Word Learning in the Developing Brain : ERP Dynamics of Learning Word-Object Associations

This dissertation investigated electrophysiological measures of individual differences in toddlers’ ability to learn novel object labels and process familiar object words and their referents. The studies measured both visual and auditory event-related potentials (ERPs) in response to pictures of objects and words in a longitudinal sample of 20- to 24-month-olds, an age of dynamic vocabulary development. These ERP measures were related to the children’s productive vocabulary size as well as behavioral measures of word comprehension and object recognition.Study I aimed to test children’s ability to map familiar words to versions of their referents displaying reduced visual information (only overall shape or isolated parts), and whether this ability correlated with vocabulary size. Children with larger vocabularies showed a stronger N400 incongruity effect in response to words paired with correct vs. incorrect shape referents specifically, and the N400 effect in the shape condition also correlated with the children’s ability to overtly identify objects from their overall shape in a behavioral test. These results are discussed in relation to previous research demonstrating the emergence of a shape bias in children’s Word extension, as well as improvements in object shape recognition, during the second year of life.Study II investigated individual differences in novel word-object mapping andchanges with age in this ability. The overall sample showed ERP evidence of novel word learning (an N400 semantic incongruity effect) after five consistent word-object pairings at 24 months but not at 20 months. Children with large vocabularies demonstrated the same linear attenuation of N400 amplitude during novel word repetition as is commonly seen in adults, while children with smaller vocabularies did not show such attenuation until the end of the learning phase.Study III focused on the 20 month data set and explored how visual ERPs weremodulated as object-word pairs were presented repeatedly, and how these measures of visual object processing related to successful fast mapping of the novel words to the objects. A larger attenuation of the Nc component (associated with attention) predicted successful word learning, measured as a larger N400 incongruity effect to the novel words after training. Furthermore, better initial recognition of familiar objects correlated with a stronger N400 effect to the words for those objects. The results present novel evidence for a link between efficient visual processing of objects and word learning ability.Taken together, these findings demonstrate that the rapid vocabulary growth and striking individual differences in productive vocabulary development seen during children’s second year are linked to the dynamics of specific brain mechanisms involved in semantic processing of words and their referents

The electrophysiological correlates of word pre-activation during associative word learning

Human beings continuously make use of learned associations to generate predictions about future occurrences in the environment. Such memory-related predictive processes provide a scaffold for learning in that mental rep-resentations of foreseeable events can be adjusted or strengthened based on a specific outcome. Learning the meaning of novel words through picture-word associations constitutes a prime example of associative learning because pictures preceding words can trigger word prediction through the pre-activation of the related mne-monic representations. In the present electroencephalography (EEG) study, we used event-related potentials (ERPs) to compare neural indices of word pre-activation between a word learning condition with maximal prediction likelihood and a non-learning control condition with low prediction. Results revealed that prediction -related N400 amplitudes in response to pictures decreased over time at central electrodes as a function of word learning, whereas late positive component (LPC) amplitudes increased. Notably, N400 but not LPC changes were also predictive of word learning performance, suggesting that the N400 component constitutes a sensitive marker of word pre-activation during associative word learning

Neuronal glucose transporter isoform 3 deficient mice demonstrate features of autism spectrum disorders.

Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans

The Missing Link between Morphemic Assemblies and Behavioral Responses:a Bayesian Information-Theoretical model of lexical processing

We present the Bayesian Information-Theoretical (BIT) model of lexical processing: A mathematical model illustrating a novel approach to the modelling of language processes. The model shows how a neurophysiological theory of lexical processing relying on Hebbian association and neural assemblies can directly account for a variety of effects previously observed in behavioural experiments. We develop two information-theoretical measures of the distribution of usages of a morpheme or word, and use them to predict responses in three visual lexical decision datasets investigating inflectional morphology and polysemy. Our model offers a neurophysiological basis for the effects of morpho-semantic neighbourhoods. These results demonstrate how distributed patterns of activation naturally result in the arisal of symbolic structures. We conclude by arguing that the modelling framework exemplified here, is a powerful tool for integrating behavioural and neurophysiological results

Aging affects steaks more than knives: Evidence that the processing of words related to motor skills is relatively spared in aging

Lexical-processing declines are a hallmark of aging. However, the extent of these declines may vary as a function of different factors. Motivated by findings from neurodegenerative diseases and healthy aging, we tested whether ‘motor-relatedness’ (the degree to which words are associated with particular human body movements) might moderate such declines. We investigated this question by examining data from three experiments. The experiments were carried out in different languages (Dutch, German, English) using different tasks (lexical decision, picture naming), and probed verbs and nouns, in all cases controlling for potentially confounding variables (e.g., frequency, age-of-acquisition, imageability). Whereas ‘non-motor words’ (e.g., steak) showed age-related performance decreases in all three experiments, ‘motor words’ (e.g., knife) yielded either smaller decreases (in one experiment) or no decreases (in two experiments). The findings suggest that motor-relatedness can attenuate or even prevent age-related lexical declines, perhaps due to the relative sparing of neural circuitry underlying such words

The Inhuman Overhang: On Differential Heterogenesis and Multi-Scalar Modeling

As a philosophical paradigm, differential heterogenesis offers us a novel descriptive vantage with which to inscribe Deleuze’s virtuality within the terrain of “differential becoming,” conjugating “pure saliences” so as to parse economies, microhistories, insurgencies, and epistemological evolutionary processes that can be conceived of independently from their representational form. Unlike Gestalt theory’s oppositional constructions, the advantage of this aperture is that it posits a dynamic context to both media and its analysis, rendering them functionally tractable and set in relation to other objects, rather than as sedentary identities. Surveying the genealogy of differential heterogenesis with particular interest in the legacy of Lautman’s dialectic, I make the case for a reading of the Deleuzean virtual that departs from an event-oriented approach, galvanizing Sarti and Citti’s dynamic a priori vis-à-vis Deleuze’s philosophy of difference. Specifically, I posit differential heterogenesis as frame with which to examine our contemporaneous epistemic shift as it relates to multi-scalar computational modeling while paying particular attention to neuro-inferential modes of inductive learning and homologous cognitive architecture. Carving a bricolage between Mark Wilson’s work on the “greediness of scales” and Deleuze’s “scales of reality”, this project threads between static ecologies and active externalism vis-à-vis endocentric frames of reference and syntactical scaffolding

Salience network and parahippocampal dopamine dysfunction in memory-impaired Parkinson disease

Objective: Patients with Parkinson disease (PD) and mild cognitive impairment (MCI) are vulnerable to dementia and frequently experience memory deficits. This could be the result of dopamine dysfunction in corticostriatal networks (salience, central executive networks, and striatum) and/or the medial temporal lobe. Our aim was to investigate whether dopamine dysfunction in these regions contributes to memory impairment in PD. Methods: We used positron emission tomography imaging to compare D2 receptor availability in the cortex and striatal (limbic and associative) dopamine neuron integrity in 4 groups: memory‐impaired PD (amnestic MCI; n = 9), PD with nonamnestic MCI (n = 10), PD without MCI (n = 11), and healthy controls (n = 14). Subjects were administered a full neuropsychological test battery for cognitive performance. Results: Memory‐impaired patients demonstrated more significant reductions in D2 receptor binding in the salience network (insular cortex and anterior cingulate cortex [ACC] and the right parahippocampal gyrus [PHG]) compared to healthy controls and patients with no MCI. They also presented reductions in the right insula and right ACC compared to nonamnestic MCI patients. D2 levels were correlated with memory performance in the right PHG and left insula of amnestic patients and with executive performance in the bilateral insula and left ACC of all MCI patients. Associative striatal dopamine denervation was significant in all PD patients. Interpretation: Dopaminergic differences in the salience network and the medial temporal lobe contribute to memory impairment in PD. Furthermore, these findings indicate the vulnerability of the salience network in PD and its potential role in memory and executive dysfunction

The Spacing Effect in Remote Information-Integration Category Learning

The present study examined whether the temporal distribution of procedural category learning experiences would impact learning outcomes. Participants completed the remote category learning study on a smartphone in one of two learning conditions: Massed (control) or distributed. Consistent with expectations, distributed learners reached higher accuracy levels. This effect disappeared after accounting for reaction time differences, suggesting that it was driven by attentional mechanisms. Distribution may have made participants more likely discover the optimal categorization strategy and more robust to sensory habituation. Counter to previous findings, participants favored distributed learning. These results suggest that adult category learning is facilitated by temporal spacing. Future work may further explore the effects of temporal and contextual distinctiveness of learning experiences on category learning outcomes