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Categorization is a complex decision-making process that requires observers to collect information about stimuli using their senses. While research on visual or auditory categorization is extensive, there has been little attention given to tactile categorization. Here we developed a paradigm for studying tactile categorization using 3D-printed objects. Furthermore, we derived a categorization model using Bayesian inference and tested its performance against human participants in our categorization task. This model accurately predicted participant performance in our task but consistently outperformed them, even after extending the learning period for our participants. Through theoretical exploration and simulations, we demonstrated that the presence of sensory measurement noise could account for this performance gap, which we determined was a present factor in participants undergoing our task through a follow-up experiment. Including measurement noise led to a better-fitting model that was able to match the performance of our participants much more closely. Overall, the work in this thesis provides evidence for the efficacy of a tactile categorization experimental paradigm, demonstrates that a Bayesian model is a good fit and predictor for human categorization performance, and underscores the importance of accounting for sensory measurement noise in categorization models. / Dissertation / Doctor of Philosophy (PhD) / The process of categorization is an essential part of our daily life as we encounter various things in the world. Here we explore a model that attempts to explain this process. This model is derived using Bayesian inference and was applied to human behavioural data in a categorization task. We found that the model accounted for most of the performance of our participants but consistently outperformed them. We conducted simulations to explore and demonstrate that this difference is primarily due to the presence of sensory noise in participants. Once we accounted for this noise, we found that our model predicted human performance even more accurately. The work in this thesis demonstrates that a Bayesian Categorization Model which accounts for sensory noise is a good fit and predictor for human performance on categorization tasks.

Every day there are somatosensory stimuli on our skin that we perceive one moment and the next not, despite their unchanged physical presence (e.g., insects, wind, clothing). Yet, which are the physiological determinants and neural correlates that accompany external stimuli to enter consciousness or not? To address this question and inform theories of consciousness, this dissertation presents three empirical studies that used weak electrical finger-nerve stimulation which led - despite being physically identical - to subjective experiences of stimulus presence and absence. The first two studies investigated the interaction of tactile conscious perception with two dominant body rhythms: the cardiac and respiratory cycle. The third study investigated the configuration of neural networks being involved in this near-threshold phenomenon. Tactile conscious perception changed over the course of the cardiac cycle (increased detection during diastole) and respiration was tuned such that stimuli occurred more likely during late inspiration / early expiration, resulting in increased detection during early expiration. On the neural level, conscious perception was accompanied by global broadcasting of sensory content across the brain without substantial reconfiguration of the whole-brain functional network in terms of graph metrics. The cardiac cycle effect on conscious tactile perception is a result of cognitive processes which model and predict our body’s internal state to inform perception and guide behavior (e.g., tuning respiration). This perceptual integration of interoceptive and exteroceptive 'beliefs' is also an explanation for widely distributed brain activity differences without whole-brain functional network changes when a tactile stimulus is perceived.

When examining objects using tactile senses, individuals often incorporate multiple sources of haptic sensory information to estimate the object’s properties. How do our brains integrate various cues to form a single percept of the object? Previous research has indicated that integration from cues across sensory modalities is optimally achieved by weighting each cue according to its variance, such that more reliable cues have more weight in determining the percept. To explore this question in the context of a within-modality haptic setting, we assessed participants’ perception of edges that cross the index, middle, and ring fingers of the right hand. We used a 2-interval forced choice (2IFC) task to measure the acuity of each digit individually, as well as the acuity of all three digits working together, by asking participants to distinguish the locations of two closely spaced plastic edges. In examining the data, we considered three perceptual models, an optimal (Bayesian) model, an unweighted average model, and a winner-take-all model. The results indicate that participants perceived sub-optimally, such that the acuity of the three digits together did not exceed that of the best individual digit. We further investigated our question by having participants unknowingly undergo a 2IFC cue conflict condition, where they thought they were touching a straight edge which was actually staggered and thus gave each digit a different positional cue. Our analyses indicate that participants did not undertake optimal cue combination but are inconclusive with respect to which suboptimal strategy they employed. / Thesis / Master of Science (MSc) / This thesis investigates the neural mechanisms behind tactile perception, specifically how the brain combines multiple sensory cues to construct a unified percept when interacting with objects through touch. Typically, optimal sensory integration involves assigning more weight to more reliable cues. Our research focused on tactile integration by examining participants’ ability to perceive the positions of edges crossing their index, middle, and ring fingers simultaneously. The results indicated that, contrary to predictions, participants exhibited various sub-optimal cue integration strategies. Their ability to perceive the combined positions of all three fingers was not superior to that of the best-performing individual finger. We also explored cue conflict situations, where the locations of the tactile cues were no longer from a straight edge, unbeknown to participants, and the results here reinforced the finding that participants did not consistently employ optimal cue combination strategies. This research offers valuable insights into how the brain processes tactile information.

In recent years, computational neuroscientists have suggested that human behaviour, including perception, occurs in a manner consistent with Bayesian inference. According to the Bayesian ideal observer model, the observer combines cues from multiple sensory streams as a weighted average based on each cue’s reliability. Most cue-combination research has focused on integration of cues between sensory modalities or within the visual modality. Cue combination within the tactile modality has been relatively rarely studied, and it is still not known whether cues from individual digits combine optimally. In this thesis, we use the ideal observer model to determine whether cues from three different digits are combined optimally. We predicted that cues from multiple digits would be combined according to the optimal cue combination model. To test our hypothesis, we devised a two-interval forced choice (2IFC) task where participants had to discriminate the distal/proximal location of a 1-mm thick edge across the fingerpad(s) of the index (D2), middle (D3), and ring (D4) fingers. We used a Bayesian adaptive method, the ψ method, to compute participants’ psychometric functions for single-digit (D2, D3, and D4) and multiple-digit (D23, D24, D34, and D234) conditions. We determined the stimulus level ∆x, the distance (mm) between the distal and proximal stimuli locations, at 76% correct probability. This distance corresponds to a sensitivity index d'=1 and is the σ value of the participant’s stimulus measurement distribution. We then used the single-digit σ values to predict optimal cue combination for the multiple-digits combinations. We did not observer optimal cue-combination between the digits in this study. We outline potential implications the results of this experimental have on determining how the nervous system combines cues between digits, focusing on theoretical and experimental updates to the experiment that might result in the observation of optimal cue combination between digits. / Thesis / Master of Science (MSc)

Submitted by Franciane Falcão (francifalcao@gmail.com) on 2017-09-05T21:54:06Z No. of bitstreams: 1 PPGDesign_UNESP-FAAC_Tese_FranFalcao_FINAL.pdf: 39549375 bytes, checksum: 22f12a9192fb70de587874aa2242701e (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-09-06T16:43:08Z (GMT) No. of bitstreams: 1 falcao_fs_dr_bauru.pdf: 39549375 bytes, checksum: 22f12a9192fb70de587874aa2242701e (MD5) / Made available in DSpace on 2017-09-06T16:43:08Z (GMT). No. of bitstreams: 1 falcao_fs_dr_bauru.pdf: 39549375 bytes, checksum: 22f12a9192fb70de587874aa2242701e (MD5) Previous issue date: 2015-05-29 / Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) / Pesquisas na área do design ergonômico têm delineado parâmetros para o desenvolvimento de diversos produtos, por meio do estudo da relação de aspectos formais de produtos e a percepção ou solicitações físicas humanas. Entretanto, estudos da correlação de aspectos formais da superfície de contato (texturas das interfaces) com a percepção humana no uso de ferramentas manuais apresentam-se ainda incipientes. Este estudo teve por objetivo avaliar a relação de três características formais de textura (disposição, densidade gráfica, profundidade) com a percepção de desconforto e agradabilidade, visando compreender o dimensionamento sensorial tátil em ferramentas manuais. Para tanto, foi aplicado a fase de avaliação do método SEQUAM, com uso de 8 mock-ups de martelos unha com distintas configurações de texturas aplicadas aos seus cabos. As simulações de uso foram realizadas com profissionais de marcenaria (PM) e usuários domésticos (UD). Os resultados desta abordagem experimental demonstraram que as características de disposição, densidade gráfica e profundidade interferem na percepção do usuário; e que entre estas três características a densidade gráfica das ranhuras apresentou um número maior de aspectos perceptíveis com diferenças significativas (p<0,05) entre os mock-ups. Outro dado expressivo foi a diferença de percepção entre os grupos de sujeitos PM e UD. Estes resultados caracterizam as texturas das superfícies de contato de ferramentas manuais como elementos formais associados a certas percepções obtidas no uso do produto; e aponta possíveis contribuições de estudos sobre dimensionamento sensorial tátil para o design ergonômico de ferramentas manuais. / Researches in the area of ergonomic design have outlined parameters for the development of several products, through the study of the relationship of formal aspects of products and the perception or human physical requests. However, studies of the correlation of formal aspects of the contact surface (interfaces textures) with human perception in the use of hand tools are still incipient. The aim of this study was to evaluate the relationship of three formal characteristics of texture (layout, graphic density, depth) with the perception of discomfort and pleasantness, in order to understand the tactile sensorial dimensioning in hand tools. Therefore, the evaluation phase of the method SEQUAM, with use of 8 mock-ups of nail hammers with distinct texture configurations applied to their cables. The use simulations were performed with carpentry professionals and home users. The results of this experimental approach demonstrated that the characteristics of layout, graphic density and depth interfere in the perception of the user; and that among these three characteristics the graphical density of the grooves presented a greater number of perceptible aspects with significant differences (p <0.05) between the mock-ups. Another expressive data was the difference of perception between the groups of subjects, carpentry professionals and home users. These results characterize the textures of contact surfaces of hand tools as formal elements associated with certain perceptions obtained in the use of the product; and points out possible contributions of studies on tactile sensorial dimensioning for the ergonomic design of hand tools. / FAPEAM: 2800/2011

Made available in DSpace on 2016-03-15T19:39:47Z (GMT). No. of bitstreams: 1 Patricia Aparecida Dall Agnol.pdf: 1818404 bytes, checksum: b31cf0df83e4242783a4c903b8811770 (MD5) Previous issue date: 2011-08-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The integrity of the sensory system is important to the development of human skills. Notwithstanding, after the loss of one or more systems, the nervous system ability of adapting itself to the new condition is variably due to type and age of loss and other factors involved on the learning of new skills, as in neural plasticity for example. Nevertheless, such adoption is possible once the remaining systems, linked to compensatory mechanisms, supply the retention of sensory loss information. Several studies have pursued neural substrates understanding towards sensorial lost in the face of sensory loss. This paper had as primary goal unravel tDCS influence on somatosensory cortex over the two points and textures discrimination tests submitted to sighted and blind subjects and verify its possible neuromodulatory effects. The results have showed that Anodic tDCS applied to the left somatosensory field produced benefits on two points discrimination performance and texture discrimination. Cathodic tDCS, by its turn, had harmful effects on texture discrimination performance in early blind and sighted subjects. It was found that tDCS has the ability of neuromodulating the excitability of somatosensorial cortex over the tactile discrimination. By taking such findings into consideration, it is possible to conclude that anodic and cathodic tDCS have considerable different effects on early blind and sighted subjects regarding their tactile perception, when applied on primary somatosensory cortex. Inasmuch as anodic tDCS has improved tactile performance, sooner may be possible that, with further researches, such tool may aid sensory loss and disturb treatments or even strengthen Braille reading for blind subjects. / A integridade do sistema sensorial é importante para o desenvolvimento das habilidades humanas. Entretanto, com a perda de um ou mais sentidos, a capacidade do sistema nervoso em adaptar-se a nova condição é variável devido ao tipo e idade de perda e outros fatores envolvidos na aprendizagem de novas habilidades, como na plasticidade neural. Todavia, essa adaptação é possível uma vez que os sentidos remanescentes associados a mecanismos compensatórios suprem a retenção da informação do sentido perdido. Muitos estudos buscam a compreensão dos substratos neurais diante da perda sensorial. Dessa forma, este estudo teve por objetivo investigar a influência da Estimulação Transcraniana por Corrente Contínua (ETCC) aplicada no Córtex Somatossensorial Primário (CS1), de indivíduos com visão preservada e de deficientes visuais, durante os testes de discriminação de dois pontos e de discriminação de texturas. Os resultados mostraram que a ETCC anódica aplicada no CS1 produziu efeito benéfico no desempenho da discriminação de dois pontos e da discriminação de textura. Já a ETCC catódica teve efeito prejudicial no desempenho da discriminação de texturas em deficientes visuais congênitos e indivíduos com visão. Esses resultados são atribuídos à capacidade que a ETCC tem em neuromodular a excitabilidade cortical do córtex somatossensorial. Por fim, concluímos que a aplicação da ETCC anódica e catódica no CS1 têm efeitos significativos na percepção tátil em deficientes visuais congênitos e indivíduos com visão durante as tarefas realizadas no presente estudo. Nesse sentido, pesquisas subsequentes com essa ferramenta poderão auxiliar em tratamentos de distúrbios e de perdas sensoriais ou mesmo potencializar a aprendizagem de deficientes visuais na leitura Braille.

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Aspectos relacionados à percepção cognitiva do homem têm sido cada vez mais considerados em projetos de produtos e nos processos de seleção de materiais. Em especial, a seleção de materiais têxteis configura uma tarefa de alta complexidade tanto devido a aspectos técnicos, quanto a aspectos percebidos através dos sentidos. Por isso, esta pesquisa objetiva contribuir com a seleção de materiais têxteis para uso em calçados, através da proposição de um processo sistematizado. O presente estudo integra atributos percebidos de maneira visual e tátil a partir de superfícies de materiais e qualidades percebidas de produtos, encontrados em bibliografia especializada, a uma escala de diferencial semântico. Em etapa posterior, através de teste piloto com designers e especialistas e utilizando os dados coletados por meio de observação direta e questionários, este conteúdo foi avaliado de maneira qualitativa, gerando o referido processo, que utiliza a lista de atributos para a classificação de materiais têxteis para uso no PDP. Como resultado, é proposto um processo industrial patenteado, amparado por uma ferramenta que viabiliza a classificação de materiais têxteis, para uso específico no projeto de calçados. / Aspects related to the cognitive perception of man have been increasingly considered in product designs and materials selection processes. The selection of textile materials constitutes a task of high complexity both due to technical aspects and to aspects perceived through the senses. From this, this research aims to contribute with the selection of textile materials for use in footwear, through the proposition of a systematized process. For this, the present study integrates visually and tactile perceived attributes from material surfaces and perceived qualities of products, found in specialized bibliography, on a semantic differential scale. In a later stage, through a pilot test with designers and specialists and using data collected through direct observation and questionnaires, this content was evaluated in a qualitative way, generating the said process, which uses the list of attributes for the classification of textile materials for use in the PDP. As a result, a patented industrial process is proposed, supported by a tool that enables the classification of textile materials for specific use in shoe design.

Voir les gestes articulatoires de son interlocuteur permet d’améliorer significativement le décodage et la compréhension du signal acoustique de parole émis. Un premier objectif de cette thèse était de déterminer si les interactions multimodales lors de la perception de parole, en plus d’impliquer classiquement les informations auditives et visuelles transmises par le son et le visage du locuteur, pouvaient être déclenchées par d’autres sources sensorielles moins communément utilisées dans la communication parlée, comme la perception tactile de la parole ou encore la perception visuelle des mouvements de la langue. Parallèlement, nos travaux avaient également pour but de déterminer l’implication possible du système moteur dans ces mécanismes de perception multisensorielle. Enfin, un autre enjeu de nos recherches était de déterminer plus avant le décours temporel et l’organisation neuroanatomique fonctionnelle de ces mécanismes d’intégration à l’aide de différentes techniques comme l’électro-encéphalographie, l’imagerie par résonance magnétique fonctionnelle ou encore la stimulation magnétique transcrânienne. Nos travaux ont permis d’élargir la notion de « multisensorialité de la parole » en mettant en évidence une facilitation des traitements temporels auditifs lors de la perception audio-tactile de la parole et lors de l’observation de nos propres mouvements articulatoires. D’autre part, nos études ont fourni de nouveaux arguments en faveur d’un rôle fonctionnel du système moteur lors de la perception de parole en montrant une activation plus importante des régions motrices lors de l’observation de mouvements de la langue ainsi qu’un recrutement plus bilatéral du cortex prémoteur ventral au cours du vieillissement. Pris ensemble, nos résultats renforcent l’idée d’un couplage fonctionnel, d’une co-structuration des systèmes de perception et de production de la parole. Les études présentées dans cette thèse appuient ainsi l’existence de connexions entre régions sensorielles, intégratives et motrices permettant la mise en œuvre de processus et traitements multisensoriels, sensorimoteurs et prédictifs lors de la perception et compréhension des actions de parole. / Seeing the speaker’s articulatory gestures significantly enhances auditory speech perception. A key issue is whether cross-modal speech interactions only depend on well-known auditory and visual inputs from the speaker’s voice and face or, rather, might also be triggered by other sensory sources less common in speech communication, such as tactile information or vision of the tongue movements. Another goal of the present research was to determine the possible role of the motor system in these multisensory processes. Finally, we used electro-encephalographic, functional magnetic resonance imaging and transcranial magnetic stimulation techniques in order to better understand the time course and the functional neuroanatomical organization of these integration mechanisms. Our results extent the concept of “multisensory speech perception” by highlighting a facilitation of auditory processes during audio-haptic speech perception as well as during the observation of our own articulatory movements. They also provide new evidence in favor of a functional role of the motor system in speech perception by demonstrating an increase of motor activity during visuo-lingual speech perception and a more bilateral ventral premotor cortex recruitment during speech perception across aging. Taken together, our results reinforce the idea of a functional coupling and a co-structuring of speech perception and production systems. Our work support the existence of connections between sensory, integrative and motor regions allowing the implementation of multisensory, sensorimotor and predictive processes in the perception and understanding of speech actions.