Biomedical subjects

Kara D Federmeier

Publications and source records attributed to Kara D Federmeier.

13 recordsLinked to original sources

PubMed2006

Multiple effects of sentential constraint on word processing.

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.

Adult↗

PubMed2006

To mind the mind: an event-related potential study of word class and semantic ambiguity.

The goal of this study was to jointly examine the effects of word class, word class ambiguity, and semantic ambiguity on the brain response to words in syntactically specified contexts. Four types of words were used: (1) word class ambiguous words with a high degree of semantic ambiguity (e.g., 'duck'); (2) word class ambiguous words with little or no semantic ambiguity (e.g., 'vote'); (3) word class unambiguous nouns (e.g., 'sofa'); and (4) word class unambiguous verbs (e.g., 'eat'). These words were embedded in minimal phrases that explicitly specified their word class: "the" for nouns (and ambiguous words used as nouns) and "to" for verbs (and ambiguous words used as verbs). Our results replicate the basic word class effects found in prior work (Federmeier, K.D., Segal, J.B., Lombrozo, T., Kutas, M., 2000. Brain responses to nouns, verbs and class ambiguous words in context. Brain, 123 (12), 2552-2566), including an enhanced N400 (250-450 ms) to nouns compared with verbs and an enhanced frontal positivity (300-700 ms) to unambiguous verbs in relation to unambiguous nouns. A sustained frontal negativity (250-900 ms) that was previously linked to word class ambiguity also appeared in this study but was specific to word class ambiguous items that also had a high level of semantic ambiguity; word class ambiguous items without semantic ambiguity, in contrast, were more positive than class unambiguous words in the early part of this time window (250-500 ms). Thus, this frontal negative effect seems to be driven by the need to resolve the semantic ambiguity that is sometimes associated with different grammatical uses of a word class ambiguous homograph rather than by the class ambiguity per se.

Adolescent↗

PubMed2006

Event-related potential signatures of relational memory.

Various lines of evidence suggest that memory for the relations among arbitrarily paired items acquired prior to testing can influence early processing of a probe stimulus. The event-related potential experiment reported here was designed to explore how early in time memory for a previously established face-scene relationship begins to influence processing of faces, under sequential presentation conditions in which a preview of the scene can promote expectancies about the to-be-presented face. Prior to the current work, the earliest component documented to be sensitive to memory for the relations among arbitrarily paired items was the late positive complex (LPC), but here relational memory effects were evident as early as 270-350 msec after face onset. The latency of these relational memory effects suggests that they may be the precursor to similar effects observed in eye movement behavior. As expected, LPC amplitude was also affected by memory for face-scene relationships, and N400 amplitude reflected some combination of memory for items and memory for the relations among items.

Adolescent↗

PubMed2005

Right hemisphere sensitivity to word- and sentence-level context: evidence from event-related brain potentials.

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.

Adult↗

PubMed2005

Aging in context: age-related changes in context use during language comprehension.

Effects of normal aging on the use of sentence context information during language comprehension were examined by measuring younger and older adults' event-related potential (ERP) responses to congruent sentence-final words as a function of contextual constraint. Half of the sentence contexts were strongly constraining, rendering the target word very predictable, whereas the other half were weakly constraining. Both age groups elicited smaller N400 responses to target words in strongly than in weakly constrained contexts, but this effect was significantly smaller and later for older adults. Older adults with lower reading spans showed greater delays. Age-related changes were driven primarily by decreases in older adults' ability to make use of the richer information available from strongly constraining contexts to guide semantic processing, as word processing (N400s) in weak contexts was qualitatively and quantitatively similar in the two age groups.

Adolescent↗

PubMed2005

Both sides get the point: hemispheric sensitivities to sentential constraint.

Behavioral studies have consistently reported striking differences in the impact of sentence-level information on the processing of words presented in the right (RVF) versus the left (LVF) visual field, with context effects apparent only for RVF items. The consistent lack of such effects in the LVF has been taken to mean that right hemisphere language comprehension is largely insensitive to message-level meaning. We used the functional specificity afforded by event-related potential measures to assess this claim. Target words completing strongly and weakly constraining sentence contexts, in which constraint arose at the sentence level rather than from lexical associations, were presented laterally in the LVF or RVF. Increased constraint significantly reduced N400 amplitudes with presentation in both VFs, with no differences in the timing or amplitude of these effects. These results are inconsistent with the view that the VF asymmetries found in behavioral measures reflect differential hemispheric capacities at the level of semantic analysis and integration, although VF-based differences on earlier components (P2) suggest asymmetries in the impact of sentential context on perceptual aspects of word processing in the two hemispheres.

Adolescent↗

PubMed2005

Hemispheric asymmetries in the time course of recognition memory.

Hemispheric specialization has been studied extensively within subfields ranging from perception to language comprehension. However, the study of asymmetries for basic memory functions--an area that holds promise for bridging these low- and high-level cognitive domains--has been sporadic at best. We examined each hemisphere's tendency to retain verbal information over time, using a continuous recognition memory task with lateralized study items and central test probes. We found that the ubiquitous advantage of the left hemisphere for the processing and retention of verbal information is attenuated and perhaps even reversed over long retention intervals. This result is consistent with theories that propose differences in the degree to which the hemispheres maintain veridical versus semantically transformed representations of the input they receive.

Adolescent↗

PubMed2003

Sounds, words, sentences: age-related changes across levels of language processing.

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.

Adolescent↗

PubMed2003

Electrophysiological analysis of context effects in Alzheimer's disease.

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.

Adult↗

PubMed2002

Learning-induced multiple synapse formation in rat cerebellar cortex.

Strengthening of synaptic connections has been proposed to underlie information storage in the brain, and experience-dependent increases in synapse number have been observed. However, the effect of these new synapses on the specific connectivity, and thus function, of a given brain area remains largely unknown. We report here that motor learning specifically induces the formation of multiple synapses--two post-synaptic contacts at a single pre-synaptic varicosity--in the cerebellum. Rats undergoing motor learning had more multiple synapses (two Purkinje cell spines contacting a given parallel fiber varicosity) per Purkinje cell than did active or inactive controls. The formation of multiple synapses provides an additional connection between a given parallel fiber and Purkinje cell, thereby enhancing particular pathways, and may constitute a fundamental mechanism of neural encoding.

Animals↗

PubMed2002

Switching languages, switching palabras (words): an electrophysiological study of code switching.

Switching languages has often been associated with a processing cost. In this study, the authors used event-related potentials to compare switches between two languages with within-language lexical switches as bilinguals read for comprehension. Stimuli included English sentences and idioms ending either with the expected English words, their Spanish translations (code switches), or English synonyms (lexical switches). As expected, lexical switches specifically enhanced the N400 response in both context types. Code switches, by contrast, elicited an increased negativity over left fronto-central sites in the regular nonidiomatic sentences (250-450 ms) and a large posterior positivity (450-850 ms) in both context types. In addition, both lexical and code switches elicited a late frontal positivity (650-850 ms) relative to expected completions, especially in idioms. Analysis of the individual response patterns showed correlations with vocabulary skills in English and in Spanish. Overall, the electrophysiological data suggest that for some speakers in some contexts, the processing of a code switch may actually be less costly than the processing of an unexpected within-language item.

Adolescent↗

PubMed2002

Picture the difference: electrophysiological investigations of picture processing in the two cerebral hemispheres.

The nature of semantic memory and the role of the two cerebral hemispheres in meaning processing were examined using event-related brain potentials (ERPs) elicited by pictures in sentences. Participants read sentence pairs ending with the lateralized presentation of three target types: (1) expected pictures, (2) unexpected pictures from the expected semantic category, and (3) unexpected pictures from an unexpected category. ERPs to contextually unexpected pictures were more negative 350-500ms (larger N400s) than those to expected pictures in both visual fields. However, while N400s to the two types of unexpected items did not differ with left visual field presentations, they were smaller to the unexpected items from the expected category with right visual field presentations. This pattern, previously observed to words [Brain Language 62 (1998) 149], suggests general differences in how the two hemispheres use context on-line. Other aspects of the N400 response-and effects on earlier ERP components-reveal differences between pictures and words, suggesting that semantic memory access is not modality-independent. The P2 component varied with ending type for right but not left visual field presentations, suggesting that the left hemisphere may use contextual information to prepare for the visual analysis of upcoming stimuli. Furthermore, there was clear evidence for an earlier negativity ("N300"), which varied with ending type but, unlike the N400, was unaffected by visual field of presentation. Overall, the results support our hypothesis that the left hemisphere actively uses top-down information to preactivate perceptual and semantic features of upcoming stimuli, while the right hemisphere adopts a "wait and see" integrative approach.

Adolescent↗

PubMed2002

The impact of semantic memory organization and sentence context information on spoken language processing by younger and older adults: an ERP study.

To examine changes in semantic memory organization and use during aging, we recorded event-related potentials as younger and older adults listened to sentences ending with the expected word, an unexpected word from the same semantic category, or an unexpected word from a different category. Half of the contexts were highly constraining. In both groups, expected words elicited less negativity 300-500 ms (N400) than unexpected ones, and unexpected words elicited smaller N400s when these were categorically related. Whereas younger adults showed the greatest N400 reduction to unexpected but related words in high constraint contexts, older adults showed the opposite tendency. Thus, unlike younger adults, older adults as a group do not seem to be using context predictively. Older adults with higher verbal fluency and larger vocabularies, however, showed the younger response pattern, suggesting resource availability may offset certain age-related changes.

Adolescent↗