Perception of speed in biological motion : more resistant to interference?

O sistema visual humano é frequentemente referido como altamente preparado para extrair informação relevante de padrões de movimento biológico. Nesse sentido, este estudo analisa o efeito de contraste na percepção de velocidade. Os participantes realizaram o julgamento de velocidade numa situação na qual dois point-light walkers simultâneos foram apresentados com diferentes contrastes relativamente ao fundo e com diferentes velocidades de translação. Na Experiência 1, o movimento de translação biológico canônico foi comparado com o movimento de translação rígido, enquanto na Experiência 2 ele foi comparado com o movimento de translação biológico invertido. O padrão biológico canônico apresenta maior taxa de erro, tempos de reação mais elevados e maior vulnerabilidade ao efeito de contraste na percepção da velocidade do que o padrão rígido. No entanto, não foram encontradas diferenças significativas entre o estímulo canônico e o invertido. A Experiência 3 foi implementada com o objetivo de se controlar o papel das pistas posicionais na tarefa de julgamento de velocidade. Os pontos iniciais e finais da trajetória foram combinados de modo a que os point-light walkers mais rápidos e os mais lentos pudessem terminar o ensaio numa posição relativamente mais avançada ou atrasada. Apesar desta variação, o padrão de resultados foi congruente com as observações das Experiências 1 e 2. Aparentemente, os participantes realizaram julgamentos de velocidade factuais, ao invés do uso de pistas espaciais como uma espécie de referência ou comparação de posicionamento. Dado que a percepção dos padrões biológicos foi mais vulnerável aos efeitos de contraste, mas não foi afetada pela familiaridade, este estudo sugere que a percepção de movimento biológico e rígido poderá obedecer às mesmas regras computacionais, pelo menos em tarefas que envolvam padrões em translação e julgamentos de velocidade.The human visual system is often referred to as being highly prepared to extract meaningful information from biological motion patterns. In the present study, the contrast effect on speed perception was analysed. Participants performed a test of speed judgment in which two simultaneous point-light walkers were animated at different translational speeds and contrasts in relation to the background. Standard translational biological motion was compared to rigid translational motion in Experiment 1 and to inverted biological motion in Experiment 2. Higher error rates, reaction times and greater vulnerability to contrast effects on speed perception were found for translational biological motion when compared to rigid motion. No significant differences were found, however, between standard and inverted stimuli. Experiment 3 was implemented in order to control the role of positional cues in speed judgment. The start and finish points of the trajectory were varied so that the faster and slower point-light walkers could finish the trial at a relatively more advanced or more withdrawn position. In spite of the variation of the start and finish points of the trajectories, the pattern of results was still consistent with the findings of Experiments 1 and 2. Participants seemed to perform factual speed judgments instead of using spatial cues as a form of reference or positional matching. Since the perception of biological patterns was more sensitive to contrast effects and not affected by familiarity, it is suggested that perception of biological and rigid motion may follow the same computational rules, at least for tasks involving translational patterns and speed judgment.Fundação para a Ciência e a Tecnologia (FCT

On the resolution of the generalized nonlinear complementarity problem

Minimization of a differentiable function subject to box constraints is proposed as a strategy to solve the generalized nonlinear complementarity problem ( GNCP) defined on a polyhedral cone. It is not necessary to calculate projections that complicate and sometimes even disable the implementation of algorithms for solving these kinds of problems. Theoretical results that relate stationary points of the function that is minimized to the solutions of the GNCP are presented. Perturbations of the GNCP are also considered, and results are obtained related to the resolution of GNCPs with very general assumptions on the data. These theoretical results show that local methods for box-constrained optimization applied to the associated problem are efficient tools for solving the GNCP. Numerical experiments are presented that encourage the use of this approach.Minimization of a differentiable function subject to box constraints is proposed as a strategy to solve the generalized nonlinear complementarity problem ( GNCP) defined on a polyhedral cone. It is not necessary to calculate projections that complicate an122303321CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçãosem informaçã

The time to passage of biological and complex motion

A significant part of human interactions occur with other human beings and not only with inanimate objects. It is important in everyday tasks to estimate the time it takes other people to reach (time to contact) or pass us (time to passage). Surprisingly, little is known about judging time to contact or time to passage of biological or other complex motions. In two experiments, rigid and non-rigid (biological, inverted, scrambled, and complex non-biological) motion conditions were compared in a time-to-passage judgment task. Subjects could judge time to passage of point-light-walker displays. However, due to relative and opponent movements of body parts, all articulated patterns conveyed a noisier looming pattern. Non-rigid stimuli were judged as passing sooner than rigid stimuli but reflected more uncertainty in the judgments as revealed by precision judgments and required longer reaction times. Our findings suggested that perceptual judgments for complex motion, including biological patterns, are built on top of the same processing channels that are involved on rigid motion perception. The complexity of the motion pattern (rigid vs. non-rigid) plays a more determinant role than the "biologicity" of the stimulus (biological vs. non-biological), at least concerning time-to-passage judgments

The time to passage of biological and complex motion

A significant part of human interactions occur with other human beings and not only with inanimate objects. It is important in everyday tasks to estimate the time it takes other people to reach (time to contact) or pass us (time to passage). Surprisingly, little is known about judging time to contact or time to passage of biological or other complex motions. In two experiments, rigid and non-rigid (biological, inverted, scrambled, and complex non-biological) motion conditions were compared in a time-to-passage judgment task. Subjects could judge time to passage of point-light-walker displays. However, due to relative and opponent movements of body parts, all articulated patterns conveyed a noisier looming pattern. Non-rigid stimuli were judged as passing sooner than rigid stimuli but reflected more uncertainty in the judgments as revealed by precision judgments and required longer reaction times. Our findings suggested that perceptual judgments for complex motion, including biological patterns, are built on top of the same processing channels that are involved on rigid motion perception. The complexity of the motion pattern (rigid vs. non-rigid) plays a more determinant role than the “biologicity” of the stimulus (biological vs. non-biological), at least concerning time-to-passage judgments.Luso-Spanish Integrated Action funded by the Spanish and Portuguese governmentsFundação para a Ciência e a Tecnologia (FCT

Uncertainty in estimating time-to-passage revealed by reaction times

Fundação para a Ciência e Tecnologia (FCT

Choosing audio devices on the basis of listeners’ spatial perception: A case study of headphones vs in-earphones

The Earphones and Headphones industry is steadily growing following the emergence of new technological advancements and new applications. New methods to determine listeners’ performance using different types of audio output devices will be in high demand. In this paper we adapt a methodology for evaluation of listeners’ auditory localization accuracy to support the choice between two devices. As a case study, we compare a particular set of in-earphones and headphones. Our goal was to present a method that allowed us to: (1) conclude which audio device provided the most accurate sense of auditory localization; (2) understand the effect of training on task performance; and (3) determine which type of device benefits the most from short sessions of training in auditory localization. Participants had better performances using headphones. Nevertheless, we can reduce the differences between devices if short training sessions are included and the same device is used between training and test.info:eu-repo/semantics/publishedVersio

Bimodal information increases spontaneous interpersonal synchronization of goal directed upper limb movements

When interacting with each other, people often synchronize spontaneously their movements, e.g. during pendulum swinging, chair rocking[5], walking [4][7], and when executing periodic forearm movements[3].Although the spatiotemporal information that establishes the coupling, leading to synchronization, might be provided by several perceptual systems, the systematic study of different sensory modalities contribution is widely neglected. Considering a) differences in the sensory dominance on the spatial and temporal dimension[5] , b) different cue combination and integration strategies [1][2], and c) that sensory information might provide different aspects of the same event, synchronization should be moderated by the type of sensory modality. Here, 9 naïve participants placed a bottle periodically between two target zones, 40 times, in 12 conditions while sitting in front of a confederate executing the same task. The participant could a) see and hear, b) see , c) hear the confederate, d) or audiovisual information about the movements of the confederate was absent. The couple started in 3 different relative positions (i.e., in-phase, anti-phase, out of phase). A retro-reflective marker was attached to the top of the bottles. Bottle displacement was captured by a motion capture system. We analyzed the variability of the continuous relative phase reflecting the degree of synchronization. Results indicate the emergence of spontaneous synchronization, an increase with bimodal information, and an influence of the initial phase relation on the particular synchronization pattern. Results have theoretical implication for studying cue combination in interpersonal coordination and are consistent with coupled oscillator models.Fundação Bial (Grant 77/12) and Fundação para a Ciência e Tecnologia - FCT: SFRH/BD/8839 6/2012; EXPL/MHC - PCN/0162/2013; FCOMP - 01 - 0124 - FEDER - 022674 and PEst - C/CTM/U10264/2011; FCOMP - 01 - 0124 - FEDER - 037281 and PEst - C/EEI/LA0014/2013. This work was financed by FEDER grants through the Operational Competitiveness Program – COMPET