Towards a model of human body perception

Item does not contain fulltextFrom just a glimpse of another person, we make inferences about their current states and longstanding traits. These inferences are normally spontaneous and effortless, yet they are crucial in shaping our impressions and behaviours towards other people. What are the perceptual operations involved in the rapid extraction of socially relevant information? To answer this question, over the last decade the visual and cognitive neuroscience of social stimuli has received new inputs through emerging proposals of social vision approaches. Perhaps by function of these contributions, researchers have reached a certain degree of consensus over a standard model of face perception. This thesis aims to extend social vision approaches to the case of human body perception. In doing so, it establishes the building blocks for a perceptual model of the human body which integrates the extraction of socially relevant information from the appearance of the body. Using visual tasks, the data show that perceptual representations of the human body are sensitive to socially relevant information (e.g. sex, weight, emotional expression). Specifically, in the first empirical chapter I dissect the perceptual representations of body sex. Using a visual search paradigm, I demonstrate a differential and asymmetrical representation of sex from human body shape. In the second empirical chapter, using the Garner selective attention task, I show that the dimension of body sex is independent from the information of emotional body postures. Finally, in the third empirical chapter, I provide evidence that category selective visual brain regions, including the body selective region EBA, are directly involved in forming perceptual expectations towards incoming visual stimuli. Socially relevant information of the body might shape visual representations of the body by acting as a set of expectancies available to the observer during perceptual operations. In the general discussion I address how the findings of the empirical chapters inform us about the perceptual encoding of human body shape. Further, I propose how these results provide the initial steps for a unified social vision model of human body perception. Finally, I advance the hypothesis that rapid social categorisation during perception is explained by mechanisms generally affecting the perceptual analysis of objects under naturalistic conditions (e.g. expectations-expertise) operating within the social domain.Bangor University, 17 februari 2020Promotor : Downing, P.E. Co-promotor : Koldewyn, K.182 p

Perceiving emotion and sex from the body: evidence from the Garner task for independent processes

Contains fulltext : 221794.pdf (Publisher’s version ) (Closed access)The appearance of the body signals socially relevant states and traits, but the how these cues are perceived is not well understood. Here we examined judgments of emotion and sex from the body's appearance. Understanding how we extract these cues is important because they are both salient and socially relevant. Participants viewed body images and either reported the emotion expressed by each body while ignoring its sex, or else reported the sex while ignoring its emotion. Following Garner's logic, two types of blocks were compared. In control blocks, the task-irrelevant dimension was fixed (e.g. all male in an emotion judgment task), whereas in orthogonal blocks it varied orthogonally to the task-relevant dimension (e.g. male-female). Where two dimensions draw on shared processes, interference results in relatively slower responses during orthogonal blocks. In contrast, a finding of no Garner interference - efficient selection of the task-relevant dimension – is taken to reflect independent processes. Bayesian analyses revealed evidence of no Garner interference between sex and emotion judgments, showing that extraction of these distinct signals from the body's appearance proceeds along largely parallel processing streams. These findings are informative about the mental architecture behind our perception of socially relevant characteristics of other people.11 p

Asymmetric visual representation of sex from human body shape

We efficiently infer others' states and traits from their appearance, and these inferences powerfully shape our social behaviour. One key trait is sex, which is strongly cued by the appearance of the body. What are the visual representations that link body shape to sex? Previous studies of visual sex judgment tasks find observers have a bias to report "male", particularly for ambiguous stimuli. This finding implies a representational asymmetry - that for the processes that generate a sex percept, the default output is "male", and "female" is determined by the presence of additional perceptual evidence. That is, female body shapes are positively coded by reference to a male default shape. This perspective makes a novel prediction in line with Treisman's studies of visual search asymmetries: female body targets should be more readily detected amongst male distractors than vice versa. Across 10 experiments (N = 32 each) we confirmed this prediction and ruled out alternative low-level explanations. The asymmetry was found with profile and frontal body silhouettes, frontal photographs, and schematised icons. Low-level confounds were controlled by balancing silhouette images for size and homogeneity, and by matching physical properties of photographs. The female advantage was nulled for inverted icons, but intact for inverted photographs, suggesting reliance on distinct cues to sex for different body depictions. Together, these findings demonstrate a principle of the perceptual coding that links bodily appearance with a significant social trait: the female body shape is coded as an extension of a male default. We conclude by offering a visual experience account of how these asymmetric representations arise in the first place

Asymmetric visual representation of sex from facial appearance

We efficiently infer others' traits from their faces, and these inferences powerfully shape our social behaviour. Here, we investigated how sex is represented in facial appearance. Based on previous findings from sex-judgment tasks, we hypothesized that the perceptual encoding of sex is not balanced but rather polarized: for the processes that generate a sex percept, the default output is "male," and the representation of female faces extends that of the male, engaging activity over unique detectors that are not activated by male faces. We tested this hypothesis with the logic of Treisman's studies of visual search asymmetries, predicting that observers should more readily detect the presence of female faces amongst male distractors than vice versa. Across three experiments (N = 32 each), each using different face stimuli, we confirmed this prediction in response time and sensitivity measures. We apply GIST analyses to the face stimuli to exclude that the search asymmetry is explained by differences in image homogeneity. These findings demonstrate a property of the coding that links facial appearance with a significant social trait: the female face is coded as an extension of a male default. We offer a mechanistic description of perceptual detectors to account for our findings and posit that the origins of this polarized coding scheme are an outcome of biased early developmental experience

Inhibition of left anterior intraparietal sulcus shows that mutual adjustment marks dyadic joint-actions in humans

Creating real-life dynamic contexts to study interactive behaviors is a fundamental challenge for the social neuroscience of interpersonal relations. Real synchronic interpersonal motor interactions involve online, inter-individual mutual adaptation (the ability to adapt one's movements to those of another in order to achieve a shared goal). In order to study the contribution of the left anterior Intra Parietal Sulcus (aIPS) (i.e. a region supporting motor functions) to mutual adaptation, here, we combined a behavioral grasping task where pairs of participants synchronized their actions when performing mutually adaptive imitative and complementary movements, with the inhibition of activity of aIPS via non-invasive brain stimulation. This approach allowed us to investigate whether aIPS supports online complementary and imitative interactions. Behavioral results showed that inhibition of aIPS selectively impairs pair performance during complementary compared to imitative interactions. Notably, this effect depended on pairs' mutual adaptation skills and was higher for pairs composed of participants who were less capable of adapting to each other. Thus, we provide the first causative evidence for a role of the left aIPS in supporting mutually adaptive interactions and show that the inhibition of the neural resources of one individual of a pair is compensated at the dyadic level

Converging evidence that left extrastriate body area supports visual sensitivity to social interactions

Navigating our complex social world requires processing the interactions we observe. Recent psychophysical and neuroimaging studies provide parallel evidence that the human visual system may be attuned to efficiently perceive dyadic interactions. This work implies, but has not yet demonstrated, that activity in body-selective cortical regions causally supports efficient visual perception of interactions. We adopt a multi-method approach to close this important gap. First, using a large fMRI dataset (N=92), we found that the left-hemisphere Extrastriate Body Area (EBA) responds more to face-to-face than non-facing dyads. Second, we replicated a behavioural marker of visual sensitivity to interactions: categorisation of facing dyads is more impaired by inversion than non-facing dyads. Third, in a pre-registered experiment, we used fMRI-guided transcranial magnetic stimulation to show that online stimulation of the left EBA, but not a nearby control region, abolishes this selective inversion effect. Activity in left EBA, thus, causally supports the efficient perception of social interactions

Sudden Onset of Lower Abdominal Pain Without Peritonitis or Ileus

A patient presented with sudden, unexplained lower abdominal pain without peritonism or signs of infection or inflammatory reaction, but with recent bloody stools and a history of radiation therapy, diabetes and immunosuppression. Plain abdominal x-ray showed only air-fluid levels and air distention of the colon, but a later abdominal CT scan revealed extensive gas gangrene of the colon. The patient’s clinical status rapidly worsened. Elective surgical rectosigmoid debridement did not prevent the patient’s death. In conclusion, the diagnosis of ‘spontaneous’ life-threatening gas gangrene requires a high degree of clinical suspicion and allows life-saving surgical intervention

Predicting LVOT Obstruction in Transcatheter Mitral Valve Replacement for Failed Surgical Annuloplasty

n/

Potencial de deriva da mistura de 2,4-D com glyphosate

The application of the mixture of glyphosate with 2,4-d took on great importance with high adoption of no-tillage system in the early 90s, and with the constant reports of weed biotypes resistant to glyphosate. However, studies on the drift of this mixture are still scarce. The aim of this study was to evaluate the potential drift of these herbicides, with or without the adjuvant, applied in wind tunnel. The experimental design was completely randomized considered, arranged in a factorial design 5 x 3, with four replications, and five tails and three collection distances (5, 10 and 15 meters). The spray tested were: glyphosate, 2,4-D, 2,4-D+glyphosate, glyphosate+2,4-D+adjuvant, and a control in which water was applied. The collection points were installed at 5, 10 and 15 meters and in this points each 20 cm of height in relation of tunnel ground until 1,0 m of height. The application of the products took place in a wind tunnel with 20 m length and cross-sectional 4 m2 with speed wind of 2.0 m s-1,. The mean values obtained in the samples were subjected to analysis of variance, and their means were compared by Tukey test at 5% probability. It was observed that herbicide application associated produces more drift than when applied alone mainly to 5 and 10 meters of distance to sprayer boom. The drift of each herbicide applied alone did not differ. When added to the adjuvant mixture glyphosate plus 2,4-D, there was a 23% reduction in drift at 5 m and 6 m to 10%.A aplicação da mistura dos herbicidas glyphosate com 2,4-D passou a ter grande importância com a adoção do sistema de semeadura direta, no início dos anos 90, e com os constantes relatos de biótipos de plantas daninhas resistentes ao herbicida glyphosate. No entanto, estudos referentes à deriva desta mistura ainda são escassos. O objetivo deste trabalho foi avaliar o potencial de deriva dos herbicidas glyphosate e 2,4-D, associados ou não a adjuvante, pulverizados em túnel de vento. O delineamento experimental considerado foi inteiramente ao acaso, arranjados em um esquema fatorial 5 x 3, com quatro repetições, sendo cinco caldas e três distâncias de coleta (5, 10 e 15 metros). As caldas testadas foram: glyphosate, 2,4-D, 2,4-D+glyphosate e 2,4-D+glyphosate+adjuvante, além de uma testemunha na qual foi pulverizada água. A aplicação dos produtos ocorreu em um túnel com 20 m de comprimento e secção transversal de 4 m2, com velocidade do vento de 2,0 m.s-1. Os pontos de coleta foram instalados a 5, 10 e 15 m de distância da barra de pulverização e nestes pontos a cada 20 cm de altura em relação ao piso do túnel até 1,0 m de altura.  Os valores médios obtidos nas coletas foram submetidos à análise de variância, e suas médias foram comparadas pelo teste Tukey a 5% de probabilidade. Observou-se que a aplicação dos herbicidas associados produz mais deriva do que quando aplicados de forma isolada, principalmente a 5 e a 10 metros de distância da barra de pulverização. A deriva de cada herbicida aplicado isoladamente não apresentou diferenças estatísticas. Quando se adicionou adjuvante a calda associada houve uma redução de 23% na deriva a 5 m e 6% a 10 m