Cyma Van Petten

Event-related potentials in clinical research: Guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400

This paper describes recommended methods for the use of event-related brain potentials (ERPs) in clinical research and reviews applications to a variety of psychiatric and neurological disorders. Techniques are presented for eliciting, recording, and quantifying three major cognitive components with confirmed clinical utility: mismatch negativity (MMN), P300, and N400. Also highlighted are applications of each of the components as methods of investigating central nervous system pathology. The guidelines are intended to assist investigators who use ERPs in clinical research, in an effort to provide clear and concise recommendations and thereby to standardize methodology and facilitate comparability of data across laboratories.

Lexical versus conceptual anticipation during sentence processing: frontal positivity and N400 ERP components.

Although the sensitivity of the N400 to semantic processing is well established, late positive ERP components are also elicited during sentence comprehension. We suggest that there are multiple such components differing in scalp topography, and that a larger frontal positivity often follows the larger N400 elicited by congruent but unexpected sentence endings as compared to predictable endings. We evaluated the lexical versus conceptual specificity of this post-N400-positivity. High- and low-constraint sentences were completed by the words most preferred by a normative group (best completions), by words that were nearly synonymous to those best completions, and by other congruent words that were semantically dissimilar to the best completions. The N400 was sensitive to both the predictability (cloze probability) of the words and their semantic similarity to the best completion, consistent with a sensitivity to conceptual expectations that could be fulfilled by alternate words. In contrast, an anterior positivity was elicited by all final words that were not highly predictable, independent of whether they were semantically similar or dissimilar to the most preferred word, indicating a sensitivity to specific lexical expectations.

Morphological agreement at a distance: Dissociation between early and late components of the event- related brain potential

Syntactic relationships among non-adjacent words are a core aspect of sentence structure. Research on complex sentences with displaced elements has concluded that resolving long-distance dependencies can tax working memory. Here we examine a simpler relationship-morphological agreement between the elements of a noun phrase-across a gradient of distance. Participants read sentences with violations of gender agreement among Spanish nouns, determiners and adjectives. For those explicitly assigned the task of detecting errors, accuracy was uniformly high across the four levels of distance between (dis)agreeing words. A second group performed a comprehension task as ERPs were recorded. Gender agreement errors elicited a left anterior negativity (LAN) regardless of the distance between (dis)agreeing words, indicating that the errors were detected. In contrast, a temporally later component of the ERP (P600) showed decreasing amplitudes as the number of words between (dis)agreeing elements increased. Smaller P600 responses were also associated with slower responses to the comprehension questions. Given other work suggesting that the P600 indexes attempted repair of a problematic sentence structure, the results suggest that the participants became increasingly unwilling to re-visit their initial parse of a sentence as the required effort increased, despite having noted an error. The results are discussed within the context of studies showing that readers often compute inadequate structural representations of sentences. We suggest that P600 amplitude may reflect the costs versus benefits of sentence re-analysis, determined by a combination of sentence structure, task requirements, and the degree to which sentence meaning hinges on a correct structural analysis.

Prospective and retrospective semantic processing: Prediction, time, and relationship strength in event-related potentials

Semantic context effects have variously been attributed to prospective processing - predictions about upcoming words - or to retrospective appreciation of relationships after reading both context and target. In two experiments, we altered the core variable distinguishing prospective from retrospective processing, namely time. Word pairs varying in strength of relationship were presented sequentially, to allow time for anticipation of the second word, or simultaneously. For both sorts of presentation, the amplitude of the N400 component of the event-related potential was graded from Unrelated to Moderate/Weak to Strong associates. Strong associates showed a temporal advantage over weaker associates - an earlier context effect - only during sequential presentation. Spatial distributions of the N400 context effects also differed for simultaneous versus sequential presentation.

Semantic access to embedded words? Electrophysiological and behavioral evidence from Spanish and English

Many multisyllabic words contain shorter words that are not semantic units, like the CAP in HANDICAP and the DURA (hard) in VERDURA (vegetable). The spaces between printed words identify word boundaries, but spurious identification of these embedded words is a potentially greater challenge for spoken language comprehension, a challenge that is handled by different mechanisms in different models of auditory word recognition. Subphonemic acoustic differences--subtle differences in pronunciation--often differentiate embedded words from genuine words. We examined semantic access to embedded words in two languages with different phonology by presenting carrier words followed by targets related to the embedded words and recording event-related potentials and lexical decision times in 34 Spanish/English bilinguals. No evidence of embedded word access was observed in brain activity or behavior, and this could not be attributed to subphonemic acoustic factors. The data place constraints on models of speech segmentation.

Selective Attention, Processing Load, and Semantics: Insights from Human Electrophysiology

Event-related potentials offer multiple signatures of attentional gain control and selective processing, and also a measure of access to meaning in the N400 component. I summarize progress on how attention influences language processing and the parallels between attentional modulation of perceptual and linguistic processes. Four issues are addressed: (1) how selective attention to physical features influences semantic processing, (2) whether preparatory attention can be tuned to words and/or the semantic features of words, (3) whether word meanings must be relevant to a subject’s assigned task for semantic processing to occur, and (4) the impact of general processing load on semantic processing. These topics are very pertinent to long-standing debates about the specificity vs generality of functional and neural resources applied to language processing.Event-related potentials offer multiple signatures of attentional gain control and selective processing, and also a measure of access to meaning in the N400 component. I summarize progress on how attention influences language processing and the parallels between attentional modulation of perceptual and linguistic processes. Four issues are addressed: (1) how selective attention to physical features influences semantic processing, (2) whether preparatory attention can be tuned to words and/or the semantic features of words, (3) whether word meanings must be relevant to a subject’s assigned task for semantic processing to occur, and (4) the impact of general processing load on semantic processing. These topics are very pertinent to long-standing debates about the specificity vs generality of functional and neural resources applied to language processing.

Gradients versus dichotomies: How strength of semantic context influences event-related potentials and lexical decision times

In experiments devoted to word recognition and/or language comprehension, reaction time in the lexical decision task is perhaps the most commonly used behavioral dependent measure, and the amplitude of the N400 component of the event-related potential (ERP) is the most common neural measure. Both are sensitive to multiple factors, including frequency of usage, orthographic similarity to other words, concreteness of word meaning, and preceding semantic context. All of these factors vary continuously. Published results have shown that both lexical decision times and N400 amplitudes show graded responses to graded changes of word frequency and orthographic similarity, but a puzzling discrepancy in their responsivity to the strength of a semantic context has received little attention. In three experiments, we presented pairs of words varying in the strengths of their semantic relationships, as well as unrelated pairs. In all three experiments, N400 amplitudes showed a gradient from unrelated to weakly associated to strongly associated target words, whereas lexical decision times showed a binary division rather than a gradient across strengths of relationship. This pattern of results suggests that semantic context effects in lexical decision and ERP measures arise from fundamentally different processes.