In this thesis I develop a syntactic representation of control that is PRO-free. I implement a mechanism of theta-role assignment that uses theta-role percolation (Neeleman and Van de Koot (2002)), which enables the apparent subject properties of controlled mfinitives to be reinterpreted as properties associated with an external theta-role, rather than a subject. I first analyse Obligatory Control using a de- compositional analysis of theta-roles (independently motivated in Samek-Lodovici 2003), according to which theta-roles are divided into two selectional requirements, one that formally licenses arguments and another that regulates interpretation. It is the latter one that regulates Obligatory Control, by being copied to the controller in the super-ordinate clause. The resulting theory makes the same predictions as one based on PRO, yet avoids dependence on this ill-defined element inherited from the GB era. I then offer an account of the case-agreement properties of predicates in Icelandic infinitival clauses this data shows not only that PRO is unnecessary but that it cannot actually fulfill the task for which it was proposed. An extra-syntactic analysis is developed for Non-Obligatory Control, since this relation is not syntactically constrained in the way that Obligatory Control is. I claim that in non-obligatory control structures the external theta-role is not saturated syntactically. This unassigned role is subject to an LF-interpretative rule that attributes it with a +human specification. This rule suffices for cases in which the interpreted subject is understood generically, but in long-distance control structures, this +human specification is further supplemented by a discourse rule that links the theta-role to a highly accessible antecedent, as developed in Ariel (1996). An attempt is made to generalise the rules operative in non-obligatory control structures, to the null-objects in Rizzi (1986), the consequence of which is that no null-element would be projected in these constructions either and the object properties would be reinterpreted in terms of the internal theta-role complex. In the final chapter, I offer an analysis of partial control (Landau 2000). On the basis of the ambiguous properties pervading this relation, which belong to both obligatory- and non-obligatory control, I analyse partial control as obligatory control + non-obligatory control.

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This thesis aimed to investigate the effect of visual speech cues on auditory-visual integration during speech perception in Arabic. Four experiments were conducted two of which were cross linguistic studies using Arabic and English listeners. To compare the influence of visual speech in Arabic and English listeners chapter 3 investigated the use of visual components of auditory-visual stimuli in native versus non-native speech using the McGurk effect. The experiment suggested that Arabic listeners’ speech perception was influenced by visual components of speech to a lesser degree compared to English listeners. Furthermore, auditory and visual assimilation was observed for non-native speech cues. Additionally when the visual cue was an emphatic phoneme the Arabic listeners incorporated the emphatic visual cue in their McGurk response. Chapter 4, investigated whether the lower McGurk effect response in Arabic listeners found in chapter 3 was due to a bottom-up mechanism of visual processing speed. Chapter 4, using auditory-visual temporal asynchronous conditions, concluded that the differences in McGurk response percentage was not due to bottom-up mechanism of visual processing speed. This led to the question of whether the difference in auditory-visual integration of speech could be due to more ambiguous visual cues in Arabic compared to English. To explore this question it was first necessary to identify visemes in Arabic. Chapter 5 identified 13 viseme categories in Arabic, some emphatic visemes were visually distinct from their non-emphatic counterparts and a greater number of phonemes within the guttural viseme category were found compared to English. Chapter 6 evaluated the visual speech influence across the 13 viseme categories in Arabic measured by the McGurk effect. It was concluded that the predictive power of visual cues and the contrast between visual and auditory speech components will lead to an increase in the McGurk response percentage in Arabic.

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A person with normal hearing has the ability to follow a particular conversation of interest in a noisy and reverberant environment, whilst simultaneously ignoring the interfering sounds. This task often becomes more challenging for individuals with a hearing impairment. Attending selectively to a sound source is difficult to replicate in machines, including devices such as hearing aids. A correctly set up hearing aid will work well in quiet conditions, but its performance may deteriorate seriously in the presence of competing sounds. To be of help in these more challenging situations the hearing aid should be able to segregate the desired sound source from any other, unwanted sounds. This thesis explores a novel approach to speech segregation based on optimal cue mapping (OCM). OCM is a signal processing method for segregating a sound source based on spatial and other cues extracted from the binaural mixture of sounds arriving at a listener's ears. The spectral energy fraction of the target speech source in the mixture is estimated frame-by-frame using artificial neural networks (ANNs). The resulting target speech magnitude estimates for the left and right channels are combined with the corresponding original phase spectra to produce the final binaural output signal. The performance improvements delivered by the OCM algorithm are evaluated using the STOI and PESQ metrics for speech intelligibility and quality, respectively. A variety of increasingly challenging binaural mixtures are synthesised involving up to five spatially separate sound sources in both anechoic and reverberant environments. The segregated speech consistently exhibits gains in intelligibility and quality and compares favourably with a leading, somewhat more complex approach. The OCM method allows the selection and integration of multiple cues to be optimised and provides scalable performance benefits to suit the available computational resources. The ability to determine the varying relative importance of each cue in different acoustic conditions is expected to facilitate computationally efficient solutions suitable for use in a hearing aid, allowing the aid to operate effectively in a range of typical acoustic environments. Further developments are proposed to achieve this overall goal.

The research described in this thesis is about investigation of the two less well understood mechanisms of balance system, namely utricular function and interactions of visual and vestibular system. Utricules are part of otolith apparatus and sense linear acceleration including gravity and lateral head tilts. Recent advances in rotational technology allow robust methods of assessment of unilateral utricular function using centrifugation techniques. Unilateral centrifugation generates substantial linear acceleration and the utricular response can be measured via tilt perception using subjective visual vertical (chapter 2). Utricular function was studied in common vestibular disorders seen in clinics, like chronic vestibular neuritis, benign positional paroxysmal vertigo, unilateral Ménière's disease, migraine and bilateral vestibular hypofunction. Bilateral vestibular hypofunction produced significantly low utricular gain (chapter 3). A detailed study of the utricular function of larger group of unilateral Ménière's disease showed significantly greater utricular asymmetry and lower utricular gain than normal controls. Interestingly, hearing loss was a predictor of utricular asymmetry (chapter 4). There was poor correlation between subjective measures and audiovestibular function. The chronic course of Ménière's disease is well known with slow decline over years and absence of correlation between symptoms and function may point to 'burn out' as long term phenomenon (chapter 5). An investigation into visual dependence and vertigo was performed to understand the effect of visual dependence on tilt perception in chronic vertigo. Individuals with vestibular symptoms can have increased visual dependency and migraineurs can have a non-adaptable increase in visual dependency (chapter 6). In summary, we found that the unilateral centrifugation is a safe and well tolerated technique and provides additional, potentially useful information about utricular function. In future, the study of utricular function during acute phases of vertigo will further help overall understanding of otolith pathophysiology and mechanisms used for compensation.

The aim of this study was to investigate the feasibility of conducting a randomised controlled trial (RCT) on the effect of motivational interviewing (MI) in facilitating hearing aid use. Methods used and their results are presented in the 3 sections below: (1) A cross-sectional survey where a questionnaire, including the International Outcome Inventory for Hearing Aids was posted to all patients fitted with hearing aids at the Royal Surrey County Hospital, Guildford, between 2011 and 2012 (N=1874). 1023 questionnaires were completed and returned (response rate of 55%). 29% of responders did not use their hearing aids on a regular basis (i.e., used them less than 4 hours per day). (2) 220 patients who reported using their hearing aid(s) less than 4 hours per day in the above survey were invited to take part in a pilot single-blind RCT. 37 were enrolled and randomised to MI combined with hearing aid adjustments (n=20) or hearing aid adjustments only (n=17). The results showed that it was feasible to deliver MI for facilitating hearing aid use. Hearing aid use as measured via data logging 1 month after interventions favoured the MI group. (3) A qualitative enquiry embedded in the above pilot RCT was conducted. 34 out of 37 participants underwent in-depth interviews. Interviews were transcribed and thematically analysed. Five themes were identified in relation to participants’ perspectives about the key components of the research programme which influenced their decision about using their hearing aids. Conclusion: Conducting an RCT on the effect of MI in facilitating hearing aid use in people who do not use their hearing aids is feasible and that MI combined with audiology standard care may have positive effects on hearing aid use.

Age-related hearing impairment (ARHI) affects 46% of the population over the age of 48 and with increasing life expectancy in Western nations, this incidence is likely to rise. The causes for this disorder are still poorly understood but there is known to be a heritable component of around 65%. In addition, epigenetic regulation of gene expression changes over time and may explain many age-related traits. The basis of this research was to explore genetic and epigenetic factors in ARHI to understand better the mechanisms involved in its pathology. Hearing data were obtained from female volunteers of the TwinsUK register using the gold standard measure, air-conduction pure-tone audiometry and a web-based speechin-noise perception test. The prevalence of ARHI in TwinsUK was comparable to previous reports. Heritability estimates based on the classical twin model confirmed a moderate heritability of hearing ability in TwinsUK, supporting the use of this sample in genetic association studies. Genome-wide association with hearing ability was performed in TwinsUK but no genome-wide significant polymorphisms were identified possibly due to inadequate sample size. Accordingly, the data were combined with existing genome-wide association studies (GWAS) of hearing function from the G-EAR consortium. This meta-analysis resulted in a genome-wide significant association with an exonic SNP of the SIK3 gene encoding salt-inducible kinase 3, a novel gene reported to regulate metabolism and skeletal development via HDAC4. Immunohistochemistry of sik3 in mouse models confirmed striking expression profiles A small epigenome-wide association study of hearing ability in TwinsUK (n=115) revealed an epigenome-wide significant association with a probe in the promoter region of TCF25. Epigenome-wide associations at two highly associated probes (TCF25 and POLE) were replicated in an independent sample from TwinsUK (n=203). DNA methylation at these genes was negatively correlated with expression of the same, indicating gene expression repression by DNA methylation. Furthermore, using identical twins discordant for hearing loss, differentially methylated regions were found at genes ACP6 and CCNDBP1. This research supports a role of common genetic variants in ARHI, including the novel association with SIK3, which may be essential for healthy hair cell development and maintenance of spiral ganglion cells with increased age. Differentially methylated in hair cells and spiral ganglion cells of mouse cochlea, validating a putative function of SIK3 in hearing ability. regions were significantly associated with ARHI and showed an effect on gene expression despite small sample size, supporting a role of epigenetic modifications in ARHI. This research is the first to report genome-wide significant association with SIK3 and epigenome-wide significant associations at TCF25 with ARHI, which may shed light on the pathways involved in this disabling condition.

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