Rebecca L. Gomez - US grants

DESCRIPTION: Although recent research shows that infants are sensitive to structural regularities in linguistic input, little is known about the degree to which these sensitivities reflect general-purpose mechanisms (e.g., association) versus innate language-specific expectations about the kinds of structure that will occur. The objective of the proposed research is to determine the nature of some of the learning mechanisms available to infants. This research will address questions pertaining to: 1) the architecture of infant language learning mechanisms; 2) kinds of input learned; and 3) developmental sequencing of such learning. Learning is assessed by exposing infants to auditory strings generated by an artificial grammar. Infants participate in training and testing phases using the head-turn preference procedure. After initial exposure to the grammar, infants are tested to see if they can discriminate new grammatical strings from ungrammatical ones. In Year 1, 9- and 12- month old infants will be trained on finite-state grammar, then tested to see if their discriminations are due to an associative learning mechanism or rules involving salient cues in linguistic input. Year 2 investigates the role played by grammatical morphemes in learning phrase categories in a phrase structure grammar.

DESCRIPTION: The generative power of human language, our ability to create an infinite variety of new words, phrases and sentences, depend critically on our ability to form implicit linguistic categories, both phonological and syntactic. For example, an adult having heard the sentence "A snerg zugged" is immediately capable of generating "is the snerg zugging?" without benefit of understanding the semantic content of either utterance. Creating the new utterance depends on implicitly treating "snerg" and "zug" as members of different lexical categories (i.e., noun and verb). The ability to group together into categories superficially distinct acoustic, lexical and phrasal tokens is key to language development in both symbolic and connectionist approaches (e.g., Elman, 1990; Guenther and Gjaja, 1996; Maye and Gerken, 1999; Pinker, 194; Valian and Coulson, 1988). Nevertheless, our understanding of the nature of these categories and how we form them is murky. Focusing, as this project will, on lexical categories, such as noun and verb, there are several questions that recur in the literature. These questions cluster along two dimensions: First, can abstract linguistic categories be induced from the input, or must the learner be born with some expectations about the category structure? Second, is the distribution of words across sentences sufficient for determining their category, or is referential information required in category formation? The proposed research locates itself at the intersection of these two dimensions. The goal of this research is to examine the limits on distributionally based category formation in an artificial language by adults and 12- to 18-month-old infants. The studies all ask the question: Under what conditions will learners generalize between training stimuli and test stimuli on the basis of distributional evidence?

The extent to which memory preserves an accurate record of the past has been debated for over a century. The veridical memory view assumes that once memory consolidation is complete, memory is stable and no longer subject to change. Furthermore, the neurobiological processes responsible for consolidation involve strengthening, but not modification of a memory. Others have argued that memories are not fixed, but instead are transformed over time as a function of experience. Mounting evidence suggests that when memories are reactivated they become labile and open to change. Retrieval can reinforce the reactivated memory, or update it through the incorporation of new information. Such transformed memories then undergo a time-dependent re-consolidation process. Although the consolidation account, emphasizing strengthening and stabilization, was the de facto paradigm of research on memory dynamics in both psychology and neuroscience for many years, there is now increasing evidence that stable memory is the exception, not the rule. Until recently we have lacked experimental approaches to systematically address memory malleability, hence the mechanisms controlling memory updating remain obscure. Furthermore, despite the extensive literature on memory reconsolidation in animals, studies in humans are rare. Drs. Lynn Nadel, Rebecca Gomez, and Almut Hupbach at the University of Arizona have developed a research paradigm for investigating reconsolidation in episodic memory, a form of memory that allows for the conscious recollection of events. This research raises important questions having to do with whether updated memories are transient or long lasting and whether the effects occur only for new memories or for old memories as well. There is also the question of what factors trigger memory reactivation, whether these factors are affected by the strength of the original memory, whether the strength of these reminders diminishes over time, and whether implicit reminders differ from explicit ones in the extent to which they affect updating of an existing memory. With support from the National Science Foundation, Drs. Nadel, Gomez, and Hupbach will address these questions. They will conduct a series of experiments in which human volunteers will learn a set of objects and two days later will be reminded of the first session or not, then immediately afterwards will learn a second set of objects. After an additional two days, participants will be asked to recall the first set only. The extent to which reminded participants recall objects from the second set when trying to recall the first set, as compared to participants who are not reminded, is an index of memory reactivation and the subsequent reconsolidation effect.

Reconsolidation, and the underlying instability it reveals, demonstrates the essential transformative nature of memory systems and could help us understand a variety of memory malleability phenomena studied broadly in human cognition, as well as the updating of prior knowledge more generally. The work will explore conditions under which memory reconsolidation is observed in human episodic memory and would support the view that memories are dynamic, not fixed, and that they can be changed as a function of subsequent experience. The work will further show how such updating is affected by the age of a memory, by the nature of the reactivating event, and by the way in which memory itself is accessed at some subsequent time. Such details will begin the process of defining the critical determinants of human episodic memory dynamics. Knowledge about how memory is changed over time, and by experience, has profound implications for everyday life, influencing assumptions made within legal and clinical settings about what counts as normal memory. Understanding memory dynamics is also important for identifying the conditions affecting the updating of prior knowledge in learning and cognitive development, both in early childhood and across the lifespan. Understanding such conditions could have a profound effect on theories of cognitive change, on understanding when normal change goes awry and could also have implications for learning in educational practice.

Recent work in language acquisition and cognitive development shows remarkable learning abilities in infancy. Much of the theoretical development in these fields is based on effects measured immediately after a learning experience, however, sleep is instrumental in transforming specific details of what is learned to a more abstract memory (Gomez, Bootzin, & Nadel, 2006; Hupbach, Gomez, Bootzin, & Nadel, 2009). The ability to abstract away from the specific details of a learning experience is crucial for infants who must be able to summarize and apply key aspects of a learning experience to novel scenarios, much like being able to abstract the block letter "A" to cursive. If memories are too specific infants will not be able to connect prior learning to new scenarios with slightly different information. A more abstract memory can more easily be applied to a wider range of information. A first project will investigate the means by which sleep leads to abstraction. A second project investigates how sleep-dependent memories are connected across time in an attempt to understand how knowledge is amassed over multiple learning experiences. Polysomnographic recording will provide information about how sleep-dependent memories are consolidated in the developing infant brain.

The proposed work is unique in bridging three areas of research: language acquisition, memory, and sleep. It has potential to be transformative to the degree that it 1) impacts language learning theories (to date based on results obtained immediately after a learning experience, not taking the changes associated with intrinsic sleep and memory processes into account); 2) the way empirical learning research is conducted (to scale up to the constraints of real-world learning researchers will need to begin to measure time-dependent effects); and 3) informs us about the relationship between phases of sleep and memory formation in the developing infant brain, dynamics that could have a profound effect on theories of language and memory change, on understanding when normal change goes awry, and for learning in educational practice. In addition to the practical benefits for society, the proposed work has benefits closer to home with training of undergraduate students a significant part of the grant. These students will gain extensive one-on-one experience in conducting scientific research that will prepare them to be highly competitive candidates for graduate programs, and ultimately, for careers in teaching and science.

DESCRIPTION (provided by applicant): Recent work on early learning shows remarkable abilities in infancy with important implications for infants learning about their visual world (Fisr & Aslin, 2002) and about language (Gomez, 2008; Saffran, Aslin, & Newport, 1996). Much of the theoretical development involving early learning is based on effects measured immediately after a learning experience, however, recent work in the sleep literature shows that memories can be transformed with sleep (Diekelmann & Born, 2010; Walker & Stickgold, 2006). In the only work investigating the effects of sleep on infant learning, Gomez and colleagues have shown that sleep within a short window after familiarization appears to be necessary for retention of learning, even at 15 months of age when many infants are napping just once a day (Gomez, Bootzin, & Nadel, 2006; Hupbach, Gomez, Bootzin, & Nadel, 2009). The proposed work investigates the role of sleep in much younger 6 month olds on a foundational form of learning during a period when sleep architecture is in flux between neonatal and infant sleep, probing the extent to which memory consolidation is affected by immediate vs. delayed sleep over 2, 4, and 24 hours. This will be the first study of its kind to directly test the effects of seep on memory consolidation. It will also be the first to document infant sleep architecture in an attempt to relate different sleep variables that have been associated with memory consolidation in adults to memory consolidation in infants. The results will inform us about the effects of sleep on early memory consolidation, a question that has not yet been addressed in the literature. In addressing the problem of how learning is affected by sleep-dependent memory processes, these studies will represent an important first step in scaling up learning research to a real-worl constraint, the fact that knowledge is consolidated over sleep and over time. PUBLIC HEALTH RELEVANCE: Poor sleep is surprisingly prevalent in young children with just one disorder, sleep-disordered breathing, affecting 1-3% of all children (Montgomery- Downs, 2006) and affecting certain developmental populations such as children with Down Syndrome. Given the relationship between poor sleep and poor cognitive outcomes, the proposed work, in establishing baselines for sleep-dependent consolidation in typically developing 6 month olds will be important for understanding memory development in populations that are compromised. This is all the more urgent given that children with poor sleep score lower on measures of receptive vocabulary and on nonverbal intelligence and the fact that such deficits persist even in children who recover normal sleep by 3 years of age (Touchette, Petit, & Seguin, 2007). To the extent that later successes in learning build on a strong foundation of prior successes, a clearer understanding of the importance of sleep for forming that foundation is an important public health mission.