No description available.

The basal ganglia are a collection of interconnected subcortical nuclei which have been implicated inmotor, cognitive and limbic functions. The subthalamic nucleus is the sole excitatory structure within the basal ganglia. Given its central position influencingmany basal ganglia nuclei, it is likely to play an important role in the processing that is performed by the basal ganglia. In this thesis a theoretical analysis of the subthalamic nucleus is presented. In order to explore the multiple facets of processing that may be occurring, models that are designed to capture aspects of the subthalamic nucleus at different levels are developed. These include anatomical, network processing and single neuron multi–compartmental models. Through the integration of the results obtained from these models a new and coherent view of the processing of the subthalamic nucleus is presented. It is predicted that the subthalamic nucleus be considered as a massively connected excitatory network. Two distinct modes of asymptotic behaviour exist in such a network: a low resting state and a high self–sustained state. The single neuron multi– compartmental model demonstrates that the calcium T–type channel is the primary determinant of characteristic neuron behaviour. Such behaviour includes a slowaction potential, initial spike clustering, and a post-response quiescence. The network and single neuron results taken togetherprovide an intrinsicmechanismfor termination of uniform high activity generated by the excitatory network. It is therefore predicted that large regions of the subthalamic nucleus respond uniformly to stimuli, in the form of a pulse of activity with a sharp rise and fall. In addition, the single neuron model indicates that pulses will occur in pairs. It is proposedthat the subthalamic nucleus acts as a “braking mechanism”. It can induce, via intermediate structures, awide-spread pulse of inhibition on basal ganglia target nuclei. Furthermore, the sequence of two pulses can generate a window of disinhibition over the basal ganglia targets. The width of this time window may be under direct striatal control. Variable interpulse duration implies a role for the subthalamic nucleus in temporal processing.

Sequential learning refers to the ability to learn the temporal and ordinal patterns of one’s environment. The current study examines the effects of synchronous and asynchronous temporal patterns on sequential learning. Twenty healthy adults participants (11 females, 18–34 years old) performed two versions of a visual sequential learning paradigm while event-related potentials (ERPs) were recorded. Reaction times to the targets following two predictor types were also recorded. Reaction time data revealed that learning occurred in both temporal conditions, although overall the synchronous condition was responded to faster. On the other hand, the mean ERP amplitudes between 300 and 700ms post-predictor onset revealed an interaction between timing condition and predictability in the posterior regions of interest. Specifically, the ERP results indicated that learning of the statistical contingencies between items was more pronounced for the synchronous temporal condition compared to the asynchronous condition.

The ability to capture the temporal dimension of a natural language text is essential to many natural language processing applications, such as Question Answering, Automatic Summarisation, and Information Retrieval. Temporal processing is a ¯eld of Computational Linguistics which aims to access this dimension and derive a precise temporal representation of a natural language text by extracting time expressions, events and temporal relations, and then representing them according to a chosen knowledge framework. This thesis focuses on the investigation and understanding of the di®erent ways time is expressed in natural language, on the implementation of a temporal processing system in accordance with the results of this investigation, on the evaluation of the system, and on the extensive analysis of the errors and challenges that appear during system development. The ultimate goal of this research is to develop the ability to automatically annotate temporal expressions, verbal events and temporal relations in a natural language text. Temporal expression annotation involves two stages: temporal expression identi¯cation concerned with determining the textual extent of a temporal expression, and temporal expression normalisation which ¯nds the value that the temporal expression designates and represents it using an annotation standard. The research presented in this thesis approaches these tasks with a knowledge-based methodology that tackles temporal expressions according to their semantic classi¯cation. Several knowledge sources and normalisation models are experimented with to allow an analysis of their impact on system performance. The annotation of events expressed using either ¯nite or non-¯nite verbs is addressed with a method that overcomes the drawback of existing methods v which associate an event with the class that is most frequently assigned to it in a corpus and are limited in coverage by the small number of events present in the corpus. This limitation is overcome in this research by annotating each WordNet verb with an event class that best characterises that verb. This thesis also describes an original methodology for the identi¯cation of temporal relations that hold among events and temporal expressions. The method relies on sentence-level syntactic trees and a propagation of temporal relations between syntactic constituents, by analysing syntactic and lexical properties of the constituents and of the relations between them. The detailed evaluation and error analysis of the methods proposed for solving di®erent temporal processing tasks form an important part of this research. Various corpora widely used by researchers studying di®erent temporal phenomena are employed in the evaluation, thus enabling comparison with state of the art in the ¯eld. The detailed error analysis targeting each temporal processing task helps identify not only problems of the implemented methods, but also reliability problems of the annotated resources, and encourages potential reexaminations of some temporal processing tasks.

Age-related hearing loss, presbycusis, is a complex disorder involving the interaction of both peripheral and central neurological deficits. Central auditory dysfunction may contribute to poor temporal discrimination of complex sounds such as speech. This research is timely since our population over 60 years old is increasing rapidly due to advances in medicine and nutrition as well as the advancing age of baby boomers. This study was designed to provide a better understanding of age-related changes in dorsal cochlear nucleus (DCN) physiology. DCN was chosen because it receives direct input from the auditory nerve and much is known about its neuronal morphology, physiology and circuitry. In young animals, DCN output neurons, fusiform cells, receive excitatory inputs from the acoustic nerve, which is modulated and shaped by inhibitory glycinergic inputs from nearby vertical cells. A number of studies in rodents suggested an age-related impairment of glycinergic neurotransmission. To access the functional impact of reduced putative glycinergic input in the central auditory system, this study compared the physiological responses of DCN neurons from young adult and aged rats in response set of simple and more complex acoustic stimuli. Single-unit extracellular recordings were made from two groups of DCN neurons: fusiform cells and cartwheel cells. Fusiform cells reflect the culmination of DCN processing, therefore were good candidates for studying the effect of aging on one ascending auditory stream. Two specific aims were directed at fusiform cell: SA1) Examine the effects of aging on fusiform cell response properties to simple tone burst stimuli; SA2) Examine the effect of aging on DCN output neuron response to complex temporal stimuli. A third aim, SA3) Examine the impact of aging on the response properties of cartwheel cells, a DCN inhibitory interneuron. Fusiform cells recorded from aged rats displayed significantly higher maximum discharge rates to characteristic frequency (CF) tones, fewer nonmonotonic CF rate-level functions and more wide-chopper type post-stimulus time histograms (PSTHs) when compared to neurons from young adult rats. These findings were consistent with an age-related loss of inhibitory glycinergic input. To elucidate how loss of inhibition could lead to functional deficits in temporal processing, fusiform cells were challenged to encode sinusoidally amplitude modulated (SAM) tones. DCN output neurons were presented with SAM tones at three modulation depths at 30 dB above hearing level/response threshold with the carrier frequency set to each unit’s CF. Temporal synchronicity to the SAM envelope was measured using vector strength from temporal modulation transfer functions (tMTFs). Firing rate to SAM tones was also assessed in rate modulation transfer functions (rMTFs). DCN output neurons from aged rats showed no loss of rate response (rMTF) but displayed a selective loss of temporal precision to SAM tones with significant age-related changes in peak vector strength (best modulation frequency), and the shape and category of tMTF. Wide-chopper PSTH types had significantly lower vector strength values than buildup and pauser PSTHs in both young and aged fusiform cells. Since a significantly greater proportion of aged neurons exhibited wide-chopper responses, this could explain, in part, the loss of temporal processing. The age-related response changes in the present study mimicked results from earlier studies were glycine inhibition onto young adult fusiform cells was pharmacologically blocked. Cartwheel cells receive excitatory inputs from granule cell parallel fibers as well as somatosensory dorsal column nucleus and project glycinergic inputs onto DCN output neurons. They appear to play a role in the integration of auditory and somatosensory inputs such as sensing head position. Aged cartwheel neurons exhibited signs of disinhibition showing increased spontaneous activity, increased maximum discharge rates and altered rate-level functions. The observed age-related changes in cartwheel cells are consistent with deafferentation studies using acoustic trauma. Collectively, the changes in DCN output neurons and cartwheel cells reflect a potentially maladaptive age-related neuroplasticity in response to a loss of excitatory acoustic nerve input. These in vivo extracellular findings were consistent with a global downregulation of glycinergic input within the DCN of aged rats. This reduced inhibition may contribute to functional deficits, particularly in activities that require precise timing of events such as response to speech-like stimuli.

Yes / In conflict with historically dominant models of time perception, recent evidence suggests that the encoding of our environment’s temporal properties may not require a separate class of neurons whose raison d'être is the dedicated processing of temporal information. If true, it follows that temporal processing should be imbued with the known selectivity found within non-temporal neurons. In the current study, we tested this hypothesis for the processing of a poorly understood stimulus parameter: visual event duration. We used sensory adaptation techniques to generate duration aftereffects: bidirectional distortions of perceived duration. Presenting adapting and test durations to the same vs different eyes utilises the visual system’s anatomical progression from monocular, pre-cortical neurons to their binocular, cortical counterparts. Duration aftereffects exhibited robust inter-ocular transfer alongside a small but significant contribution from monocular mechanisms. We then used novel stimuli which provided duration information that was invisible to monocular neurons. These stimuli generated robust duration aftereffects which showed partial selectivity for adapt-test changes in retinal disparity. Our findings reveal distinct duration encoding mechanisms at monocular, depth-selective and depthinvariant stages of the visual hierarchy. / The Wellcome Trust [WT097387].

No description available.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / In this paper, we propose applying the spatio-temporal signal processing and OFDM techniques to a multiple-antenna system in order to achieve high data rate and high performance transmission capability. In order to perform real time processing for this system, we also propose a complexity reduced QR beamforming algorithm. The performance of the proposed system has been investigated for a two-ray frequency-selective fading model by extensive computer simulations. These results show that significant benefits can be realized in terms of lower bit error rate and higher data transmission rate.

Doctor of Philosophy / Department of Psychology / Lester C. Loschky / While watching a film, the viewer begins to construct mental representations of it, which are called events. During the opening scene of a film, the viewer is presented with two distinct pieces of information that can be used to construct the event, namely the setting and an action by the main character. But, which of these two constructs are first cognitively represented by the viewer? Experiment 1 examined the time-course of basic level action categorization with superordinate and basic level scene categorization using masking. The results indicated that categorization occurred in a course-to-fine manner, inconsistent with Rosch et al.’s (1976) basic level theory. Interestingly, basic level action categorization performance did not reach ceiling when it was processed for a 367 ms SOA, suggesting that additional scene information and processing time were required. Thus, Experiment 2 examined scene and action categorization performance over multiple fixations, and the scene information that was fixated for each categorization task. Both superordinate and basic level scene categorization required only a single fixation to reach ceiling performance, inconsistent with basic level primacy, whereas basic level action categorization took two to three fixations, and led to more object fixations than in either scene categorization task. Eye movements showed evidence of a person bias across all three categorization tasks. Additionally, the categorization task did produce differences in the scene information that was fixated (Yarbus, 1967). However, could basic level theory still be correct when subjects are given a different task? When the same scene images were named, basic level action terms were used more often than basic level scene category terms, while superordinate level action terms were used relatively less often, and superordinate level scene category terms were hardly ever used. This shows that linguistic categorization (naming) is sensitive to informative, middle-level categories, whereas early perceptual categorization makes use of coarse high level distinctions. Additionally, the early perceptual advantage for scene categorization over basic level action categorization suggests that the scene category is the first construct that is used to represent events in scene images, and maybe even events in visual narratives like film.

Pessoas com fissura lábio palatina apresentam alterações na acuidade auditiva por um grande período de suas vidas, ou por toda vida, devido à constante disfunção tubária, que acarreta a otite média, impedindo assim uma recepção adequada dos sons da fala. Influência de otite média durante a infância é uma das características que está associada com o distúrbio de aprendizagem e transtornos de processamento auditivo. A consciência fonológica envolve o reconhecimento de que as palavras são formadas por diferentes sons que podem ser manipulados, abrangendo além da capacidade de reflexão (constatar e comparar), também a de operação com fonemas, sílabas, rimas e aliterações (contar, segmentar, unir, adicionar, suprimir, substituir e transpor). O objetivo principal deste trabalho foi estudar a associação entre a consciência fonológica e o processamento temporal em crianças com fissura labiopalatina. Foram avaliadas 41 crianças de ambos os sexos, com idades entre 7 anos e 10 anos e 11 meses, com fissura labiopalatina transforame unilateral, sem outras anomalias associadas ou síndromes. As crianças foram submetidas ao teste de processamento temporal Random Gap Detection Test (RGDT) e a avaliação de consciência fonológica CONFIAS adaptada com figuras. Os resultados indicaram não haver associação, nesta amostra, entre a consciência fonológica e o processamento temporal. Porem outros estudos devem ser realizados com um número maior de crianças na amostra. / Persons with cleft lip and palate presents alterations in the auditory sharpness by a big period of his lives, or by all life, because the constant tube dysfunction, that causes otitis media, stopping like this an adequate reception of the sounds of the speak. Influence of the otitis media during the childhood is one of the characteristics that is associated with the disturbance of learning and auditory process disorders. The phonological awareness involves the recognition of that the words are graduates by different sounds that can be manipulated, including beyond the capacity of reflection (establish and compare), also the operation with phonemes, syllables, rhymes and alliterations (count, segment, unite, add, suppress, replace and transpose). The main objective of this work was study the association between the phonological awareness and the temporal processing in childrens with cleft lip and palate.The work counted on 41 children of both sexes, with ages between 7 years and 10years and 11 monts, with cleft lip and palate, without other anomalies associated or syndromes. The children were submitted temporal processing test Random Gap Detection Test (RGDT) and the evaluation of the phonological awareness CONFIAS, adapted with figures. The results showed there isnt association, in this sample, bettween the phonological awareness and the temporal processing. But others studies should be realized with more children in the sample.