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ABSTRACT: The N400, a component of the event-related potential (ERP) associated with the processing of meaning, is sensitive to a wide array of lexico-semantic, sentence-level, and discourse-level manipulations across modalities. In sentence contexts, N400 amplitude varies inversely and nearly linearly with the predictability of a word in its context. However, recent theories and empirical evidence from studies employing the visual half-field technique (to selectively bias processing to one cerebral hemisphere) suggest that the two hemispheres use sentence context information in different ways. Thus, each hemisphere may not respond to manipulations of contextual predictability in an equivalent manner. This possibility was investigated by recording ERPs while presenting [in the left and right visual fields (VFs)] sentence-final words that varied over the full range of sentence-level predictability. RVF/left hemisphere items were facilitated (as evidenced by reduced N400 amplitudes) over a broader range of predictability compared with LVF/right hemisphere items, although both strongly predictable and completely unexpected items evoked similar responses in each VF/hemisphere. Further, the pattern of N400 amplitudes over the full range of predictability significantly differed from a linear response function for both VFs/hemispheres. This suggests that the N400 response recorded with standard central field presentation comprises different contributions from both cerebral hemispheres, neither of which on its own is sensitive to contextual predictability in an evenly graded manner. These data challenge the notion of a singular or unitary mode of comprehension and instead support the view that the left and right hemispheres instantiate unique, complementary language comprehension architectures in parallel.
Frontiers in psychology. 01/2013; 4:181.
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ABSTRACT: Older adults (as a group) are less likely than younger adults to engage in an anticipatory mode of language comprehension, failing to successfully preactivate information about upcoming likely (predictable) words during online processing. To assess (within one set of materials) age-related changes in the use of sentential context to affect processing of predictable words and in the consequences of violating predictions, event-related brain potentials were recorded while older adults read sentences that varied in sentence-level constraint and expectancy of sentence-final words. Strongly constraining sentences were completed by their most expected, predictable words and weakly constraining sentences were completed by their most expected, less predictable words. Both types of sentences also were completed by unexpected (but plausible) words. Older adults showed reduced and delayed effects of sentential context on processing predictable words. Whereas younger adults elicit an enhanced positive ERP (starting around 500 ms poststimulus onset, largest over prefrontal electrode sites), specifically for unexpected words that violate strong expectancies for a different word, older adults as a group did not exhibit this neural consequence of disconfirmed predictions. Older adults were instead more likely to show a left-lateralized frontal negativity for predictable items. This ERP response has been attributed to processes needed to revisit contextual material in forming an interpretation of message-level meaning, which may be more likely when anticipatory modes of comprehension are not engaged. Taken together, the results suggest that normal aging can affect allocation of resources to different cognitive and neural pathways in achieving comprehension outcomes. (PsycINFO Database Record (c) 2012 APA, all rights reserved).
Psychology and Aging 07/2012; · 2.73 Impact Factor
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ABSTRACT: Factors that modulate the influence of contextual information on semantic processing in language comprehension have been thoroughly investigated with the N400 component of the event-related potential (ERP), a direct measure of initial contact with semantic memory. Although context has a strong and immediate impact on processing, multiple mechanisms contribute to the construction of message-level representations during normal comprehension. Some of these may be engaged after or concurrent with the formation of an initial meaning representation, and can then serve to revise or reshape meaning. In this study, ERPs were recorded while participants read plausible sentences that continuously varied in the amount of contextual constraint for the sentence-final word, defined via extensive norming data including the range of possible alternative completions for the contexts. Consistent with numerous past studies, the amplitude of the N400 was graded with expectancy, as amplitudes decreased with increasing constraint. Additionally, a left-lateralized, broad, slow negativity onsetting around 400-500 ms was largest for sentences with moderately strong constraint. Within this range of constraint, the negativity was larger for sentences with fewer alternative completions compared to those with many different ones. The timing and scalp distribution of the effect resemble brain responses linked to engagement of working memory resources, ambiguity resolution, and comprehension of jokes. Similar to cases of "frame-shifting" in non-literal language, this effect may reflect processing associated with reinterpretation or reconsideration of contextual material when multiple interpretations of a sentence were likely.
NeuroImage 05/2012; 62(1):356-66. · 5.89 Impact Factor
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ABSTRACT: Contextual information influences multiple aspects of language comprehension extended over time. To determine how age-related changes impact normal comprehension, effects of contextual strength were examined with event-related potentials. Increased contextual constraint facilitated semantic processing (reduced N400s). Effects were smaller and delayed for older adults, and sensitivity to contextual information was diminished for weak contexts. Both groups elicited a later left-lateralized frontal negativity associated with reinterpretation of context when multiple interpretations of a sentence were likely. Older adults evidenced the frontal negativity over a wider range of constraint. The change in the use of contextual information across age is attributed to decreased reliance on predictive processing for older adults. Thus, age-related changes in comprehension lead to differential engagement of processing resources over time for older adults.
Psychophysiology 04/2012; 49(6):770-85. · 3.29 Impact Factor
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ABSTRACT: Normal aging brings increased richness in knowledge and experience as well as declines in cognitive abilities. Event-related brain potential (ERP) studies of language comprehension corroborate findings showing that the structure and organization of semantic knowledge remains relatively stable with age. Highlighting the advantages of the temporal and functional specificity of ERPs, this survey focuses on age-related changes in higher-level processes required for the successful comprehension of meaning representations built from multiple words. Older adults rely on different neural pathways and cognitive processes during normal, everyday comprehension, including a shift away from the predictive use of sentential context, differential recruitment of neural resources, and reduced engagement of controlled processing. Within age groups, however, there are important individual differences that, for example, differentiate a subset of older adults whose processing patterns more closely resemble that of young adults, providing a window into cognitive skills and abilities that may mediate or moderate age-related declines.
Language and Linguistics Compass 08/2010; 4(8):623-638.
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Language and Linguistics Compass. 01/2008; 2:1-17.
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ABSTRACT: Although the term "nonverbal" is often applied to the right cerebral hemisphere (RH), a growing body of work indicates that the RH can comprehend language and, indeed, that it makes critical contributions to normal language functions. Reviewed here are studies that have examined RH language capabilities by combining visual half-field presentation methods with event-related potential (ERP) measures. Because they afford temporal and functional specificity and can be obtained as participants simply process language for meaning, ERPs provide especially valuable insights into RH language functions. Such studies suggest that the RH appreciates word and message-level meaning information, and that it may play a particularly important role in the processing of relatively unpredictable semantic relationships. In addition, this work suggests that patterns observed for everyday language processing may often be an emergent property of multiple, distinct mechanisms operating in parallel as the left and right hemispheres jointly comprehend language.
Language and Linguistics Compass 01/2008; 2(1):1-17.
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ABSTRACT: The cerebral hemispheres have been shown to be differentially sensitive to sentence-level information; in particular, it has been suggested that only the left hemisphere (LH) makes predictions about upcoming items, whereas the right (RH) processes words in a more integrative fashion. The current study used event-related potentials to jointly examine the effects of expectancy and sentential constraint on word processing. Expected and unexpected but plausible words matched for contextual fit were inserted into strongly and weakly constraining sentence frames and presented to the left and right visual fields (LVF and RVF). Consistent with the prediction/integration view, the P2 was sensitive to constraint: words in strongly constraining contexts elicited larger P2s than those in less predictive contexts, for RVF/LH presentation only. N400 responses for both VFs departed from the typical pattern of amplitudes graded by cloze probability. Expected endings in strongly and weakly constraining contexts were facilitated to a similar degree with RVF/LH presentation, and expected endings in weakly constraining contexts were not facilitated compared to unexpected endings in those contexts for LVF/RH presentation. These data suggest that responses seen for central presentation reflect contributions from both hemispheres. Finally, a late positivity, larger for unexpected endings in strongly constraining contexts, observed for these stimuli with central presentation was not seen here for either VF. Thus, some phenomena observed with central presentation may be an emergent property of mechanisms that require interhemispheric cooperation. These data highlight the importance of understanding hemispheric asymmetries and their implications for normal language processing.
Neuropsychologia 11/2007; 45(13):3001-14. · 3.64 Impact Factor
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ABSTRACT: Behavioral and electrophysiological studies have uncovered different patterns of constraint effects on the processing of words in sentences. Whereas response time measures have indicated a reduced scope of facilitation from strongly constraining contexts, event-related brain potential (ERP) measures have instead revealed enhanced facilitation for semantically related endings in such sentences. Given this disparity, and the concomitant possibility of functionally separable stages of context effects, the current study jointly examined expectancy (cloze probability) and constraint effects on the ERP response to words. Expected and unexpected (but plausible) words completed strongly and weakly constraining sentences; unexpected items were matched for contextual fit across the two levels of constraint and were semantically unrelated to the most expected endings. N400 amplitudes were graded by expectancy but unaffected by constraint and seemed to index the benefit of contextual information. However, a later effect, in the form of increased frontal positivity from 500 to 900 ms post-stimulus-onset, indicated a possible cost associated with the processing of unexpected words in strongly constraining contexts.
Brain Research 06/2007; 1146:75-84. · 2.73 Impact Factor
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ABSTRACT: Adults learned the meanings of rare words (e.g., gloaming) and then made meaning judgments on pairs of words. The 1st word was a trained rare word, an untrained rare word, or an untrained familiar word. Event-related potentials distinguished trained rare words from both untrained rare and familiar words, first at 140 ms and again at 400-600 ms after onset of the 1st word. These results may point to an episodic memory effect. The 2nd word produced an N400 that distinguished trained and familiar word pairs that were related in meaning from unrelated word pairs. Skilled comprehenders learned more words than less skilled comprehenders and showed a stronger episodic memory effect at 400-600 ms on the 1st word and a stronger N400 effect on the 2nd word. These results suggest that superior word learning among skilled comprehenders may arise from a stronger episodic trace that includes orthographic and meaning information and illustrate, how an episodic theory of word identification can explain reading skill.
Journal of Experimental Psychology Learning Memory and Cognition 12/2005; 31(6):1281-92. · 2.85 Impact Factor
