https://journals.physiology.org/doi/pdf/10.1152/jn.1994.71.1.33 (Publisher version)
Westheimer, G., & Wehrhahn, C. (1994). Discrimination of direction of motion in human vision. Journal of Neurophysiology, 71(1), 33-37. doi:10.1152/jn.1994.71.1.33.