424 research outputs found
Prosopagnosia: when all faces look the same
No full textThis book provides readers with a simplified and comprehensive account of the cognitive and neural bases of face perception in humans. Faces are ubiquitous in our environment and we rely on them during social interactions. The human face processing system allows us to extract information about the identity, gender, age, mood, race, attractiveness and approachability of other people in about a fraction of a second, just by glancing at their faces. By introducing readers to the most relevant research on face recognition, this book seeks to answer the questions: “Why are humans so fast at recognizing faces?”, “Why are humans so efficient at recognizing faces?”, “Do faces represent a particular category for the human visual system?”, What makes face perception in humans so special?, “Can our face recognition system fail”? This book presents the author’s findings on face perception during his research studies on both normal subjects and subjects with prosopagnosia, a neurological disorder characterized by the inability to recognize faces. The book describes two known forms of prosopagnosia: acquired prosopagnosia, which is the result of a brain lesion, and congenital prosopagnosia, which refers to a lifelong, developmental impairment of face recognition. Written in a comprehensive and accessible style, this book addresses both experts (cognitive scientists, psychologists, neuroscientists and computer scientists) and the general public, and aims at raising awareness for a debilitating face recognition disorder, such as prosopagnosia, which is often ignored or misdiagnosed as autism, with serious consequences for the affected persons and their families
Prosopagnosia. Un mondo di facce uguali
No full textIn questo libro l'autore racconta le basi cognitive e neurali del processamento dei volti. In particolare descrive la ricerca effettuata in persone normali ed in persone con Prosopagnosia, una condizione per cui, chi ne soffre, e’ incapace di utilizzare i volti per riconoscere le persone, riportando i risultati più importanti che coinvolgono le due forme conosciute di prosopagnosia, quella acquisita (conseguenza di un danno cerebrale) e quella congenita (condizione che si riferisce all’incapacità’ di riconoscere i volti dalla nascita)
Deep learning applied to EEG source-data reveals both ventral and dorsal visual stream involvement in holistic processing of social stimuli
No full textAbstract Perception of social stimuli (faces and bodies) relies on “holistic” (i.e., global) mechanisms, as supported by picture-plane inversion: perceiving inverted faces/bodies is harder than perceiving their upright counterpart. Albeit neuroimaging evidence suggested involvement of face-specific brain areas in holistic processing, their spatiotemporal dynamics and selectivity for social stimuli is still debated. Here, we investigate the spatiotemporal dynamics of holistic processing for faces, bodies and houses (adopted as control non-social category), by applying deep learning to high-density electroencephalographic signals (EEG) at source-level. Convolutional neural networks were trained to classify cortical EEG responses to stimulus orientation (upright/inverted), separately for each stimulus type (faces, bodies, houses), resulting to perform well above chance for faces and bodies, and close to chance for houses. By explaining network decision, the 150–200 ms time interval and few visual ventral-stream regions were identified as mostly relevant for discriminating face and body orientation (lateral occipital cortex, and for face only, precuneus cortex, fusiform and lingual gyri), together with two additional dorsal-stream areas (superior and inferior parietal cortices). Overall, the proposed approach is sensitive in detecting cortical activity underlying perceptual phenomena, and by maximally exploiting discriminant information contained in data, may reveal spatiotemporal features previously undisclosed, stimulating novel investigations
Influence of single- and double-aging treatments on the mechanical and corrosion resistance of Alloy 625
No full textNickel–chromium–molybdenum Alloy 625 exhibits an excellent combination of mechanical
properties and corrosion resistance. However, the high-temperature plastic deformation process and the heat treatment represent critical aspects for the loss in mechanical strength by grain coarsening. This detrimental behavior is worsened by the absence of phase transformation temperatures. However, the chemical composition permits slow precipitation-hardening response upon single aging. Therefore, when the soft- or solution-annealed condition is associated with insufficient mechanical properties, this potentiality can be exploited to improve the mechanical strength. Since the gamma double prime precipitation can be accelerated by double-aging treatment, different time–temperature combinations of double aging at 732 °C and 621 °C are investigated. The simultaneous precipitation of intergranular carbides can dramatically affect the corrosion resistance. Such an undesired phenomenon occurs very quickly at 732 °C, but it is obtained only after very long exposure times at 621 °C. For this reason, a performance chart is developed to compare all the tested conditions. In particular, single aging at 621 °C for 72 h and 130 h are associated with an acceptable combination of mechanical and corrosion properties. Double aging permits a conspicuous acceleration of the aging response. For instance, with double aging at 732 °C 3 h and 621 °C 72 h, it is possible to obtain the same mechanical properties of single aging at 621 °C for 260 h. Such acceleration is accompanied by a more critical corrosion behavior, especially because of the primary step. However, even after its optimization, none of the tested conditions were acceptable
Selective Laser-Melted Alloy 625: Optimization of Stress-Relieving and Aging Treatments
No full textAdditive manufacturing is an innovative solution to produce components characterized by complex geometries. The use of such parts requires a deep knowledge of their behavior under different service conditions, especially from mechanical and corrosion resistance points of view. One of the most well-known and employed materials produced by selective laser melting is nickel alloy 625. It is already commonly used in its conventional form, but the additive manufacturing technology, despite its higher production costs and lower productivity, is becoming competitive because of its excellent mechanical strength. It is in fact significantly higher compared to the conventionally manufactured alloy whose properties are often limited by the difficulty in retaining a fine grain size during plastic deformation and heat treatment. Even though the as-built performance is already quite good, further strength improvement can be attained upon tailored single- and double-aging treatments that are optimized starting from the experimental results obtained in the conventional alloy and also considering the influence on corrosion resistance. In addition, considering that the stress-relieving treatment recommended for the conventional forged alloy at 870 °C is not suitable for the selective laser-melted material because of the more rapid precipitation response, this temperature is optimized to improve both the tensile deformability and the corrosion behavior
More than just a problem with faces: altered body perception in a group of congenital prosopagnosics
No full textIt has been estimated that one out of 40 people in the general population suffer from congenital prosopagnosia (CP), a neurodevelopmental disorder characterized by difficulty identifying people by their faces. CP involves impairment in recognizing faces, although the perception of non-face stimuli may also be impaired. Given that social interaction depends not only on face processing, but also on the processing of bodies, it is of theoretical importance to ascertain whether CP is also characterized by body perception impairments. Here, we tested 11 CPs and 11 matched control participants on the Body Identity Recognition Task (BIRT), a forced-choice match-to-sample task, using stimuli that require processing of body-specific, not clothing-specific, features. Results indicated that the group of CPs were as accurate as controls on the BIRT, which is in line with the lack of body perception complaints by CPs. However, the CPs were slower than controls, and when accuracy and response times were combined into inverse efficiency scores (IESs), the group of CPs were impaired, suggesting that the CPs could be using more effortful cognitive mechanisms to be as accurate as controls. In conclusion, our findings demonstrate that CP may not generally be limited to face processing difficulties, but may also extend to body perception
Stimulus Inversion and Emotional Expressions Independently Affect Face and Body Perception: An ERP Study
No full textFaces and bodies provide critical cues for social interaction and communication. Their structural encoding depends on configural processing, as suggested by the detrimental effect of stimulus inversion for both faces (i.e., face inversion effect - FIE) and bodies (body inversion effect - BIE). An occipito-temporal negative event-related potential (ERP) component peaking around 170 ms after stimulus onset (N170) is consistently elicited by human faces and bodies and is affected by the inversion of these stimuli. Albeit it is known that emotional expressions can boost structural encoding (resulting in larger N170 components for emotional than for neutral faces), little is known about body emotional expressions. Thus, the current study investigated the effects of different emotional expressions on structural encoding in combination with FIE and BIE. Three ERP components (P1, N170, P2) were recorded using a 128-channel electroencephalogram (EEG) when participants were presented with (upright and inverted) faces and bodies conveying four possible emotions (happiness, sadness, anger, fear) or no emotion (neutral). Results demonstrated that inversion and emotional expressions independently affected the Accuracy and amplitude of all ERP components (P1, N170, P2). In particular, faces showed specific effects of emotional expressions during the structural encoding stage (N170), while P2 amplitude (representing top-down conceptualisation) was modified by emotional body perception. Moreover, the task performed by participants (i.e., implicit vs. explicit processing of emotional information) differently influenced Accuracy and ERP components. These results support integrated theories of visual perception, thus speaking in favour of the functional independence of the two neurocognitive pathways (one for structural encoding and one for emotional expression analysis) involved in social stimuli processing. Results are discussed highlighting the neurocognitive and computational advantages of the independence between the two pathways
Selective laser melted 316L stainless steel: Influence of surface and inner defects on fatigue behavior
No full textIn additive manufacturing, despite its several indisputable advantages, detrimental variables to fatigue strength still remain poor surface finishing and porosities. However, because the majority of defects locate close to the surface, their mechanical removal is expected to appreciably improve fatigue strength. Considering SLMed 316L, fully-reversed rotating-bending fatigue tests in both as-built and machined conditions are performed. Fatigue failures are discussed using the Kitagawa-Takahashi diagram. In each condition, the fatigue stress is related to the equivalent micro-notch length of the killer defect. Then, this work analyses the possibility of predicting fatigue limits at 50 % probability considering the equivalent micro-notch length
Optimization of the mechanical and corrosion resistance of Alloy 625 through aging treatments
No full textIn the as-annealed condition, the nickel-based Alloy 625 has excellent mechanical and corrosion properties compared to those of common stainless steels. This peculiarity enables its exploitation in several industrial fields at cryogenic and high temperatures and in the presence of severely corrosive atmospheres. However, in this alloy, when high-temperature plastic deformation processes and heat treatments are not carefully optimized, the occurrence of excessive grain coarsening can irremediably deteriorate the mechanical strength, possibly leading to incompatibility with the standard requirements. Therefore, this research work investigated the possibility of adopting single- and double-aging treatments aimed at improving such strength loss. Their optimization involved identifying the best compromise between the hardening effect and the loss in corrosion resistance induced by the simultaneous formation of intergranular chromium-rich carbides during aging. The investigation of the aging treatments was performed using hardness, tensile and intergranular corrosion tests considering different time–temperature combinations in a range from 621 °C to 732 °C. Double aging resulted in a considerable acceleration in the hardening response compared to single aging. However, even after its optimization in terms of both temperature and time, the intergranular corrosion resistance remained a critical aspect. Among all the tested conditions, only single aging at 621 °C for 72 h was acceptable in terms of both mechanical and corrosion properties. The influence of longer exposures will be investigated in a future study
Covert face recognition in congenital prosopagnosia: A group study
No full textIntroduction: Even though people with congenital prosopagnosia (CP) never develop a normal ability to "overtly" recognize faces, some individuals show indices of "covert" (orimplicit) face recognition. The aim of this study was to demonstrate covert face recognition in CP when participants could not overtly recognize the faces. Methods: Eleven people with CP completed three tasks assessing their overt face recognition ability, and three tasks assessing their "covert" face recognition: a Forced choice familiarity task, a Forced choice cued task, and a Priming task. Results: Evidence of covert recognition was observed with the Forced choice familiarity task, but not the Priming task. In addition, we propose that the Forced choice cued task does not measure covert processing as such, but instead "provoked-overt" recognition. Conclusions: Our study clearly shows that people with CP demonstrate covert recognition for faces that they cannot overtly recognize, and that behavioural tasks vary in their sensitivity to detect covert recognition in CP. © 2011 Elsevier Srl
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