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It is well established in developmental science that 14-month-old infants have significant difficulty associating pairs of objects with pairs of words that differ by a single phoneme (i.e., minimal pairs). This study used a traditional switch procedure in two experimental conditions (i.e., no face versus face with shifting gaze) to habituate infants with objects and minimal pair labels. Additionally, infants participated in a joint attention task and parents completed questionnaires related to family demographics and infant health and development, to compare to switch task performance. It was expected that infants' difficulty with minimal pair associative learning would be replicated in the no face condition. It was also predicted that the addition of a female face and the cues it could provide would abate the challenge that this task typically presents. As a group, infants' performances in the two conditions were not significantly different from each other and were not significantly different from chance. Analyses explored the relations between switch performance, joint attention task performance and questionnaire data, resulting in a significant correlation between performance in the face condition of the switch task and number of ear infections (r = .62, p < .05). Taken together, the addition of a female face with shifting gaze to a challenging word learning task does not sufficiently attenuate the cognitive load created by the task. The implications of these results are discussed further. / Master of Science

During word learning, many words are associated with many meanings to build a lexicon. A model by McMurray et al. (2012) suggests that vocabulary acquisition may not only depend on building correct associations, but also pruning incorrect ones. Additional evidence for the importance of pruning comes from a word learning analog in pigeons, where the opportunity for pruning incorrect associations between objects and symbols was manipulated during training (Roembke et al., 2016). To investigate pruning in humans, we conducted six supervised word learning experiments. Participants were first trained to link two objects to each word, and subsequently were tested how quickly these were pruned. Across experiments, association strength was measured by using either eye movements to to-be pruned objects, or a post-training accuracy assessment. Learners showed rapid—though potentially not complete—pruning of incorrect associations, but this depended on whether the symbols were auditory words, orthographic words or non-linguistic symbols. Thus, this dissertation provides first evidence that pruning is operative during word learning. We also examined how newly learned words compete against known words for recognition using eye-tracking and found that despite very high accuracy these words were not strong competitors.

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Research on word learning has focused on childrens ability to identify a target object when given the word form after a minimal number of exposures to novel word-object pairings. However, relatively little research has focused on childrens ability to retrieve the word form when given the target object. The exceptions involve asking children to recall and produce forms, and children typically perform near floor on these measures. In the current study, 3- to 5-year-old children were administered a novel test of word form that allowed for recognition memory and manual responses. Specifically, when asked to label a previously trained object, children were given three forms to choose from: the target, a minimally different form, and a maximally different form. Children demonstrated memory for word forms at three post-training delays: 10 mins (short-term), 23 days (long-term), and 6 months to 1 year (very long-term). However, children performed worse at the very long-term delay than the other time points, and the length of the very long-term delay was negatively related to performance. When in error, children were no more likely to select the minimally different form than the maximally different form at all time points. Overall, these results suggest that children remember word forms that are linked to objects over extended post-training intervals, but that their memory for the forms gradually decreases over time without further exposures. Furthermore, memory traces for word forms do not become less phonologically specific over time; rather children either identify the correct form, or they perform at chance.

The hippocampus plays a critical role in binding together information into an integrated memory, and memory for these arbitrary associations is important when learning new words. Recent studies have investigated a learning mechanism called fast mapping (FM), showing that rapid acquisition of novel arbitrary associations can be learned independent of the hippocampus. In the current study we examine word-learning across two conditions more and less likely to require information integration via the hippocampus in typically developing children and individuals with hippocampal dysfunction (e.g., Down syndrome). Individuals with Down syndrome (DS) manifest hippocampal dysfunction and display memory and learning difficulties, hence could potentially benefit from alternative learning strategies. The current study found no benefit of the FM condition in either group. Both groups performed similarly and above chance level across the two conditions and over a week's delay, but a delay by group interaction suggested that the typically developing children showed improvement across all conditions after 1 week whereas performance in DS stayed consistent. Given evidence for sleep deficits in DS we examined how sleep disturbance related to delayed word retention. Sleep efficiency did not appear to be driving maintenance in either group. Future studies investigating when an individual with DS sleeps after learning, could provide a better understanding of how sleep can influence the word learning process. Additionally, future studies in an older group of children can also provide information on when the hippocampus and sleep dependent learning may develop in childhood.

Previous natural observations have found a robust correlation between infants’ spontaneous gesture production and vocabulary development: the onset and frequency of infants’ pointing gestures are significantly correlated to their subsequent vocabulary size (Colonnesi, Stams, Koster, & Noom, 2010). The present study first examined the correlations between pointing and vocabulary size in an experimental setting, and then experimentally manipulated responses to pointing, to investigate the role of pointing in infants’ forming word-object associations. In the first experiment, we elicited 12- to 24-month old infants’ pointing gestures to 8 familiar and 8 novel objects. Their vocabulary was assessed by the MacArthur Communicative Development Inventory (MCDI): Words and Gestures. Results showed that 12-16 month old infants’ receptive vocabulary was positively correlated to infants’ spontaneous pointing. This correlation, however, was not significant in 19-24 month old infants. This experiment thus generalizes the previous naturalistic observation findings to an experimental setting, and shows a developmental change in the relation between pointing and receptive vocabulary. Together with prior studies, it suggests a possible positive social feedback loop of pointing and language skills in infants younger than 18 months old: the bigger vocabulary size infants have, the more likely they point, the more words they hear, and then the faster they develop their vocabulary. In the second experiment, we tested whether 16-month-old infants’ pointing gestures facilitate infants’ word learning in the moment. Infants were randomly assigned to one of three conditions: the experimenter labeled an unfamiliar object with a novel name 1) immediately after the infant pointed to it (the point contingent condition); 2) when the infant looked at it; or 3) at a schedule predetermined by a vocabulary-matched infant in the point contingent condition. After hearing the objects’ names, infants were presented with a word learning test. Results showed that infants successfully selected the correct referent above chance level only in the point contingent condition, and their performance was significantly better in the point contingent condition than the other two conditions. Therefore, only words that were provided contingently after pointing were learned. Taken together, these two studies further our understanding of the correlation between early gesture and vocabulary development and suggest that pointing plays a role in early word learning.

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In order to learn a new word, a young child must extricate the correct object from multiple possible items in front of them, make an initial association between the specific word-form and the particular referent, robustly link the new word and referent and integrate the new word into their lexicon. Recent research suggests processes that focus attention on the most novel objects in a complex environment, as well as the child's own developing vocabulary play critical roles in this process. This thesis aims to understand the influence of novelty and prior vocabulary knowledge on referent selection and how the interaction of novelty and knowledge can lead to word learning. A series of empirical studies first probed the use of children's endogenous novelty bias in a referent selection task, and then explored how the use of novelty was related to retention of newly mapped word-referent pairs. A second set of studies explored children's use of vocabulary knowledge in ambiguous learning situations by varying the strength of knowledge for competing items present during novel word learning. Finally, a Hebbian Normalized Recurrent Network model was used to explore the underlying associative process of referent selection and retention in novelty- or knowledge-based word learning tasks. Counter to prior work, results here suggest that novelty can override knowledge and in fact, be a detriment to word learning. Children demonstrate a novelty bias across multiple contexts and tasks, but the dominant use of novelty does not translate to retention and does not appear to implicate the use of the child's lexicon. As novelty diminishes and vocabulary knowledge increases, some children can overcome this bias and demonstrate retention for new word-referent pairs. Moreover, the results also suggest that when disambiguation requires the use of weak prior knowledge, more cognitive processing is necessary. The increases in processing subsequently translate to retention for new word-referent pairs. The empirical and computational results together suggest potential limitations of these findings to word learning and suggest future directions exploring variability in object and word representations during learning.

Previous work shows that young children focus on holistic (or overall) similarity and older children focus on dimensional similarity (selectively attending to one property to the exclusion of others). Research on early word learning, however, suggests that process of learning new words trains attention towards category-relevant dimensions via regularities in the linguistic and physical environment. Thus, over development, children learn to attend to specific dimensions when making nominal category judgments--they selectively attend to shape, for example, when learning names for solid objects. In four experiments, I asked a question fundamental to our understanding of dimensional attention: does word learning scaffold attention to dimensional similarity in more general contexts. The results of Experiment 1 showed that children who are holistic classifiers are slower than dimensional classifiers to learn categories of objects that vary along both a category-relevant dimension (e.g. size) and a category-irrelevant dimension (e.g. brightness). However, the results of Experiment 2 showed that when children were presented with incidental labels during category learning, holistic classifiers learn the categories as quickly as dimensional classifiers. In a follow-up similarity classification task, children who had been holistic classifiers showed an increase in dimensional attention only if they had been in the label experiment. In Experiments 3 and 4, I examined category learning with and without a label in children who preferred to selectively attend to one dimension of similarity (e.g. brightness) regardless of whether this means selecting dimensional or holistic matches in a classification task. The results of these experiments provide a more complete picture of the continuous developmental trajectory of increasing selective and flexible dimensional attention. By showing how labels support dimensional attention, these results clarify the processes involved in development of similarity perception and potentially unify our understanding of attentional processes in word learning with those in a broader context.