Stereopsis provides a constant feed to visual shape representation.

The contribution of stereopsis in human visual shape perception was examined using stimuli with either null, normal, or reversed binocular disparity in an old/new object recognition task. The highest levels of recognition performance were observed with null and normal binocular disparity displays, which did not differ. However, reversed disparity led to significantly worse performance than either of the other display conditions. This indicates that stereopsis provides a continuous input to the mechanisms involved in shape perception.

A surface-based code contributes to visual shape perception.

Considerable uncertainty remains regarding the types of features human vision uses for shape representation. Visual-search experiments are reported which assessed the hypothesis of a surface-based (i.e., edge-bounded polygons) code for shape representation in human vision. The results indicate slower search rates and/or longer response times when the target shape shares its constituent surfaces with distractors (conjunction condition) than when the target surfaces are unique in the display (nonconjunction condition). This demonstration is made using test conditions that strictly control any potential artifact pertaining to target-distractor similarity. The surface-based code suggested by this surface-conjunction effect is strictly 2-D, since the effect occurs even when the surfaces are shared between the target and distractors in the 2-D image but not in their 3-D instantiation. Congruently, this latter finding is unaltered by manipulations of the richness of the depth information offered by the stimuli. It is proposed that human vision uses a 2-D surface-based code for shape representation which, considering other key findings in the field, probably coexists with an alternative representation mode based on a type of structural description that can integrate information pertaining to the 3-D aspect of shapes.

An ERP study on hostile attribution bias in aggressive and nonaggressive individuals.

Hostile attribution bias (e.g., tendency to interpret the intention of others as hostile in ambiguous social contexts) has been associated with impulsive aggression in adults, but the results are mixed and the complete sequence of hostile inferential processes leading to aggression has not been investigated yet. The goal of this event-related brain potentials (ERPs) study was to track the neural activity associated with the violation of expectations about hostile versus nonhostile intentions in aggressive and nonaggressive individuals and examine how this neural activity relates to self-reported hostile attributional bias and impulsive aggression in real life. To this end, scenarios with a hostile versus nonhostile social context followed by a character's ambiguous aversive behavior were presented to readers, and ERPs to critical words that specified the hostile versus nonhostile intent behind the behavior were analysed. Thirty-seven aggressive and fifty nonaggressive individuals participated in the study. The presentation of a critical word that violated hostile expectation caused an N400 response that was significantly larger in aggressive than nonaggressive individuals. Results also showed an enhanced late positive potential-like component in aggressive individuals when hostile intention scenarios took place in a nonhostile context, which is associated with impulsive aggression in real life even after having controlled for the effect of self-reported hostile attributional bias. The Hostile Expectancy Violation paradigm evaluated in this study represents a promising tool to investigate the relationship between the online processing of hostile intent in others and impulsive aggression. Aggr. Behav. 43:217-229, 2017. © 2016 Wiley Periodicals, Inc.

Neural mechanisms underlying attribution of hostile intention in nonaggressive individuals: An ERP study.

Although the perception of hostile intentions in other people can have a clear adaptive function, researchers have paid little attention to the capacity of nonaggressive individuals to infer hostile intentions in others. The goal of the present study was to study brain mechanisms associated with expectations of hostile/non-hostile intent and their on-line evaluation. Scenarios with a hostile versus non-hostile social context followed by a character's ambiguous aversive behavior were presented to readers, and we recorded and analyzed event-related brain potentials (ERPs) to critical words that disambiguated the hostile versus non-hostile intent behind the behavior. Fifty nonaggressive individuals participated in the study. Non-hostile critical words that violated hostile intention expectations elicited a larger negative-going ERP deflection with central and posterior maximums between 400 and 600ms after word onset compatible with an N400 effect. Finally, there were marginally significant correlations between N400 effect sizes and hostile as well as neutral attribution bias measured by a self-report questionnaire. The results suggest that nonaggressive individuals evaluate rapidly, on-line, their attributions of the hostile intent of others. The methodology we developed provides the field with a new paradigm with which to study social attributions of hostile intent likely to contribute to hostile or aggressive reactions.

Decoding the Locus of Covert Visuospatial Attention from EEG Signals.

Visuospatial attention can be deployed to different locations in space independently of ocular fixation, and studies have shown that event-related potential (ERP) components can effectively index whether such covert visuospatial attention is deployed to the left or right visual field. However, it is not clear whether we may obtain a more precise spatial localization of the focus of attention based on the EEG signals during central fixation. In this study, we used a modified Posner cueing task with an endogenous cue to determine the degree to which information in the EEG signal can be used to track visual spatial attention in presentation sequences lasting 200 ms. We used a machine learning classification method to evaluate how well EEG signals discriminate between four different locations of the focus of attention. We then used a multi-class support vector machine (SVM) and a leave-one-out cross-validation framework to evaluate the decoding accuracy (DA). We found that ERP-based features from occipital and parietal regions showed a statistically significant valid prediction of the location of the focus of visuospatial attention (DA = 57%, p < .001, chance-level 25%). The mean distance between the predicted and the true focus of attention was 0.62 letter positions, which represented a mean error of 0.55 degrees of visual angle. In addition, ERP responses also successfully predicted whether spatial attention was allocated or not to a given location with an accuracy of 79% (p < .001). These findings are discussed in terms of their implications for visuospatial attention decoding and future paths for research are proposed.

Stereo and shading contribute independently to shape convexity-concavity discrimination.

The present study examined the joint contribution of shading and stereopsis to the perception of shape convexity-concavity. The stimuli were the images of a synthetic convex 3-D shape seen from viewpoints leading to ambiguity as to its convexity. Illumination came from either above or below, and from either the right or the left, and stimuli were presented dichoptically with normal binocular disparity, reversed disparity, or no disparity. Participants responded "convex" more often when the lighting came from above than from below. Also, participants responded that the shape was convex more often with normal than with zero disparity, and more often with zero disparity than with reversed stereopsis. The effects of lighting direction and display mode were additive--that is, they did not interact. This indicates that shading and stereopsis contribute independently to shape perception.