I've seen neuroscience and facial recognition studies that give evidence for this idea of simple geometric shapes causing emotional responses or quicker recognition of negative affect.
Are there studies exploring the other end? (i.e. positive valence of simple geometric shapes)
Larson, C. L., Aronoff, J., Sarinopoulos, I. C., & Zhu, D. C. (2009). Recognizing threat: A simple geometric shape activates neural circuitry for threat detection. Journal of cognitive neuroscience, 21(8), 1523-1535. Watson, D. G., Blagrove, E., Evans, C., & Moore, L. (2012). Negative triangles: Simple geometric shapes convey emotional valence. Emotion, 12(1), 18-22. doi:10.1037/a0024495