Discovering words and rules from speech input: an investigation into early morphosyntactic acquisition mechanisms

To acquire language proficiently, learners have to segment fluent speech into units \u2013 that is, words -, and to discover the structural regularities underlying word structure. Yet, these problems are not independent: in varying degrees, all natural languages express syntax as relations between nonadjacent word subparts. This thesis explores how developing infants come to successfully solve both tasks. The experimental work contained in the thesis approaches this issue from two complementary directions: investigating the computational abilities of infants, and assessing the distributional properties of the linguistic input directed to children. To study the nature of the computational mechanisms infants use to segment the speech stream into words, and to discover the structural regularities underlying words, I conducted seventeen artificial grammar studies. Along these experiments, I test the hypothesis that infants may use different mechanisms to learn words and word-internal rules. These mechanisms are supposed to be triggered by different signal properties, and possibly they become available at different stages of development. One mechanism is assumed to compute the distributional properties of the speech input. The other mechanism is hypothesized to be non-statistical in nature, and to project structural regularities without relying on the distributional properties of the speech input. Infants at different ages (namely, 7, 12 and 18 months) are tested in their abilities to detect statistically defined patterns, and to generalize structural regularities appearing inside word-like units. Results show that 18-month-old infants can both extract statistically defined sequences from a continuous stream (Experiment 12), and find internal-word rules only if the familiarization stream is segmented (Experiments 13 and 14). Twelve-month-olds can also segment words from a continuous stream (Experiment 5), but they cannot detect wordstraddling sequences even if they are statistically informative (Experiments 15 and 16). In contrast, they readily generalize word-internal regularities to novel instances after exposure to a segmented stream (Experiments 1-3 and 17), but not after exposure to a continuous stream (Experiment 4). Instead, 7-month-olds do not compute either statistics (Experiments 10 and 11) or within-word relations (Experiments 6 and 7), regardless of input properties. Overall, the results suggest that word segmentation and structural generalization rely on distinct mechanisms, requiring different signal properties to be activated --that is, the presence of segmentation cues is mandatory for the discovery of structural properties, while a continuous stream supports the extraction of statistically occurring patterns. Importantly, the two mechanisms have different developmental trajectories: generalizations became readily available from 12 months, while statistical computations remain rather limited along the first year. To understand how the computational selectivities and the limits of the computational mechanisms match up with the limitations and the properties of natural language, I evaluate the distributional properties of speech directed to children. These analyses aim at assessing with quantitative and qualitative measures whether the input children listen to may offer a reliable basis for the acquisition of morphosyntactic rules. I choose to examine Italian, a language with a rich and complex morphology, evaluating whether the word forms used in speech directed to children would provide sufficient evidence of the morphosyntactic rules of this language. Results show that the speech directed to children is highly systematic and consistent. The most frequently used word forms are also morphologically well-formed words in Italian: thus, frequency information correlates with structural information -- such as the morphological structure of words. While a statistical analysis of the speech input may provide a small set of words occurring with high frequency, how learners come to extract structural properties from them is another problem. In accord with the results of the infant studies, I propose that structural generalizations are projected on a different basis than statistical computations. Overall, the results of both the artificial grammar studies an the corpus analysis are compatible with the hypothesis that the tasks of segmenting words from fluent speech, and that of learning structural regularities underlying word structure rely on statistical and non-statistical cues respectively, placing constraints on computational mechanisms having different nature and selectivities in early development

A real variation on the stationary phase lemma

Lo scopo dell'elaborato è quello di dimostrare il lemma della fase stazionaria assumendo come ipotesi di avere lo spazio bordato dato retta reale estesa invece che lo spazio bordato dato dalla linea proiettiva associata a uno spazio vettoriale unidimensionale complesso. Nei primi due capitoli vengono introdotti gli oggetti e le operazioni utilizzati nella trattazione, in particolare il prodotto di convoluzione per fasci e indfasci, la categoria dei fasci arricchiti e la categoria degli indfasci arricchiti. Nel terzo capitolo viene fatto un breve richiamo della corrispondenza di Riemann-Hilbert, mentre nel quarto vengono presentati i funtori associati alle trasformazioni integrali e ne vengono studiate alcune proprietà. Infine nell'ultimo capitolo si richiama il lemma della fase stazionaria nel caso complesso e in seguito, dopo opportune considerazioni, ne viene data una versione nel caso reale, che viene poi dimostrata con calcoli espliciti.ope

CLOSER: A Collaborative Locality-aware Overlay SERvice

Current Peer-to-Peer (P2P) file sharing systems make use of a considerable percentage of Internet Service Providers (ISPs) bandwidth. This paper presents the Collaborative Locality-aware Overlay SERvice (CLOSER), an architecture that aims at lessening the usage of expensive international links by exploiting traffic locality (i.e., a resource is downloaded from the inside of the ISP whenever possible). The paper proves the effectiveness of CLOSER by analysis and simulation, also comparing this architecture with existing solutions for traffic locality in P2P systems. While savings on international links can be attractive for ISPs, it is necessary to offer some features that can be of interest for users to favor a wide adoption of the application. For this reason, CLOSER also introduces a privacy module that may arouse the users' interest and encourage them to switch to the new architectur

Pragmatic language disorder in Parkinson's disease and the potential effect of cognitive reserve

It is known that patients with Parkinson\u2019s Disease (PD) may show deficits in several areas of cognition, including speech and language abilities. One domain of particular interest is pragmatics, which refers to the capacity of using language in context for a successful communication. Several studies showed that some specific aspects of pragmatics \u2013 both in production and in comprehension \u2013 might be impaired in patients with PD. However, a clear picture of pragmatic abilities in PD is still missing, as most of the existing studies focused on specific aspects of the pragmatic competence rather than on sketching a complete pragmatic profile. Moreover, little is known on the potential role of protective factors in compensating the decline of communicative skills as the disease progresses. The present study has two aims: (1) to provide a complete picture of pragmatic abilities in patients with PD, by using a comprehensive battery (Assessment of Pragmatic Abilities and Cognitive Substrates, APACS) and by investigating the relationship with other aspects of cognitive functioning (e.g., working memory and Theory of Mind) and (2) to investigate whether Cognitive Reserve, i.e., the resilience to cognitive impairment provided by life experiences and activities, may compensate for the progressive pragmatic deficits in PD. We found that patients with PD, compared to healthy matched controls, had worse performance in discourse production and in the description of scenes, and that these impairments were tightly correlated with the severity of motor impairment, suggesting reduced intentionality of engaging in a communicative exchange. Patients with PD showed also an impairment in comprehending texts and humor, suggesting a problem in inferring from stories, which was related to general cognitive impairment. Notably, we did not find any significant difference between patients and controls in figurative language comprehension, a domain that is commonly impaired in other neurodegenerative diseases. This might be indicative of a specific profile of pragmatic impairment in patients with PD, worth of further investigation. Finally, Cognitive Reserve measures showed a high degree of association with pragmatic comprehension abilities, suggesting that the modification of life-styles could be a good candidate for compensating the possible problems in understanding the pragmatic aspects of language experienced by patients with PD

Report on fitting the Italian national method for the evaluation of the ecological quality of lake waterbodies using benthic diatoms (EPI-L) in the "phytobenthos cross-GIG" intercalibration exercise

When the Cross-GIG phytobenthos intercalibration exercise was carried out, there was no specific Italian national method for the evaluation of the ecological quality of lake waterbodies using benthic diatoms. It was assumed that the common intercalibration metric could be used to replace the national method. However, during the exercise itself it became evident that the common metrics was not strongly correlated to the trophic pressure in the Italian lakes. As a consequence, a new method was developed, namely EPI-L, on the basis of data collected by Environmental Agencies and Research Institutes in 80 lakes covering a long trophic gradient in both the Alpine and Mediterranean ecoregion. This reports aims to evaluate to compare the value of the class boundaries of EPI-L with those agreed in the inter-GIG intercalibration exercise following the "Instruction manual to fit new or revised national classifications to the completed IC exercise". Lake quality classification should be carried out at the biological quality element (BQE) level. However, no intercalibration exercise was carried out for the "macrophyte and phytobenthos" BQE. For this reason, this report will only deal with the phytoplankton subelement