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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.

Two experiments examined the hypothesis that dual systems of stimulus evaluation for categorization can be observed in event-related potentials: one whose duration is indexed by the latency of the P3 component, and a second evident in a later frontal potential. Subjects categorized artificial animals by a "two out of three" rule. Stimuli with two visual features of their own category and one feature of a different category (i.e., near the boundary between categories) elicited very prolonged reaction times as compared to stimuli with three features from a single category. This response time (RT) delay was not accompanied by a delayed P3, suggesting that the P3 indexed only a first pass of stimulus evaluation. The near-boundary stimuli elicited more positive potentials than far-boundary stimuli at prefrontal and frontotemporal sites, suggesting that a secondary stage of stimulus evaluation was triggered when detection of single features or simple conjunctions was insufficient to support a correct decision. The frontal potential that was sensitive to categorization difficulty was of opposite polarity to frontal potentials previously observed in manipulations of working memory. The roles of frontal executive processes in categorization and memory tasks are discussed.

It is well established that source memory retrieval – remembering relationships between a core item and some additional attribute of an event – engages prefrontal cortex (PFC) more than simple item memory. In event-related potentials (ERPs), this is manifest in a late-onset difference over PFC between studied items which mandate retrieval of a second attribute, and unstudied items which can be immediately rejected. Although some sorts of attribute conjunctions are easier to remember than others, the role of source retrieval difficulty on prefrontal activity has received little attention. We examined memory for conjunctions of object shape and color when color was an integral part of the depicted object, and when monochrome objects were surrounded by colored frames. Source accuracy was reliably worse when shape and color were spatially separated, but prefrontal activity did not vary across the object–color and frame-color conditions. The insensitivity of prefrontal ERPs to this perceptual manipulation of difficulty stands in contrast to their sensitivity to encoding task: deliberate voluntary effort to integrate objects and colors during encoding reduced prefrontal activity during retrieval, but perceptual organization of stimuli did not. The amplitudes of ERPs over parietal cortex were larger for frame-color than object–color stimuli during both study and test phases of the memory task. Individual variability in parietal ERPs was strongly correlated with memory accuracy, which we suggest reflects a contribution of visual working memory to long-term memory. We discuss multiple bottlenecks for source memory performance.

It has been suggested that performing a physical action (enactment) is an optimally effective encoding task, due to the incorporation of motoric information in the episodic memory trace, and later retrieval of that information. The current study contrasts old/new recognition of objects after enactment to a conceptual encoding task of cost estimation. Both encoding tasks yielded high accuracy, and robust differences in brain activity as compared to new objects, but no differences between encoding tasks. These results are not supportive of the idea that encoding by enactment leads to the spontaneous retrieval of motoric information. When participants were asked to discriminate between the two classes of studied objects during a source memory task, perform-encoded objects elicited higher accuracy and different brain activity than cost-encoded objects. The extent and nature of what was retrieved from memory thus depended on its utility for the assigned memory test: object information during the old/new recognition test, but additional information about the encoding task when necessary for a source memory test. Event-related potentials (ERPs) recorded during the two memory tests showed two orthogonal effects during an early (300-800 msec) time window: a differentiation between studied and unstudied objects, and a test-type (retrieval orientation) effect that was equivalent for old and new objects. Later brain activity (800-1300 msec) differentiated perform- from cost-encoded objects, but only during the source memory test, suggesting temporally distinct phases of retrieval.

It has been suggested that the right hemisphere (RH) has a privileged role in the processing of figurative language, including metaphors, idioms, and verbal humor. Previous experiments using hemifield visual presentation combined with human electrophysiology support the idea that the RH plays a special role in joke comprehension. The current study examines metaphoric language. Event-related potentials (ERPs) were recorded as healthy adults read English sentences that ended predictably (High-cloze Literals), or with a plausible but unexpected word (Low-cloze Literals and Low-cloze Metaphoricals). Sentence final words were presented in either the left or the right visual hemifield. Relative to High-cloze Literals, Low-cloze Literals elicited a larger N400 component after presentation to both the left and the right hemifield. Low-cloze Literals also elicited a larger frontal positivity following the N400, but only with presentation to the right hemifield (left hemisphere). These data suggest both cerebral hemispheres can benefit from supportive sentence context, but may suggest an important role for anterior regions of the left hemisphere in the selection of semantic information in the face of competing alternatives. Relative to Low-cloze Literals, Low-cloze Metaphoricals elicited more negative ERPs during the timeframe of the N400 and afterwards. However, ERP metaphoricity effects were very similar across hemifields, suggesting that the integration of metaphoric meanings was similarly taxing for the two hemispheres, contrary to the predictions of the right hemisphere theory of metaphor.

Age-related deficits in source memory have been attributed to alterations in prefrontal cortex (PFC) function, but little is known about the neural basis of such changes. The present study examined the time course of item and source memory retrieval by recording event-related potentials (ERPs) in patients with focal lesions in lateral PFC and in healthy older and young controls. Both normal aging and PFC lesions were associated with decrements in item and source memory. However, older controls showed a decrease in item hit rate with no change in false alarms, whereas patients showed the opposite pattern. Furthermore, ERPs revealed notable differences between the groups. The early positive-going old/new effect was prominent in the young but reduced in patients and older adults, who did not differ from each other. In contrast, older adults displayed a prominent left frontal negativity (600–1200 ms) not observed in the young. This left frontal effect was substantially smaller and delayed in the patients. The current results provide novel insights into the effects of aging on source memory and the role of the lateral PFC in these processes. Older controls appeared to adopt alternate memory strategies and to recruit compensatory mechanisms in left PFC to support task performance. In contrast, the lateral frontal patients were unable to use these mechanisms, thus exhibiting difficulties with strategic memory and monitoring processes.

Forty participants assigned artificial creatures to categories after explicit rule instruction or feedback alone. Stimuli were typical and atypical exemplars of 2 categories with independent prototypes, conflicting exemplars sharing features of both categories, and "Others" with only 1 or 2 features of the well-defined categories. Ten feedback-only participants spontaneously adopted a unidimensional rule; 10 used a multidimensional similarity strategy. Event-related potentials (ERPs) recorded during the transfer phase showed a commonality between multidimensional rule and similarity strategies in late frontal brain activity that differentiated both from unidimensional rule use. Multidimensional rule users alone showed an earlier prefrontal ERP effect that may reflect inhibition of responses based on similarity. The authors also discuss the role of declarative memory for features and exemplars.

Poor memory ability and small hippocampal volume measurements in magnetic resonance images co-occur in neurological patients. Numerous studies have examined the relationship between memory performance and hippocampal volumes in participants without neurological or psychiatric disorders, with widely varying results. Three hypotheses about volume-memory relationships in the normal human brain are discussed: "bigger is always better", a neuropsychological view that volume decreases due to normal aging are accompanied by memory decline, and a developmental perspective that regressive events in development may result in negative correlations between hippocampal volume and memory ability. Meta-analysis of results from 33 studies led to little support for the bigger-is-better hypothesis. A negative relationship between hippocampal volume and memory (smaller is better) was significant for studies with children, adolescents, and young adults. For studies with older adults, the most striking observation was extreme variability: the evidence for a positive relationship between hippocampal size and episodic memory ability in older adults was surprisingly weak. Some of the variability in results from older adults was associated with statistical methods of normalizing for age and head size, which are discussed.

Age-related changes in sensory, lexical, and sentence processing were examined and compared using event-related potentials (ERPs) recorded as young and elderly participants listened to natural speech for comprehension. Lexically associated and unassociated word pairs were embedded in meaningful or syntactically legal but meaningless sentences. Early, general sensory, and attention-related responses (N1, P2) were delayed by about 25 ms for older participants, but later components indexing semantic processing (N400) were not delayed. There were no differences in the size, timing, or distribution of lexical associative effects for the two groups. In contrast, message-level context effects were delayed by more than 200 ms in the elderly group. The results support models that posit age-related changes primarily in higher order language processes.

Event-related potentials elicited by semantically associated and unassociated word pairs embedded in congruous and semantically anomalous spoken sentences were recorded from patients with Alzheimer's disease (AD) and healthy older and young controls as a means of examining the nature, time course, and relation between word and sentence context effects. All groups demonstrated lexical priming in nonsensical sentences, but it was earlier in the young (200-600 ms) than in the older controls (600-800 ms), and even later in the probable AD patients (800-1,000 ms). Moreover, processing in both the elderly and AD groups benefited disproportionately from a meaningful sentence context. The results do not accord well with either a strictly structural or a strictly functional account of the semantic impairments in AD.

Cognitive research shows that people typically remember actions they perform better than those that they only watch or imagine doing, but also at times misremember doing actions they merely imagined or planned to do (source memory errors). Neural research suggests some overlap between brain regions engaged during action production, motor imagery, and action observation. The present study evaluates the similar-ities/differences in brain activity during the retrieval of various types of action and nonaction memories. Participants study real objects in one of four encoding conditions: performing an action, watching the experimenter perform an action, or imagining an action with an object, or a nonmotoric task of estimating an object's cost. At test, participants view color photos of the objects, and make source memory judgments about the initial encoding episodes. Event-related potentials (ERPs) during test reveal (1) content-specific brain activity depending on the nature of the encoding task, and (2) a hand tag, i.e., sensitivity to the hand with which an object had been manipulated at study. At fronto-central sites, ERPs are similar for the three action-retrieval conditions, which are distinct from those to the cost-encoded objects. At occipital sites ERPs distinguished objects from encoding conditions with visual motion (Perform and Watch) from those without visual motion (Imagine and Cost). Results thus suggest some degree of recapitulation of encoding brain activity during retrieval of memories with qualitatively distinct attributes.

With increasing availability of digital text, there has been an explosion of computational methods designed to turn patterns of word co-occurrence in large text corpora into numerical scores expressing the “semantic distance” between any two words. The success of such methods is typically evaluated by how well they predict human judgments of similarity. Here, I examine how well corpus-based methods predict amplitude of the N400 component of the event-related potential (ERP), an online measure of lexical processing in brain electrical activity. ERPs elicited by the second words of 303 word pairs were analyzed at the level of individual items. Three corpus-based measures (mutual information, distributional similarity, and latent semantic analysis) were compared to a traditional measure of free association strength. In a regression analysis, corpus-based and free association measures each explained some of the variance in N400 amplitude, suggesting that these may tap distinct aspects of word relationships. Lexical factors of concreteness of word meaning, word frequency, number of semantic associates, and orthographic similarity also explained variance in N400 amplitude at the single-item level.

Event-related potentials (ERPs) were recorded as 16 adults with learning disabilities (LD) and 16 controls were presented with two sets of stimuli. The first set comprised pairs of line drawings and environmental sounds (nonverbal condition); the second consisted of printed and spoken words (verbal condition). In the controls, semantically related items elicited smaller N400s than unrelated items in both conditions, with opposing hemispheric asymmetries for spoken words and environmental sounds. The LD group did not show a significant difference between related and unrelated words, despite a robust context effect for nonspeech sounds. The results suggest anomalous processing limited to the verbal domain in a simple semantic association task in the LD group. Semantic deficits in this group may reflect a relatively specific deficit in forming verbal associations rather than a more general difficulty that spans both verbal and nonverbal domains.

Event-related potentials (ERPs) were recorded during recognition tasks for line drawings (items) or for both drawings and their spatial locations (sources). Recognized drawings elicited more positive ERPs than new drawings. Independent of accuracy in the spatial judgment, the old/new effect in the source recognition task was larger over the prefrontal scalp, and of longer temporal duration than in the item recognition task, suggesting that the source memory task engaged a qualitatively distinct memory process. More posterior scalp sites were sensitive to the accuracy of the source judgment, but this effect was delayed relative to the difference between studied and unstudied drawings, suggesting that source memory processes are completed after item recognition. Similarities and differences between spatial source memory and memory for conjunctions of other stimulus attributes are discussed, together with the role of prefrontal cortex in memory.

In a study/recognition paradigm, new words at test were recombinations of studied syllables (e.g. BARLEY from BARTER and VALLEY), shared one syllable with studied words, or were completely new. False alarm rates followed the gradient of similarity with studied items. Event-related potentials to the three classes of false alarms were indistinguishable. False alarms elicited different brain activity than did hits, arguing against the idea that conjunction errors occur during encoding and are later retrieved liked genuine memories. In Experiment 2, with healthy older adults, neuropsychological tests sensitive to frontal lobe function predicted false alarm rate, but not hit rate. Performance on standardised memory scales sensitive to medial temporal/diencephalic function influenced the pattern of false alarm rates across the three classes of new words. The experiments suggest that false alarms to conjunction lures are not similar to true recollections, but are products of faulty monitoring at retrieval.

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.

Semantically associated and unassociated word pairs were embedded in normal meaningful sentences and in sentences that were semantically anomalous throughout The influence of lexical context was isolated via comparison of responses to the second words of the associated and unassociated pairs The influence of sentence-level context was isolated by comparing responses to the same words in the two sentence types Subjects of high, medium and low working memory capacity (as evaluated by the reading span test) showed modulations of event-related brain potentials in response to lexical context In contrast, only the high- and medium-capacity groups were responsive to purely sentence-level semantic context The results demonstrate that sentential context influences the processing of words in intermediate sentence positions at normal reading speeds but that the on-line utilization of this context is more demanding of working memory than single-word contexts

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.

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.

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.

Event-related brain potentials elicited by lexically associated and unassociated word pairs embedded in normal or semantically anomalous sentences were recorded in order to compare the influences of lexical and sentential context. The design of the experiment was such that second words of associated pairs in anomalous sentences could be subject to lexical context alone, while the second words of unassociated pairs in normal sentences could draw on both types of context, while unassociated words in anomalous sentences were included as a control condition wherein no context effects were expected. N400 amplitude was reduced by both lexical and sentential contexts, and the onset latencies of the two effects were similar. The sentential context effect proved to be longer in duration, and exhibited greater variability across subjects. The amplitude of the purely sentential context effect was predictive of subsequent recognition accuracy for other words occurring in the same sentence. The amplitude of t...

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.

Word repetition has been a staple paradigm for both psycholinguistic and memory research; several possible loci for changes in behavioral performance have been proposed. These proposals are discussed in light of the event-related brain potential (ERP) data reported here. ERPs were recorded as subjects read nonfiction articles drawn from a popular magazine. The effects of word repetition were examined in this relatively natural context wherein words were repeated as a consequence of normal discourse structure. Three distinct components of the ERP were found to be sensitive to repetition: a positive component peaking at 200 msec poststimulus, a negative one at 400 msec (N400), and a later positivity. The components were differentially sensitive to the temporal lag between repetitions, the number of repetitions, and the normative frequency of the eliciting word. The N400 responded similarly to repetition in text as it has in experimental lists of words, but the late positivity showed a different pattern of results than in list studies.

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.

We manipulated categorical typicality and the presence of conflicting information as participants categorized multifeatured artificial animals. In Experiment 1, rule-irrelevant features were correlated with particular categories during training. In the test phase, participants applied a one-dimensional rule to stimuli with rule-irrelevant features that were category-congruent, category-incongruent, or novel. Category-incongruent and novel features delayed RT and P3 latency, but had no effect on the N2. Experiment 2 used a two-dimensional rule to create conflict between rule-relevant features. Conflict resulted in prolonged RTs and larger amplitudes of a prefrontal positive component, but had no impact on the N2. Stimuli with novel features did elicit a larger N2 than those with frequent features. These results suggest limitations on the generality of the N2's sensitivity to conflicting information while confirming its sensitivity to attended visual novelty.

It has been suggested that the right hemisphere (RH) has a privileged role in the processing of figurative language, including metaphors, idioms, and verbal humor. Previous experiments using hemifield visual presentation combined with human electrophysiology support the idea that the RH plays a special role in joke comprehension. The current study examines metaphoric language. Event-related potentials (ERPs) were recorded as healthy adults read English sentences that ended predictably (High-cloze Literals), or with a plausible but unexpected word (Low-cloze Literals and Low-cloze Metaphoricals). Sentence final words were presented in either the left or the right visual hemifield. Relative to High-cloze Literals, Low-cloze Literals elicited a larger N400 component after presentation to both the left and the right hemifield. Low-cloze Literals also elicited a larger frontal positivity following the N400, but only with presentation to the right hemifield (left hemisphere). These data suggest both cerebral hemispheres can benefit from supportive sentence context, but may suggest an important role for anterior regions of the left hemisphere in the selection of semantic information in the face of competing alternatives. Relative to Low-cloze Literals, Low-cloze Metaphoricals elicited more negative ERPs during the timeframe of the N400 and afterwards. However, ERP metaphoricity effects were very similar across hemifields, suggesting that the integration of metaphoric meanings was similarly taxing for the two hemispheres, contrary to the predictions of the right hemisphere theory of metaphor.

The importance of phonological syllables in recognition and pronunciation of visual words has been demonstrated in languages with a high degree of spelling-sound correspondence. In Spanish, multisyllabic words with frequent first syllables are named more quickly than those with less frequent first syllables, but receive slower lexical decisions. The latter effect is attributed to lexical competition from other words beginning with the same syllable. We examined syllable frequency effects on naming and lexical decision for 3029 visually presented words in English, a language with a high degree of irregularity in spelling/sound relationships, and in which phonological syllables are less clearly marked in printed words. The results showed facilitative effects of syllable frequency in both tasks, and these were stronger when syllables were defined orthographically than phonologically. The results suggest that activation of lexical candidates based on a syllabic code does not occur rapidly enough to interfere with lexical decision in English.

Most words have several meanings, yet readers and listeners are able to determine a writer's or speaker's intent from the word's context. Research on the resolution of lexical ambiguity has developed not only theories on how comprehenders settle on a single meaning, but also experimental paradigms for examining this process. Keywords: ambiguous words; semantic context; event-related potential; eye movement; word meaning

Publisher Summary In 1994, there were only two dominant noninvasive techniques to offer insight about the functional organization of language from its brain bases: the behavior of brain-damaged patients (neuropsychology), and event-related brain potential (ERPs). Positron emission tomographic and magnetoencephalographic (MEG) measures begin to contribute in understanding neuropsychology. Over the ensuing decade plus, these have been joined by functional magnetic resonance imaging, transcranial magnetic stimulation, event related spectral changes in the electroencephalogram (EEG), and noninvasive optical imaging. These methods are closely related in their neural and physical bases: ERPs, event-related frequency changes in the EEG and MEG. The amplitude of the EEG is considerably smaller than invasively recorded field potentials because the skull is a strong electrical insulator. Like field potentials, the amplitude and polarity of the EEG depends on the number and amplitude of the contributing synaptic potentials, on whether current is flowing into or out of cells (i.e., movement of positive or negative ions, excitatory or inhibitory synaptic potentials), and on the geometric relationship between the synapses and electrode.

Researchers using lateralized stimuli have suggested that the left hemisphere is sensitive to sentence-level context, whereas the right hemisphere (RH) primarily processes word-level meaning. The authors investigated this message-blind RH model by measuring associative priming with event-related brain potentials (ERPs). For word pairs in isolation, associated words elicited more positive ERPs than unassociated words with similar magnitudes and onset latencies in both visual fields. Embedded in sentences, these same pairs showed large sentential context effects in both fields. Small effects of association were observed, confined to incongruous sentences after right visual hemifield presentation but present for both congruous and incongruous sentences after left visual hemifield presentation. Results do not support the message-blind RH model but do suggest hemispheric asymmetries in the use of word and sentence context during real-time processing.

Forty-eight healthy adults aged 65–85 were recruited for structural magnetic resonance scans after an extensive neuropsychological battery that ensured a high degree of variability across the sample in performance on long-term memory tests, and on tests traditionally thought to rely on prefrontal cortex. Gray matter volumes were measured for three gyri in the frontal lobe (superior, middle, inferior), six gyri in the temporal lobe (superior, middle, inferior, fusiform, parahippocampal, and hippocampus), and the occipital lobe. Gray matter volumes declined across the age range evaluated, but with substantial regional variation—greatest in the inferior frontal, superior temporal, and middle temporal gyri but negligible in the occipital lobe. Both memory performance and executive function declined as the number of hyperintense regions in the subcortical white matter increased. Memory performance was also significantly correlated with gray matter volumes of the middle frontal gyrus (MFG), and several regions of temporal neocortex. However, the correlations were all in the negative direction; better memory performance was associated with smaller volumes. Several previous reports of significant negative correlations between gray matter volumes and memory performance are described, so that the possible reasons for this surprising finding are discussed. © 2004 Elsevier Ltd. All rights reserved.

Words have been found to elicit a negative potential at the scalp peaking at approximately 400 ms that is strongly modulated by semantic context. The current study used whole-head magnetoencephalography (MEG) as male subjects read sentences ending with semantically congruous or incongruous words. Compared with congruous words, sentence-terminal incongruous words consistently evoked a large magnetic field over the left hemisphere, peaking at approximately 450 ms. Source modeling at this latency with conventional equivalent current dipoles (ECDs) placed the N400 m generator in or near the left superior temporal sulcus. A distributed solution constrained to the cortical surface suggested a sequence of differential activation, beginning in Wernicke's area at approximately 250 ms, spreading to anterior temporal sites at approximately 270 ms, to Broca's area by approximately 300 ms, to dorsolateral prefrontal cortices by approximately 320 ms, and to anterior orbital and frontopolar cortices by approximately 370 ms. Differential activity was exclusively left-sided until >370 ms, and then involved right anterior temporal and orbital cortices. At the peak of the N400 m, activation in the left hemisphere was estimated to be widespread in the anterior temporal, perisylvian, orbital, frontopolar, and dorsolateral prefrontal cortices. In the right hemisphere, the orbital, as well as, weakly, the right anterior temporal cortices were activated. Similar but weaker field patterns were evoked by intermediate words in the sentences, especially to low-frequency words occurring in early sentence positions where there is little preceding context. The locations of the N400 m sources identified with the distributed solution correspond well with those previously demonstrated with direct intracranial recordings, and suggested by functional magnetic resonance imaging (fMRI). These results help identify a distributed cortical network that supports online semantic processing.

Event-related brain potentials (ERPs) were recorded from 24 young adults during a recognition test including Old, New, and Recombined pairs composed of two words studied in different pairs. Recombined pairs called for a response of ‘new’. Task difficulty was increased by repetition of some words during the study phase; a subject might study tower/pie, puppet/pie, drill/wreath and bee/wreath (pairs with a Common word), and at test, encounter the Common Recombined pair of puppet/wreath (in addition to Unique Recombined pairs composed of two words studied once). Individual accuracy in the Recombined conditions varied widely, but was unrelated to general memory ability as indexed by accuracy on the Old and New pairs. Posterior brain potentials showed graded amplitudes dependent on the oldness of both the individual words and their combinations (Old > Recombined > New, and Common > Unique), but were also unrelated to accuracy in the Recombined conditions. Amplitudes of ERPs recorded over prefrontal scalp accounted for a large proportion of the individual variability in differentiating studied combinations of words from recombinations of studied elements. The experimental design differentiates three possible roles of prefrontal cortex in source or associative memory tests: resolving a conflict between familiarity and a response of ‘new’, extended memory search, and evaluation of ambiguous memory signals.

Interactions between sentences and the individual words that comprise them are reviewed in studies using the event-related brain potential (ERP). Results suggest that, for ambiguous words preceded by a biasing sentence context, context is used at an early stage to constrain the relevant sense of a word rather than select among multiple active senses. A study comparing associative single-word context and sentence-level context also suggests that sentence context influences the earliest stage of semantic analysis, but that the ability to use sentence context effectively is more demanding of working memory than the ability to use single-word contexts. Another indication that sentence context has a dramatic effect on single-word processing was the observation that high- and low-frequency words elicit different ERPs at the beginnings of sentences but that this effect is suppressed by a meaningful sentence context.

In two experiments, event-related brain potentials (ERPs) and cued-recall performance measures were used to examine the consequences of semantic congruity and repetition on the processing of words in sentences. A set of sentences, half of which ended with words that rendered them semantically incongruous, was repeated either once (eg, Experiment 1) or twice (e.g., Experiment 2). After each block of sentences, subjects were given all of the sentences and asked to recall the missing final words. Repetition benefited the recall of both congruous and incongruous endings and reduced the amplitude and shortened the duration of the N400 component of the ERP more for (1) incongruous than congruous words, (2) open class than closed class words, and (3) low-frequency than high-frequency open class words. For incongruous sentence terminations, repetition increased the amplitude of a broad positive component subsequent to the N400. Assuming additive factors logic and a traditional view of the lexicon, our N400 results indicate that in addition to their singular effects, semantic congruiry, repetition, and word frequency converge to influence a common stage of lexical processing. Within a parallel distributed processing framework, our results argue for substantial temporal and spatial overlap in the activation of codes subserving word recognition so as to yield the observed interactions of repetition with semantic congruity, lexical class, and word frequency effects.

Publisher Summary This chapter presents pervasive influence of sentence-level context. The sentence-level context effects are seen in the same experimental tasks that yield associative context and frequency effects, the question arises as to which, if any, of these effects originates in the lexicon. This leads to the more general question concerning the constituents of a “lexical entry”: abstract orthographic and/or phonemic information only, the syntactic category of the word, and some basic semantic information. The process that yields frequency effects for words presented in isolation is neither mandatory nor immune to sentence-level context. The influence of sentence-level context can be as powerful and act as early as that of a single lexically associated word, and sentence context can be used to pick out the appropriate core meaning of an ambiguous word without first passing through an early stage of indiscriminate semantic activation.

Speech comprehension requires rapid decoding of grammatical relationships. Electrical scalp recordings show that the brain responds immediately to intonational cues signifying phrase boundaries. Thus, these cues may control initial decisions about sentence structure.

Recent years have seen an explosion of research on the N2 component of the event-related potential, a negative wave peaking between 200 and 350 ms after stimulus onset. This research has focused on the influence of ‘‘cognitive control,’’ a concept that covers strategic monitoring and control of motor responses. However, rich research traditions focus on attention and novelty or mismatch as determinants of N2 amplitude. We focus on paradigms that elicit N2 components with an anterior scalp distribution, namely, cognitive control, novelty, and sequential matching, and argue that the anterior N2 should be divided into separate control- and mismatch-related subcomponents. We also argue that the oddball N2 belongs in the family of attention-related N2 components that, in the visual modality, have a posterior scalp distribution. We focus on the visual modality for which components with frontocentral and more posterior scalp distributions can be readily distinguished.

Human speech consists of a nearly continuous stream of auditory input, so that the semantic message formed by combinations of words must be analyzed as the input continues. The minimum duration signal necessary to identify a set of words was established via the gating technique: Subjects were asked to identify (or guess) words after hearing only the initial 50, 100, or 150 ms, etc. Results showed that most words were identified before their acoustic offset: Average word duration was 600 ms, but identification accuracy was close to 90% after 350 ms of input. The isolation points established in the gating experiment were compared to the time course of semantic integration evident in event‐related brain potentials (ERPs). The gated words were used as congruous and incongruous sentence completions (in their full‐duration versions). Differential ERP responses to contextually appropriate and inappropriate words were observed by 200 ms after word onset, before the acoustic signal was sufficient to uniquely identify the words. These results indicate that semantic integration can begin to operate with only partial, incomplete information about word identity. If time allows, the talk will also describe similarities and differences between the semantic processing of words and environmental sounds.

Words with a single spelling and pronunciation but at least two distinct meanings (homographs) were used to terminate sentences of moderate contextual constraint. Following each sentence, a target was presented which was either (1) related to the contextually biased meaning of the homograph, (2) related to the unbiased meaning, or (3) unrelated to either meaning. Across subjects, the stimulus onset asynchrony (SOA) between homograph and target was either short (200 ms) or long (700 ms). The naming latencies recorded in Experiment 1 revealed priming for both contextually appropriate and inappropriate related targets at the short SOA but for only the contextually appropriate targets at the long SOA. The event-related potentials elicited by these same stimuli in Experiment 2 showed a similar pattern of priming at the long SOA. At the short SOA, however, the priming effect for contextually inappropriate targets had a later onset than that for contextually appropriate targets. We interpret these data as indicating that both meanings of ambiguous words are not activated at the same time. The late priming effect for contextually inappropriate targets is discussed in tems of backward priming.

Cats were studied behaviorally to determine their suitability as an animal model for the post-sympathectomy hyperalgesia reported to occur in humans. For this study a device and methodology were developed which allow humane testing of tolerance for intense mechanical stimulation of the hindlegs. Behavioral tolerance was measured quantitatively before and after unilateral sympathectomy. The results from this preliminary study of 6 cats are remarkably similar to those reported for humans; 1 of the 6 cats showed a decreased tolerance on the sympathectomized side which was delayed in onset and of limited duration. The new methodology appears to provide relatively stable, quantitative measures of tolerance for aversive stimulation and the cat shows promise as an animal model for post-sympathectomy hyperalgesia.

Publisher Summary This chapter reports two experiments in the application of event related potentials (ERPs) to the problem of lexical ambiguity resolution. The first is similar to ambiguity studies in using naming latency as the dependent measure. The primary purpose of the first experiment explained in the chapter is to insure that the stimulus materials constructed for this study would produce the expected priming effects for both contextually appropriate and inappropriate semantic associates of ambiguous words relative to unrelated target words. In the second experiment, ERPs were recorded to these same stimuli. The fact that ambiguous words have a single physical representation but two or more semantic representations makes them a useful tool for examining the balance between data-driven and concept-driven processes in word recognition.The phoneme monitoring paradigm relies on the assumption that accessing multiple meanings of a word drains more cognitive resources than accessing one meaning. Reaction times in the secondary task of phoneme monitoring are thus used as an index of the number of meanings that were accessed for a given word.

A commissurotomy patient, with MRI-revealed sparing of some rostral and splenial fibers of the corpus callosum, judged whether pairs of words rhymed. We presented one word in each pair to her left visual field and the other to her right visual field. The 2 words in each pair either sounded and looked alike (R + L +), sounded alike but looked different (R + L -), sounded different but looked alike (R - L +), or both sounded and looked different (R - L -). Although in previous studies the patient has demonstrated little or no ability to transfer information between her brain hemispheres, she was able to perform the rhyming judgment significantly better than chance when the words both looked and sounded alike. However, her accuracy did not differ from chance in the other 3 conditions, or when she was asked to indicate if 2 letters presented to her opposing visual fields were the same or different. A second commissurotomy patient, with an MRI-verified full callosal section, performed at chance in all conditions, and normal control subjects were significantly better than chance in all conditions but R + L -. We discuss the results in terms of the specificity of the information carried by groups of callosal fibers.

Event-related brain potentials (ERPs) were recorded from 18 normal adults as they read sentences that ended with words used literally, metaphorically, or in an intermediate literal mapping condition. In the latter condition, the literal sense of the word was used in a way that prompted readers to map conceptual structure from a different domain. ERPs measured from 300 to 500 msec after the onset of the sentence-final words differed as a function of metaphoricity: Literal endings elicited the smallest N400, metaphors the largest N400, whereas literal mappings elicited an N400 of intermediate amplitude. Metaphoric endings also elicited a larger posterior positivity than did either literal or literal mapping words. Consistent with conceptual blending theory, the results suggest that the demands of conceptual integration affect the difficulty of both literal and metaphorical language.