Bifurcation analysis applied to a model of motion integration with a multistable stimulus

A computational study into the motion perception dynamics of a multistable psychophysics stimulus is presented. A diagonally drifting grating viewed through a square aperture is can be perceived as moving in the actual grating direction or in line with the aperture edges (horizontally or vertically). The different percepts are the product of interplay between ambiguous contour cues and specific terminator cues. We present a dynamical model of motion integration that performs direction selection for such a stimulus and link the different percepts to coexisting steady-states of the underlying equations. We apply the powerful tools of bifurcation analysis and numerical continuation to study the changes to the model's solution structure under the variation of parameters. Indeed, we apply these tools in a systematic way, taking into account biological and mathematical constraints, in order to fix model parameters. A region of parameter space is identified for which the model reproduces the qualitative behaviour observed in experiments. The temporal dynamics of motion integration are studied within this region; specifically, the effect of varying the stimulus gain is studied, which allows for qualitative predictions to be made

Masking and color inheritance along the apparent motion path

Long-range apparent motion is the illusory motion that can be perceived when two static and distant stimuli are presented in succession. Within some spatiotemporal range not only is motion sensed, but it appears as if one stimulus is displaced from one place to another (termed beta or optimal motion). Several groups have found that this illusory percept can interact with perception of a physically present stimulus, but some disagree on the origin of these interactions. We know little about how suppressive effects depend on feature-similarity between a target and the stimuli in apparent motion (inducers)-which would indicate an early perceptual locus-or even about the minimal conditions under which to obtain this effect. Unlike early studies that used a two-stroke apparent motion paradigm, we were able to demonstrate that motion can mask stimuli presented at interpolated locations along the apparent motion path, as shown by the elevation of contrast thresholds compared to a control condition. Apparent motion masking depended on color similarity between target and inducers. Further, we found evidence that the color of inducers alters the apparent color of intervening gray probes, indicating some inheritance or chromatic averaging across distant locations, but no clear evidence of predictive updating. Finally, the analysis of the presentation times delivering maximal masking effects suggests a predictive interpolation process is responsible for interference by apparent motion filling-in. We discuss alternative mechanisms, in particular the possible role of apparent-motion-induced metacontrast masking in generating this pattern of results

Experimental Manipulation of Action Perception Based on Modeling Computations in Visual Cortex

Action perception, planning and execution is a broad area of study, crucial for future development of clinical therapies treating social cognitive disorders, as well as for building human-computer interaction systems and for giving foundation to an emerging field of developmental robotics. We took interest in basic mechanisms of action perception, and as a model area chose dynamic perception of body motion. The focus of this thesis has been on understanding how perception of actions can be manipulated, how to distill this understanding experimentally, and how to summarize via numerical simulation the neural mechanisms helping explain observed dynamic phenomena. Experimentally we have, first, shown how a careful manipulation of a static object depth cue can in principle modulate perception of actions. We chose the luminance gradient as a model cue, and linked action perception to a perceptual prior previously studied in object recognition – the lighting from above-prior. Second, we have explored the dynamic relationship between representations of actions that are naturally observed in spatiotemporal proximity. We have shown an adaptation aftereffect that may speak of brain mechanisms encoding social interactions. To qualitatively capture neural mechanisms behind ours and previous findings, we have additionally appealed to the perceptual bistability phenomenon. Bistable perception refers to the ability to spontaneously switch between two perceptual alternatives arising from an observation of a single stimulus. Addition of depth cues to biological motion stimulus resolves depth-ambiguity. To account for neural dynamics as well as for modulation of action percept by light source position, we used a combined architecture with a convolutional neural network computing shading and form features in biological motion stimuli, and a 2-dimensional neural field coding for walking direction and body configuration in the gait cycle. This single unified model matches experimentally observed switching statistics, dependence of recognized walking direction on the light source position, and makes a prediction for the adaptation aftereffect in perception of biological motion

Estudio de una nueva técnica psicoterapéutica grupal para la esquizofrenia basada en el uso del cine de ficción: Efectos sobre síntomas positivos

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Psiquiatría. Fecha de lectura: 23-02-2016Esta tesis tiene embargado el acceso al texto completo hasta el 23-08-2017Introducción La esquizofrenia es uno de los trastornos mentales que mayor sufrimiento y limitación causa en las personas que la padecen y el tratamiento de la misma dista de estar resuelto de un modo satisfactorio. El cine de ficción posee una extraordinaria capacidad para desencadenar procesos mentales y respuestas cerebrales en los espectadores aunque su potencial terapéutico en pacientes con esquizofrenia no ha sido estudiado de forma experimental y sistemática. Objetivos Comprobar la eficacia de una nueva técnica psicoterapéutica grupal, que utiliza el cine de ficción y se inspira en el análisis fílmico, en pacientes con trastornos psicóticos del espectro de la esquizofrenia. Metodología 48 pacientes con esquizofrenia participaron en un ensayo clínico aleatorizado, multicéntrico y en grupos paralelos. Se compararon los efectos de una nueva técnica psicoterapéutica grupal (que utiliza el cine como soporte cognitivo y se inspira en el análisis fílmico) frente a una técnica grupal más inespecífica que utiliza también el cine. Se utilizaron los 13 capítulos de la primera temporada de la serie de televisión “Los Soprano”. Ambos grupos veían dos veces cada episodio por lo que realizaban un total de 26 sesiones. Las medidas primarias de resultado fueron los cambios obtenidos en las subescalas de la PANNS, según el modelo pentafactorial de Wallwork, entre la situación basal y la de post-tratamiento. Las medidas de resultados cognitivas fueron los cambios en las escalas de cognición general (MCCB) y cognición social (MSCEIT, FEIT y FBS) antes y después del tratamiento. Resultados Se encontró una mejoría estadísticamente significativa del grupo experimental frente al grupo control en los síntomas positivos [p=0,01, d=0,82 (0,2-1,43)], negativos [p=0,005, d=0,89 (0,26-1,51)] y desorganizados [p=0,013, d=0,49 (0,11-1,09)]. En el análisis “post hoc” del factor positivo se encuentra una mejoría estadísticamente significativa en el grupo experimental frente al control en los delirios [p=0,01, d=0.82 (0,2-1,4)]. No se encontraron diferencias significativas entre ambos grupos tras la intervención en ninguno de los dominios cognitivos estudiados. Conclusiones El uso de la nueva técnica psicoterapéutica grupal en la que se realiza un análisis por secuencias del cine, puede servir para mejorar los síntomas positivos de pacientes con esquizofrenia, en especial, las creencias delirantes. Asimismo, puede producir mejoría en otros síntomas como los negativos o desorganizados.Background Schizophrenia is a mental disorder that originates a great amount of suffering and limitations in those who suffer from it. The treatment of the disease is far from being solved satisfactorily. Fiction films have an extraordinary ability to trigger mental processes and brain responses in viewers, but its therapeutic potential in patients with schizophrenia has not been studied in an experimental and systematical way. Objectives To test the effectiveness of a new group psychotherapeutic technique in patients with schizophrenia and other psychotic disorders, that uses fiction films and is inspired by film analysis. Methods 48 patients with schizophrenia participated in a multicentric randomized controlled clinical trial in parallel groups. The effects of the new group psychotherapeutic technique (which uses films as a cognitive support and is inspired by film analysis) is compared to a more unspecific group technique that also uses films. Thirteen episodes of the first season of the television series "The Sopranos" were used. Both groups completed a total of 26 sessions and saw each episode twice. The primary outcome measures were the changes obtained on the subscales of the PANSS, according to the five-factor model of Wallwork, between baseline and post-treatment. Cognitive outcome measures were measured by scales of general cognition (MCCB) and social cognition (MSCEIT , FEIT and FBS) before and after treatment. Results A statistically significant improvement in the experimental group versus control group was found in positive symptoms [p=0.01, d=0.82 (0.2-1.43)], negative symptoms [p=0.005, d=0.89 (0.26-1.51)] and disorganized symptoms [p=0.013, d=0.49 (0.11- 1.09)]. In the "post hoc" analysis of the positive factor a statistically significant improvement in the experimental group compared to the control was also found in delusions [p=0.01, d=0.82 (0.2-1.4)]. No significant differences were found between the two groups after the intervention in any of the cognitive domains. Conclusions The use of the new group psychotherapeutic technique in which the film sequence analysis is performed, can serve to improve the positive symptoms of schizophrenia patients, especially delusional beliefs. It can also improve the negative or disorganized symptoms