The purpose of this thesis is to evaluate the possibilities of using 3D perspective displays in different military settings, and to illustrate the limitations of 3D displays, that is, when 2D displays are to be preferred. More specifically, this thesis explores (a) readability during vibrations, (b) perception aspects on perspective aircraft displays, and (c) the value of spatial cues in 3D air traffic displays in military settings. The results show, for example, that vertical vibrations influence recognition performance negatively. The recognition of 2D and 3D symbols, as well as judgment of relations between symbols on a 3D display, may indeed be an arduous task. Results, further, indicate improved performance for relation judgments between objects in 3D space in dynamic rather than static scenarios in tactical indicators. In situations where perception of a direction nevertheless is problematic, enhancements like, for example, drop-lines may improve performance. From a practical point of view the goal has been to investigate the possibility to develop and use a 3D perspective display in an airplane like JAS 39 Gripen. A general conclusion is that 3D displays indeed can be used in many situations but it is important to seriously consider any possible limitations of 3D displays. The future work should be focused on implementing and testing the tactical display in a real setting with real military pilots.

A atenção visual é um conjunto de processos que permite processar preferencialmente uma informação visual em um dado momento. Muitos modelos de atenção visual propõem que a atenção pode ser destinada e focalizada a uma única localização no espaço por vez quando dicas espaciais são usadas para orientar esse deslocamento. Porém, diferentes estudos têm encontrado evidências de que em circunstâncias apropriadas, a atenção pode ser destinada a áreas não adjacentes do campo visual. O objetivo deste estudo foi investigar a distribuição da atenção por estas áreas quando o tamanho e a localização de dicas espaciais periféricas foram manipulados. Os resultados sugerem que a atenção visual pode ser destinada a mais de uma localização ao mesmo tempo como um gradiente com picos de processamento, mas que o tamanho das áreas indicadas não deve ser determinante para isso ocorrer. Os resultados indicam também que a habilidade para dividir a atenção pode depender da localização em que os eventos ocorrem em relação aos lados do campo visual. Eventos que ocorrem em lados opostos têm uma chance maior de serem beneficiados por focos independentes de atenção, enquanto eventos que ocorrem do mesmo lado do campo visual parecem ter mais chance de serem processados por um foco único de atenção, mas essa diferença parece ser relativa do que absoluta. Este estudo traz também contribuições para o entendimento do processo de focalização quando diferentes tarefas são solicitadas, revelando que o ajuste da atenção ao tamanho de uma área indicada é mais facilmente verificado em tarefas que requerem a detecção rápida de um alvo do que quando julgamentos de ordem temporal são solicitados. / Visual attention is a set of processes which permits a preferential processing of visual information in a given moment. Several models of visual attention propose that attention might be allocated and focused in only one location by time when spatial cues are used to orient this displacement. However, different studies have been finding evidences that in appropriate circumstances, attention can be deployed to non-adjacent areas of the visual field. The main objective of the present study was to investigate the distribution of attention on these areas when the size and the localization of peripheral spatial cues were manipulated. The results suggest that visual attention can be deployed to more than one location simultaneously as a gradient with peaks in processing quality. The results also indicate that the ability to divide attention might depend on the localization in which the events occur in relation to each hemifield. Events that occur in different hemifields have more chance to take advantage of independent focus of attention while events that happen on the same hemifield have more chance to be processed by a single attentional focus but that this difference seems to be relative than absolute. This study have also contributions for the understanding of the focalization process when different tasks are requested revealing that the adjustment of the attentional focus to the size of a cued area is more easily verified in tasks that require fast detection of an target than when temporal order judgments are requested.

A atenção visual é um conjunto de processos que permite processar preferencialmente uma informação visual em um dado momento. Muitos modelos de atenção visual propõem que a atenção pode ser destinada e focalizada a uma única localização no espaço por vez quando dicas espaciais são usadas para orientar esse deslocamento. Porém, diferentes estudos têm encontrado evidências de que em circunstâncias apropriadas, a atenção pode ser destinada a áreas não adjacentes do campo visual. O objetivo deste estudo foi investigar a distribuição da atenção por estas áreas quando o tamanho e a localização de dicas espaciais periféricas foram manipulados. Os resultados sugerem que a atenção visual pode ser destinada a mais de uma localização ao mesmo tempo como um gradiente com picos de processamento, mas que o tamanho das áreas indicadas não deve ser determinante para isso ocorrer. Os resultados indicam também que a habilidade para dividir a atenção pode depender da localização em que os eventos ocorrem em relação aos lados do campo visual. Eventos que ocorrem em lados opostos têm uma chance maior de serem beneficiados por focos independentes de atenção, enquanto eventos que ocorrem do mesmo lado do campo visual parecem ter mais chance de serem processados por um foco único de atenção, mas essa diferença parece ser relativa do que absoluta. Este estudo traz também contribuições para o entendimento do processo de focalização quando diferentes tarefas são solicitadas, revelando que o ajuste da atenção ao tamanho de uma área indicada é mais facilmente verificado em tarefas que requerem a detecção rápida de um alvo do que quando julgamentos de ordem temporal são solicitados. / Visual attention is a set of processes which permits a preferential processing of visual information in a given moment. Several models of visual attention propose that attention might be allocated and focused in only one location by time when spatial cues are used to orient this displacement. However, different studies have been finding evidences that in appropriate circumstances, attention can be deployed to non-adjacent areas of the visual field. The main objective of the present study was to investigate the distribution of attention on these areas when the size and the localization of peripheral spatial cues were manipulated. The results suggest that visual attention can be deployed to more than one location simultaneously as a gradient with peaks in processing quality. The results also indicate that the ability to divide attention might depend on the localization in which the events occur in relation to each hemifield. Events that occur in different hemifields have more chance to take advantage of independent focus of attention while events that happen on the same hemifield have more chance to be processed by a single attentional focus but that this difference seems to be relative than absolute. This study have also contributions for the understanding of the focalization process when different tasks are requested revealing that the adjustment of the attentional focus to the size of a cued area is more easily verified in tasks that require fast detection of an target than when temporal order judgments are requested.

Depuis une dizaine d’années, des techniques de codage joint, exploitant les relations et les redondances entre canaux audios, ont été développées afin de réduire davantage la quantité d’information nécessaire à la représentation des signaux multicanaux. Dans cette thèse, nous étudions plus particulièrement le codage des signaux audio stéréo en l’absence d’informations à priori sur la nature des sources en présences, leur nombre et la manière dont elles sont spatialisées. Cette situation correspond à l’immense majorité des enregistrements commerciaux dans l’industrie de la musique et du multimédia de manière générale. Nous étudions des approches paramétrique et signal de la problématique de codage de ces sources, où les deux sont souvent mêlées. Dans ce contexte, trois types d’approches sont utilisés. L’approche paramétrique spatiale consiste à réduire le nombre de canaux audio de la source à coder et à recréer le nombre de canaux d’origine à partir des canaux réduits et de paramètres spatiaux, extraits des canaux d’origine. L’approche signal conserve le nombre de canaux d’origine, mais encode des canaux construits à partir de ces derniers et présentant moins de redondances. Enfin, l’approche mixte introduite dans MPEG USAC utilise un signal audio et un signal résiduel, issu d’une prédiction, et dont les paramètres sont codés conjointement. Dans cette thèse, nous analysons tout d’abord les caractéristiques d’un signal stéréo issu d’un enregistrement commercial et les techniques de production associées. Cette étude nous mène à une réflexion sur les rapports entre les modèles paramétriques d’émetteur, obtenus en analysant les techniques de production des enregistrements commerciaux, et les modèles de récepteur qui sont au coeur du codage spatial paramétrique. A partir de cette mise en perspective nous présentons et étudions les trois approches évoquées plus haut. Pour l’approche purement paramétrique, nous montrons l’impossibilité d’arriver à la transparence pour la majorité des sources audios, nous menons une réflexion sur les représentations paramétriques et proposons des techniques afin de réduire le débit de leurs paramètres et d’améliorer la qualité audio. Ces améliorations passent par une meilleur segmentation du signal audio, basée sur les transitoires, sur des caractéristiques perceptives de certains indices spatiaux et sur une meilleur estimation des indices spatiaux. L’approche mixte étant récemment standardisée dans MPEG USAC, nous l’étudions en détail, puis nous proposons une nouvelle technique de codage qui exploite au mieux l’allocation du résidu aux bandes fréquentielles, lorsque celui-ci n’est pas utilisé sur l’ensemble de la bande passante du signal. Enfin, nous concluons en évoquant l’avenir du codage audio spatial généraliste et mettons l’accent sur l’importance de développer des techniques de classification et de segmentation audio pour optimiser le rapport qualité/débit. / During the last ten years, technics for joint coding exploiting relations and redundancies between channels have been developped in order to further reduce the amount of information needed to represent multichannel audio signals.In this document, we focus on the coding of stereo audio signals where prior informations on the nature of sources in presence, their number or the manner they are spatialized is unknown. Such signals are actually the most representative in commercial records of music industry and in multimedia entertainment in general. To address the coding problematic of these signals, we study parametric and signal approaches, where both of them are often mixed.In this context, three types of approaches are used. The spatial parametric approach reduce the number of audio channels of the signal to encode and recreate the original number of channels from reduced channels and spatial parameters extracted from original channels. The signal approach keep the original number of channels, but encode mono signals, built from the combination of the original ones and containing less redundancies. Finally, the hybrid approach introduced in the MPEG USAC standard keep the two channels of a stereo signal, but one is a mono downmix and the other is a residual signal, resulting from a prediction on the downmix, where prediction parameters are encoded as side information.In this document, we first analyse the characteristics of a stereo audio signal coming from a commercial recording and the associated production techniques. This study lead us to consider the relations between the emitter parametric models, elaborated from our analysis of commercial recording production techniques, and the receiver models which are the basis of spatial parametric coding. In the light of these considerations, we present and study the three approaches mentioned earlier. For the parametric approach, we show that transparency cannot be achieved for most of the stereo audio signals, we have a reflection on parametric representations and we propose techniques to improve the audio quality and further reduce the bitrate of their parameters. These improvements are obtained by applying a better segmentation on the signal, based on the significant transient, by exploiting perceptive characteristics of some spatial cues and by adapting the estimation of spatial cues. As the hybrid approach has been recently standardized in MPEG USAC, we propose a full review of it, then we develop a new coding technique to optimize the allocation of the residual bands when the residual is not used on the whole bandwidth of the signal to encode. In the conclusion, we discuss about the future of the general spatial audio coding and we show the importance of developping new technics of segmentation and classification for audio signals to further adapt the coding to the content of the signal.

Dans un contexte sonore constitué de plusieurs sources sonores, l’analyse de scène auditive a pour objectif de dresser une représentation précise et utile des sons perçus. Résoudre ce type de scènes consiste à regrouper les sons provenant d’une même source et de les séparer des autres sons. Ce travail de thèse a eu pour but d’approfondir nos connaissances du traitement de ces scènes auditives complexes par le système auditif. En particulier, il s’agissait d’étudier l’influence potentielle des indices spatiaux sur la ségrégation. Une attention particulière a été portée tout au long de cette thèse pour intégrer des éléments réalistes dans toutes les études menées. Dans un environnement réel, la salle et la tête entraînent des distorsions des signaux de parole en fonction des positions de la source et du récepteur. Ce phénomène est appelé coloration. Comme première approximation de la parole, des bruits avec un spectre de parole ont été utilisés pour évaluer l’effet de la coloration. Les résultats ont montré que les fines différences spectrales monaurales induites par la coloration due à la tête et à la salle peuvent engendrer de la ségrégation. De plus, cette ségrégation peut être renforcée en ajoutant les indices binauraux associés à une position donnée (ILD, ITD). En particulier, une deuxième étude a suggéré que les variations monaurales d’intensité au cours du temps à chaque oreille étaient plus utiles pour la ségrégation que les différences interaurales de niveau. Les résultats ont également montré que le percept de latéralisation, associé à un ITD donné, favorise la ségrégation lorsque ce percept est suffisamment saillant. Par ailleurs, l’ITD per se peut induire de la ségrégation. La capacité naturelle à résoudre perceptivement une scène auditive est pertinente pour l’intelligibilité de la parole. L’objectif était de répliquer ces premières expériences, donc évaluer l’influence des indices spatiaux sur la ségrégation de signaux de parole à la place de bruits gelés. Une caractéristique de la parole est la grande variabilité de ses paramètres acoustiques qui permettent de transmettre de l’information. Ainsi, la première étape a été d’étudier dans quelle mesure la ségrégation basée sur une différence de fréquence peut être influencée par l’introduction de variabilité spectrale au sein des stimuli. L’étape suivante a été d’évaluer la différence de fréquence fondamentale requise pour séparer des flux de parole. En effet, il a été supposé que des indices de position pourraient être utiles pour renforcer la ségrégation basée sur un indice plus robuste comme une différence de F0 du fait de leur stabilité au cours du temps dans des situations réelles. Les résultats de ces expériences préliminaires ont montré que l’introduction d’une large variabilité spectrale au sein de flux de sons purs pouvait entraîner un percept compliqué, probablement constitué des multiples flux sonores. De plus, les résultats ont indiqué qu’une différence de F0 comprise entre 3 et 5 demi-tons permettait de séparer des signaux de parole. Les résultats de ces expériences pourront être utilisés pour concevoir la prochaine expérience visant à étudier dans quelle mesure un percept ambigu peut évoluer vers de la ségrégation par l’introduction d’indices de position. / In a context of competing sound sources, the auditory scene analysis aims to draw an accurate and useful representation of the perceived sounds. Solving such a scene consists of grouping sound events which come from the same source and segregating them from the other sounds. This PhD work intended to further our understanding of how the human auditory system processes these complex acoustic environments, with a particular emphasis on the potential influence of spatial cues on perceptual stream segregation. All the studies conducted during this PhD endeavoured to rely on realistic configurations.In a real environment, the diffraction and reflection properties of the room and the head lead to distortions of the sounds depending on the source and receiver positions. This phenomenon is named colouration. Speechshaped noises, as a first approximation of speech sounds, were used to evaluate the effect of this colouration on stream segregation. The results showed that the slight monaural spectral differences induced by head and room colouration can induce segregation. Moreover, this segregation was enhanced by adding the binaural cues associated with a given position (ITD, ILD). Especially, a second study suggested that the monaural intensity variations across time at each ear were more relevant for stream segregation than the interaural level differences. The results also indicated that the percept of lateralization associated with a given ITD helped the segregation when the lateralization was salient enough. Besides, the ITD per se could also favour segregation.The natural ability to perceptually solve an auditory scene is relevant for speech intelligibility. The main idea was to replicate the first experiments with speech items instead of frozen noises. A characteristic of running speech is a high degree of acoustical variability used to convey information. Thus, as a first step, we investigated the robustness of stream segregation based on a frequency difference to variability on the same acoustical cue (i.e., frequency). The second step was to evaluate the fundamental frequency difference that enables to separate speech items. Indeed, according to the limited effects measured in the two first experiments, it was assumed that spatial cues might be relevant for stream segregation only in interaction with another “stronger” cue such as a F0 difference.The results of these preliminary experiments showed first that the introduction of a large spectral variability introduced within pure tone streams can lead to a complicated percept, presumably consisting of multiple streams. Second, the results suggested that a fundamental frequency difference comprised between 3 and 5 semitones enables to separate speech item. These experiments provided results that will be used to design the next experiment investigating how an ambiguous percept could be biased toward segregation by introducing spatial cues.

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