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"In this paper we report the results of a study investigating the phenomenon of subject and direct object omissions in child Russian. While omissions have been extensively studied in a number of other languages, they all focused on either non-pro-drop languages (e.g. English (Haegeman 1990; Valian 1991; Hyams and Wexler 1993; Rizzi 1994; Hyams 1996; Matushansky and Wexler 2002, to mention a few), German and Dutch (de Haan and Tuijnman 1989; Weverink 1989; Kraemer 1993; Hamann 1995, etc.)) or obligatory pro-drop languages such as Italian (Valian 1991, among others). Russian in this sense presents a particular interest because the adult system allows for apparent optionality"

Word frequencies in a text follow a curious pattern. A few of them appear extremely frequently, while by far most of them appear only once or twice. This pattern is considered a law of word frequencies, and better known as Zipf’s law. Its universality renders Zipf’s law one of the very few true language universals. The existence of this law has been known for more than a century. It has extensively been studied in large corpora of written texts and in many different languages, but hardly so in more singular cases such as spoken language and speech from people with a language disorder such as aphasia. This dissertation aims to fill this gap, to gain more insight into the workings of word frequencies on the one hand, and in the organization of the mental lexicon in people with and without aphasia on the other. First, the process of speech production is discussed, both in people with and without aphasia. Next, a thorough discussion of the hypotheses for the existence of Zipf’s law is presented. These explanations fall into a number of categories: The Principle of Least Effort, intermittent silence, preferential attachment, new optimization models (present day versions of the Principle of Least Effort) and a variety of semantic explanations. It is argued that models based on preferential attachment are most plausible. Next, it is shown how the values of the parameters of Zipf’s law vary depending on medium (written or spoken) and text length. In addition, a text is created for which Zipf’s law does not hold, to test if this is possible and how readers respond to such a text. These insights are then used to study Zipf’s law in different types of aphasic speech: in long samples from Dutch non-fluent aphasic speakers at 2, 5 and 8 months post onset and in short samples from English, Greek and Hungarian fluent and non-fluent aphasic speakers in the chronic stage of aphasia. It is shown that aphasia influences the values of the parameters, as does the language under consideration. But in all cases, Zipf’s law continues to apply. This finding strengthens the hypothesis that the system for word retrieval in aphasia is still intact.

What makes a sentence hard to process? Apart from the meanings of the words it contains, their number, and the way these words combine into constituents, words also contribute to processing difficulty on the basis of their accessibility in lexical retrieval. Apart from their frequency of use or their complexity in form, the words’ accessibility is also influenced by the number and roles of related forms in the structure in which they are stored. This is a factor that so far has not been sufficiently taken into account. As is experimentally shown in this dissertation, a measure for this is the inflectional entropy of the paradigm, an information theoretic measure that quantifies the support that a word can receive from its inflectional paradigm during activation. This study investigates how the interplay between the available processing resources, as predicted by the inflectional entropy, and the linguistic constraints, modulates the speed of processing within and between-sentences, as well as within- and between-languages. I follow the ACT-R model of sentence comprehension, proposed by Lewis and Vasishth (2005), which states that processing delays in working memory result from interference during retrieval induced by the similarity between the target and the already processed items. Assuming that interference effects are present across the board, I focus on the stage of lexical activation (the stage before interpretation) and on verbs, in particular. The experimental results reported in this dissertation demonstrate that a verb's accessibility in long term memory, what I call the Activation Potential (AP), is proportional to the inflectional entropy of its paradigm, determining the speed, and thus the effort, with which it is processed, and also, crucially,modulating the processing of the rest of the sentence. In fact, the processing speed of a reflexive object, like the Dutch zichzelf, and unlike a definite NP like Maria, depends on the way the main verb was processed, providing evidence that the reflexive’s interpretation requires an operation on the verb. The processing speed of dependent elements in a sentence follows the “easy-to-activate-hard-to-re-access” principle and can either be boosted or delayed by the amount of available processing resources: reflexives will be processed more slowly as an object of a quickly processed verb than as an object of a hardly processed verb, unless the processing system abounds in resources and can boost the slow processing of the former. This principle holds within a sentence but is more apparent at a between-language level. More precisely, languages with rich inflection, like Greek, although they have longer words and more complicated paradigms, nevertheless benefit in terms of processing effort, at least during theinitial processing stages. This is because they have verbs with higher inflectional entropy which require fewer resources during first activation when compared to languages with poor inflection, like Dutch. Saving on resources at the first stages of sentence processing can boost computations that are costly but can also lead to excessive processing effort in subsequent steps. I take this to be a reflection of the necessary trade-off between space and information for the sake of successful real-time computations.

This thesis offers a new scientific approach to word finding difficulties in language-disordered individuals. Concepts from information theory are used to calculate complexity of word forms and the effect of this complexity on processing is investigated for Dutch adults with aphasia and children with SLI. Unlike previous research, this project is the first to provide quantitative measures of “complexity” of linguistic material, using statistical measures from information theory to calculate complexity of specific word forms and inflectional paradigms encompassing both frequency and linguistic factors. An application of information theory to visual processing is also explored. Research questions: 1.To what extent can limitation of information processing capacity as measured within an information theoretic paradigm explain apparent agrammatic behaviour in Dutch people with aphasia? 2.Is the above limitation language - specific or it is observable in other cognitive domains, specifically visual cognition? 3.To what extent can limitation of information processing capacity as measured within an information theoretic paradigm explain the article retrieval difficulties of Dutch children with Specific Language Impairment? The thesis is divided into two parts: Part A: the experimental part describes an auditory lexical decision and a visual search experiment conducted with three groups: healthy young, elderly and aphasic participants. The effects of several information theoretic measures (two of which are new) on lexical retrieval in these three groups are discussed. In chapter 4 the results of a visual search task are discussed and related to the auditory lexical decision results. Part B: spontaneous speech analyses looks at data from both aphasic speakers and children with SLI. The first chapter discusses a new application of Zipf’s law and speaker entropy and the use of these tools in aphasic speech samples. The second chapter explores a third way to use information theoretic measures to investigate reduced processing capacity: the Kullback- Leibler divergence between input and output distribution. Article production is investigated for adults with aphasia and children with SLI. Overall the results suggest that linguistic structure is not impaired in adults with aphasia, but rather that they have difficulty processing linguistic (and non-linguistic) complex material. Furthermore, the final chapter shows that, although children with SLI and adults with aphasia have similar apparent difficulties with article production, the underlying cause is different. This thesis provides a first attempt to investigate reduced processing in language-impaired individuals within an information theoretic framework. The results on an auditory lexical decision task, a visual search task and two types of spontaneous speech analyses for language disordered individuals and healthy controls showed that a) information theory provides us with the tools to quantify linguistic material and that b) we can relate the effect of this complexity to the (reduced) processing capacity in adults with aphasia and children with SLI.

The results of the crosslinguistic (Dutch, Italian and German) database analysis and experiments presented in my study show that there are interesting similarities between the pattern of article omission by adults in newspaper headlines and the pattern of article omission observed in language acquiring children. Further, I show that in both languages and in both groups of speakers article omission is optional. Moreover, article omission appears to be influenced by the presence of a finite verb or a preposition and by the sentence position of the article-requiring noun. Although this effect works in the same direction in all three languages (less omissions if the verb is finite, less omissions after a preposition, less omissions in sentence-internal position), the concrete consequences are different. In order to come to a unified model that can account for these findings I introduce a base model of article selection that describes the process of article selection under normal and specific circumstances, with normal speakers and speakers with limited processing resources. According to this model, for an article to be produced, the targeted form needs to receive the highest activation among the members of the article set. I argue that the final output of the article selection process is the result of a competition between all members of the set. In a sense, the article selection process therefore can be characterized as resolving uncertainty with regard to which element of the set will win the competition. The higher the uncertainty, the more processing resources are necessary to select an article from the set. In my study I present an information-theoretical method to calculate the uncertainty level in the article set, the relative entropy value. The relative entropy of the article system reflects the differences in probability distribution between the elements: the higher the differences in probability distribution (and, thus the higher the value of relative entropy), the more processing resources are required to select an article from the article set. I show that the relative entropy value is higher in Dutch than in German, and higher in German than in Italian. I argue that both children and headline writers are sensitive to differences in the processing resources necessary for article selection, children because of their limited processing resources, headline writers (and readers) because of the restricted time readers have available. I show that with the measure of relative entropy we can account not only for the crosslinguistic differences in omission pattern, but also for the relation between article omission and finiteness, for the influence of the use of a preposition before the article-requiring noun on the omission of articles, for the relation between article omission and sentence position and for differences in omission pattern of different articles (particularly the differences in omissions of ‘de’ and ‘het’ in Dutch and the differences between omission of definite and indefinite articles in Italian).

This dissertation addresses the issue of the relation between deviant behavior in agrammatic Broca's aphasia and the theory of grammar. Agrammatic Broca's aphasics have particular difficulties comprehending semantically reversible sentences in which the canonical order of arguments have been inverted. The working hypothesis is that agrammatic comprehension deficits with movement derived sentences are reducible to special cases of syntactic islands and ultimately can be explained as a minimality (in the sense of Rizzi 1990, 2004b) effect generated by an underspecification of the morphosyntactic featural make-up normally associated with syntactic categories. This impoverishment is attributed to a syntactic specific processing deficit which allows for a partial recovery of the full feature array needed to distinguish between a moved element and any potential intervener. The underspecification hypothesis is extended to comprehension and production deficits and, on this basis, parallels between deficits with movement and binding are drawn. Particular emphasis is given to the analysis of passives. Following Gehrke and Grillo's (2007, 2008) analysis of passivization as an operation on the event structure of the predicate, a novel approach to comprehension difficulties with passives in language acquisition and breakdown is discussed. Experimental data on production (originally discussed in Garraffa and Grillo 2008) of wh-questions in Italian is also discussed. This work is of interest to scholars working in the field of language breakdown, language acquisition as well as to linguists interested in the syntax of movement, locality and passivization.