PSZ were unable to improve RT speed or variability or to modulate the LRP under speed pressure, despite showing a decrease in accuracy. Notably, response-related deficits in PSZ emerged only in the speeded condition; behavioral and ERP measures did not differ between groups in the unspeeded condition. Together, these results indicate that impairment in the ability to exert control over response-related processing may underlie response-related deficits in schizophrenia.

Cognitive Control of Episodic Memory in Schizophrenia: Differential Role of Dorsolateral and Ventrolateral Prefrontal Cortex.

BACKGROUND: Dorsal (DLPFC) and ventral (VLPFC) subregions in lateral prefrontal cortex play distinct roles in episodic memory, and both are implicated in schizophrenia. We test the hypothesis that schizophrenia differentially impairs DLPFC versus VLPFC control of episodic encoding. METHODS: Cognitive control was manipulated by requiring participants to encode targets and avoid encoding non-targets based upon stimulus properties of test stimuli. The more automatic encoding response (target versus non-target) was predicted to engage VLPFC in both groups. Conversely, having to overcome the prepotent encoding response (non-targets versus targets) was predicted to produce greater DLPFC activation in controls than in patients. Encoding occurred during event-related fMRI in a sample of 21 individuals with schizophrenia and 30 healthy participants. Scanning was followed by recognition testing outside the scanner. RESULTS: Patients were less successful differentially remembering target versus non-target stimuli, and retrieval difficulties correlated with more severe disorganized symptoms. As predicted, the target versus non-target contrast activated the VLPFC and correlated with retrieval success in both groups. Conversely, the non-target versus target contrast produced greater DLPFC activation in controls than in patients, and DLPFC activation correlated with performance only in controls. CONCLUSION: Individuals with schizophrenia can successfully engage the VLPFC to provide control over semantic encoding of individual items, but are specifically impaired at engaging the DLPFC to main context for task-appropriate encoding and thereby generate improved memory for target versus non-target items. This extends previous cognitive control models based on response selection tasks to the memory domain.

Sensitivity to Referential Ambiguity in Discourse: The Role of Attention, Working Memory, and Verbal Ability.

The establishment of reference is essential to language comprehension. The goal of this study was to examine listeners' sensitivity to referential ambiguity as a function of individual variation in attention, working memory capacity, and verbal ability. Participants listened to stories in which two entities were introduced that were either very similar (e.g., two oaks) or less similar (e.g., one oak and one elm). The manipulation rendered an anaphor in a subsequent sentence (e.g., oak) ambiguous or unambiguous. EEG was recorded as listeners comprehended the story, after which participants completed tasks to assess working memory, verbal ability, and the ability to use context in task performance. Power in the alpha and theta frequency bands when listeners received critical information about the discourse entities (e.g., oaks) was used to index attention and the involvement of the working memory system in processing the entities. These measures were then used to predict an ERP component that is sensitive to referential ambiguity, the Nref, which was recorded when listeners received the anaphor. Nref amplitude at the anaphor was predicted by alpha power during the earlier critical sentence: Individuals with increased alpha power in ambiguous compared with unambiguous stories were less sensitive to the anaphor's ambiguity. Verbal ability was also predictive of greater sensitivity to referential ambiguity. Finally, increased theta power in the ambiguous compared with unambiguous condition was associated with higher working-memory span. These results highlight the role of attention and working memory in referential processing during listening comprehension.

Language Membership Identification Precedes Semantic Access: Suppression during Bilingual Word Recognition.

Previous research suggests that bilingual comprehenders access lexical representations of words in both languages nonselectively. However, it is unclear whether global language suppression plays a role in guiding attention to target language representations during ongoing lexico-semantic processing. To help clarify this issue, this study examined the relative timing of language membership and meaning activation during visual word recognition. Spanish-English bilinguals performed simultaneous semantic and language membership classification tasks on single words during EEG recording. Go/no-go ERP latencies provided evidence that language membership information was accessed before semantic information. Furthermore, N400 frequency effects indicated that the depth of processing of words in the nontarget language was reduced compared to the target language. These results suggest that the bilingual brain can rapidly identify the language to which a word belongs and subsequently use this information to selectively modulate the degree of processing in each language accordingly.

Graded expectations: Predictive processing and the adjustment of expectations during spoken language comprehension.

The goal of this study was to investigate the use of the local and global contexts for incoming words during listening comprehension. Local context was manipulated by presenting a target noun (e.g., "cake," "veggies") that was preceded by a word that described a prototypical or atypical feature of the noun (e.g., "sweet," "healthy"). Global context was manipulated by presenting the noun in a scenario that was consistent or inconsistent with the critical noun (e.g., a birthday party). Event-related potentials (ERPs) were examined at the feature word and at the critical noun. An N400 effect was found at the feature word, reflecting the effect of compatibility with the global context. Global predictability and the local feature word consistency interacted at the critical noun: A larger N200 was found to nouns that mismatched predictions when the context was maximally constraining, relative to nouns in the other conditions. A graded N400 response was observed at the critical noun, modulated by global predictability and feature consistency. Finally, post-N400 positivity effects of context updating were observed to nouns that were supported by one contextual cue (global/local) but were unsupported by the other. These results indicate that (1) incoming words that are compatible with context-based expectations receive a processing benefit; (2) when the context is sufficiently constraining, specific lexical items may be activated; and (3) listeners dynamically adjust their expectations when input is inconsistent with their predictions, provided that the inconsistency has some level of support from either the global or the local context.

Effects of prediction and contextual support on lexical processing: prediction takes precedence.

Readers may use contextual information to anticipate and pre-activate specific lexical items during reading. However, prior studies have not clearly dissociated the effects of accurate lexical prediction from other forms of contextual facilitation such as plausibility or semantic priming. In this study, we measured electrophysiological responses to predicted and unpredicted target words in passages providing varying levels of contextual support. This method was used to isolate the neural effects of prediction from other potential contextual influences on lexical processing. While both prediction and discourse context influenced ERP amplitudes within the time range of the N400, the effects of prediction occurred much more rapidly, preceding contextual facilitation by approximately 100 ms. In addition, a frontal, post-N400 positivity (PNP) was modulated by both prediction accuracy and the overall plausibility of the preceding passage. These results suggest a unique temporal primacy for prediction in facilitating lexical access. They also suggest that the frontal PNP may index the costs of revising discourse representations following an incorrect lexical prediction.

Evidence for Priming Across Intervening Sentences During On-Line Sentence Comprehension.

Three experiments investigated factors contributing to syntactic priming during on-line comprehension. In all of the experiments, a prime sentence containing a reduced relative clause was presented prior to a target sentence that contained the same structure. Previous studies have shown that people respond more quickly when a syntactically related prime sentence immediately precedes a target. In the current study, ERP and eyetracking measures were used to assess whether priming in sentence comprehension persists when one or more unrelated filler sentences appear between the prime and the target. In experiment 1, a reduced P600 was found to target sentences both when there were no intervening unrelated fillers, and when there was one unrelated filler between the prime and the target. Thus, processing the prime sentence facilitated processing of the syntactic form of the target sentence. Experiments 2 and 3, eye-tracking experiments, showed that target sentence processing was facilitated when three filler sentences intervened between the prime and the target. These experiments show that priming effects in comprehension can be observed when unrelated material appears after a prime sentence and before the target. We interpret the results with respect to residual activation and implicit learning accounts of priming.

Memory availability and referential access.

Most theories of coreference specify linguistic factors that modulate antecedent accessibility in memory; however, whether non-linguistic factors also affect coreferential access is unknown. Here we examined the impact of a non-linguistic generation task (letter transposition) on the repeated-name penalty, a processing difficulty observed when coreferential repeated names refer to syntactically prominent (and thus more accessible) antecedents. In Experiment 1, generation improved online (event-related potentials) and offline (recognition memory) accessibility of names in word lists. In Experiment 2, we manipulated generation and syntactic prominence of antecedent names in sentences; both improved online and offline accessibility, but only syntactic prominence elicited a repeated-name penalty. Our results have three important implications: first, the form of a referential expression interacts with an antecedent's status in the discourse model during coreference; second, availability in memory and referential accessibility are separable; and finally, theories of coreference must better integrate known properties of the human memory system.

Disrupted action monitoring in recent-onset psychosis patients with schizophrenia and bipolar disorder.

Schizophrenia patients experience cognitive control disturbances, manifest in altered neural signatures during action monitoring. It remains unclear whether error- and conflict-monitoring disturbances co-occur, and whether they are observed in recent-onset psychosis patients with schizophrenia or bipolar disorder. We tested electrophysiological measures of action monitoring in these patients. Seventy-three schizophrenia patients (SZ), 26 bipolar disorder type I patients (BP), each within one year of psychosis onset, and 54 healthy control subjects (HC) underwent EEG during Stroop task performance. In the trial-averaged EEG at three midline scalp electrodes, the error-related negativity (ERN), error positivity (Pe) and conflict-related N450 were measured. Compared to HC (1) SZ exhibited an attenuated ERN and N450, and Pe unchanged and (2) BP exhibited an attenuated ERN but normal Pe and N450. Between patient groups, SZ showed an attenuated N450; ERN and Pe were not significantly different. A small (n=10) SZ subgroup that was not receiving antipsychotic medication showed normal ERPs. Altered error- and conflict-monitoring occur together in the first-episode schizophrenia patients, and these measures are comparable in patients with the first-episode bipolar disorder. Antipsychotic medication may be associated with altered measures of error-monitoring in schizophrenia.

Priming prepositional phrase attachment: evidence from eye-tracking and event-related potentials.

Three syntactic-priming experiments investigated the effect of structurally similar or dissimilar prime sentences on the processing of target sentences, using eye tracking (Experiment 1) and event-related potentials (ERPs) (Experiments 2 and 3) All three experiments tested readers' response to sentences containing a temporary syntactic ambiguity. The ambiguity occurred because a prepositional phrase modifier (PP-modifier) could attach either to a preceding verb or to a preceding noun. Previous experiments have established that (a) noun-modifying expressions are harder to process than verb-modifying expressions (when test sentences are presented in isolation); and (b) for other kinds of sentences, processing a structurally similar prime sentence can facilitate processing a target sentence. The experiments reported here were designed to determine whether a structurally similar prime could facilitate processing of noun-attached modifiers and whether such facilitation reflected syntactic-structure-building or semantic processes. These findings have implications for accounts of structural priming during online comprehension and for accounts of syntactic representation and processing in comprehension.