Modeling geometric–optical illusions: A variational approach

Visual distortions of perceived lengths, angles, or forms, are generally known as “geometric–optical illusions” (goi). In the present paper we focus on a class of gois where the distortion of a straight line segment (the “target” stimulus) is induced by an array of non-intersecting curvilinear elements (“context” stimulus). Assuming local target–context interactions in a vector field representation of the context, we propose to model the perceptual distortion of the target as the solution to a minimization problem in the calculus of variations. We discuss properties of the solutions and reproduction of the respective form of the perceptual distortion for several types of contexts. Moreover, we draw a connection between the interactionist model of gois and Riemannian geometry: the context stimulus is understood as perturbing the geometry of the visual field from which the illusory distortion naturally arises. The approach is illustrated by data from a psychophysical experiment with nine subjects and six different contexts.     

The influence of emotion type,social value orientation and processing focus on approach-avoidance tendencies to negative dynamic facial expressions

Facial expressions of anger and fear have been seen to elicit avoidance behavior in the perceiver due to their negative valence. However, recent research uncovered discrepancies regarding these immediate motivational implications of fear and anger, suggesting that not all negative emotions trigger avoidance to a comparable extent. To clarify those discrepancies, we considered recent theoretical and methodological advances, and investigated the role of social preferences and processing focus on approach-avoidance tendencies (AAT) to negative facial expressions. We exposed participants to dynamic facial expressions of anger, disgust, fear, or sadness, while they processed either the emotional expression or the gender of the faces. AATs were assessed by reaction times of lever movements, and by posture changes via head-tracking. We found that—relative to angry faces-, fearful and sad faces triggered more approach, with a larger difference between fear and anger in prosocial compared to individualistic participants. Interestingly, these findings are in line with a recently developed concern hypothesis, suggesting that—relative to other negative expressions—expressions of distress may facilitate approach, especially in participants with prosocial preferences.     

Disentangling the adult attention-deficit hyperactivity disorder endophenotype: parametric measurement of attention

Attention deficit hyperactivity disorder (ADHD) persists frequently into adulthood. The decomposition of endophenotypes by means of experimental neuro-cognitive assessment has the potential to improve diagnostic assessment, evaluation of treatment response, and disentanglement of genetic and environmental influences. We assessed four parameters of attentional capacity and selectivity derived from simple psychophysical tasks (verbal report of briefly presented letter displays) and based on a "theory of visual attention." These parameters are mathematically independent, quantitative measures, and previous studies have shown that they are highly sensitive for subtle attention deficits. Potential reductions of attentional capacity, that is, of perceptual processing speed and working memory storage capacity, were assessed with a whole report paradigm. Furthermore, possible pathologies of attentional selectivity, that is, selection of task-relevant information and bias in the spatial distribution of attention, were measured with a partial report paradigm. A group of 30 unmedicated adult ADHD patients and a group of 30 demographically matched healthy controls were tested. ADHD patients showed significant reductions of working memory storage capacity of a moderate to large effect size. Perceptual processing speed, task-based, and spatial selection were unaffected. The results imply a working memory deficit as an important source of behavioral impairments. The theory of visual attention parameter working memory storage capacity might constitute a quantifiable and testable endophenotype of ADHD.