Low-constraint Contexts Research Articles

A Tale of Two Positivities and the N400: Distinct Neural Signatures Are Evoked by Confirmed and Violated Predictions at Different Levels of Representation.

It has been proposed that hierarchical prediction is a fundamental computational principle underlying neurocognitive processing. Here, we ask whether the brain engages distinct neurocognitive mechanisms in response to inputs that fulfill versus violate strong predictions at different levels of representation during language comprehension. Participants read three-sentence scenarios in which the third sentence constrained for a broad event structure, for example, {Agent caution animate-Patient}. High constraint contexts additionally constrained for a specific event/lexical item, for example, a two-sentence context about a beach, lifeguards, and sharks constrained for the event, {Lifeguards cautioned Swimmers}, and the specific lexical item swimmers. Low constraint contexts did not constrain for any specific event/lexical item. We measured ERPs on critical nouns that fulfilled and/or violated each of these constraints. We found clear, dissociable effects to fulfilled semantic predictions (a reduced N400), to event/lexical prediction violations (an increased late frontal positivity), and to event structure/animacy prediction violations (an increased late posterior positivity/P600). We argue that the late frontal positivity reflects a large change in activity associated with successfully updating the comprehender's current situation model with new unpredicted information. We suggest that the late posterior positivity/P600 is triggered when the comprehender detects a conflict between the input and her model of the communicator and communicative environment. This leads to an initial failure to incorporate the unpredicted input into the situation model, which may be followed by second-pass attempts to make sense of the discourse through reanalysis, repair, or reinterpretation. Together, these findings provide strong evidence that confirmed and violated predictions at different levels of representation manifest as distinct spatiotemporal neural signatures.

Getting it right: Word learning across the hemispheres

The brain is able to acquire information about an unknown word's meaning from a highly constraining sentence context with minimal exposure. In this study, we investigate the potential contributions of the cerebral hemispheres to this ability. Undergraduates first read weakly or strongly constraining sentences completed by known or unknown (novel) words. Subsequently, their knowledge of the previously exposed words was assessed via a lexical decision task in which each word served as visual primes for lateralized target words that varied in their semantic relationship to the primes (unrelated, identical or synonymous). As expected, smaller N400 amplitudes were seen for target words preceded by identical (vs. unrelated) known word primes, regardless of visual field of presentation. When Unknown words served as primes, N400 reductions to synonymous target words were observed only if the prime had appeared under High sentential constraint; targets appearing in the LVF/RH elicited a small N400 effect and modulation of a subsequent late positivity whereas those in the RVF/LH elicited modulation on the late positivity only. Unknown words initially seen in Low constraint contexts showed priming effects only in a late positivity and only in the RVF/LH. Strength of contextual constraint clearly seems to impact the hemispheres’ rapid acquisition of novel word meanings. N400 modulation for novel words under strong contextual constraint in the LVH/RH suggests that fast-mapped lexical representations may initially activate meanings that are weakly, distantly, associatively or thematically-related. More extensive and bilateral semantic processing seems to occur at longer processing latencies (post N400).

Frequency drives lexical access in reading but not in speaking: the frequency-lag hypothesis.

To contrast mechanisms of lexical access in production versus comprehension we compared the effects of word frequency (high, low), context (none, low constraint, high constraint), and level of English proficiency (monolingual, Spanish-English bilingual, Dutch-English bilingual) on picture naming, lexical decision, and eye fixation times. Semantic constraint effects were larger in production than in reading. Frequency effects were larger in production than in reading without constraining context but larger in reading than in production with constraining context. Bilingual disadvantages were modulated by frequency in production but not in eye fixation times, were not smaller in low-constraint contexts, and were reduced by high-constraint contexts only in production and only at the lowest level of English proficiency. These results challenge existing accounts of bilingual disadvantages and reveal fundamentally different processes during lexical access across modalities, entailing a primarily semantically driven search in production but a frequency-driven search in comprehension. The apparently more interactive process in production than comprehension could simply reflect a greater number of frequency-sensitive processing stages in production.

Professional knowledge in action: How experienced ESOL teachers respond to feedback from learners within syllabus and contextual constraints

It is now generally acknowledged that teachers are curriculum makers and adapters rather than mere transmitters of written plans and prescriptions. This study reports on the curriculum making practices of three capable, experienced teachers of adult ESOL in high, medium and low constraint contexts over the duration of one complete course for each teacher. Through iterative interviewing and analysis of curriculum documents, it details the tentativeness and sketchiness of teachers’ written planning (particularly in the pre-course phase). It goes on to describe how teachers’ plans were constantly revised in response to the powerful influence of learner feedback, received through explicit negotiations and responses as well as their own perceptions about the way the instructional curriculum was being received. Teachers in all three types of instructional context responded to learners’ developmental and affective needs in a variety of ways, and to the fullest extent possible within the constraints of their teaching situations and their own theories of best practice. Study findings indicate the importance of assisting novice teachers to acquire awareness and abilities in this area as a goal for second language teacher education. Areas of research are suggested as possible further contributions to the development of an epistemology of practice for TESOL.

Lexical Quality in the Brain: ERP Evidence for Robust Word Learning From Context

We examined event-related potentials (ERPs) before and after word learning, using training contexts that differed in their level of contextual support for meaning acquisition. Novel words appeared either in contexts that were semantically constraining, providing strong cues to meaning, or in contexts that were weakly constraining, that is, uninformative. After each sentence, participants were shown the word in isolation and were asked to generate a close synonym. Immediately after training, words trained in high-constraint contexts elicited a smaller left temporal negativity (N300FT7) compared with words trained in low-constraint contexts, and both types of trained words elicited a stronger medial frontal negativity (N350Fz) relative to familiar words. Two days after training the N300FT7 disappeared and was replaced by a later, left parietal (P600Pz) effect. To examine robust learning, we administered a semantic priming test two days after training. Familiar words and words trained in high-constraint contexts elicited strong N400 effects. By contrast, words trained in low-constraint contexts elicited a weak N400 effect, and novel (untrained rare) words elicited no semantic priming. These findings suggest that supportive contexts and the use of an active meaning-generation task may lead to robust word learning. The effects of this training can be observed as changes in an early left frontal component, as well as the classical N400 effect. We discuss implications for theories of “partial” semantic knowledge and for robust word learning and instruction.

On the functional nature of the N400: Contrasting effects related to visual word recognition and contextual semantic integration

Electrical scalp recordings revealed the brain's sensitivity to both lexical properties of words and their contextual fit with a previous sentence context around 400 ms after word presentation. The so-called N400 component has been suggested to reflect the cost either of target word recognition or of a postlexical process for integrating word meaning into a context. In a sentence comprehension study, we manipulated the potential interference exerted in visual word recognition by target words' orthographic neighbors and the semantic constraints induced by the context in one and the same experiment. Neighbor frequency modulated the N400 only in low-constraint contexts; in high-constraint contexts the largely suppressed N400 did not show this neighbor interference effect. Furthermore, the earlier onset of the ERP effect (about 100 ms) induced by the contextual manipulation compared to the neighbor manipulation suggests distinct neurocognitive processes affecting the N400 component in an interactive manner.

The influence of sentence constraint on the scope of facilitation for upcoming words

Four experiments were performed to examine the influence of sentence constraint and cue validity on the processing of expected and unexpected congruous sentence completions. Experiment 1 showed that high constraint sentences aided lexical decisions only for expected completions whereas low constraint contexts demonstrated a broader, although weaker context effect. Increasing the proportion of expected completions in Experiment 2 caused inhibition of lexical decisions for unexpected words appearing in high constraint sentences. A similar manipulation for low constraint sentences in Experiment 3 did not show such an effect for unexpected completions. The addition of an incongruous completion condition in Experiment 4 had a negligible effect on the relative proportions of facilitation found in every condition. These findings are consistent with the view that more featural restrictions are generated as sentence constraint and cue validity increase.