The evil eye effect: vertical pupils are perceived as more threatening

Popular culture has many examples of evil characters having vertically pupilled eyes. Humans have a long evolutionary history of rivalry with snakes and their visual systems were evolved to rapidly detect snakes and snake-related cues. Considering such evolutionary background, we hypothesised that humans would perceive vertical pupils, which are characteristics of ambush predators including some of the snakes, as threatening. In seven studies (aggregate N?=?1458) conducted on samples from American and Turkish samples, we found that vertical pupils are perceived as more threatening on both explicit (Study 1) and implicit level (Studies 2–7) and they are associated with physical, rather than social, threat (Study 4). Findings provided partial support regarding our hypothesis about the relevance of snake detection processes: Snake phobia, and not spider phobia, was found to be related to perceiving vertical pupils as threatening (Study 5), however an experimental manipulation of saliency of snakes rendered no significant effect (Study 6) and a comparison of fears of snakes, alligators, and cats did not support our prediction (Study 7). We discuss the potential implications and limitations of these novel findings.     

Functional and anatomical profile of visual motion impairments in stroke patients correlate with fMRI in normal subjects

We used six psychophysical tasks to measure sensitivity to different types of global motion in 45 healthy adults and in 57 stroke patients who had recovered from the initial results of the stroke, but a large subset of them had enduring deficits on selective visual motion perception tasks. The patients were divided into four groups on the basis of the location of their cortical lesion: occipito-temporal, occipito-parietal, rostro-dorsal parietal, or frontal-prefrontal. The six tasks were: direction discrimination, speed discrimination, motion coherence, motion discontinuity, two-dimensional form-from-motion, and motion coherence – radial. We found both qualitative and quantitative differences among the motion impairments in the four groups: patients with frontal lesions or occipito-temporal lesions were not impaired on any task. The other two groups had substantial impairments, most severe in the group with occipito-parietal damage. We also tested eight healthy control subjects on the same tasks while they were scanned by functional magnetic resonance imaging. The BOLD signal provoked by the different tasks correlated well with the locus of the lesions that led to impairments among the different tasks. The results highlight the advantage of using psychophysical techniques and a variety of visual tasks with neurological patients to tease apart the contribution of different cortical areas to motion processing.