From https://www.aaup.org/report/trigger-warnings

See also https://www.insidehighered.com/news/2019/03/21/new-study-says-trigger-warnings-are-useless-does-mean-they-should-be-abandoned

Also, this looks good: https://rowman.com/ISBN/9781442273719/Trigger-Warnings-History-Theory-Context

Available via SFSU library