Neurocognitive bases of learning and consolidation for spoken and written language.

Sunday, October 02nd,   2011 [09:30 - 11:10]

SY_23. Neurocognitive bases of learning and consolidation for spoken and written language

Pugh, K. M. ^{1, 2, 3} & Rueckl, J. G. ^{1, 2}

1 Haskins Laboratories
2 University of Connecticut
3 Yale University

Attempts to identify the mechanisms underlying reading disabilities have revealed the need to understand the neurobiological and cognitive bases of language learning abilities more generally. The current symposium brings together experts in cognitive studies of spoken and printed word learning, multi-modal neuroimaging, computational modeling, and the neurobiology of general learning and consolidation. Each presentation focuses on novel language learning from these distinctive but potentially linked perspectives, with the general aim of identification of critical next steps in understanding neuroplasticity as it applies to speech and reading. We will consider new research on spoken word learning, print learning, learning difficulties and brain pathways, computational modeling, and the neural mechanisms associated with consolidation in procedural and declarative learning as we seek general principles that link neural pathways to typical and atypical language learning, and, ultimately, differences within and across these populations

 

TALKS

SY_23.1 - A motor perspective on language 'rule' learning with a critical look at 'critical periods' in skill acquisition

Karni , A.

Department of Human Biology & the Edmund J Safra Brain Research Center for the Study of Learning & Learning Disabilities, University of Haifa

The language superiority of children has been ascribed to a childhood advantage in the acquisition of skills (procedural memory) specifically in language domains. It is commonly assumed that while declarative ("what", explicit) memory undergoes maturation, procedural ("how-to", implicit) memory, is well established at an early age and is superior to that of adults. This has been tied to a widely accepted notion of "critical periods" as restricted periods of brain malleability (plasticity) during childhood. Nevertheless, there is increasing evidence showing that adults are highly effective in acquiring and consolidating perceptual and motor skills, and in some controlled conditions are better learners than children. A recent study (Ferman & Karni, PLoSone, 2010) suggests a clear advantage for adults in a laboratory language task, both in learning implicit task aspects and in the long-term retention of the skill; findings that support the notion of age-dependent maturation in the establishment of both declarative and procedural memory. In line with recent studies of motor skill learning, it is conjectured that the adult brain may become more selective in the making of long-term skill memory, rather than lose its potential to undergo experience-driven plasticity. CNS maturation may affect the time constants of memory consolidation processes, which in turn change the conditions and constraints under which procedural memory is consolidated before and after puberty. The potential for, and effectiveness of, skill acquisition per-se may remain unchanged or even increase. Under some learning conditions adults can effectively express their language skill acquisition potential.

SY_23.2 - Neuroimaging studies of reading and language development: An update on recent findings

Pugh, K. R.

Haskins Laboratories and the University of Connecticut

Reading disability (RD) has been characterized as a brain-based difficulty in acquiring fluent reading skill associated with problems in operating on the phonological structures of language. The claim of brain-basis is supported by a growing literature rife with reports of various sorts of anomalies in brain structure and function in RD. We will present data showing that relative to typically developing (TD) readers, RD children and adolescents fail to coherently activate left hemisphere (LH) occipitotemporal (OT) and temporoparietal (TP) regions during reading. Additionally, structural neuroimaging studies reveal group differences in both grey matter density and white matter connectivity in key LH regions. Brain/behavior analyses have indicated that the development of reading fluency in children is strongly associated with the development of a well-integrated left hemisphere posterior reading system. With regard to plasticity and learning, intervention studies have examined the influence of intensive phonological remediation in at-risk children and adolescents, revealing substantial gains in both reading scores and development of these posterior LH reading systems for readers afforded this treatment. Recent extensions of learning studies with older RD readers continue to suggest a high degree of plasticity in this age-range. Implications for theory and practice will be discussed. New extensions focus on individual differences in bilingual populations and will be discussed

SY_23.3 - The impact of prior knowledge on word learning

Rueckl, J. G.

Haskins Laboratories and the University of Connecticut

Studies of novel word learning in adult readers have demonstrated the importance of how novel words are processed during the learning stage, how learning is assessed, and when it is assessed. In some of our recent research we have focused on another factor: the role of the knowledge that that the learner brings to the learning situation. Specifically, we’ve asked whether learning a new word depends on its similarity to familiar words. We’ve operationalized ‘similarity’ at both the lexical and sublexical levels. (Lexical: orthographic and phonological neighborhood size; sublexical: the sequential probability of the constituent letters or phonemes). In our central experiment we contrasted the learning of ‘wordy’ and ‘less wordy’ novel words, intentionally confounding orthographic and phonological similarity to maximize the difference between conditions. Not surprisingly, we found that more wordy novel words were learned faster at the form level. More interestingly, we also found that the meanings associated with more wordy forms were learned faster too. This pattern is readily accommodated by the lexical quality hypothesis (Perfetti & Hart, 2001) and, at a more mechanistic level, the triangle model (Harm & Seidenberg, 2004). Ongoing experiments are aimed towards disentangling orthographic and phonological contributions to this effect and isolating its neural bases.

SY_23.4 - A complementary systems account of spoken word learning: fMRI and MEG evidence

Davis, M. H.

Medical Research Council, Cognition and Brain Sciences Unit, Cambridge, UK.

This presentation provides neuroimaging evidence in support of two neural processes in initial learning and later consolidation of novel spoken words. This proposal builds on neuro-computational accounts of lexical processing and complementary learning systems (CLS) models of memory. As in other domains, the CLS account suggests a division of labour between medial temporal systems responsible for rapid encoding of novel items and the contexts in which they occur, followed by slower, offline integration of novel and existing items in cortical representations. A review and meta-analysis of recent fMRI studies of spoken word learning shows that: (1) successful initial acquisition is associated with the magnitude of hippocampal activity, (2) rapid changes in cortical responses to pseudowords following familiarization are best explained as task-specific repetition priming, or consequences of hippocampal encoding, rather than new, word-like cortical representations, (3) cortical responses to pseudowords (e.g. in the superior temporal gyrus) only become word-like in test sessions that follow a period of overnight consolidation. A recent MEG study of spoken word learning and consolidation (with Pierre Gagnepain and Rik Henson) provides additional evidence concerning the specific cortical computations that are consolidated overnight. We assessed the time-course and location of evoked responses to trained novel words (cathedruke), real word (cathedral) and non-word neighbours (cathedron) at different stages during learning and consolidation. Consolidation-induced differences in evoked responses to learned items are: (1) time-locked to the phonetic deviation point between these triples, (2) localized to the same cortical regions that show consolidation effects in fMRI, and (3) simulated by changes in segment prediction error rather than lexical competition in neural network inspired models. These findings suggest an important role for consolidated cortical representations in supporting efficient recognition of newly learned words and provide initial ideas concerning the integration of behavioural, computational and neural evidence in spoken word learning.

SY_23.5 - Individual differences in learning artificial lexicons

Magnuson, J. S.

University of Connecticut and Haskins Laboratories

Among the most important tools in the psycholinguist\'s kit are corpora, which allow us to estimate individual language experience from large-scale averages from many sources. Corpus estimates are the basis for crucial theoretical constructs such as frequency and neighborhood density, and analogous dimensions of computational models. However, there are obvious challenges in applying such estimates to understanding variation in language ability. For example, findings that children with Specific Language Impairment do not show typical effects of phonological neighborhood density in spoken word recognition may indicate theoretically interesting differences in lexical organization, but they might also reflect simple differences in vocabulary -- it would seem that this issue is unresolvable without comprehensively documenting each child\'s lexicon. An alternative is to use \'human models\' that put participants on maximally equal footing, as with artificial lexicon learning tasks. I discuss recent work my colleagues and I have carried out using this approach, and complementary computational and statistical modeling of the dynamics of lexical processing. In particular, I will focus on recent results with a rigorously assessed group of low-literacy adults and discuss the potential for individual differences in spoken language comprehension to illuminate difficulties with reading.