Threatening shapes: the impact of simple geometric configurations on peripheral physiological markers

The fast and reliable neuronal and behavioral responses to negative affective stimuli have been suggested to be at least partly based on the processing of simple geometric configurations within complex visual stimuli. In this context, one line of experimental and neuroimaging evidence suggests that simple V-shaped stimuli result in patterns of neuronal activation and behavioral responses akin to pictures of negative facial expressions. The present study investigated the effects of circles as well as upward and downward pointing triangles in healthy young adults on three peripheral physiological markers - skin conductance response (SCR), facial EMG, and startle reflex - in order to further narrow the gap between neuroimaging findings and behavioral data regarding the impact of geometric shapes. We found significant effects of geometric forms on the startle reflex (p≤0.001, η(2)=0.080) and the SCR (p=0.029, η(2)=0.078), but not on facial EMG. Furthermore, subjective valence and arousal ratings of geometric stimuli differed significantly, with downward pointing triangles being perceived as less pleasant and more arousing. In sum, our findings provide further evidence that simple geometric shapes convey emotional meaning. Particularly, the observed changes in SCR and startle response underscore the notion that geometric shapes lead to preparatory changes in physiological activation patterns, which are essential for facilitation of appropriate behavioral responses. However, the smaller effect sizes compared to more realistic affective pictures also highlight the organisms' ability to differentiate between real impending danger and abstract cues in order to avoid unnecessary excessive responses.