Challenges to normal neural functioning provide insights into separability of motion processing mechanisms

► Ongoing debate on separability of first- and second-order motion processing. ► Threshold data from one of the largest age samples studied so far (N = 102). ► Threshold data from patients (N = 18) with widely distributed cortical lesions. ► Functional vulnerabilities offer an important window to neural substrates. ► Data support shared processing pathways for first- and second-order motion.