If the human subjects research isn’t supported by the US Department of Health and Human Services, and isn’t supported by an institution that holds an FWA, then the research isn’t covered by regulations on human subjects research.
At a cognitive science lab at Stanford I worked in, it was quite common to run studies using Mechanical Turk.
For studies in the US, see this flowchart.
If the human subjects research isn’t supported by the US Department of Health and Human Services, and isn’t supported by an institution that holds an FWA, then the research isn’t covered by regulations on human subjects research.
At a cognitive science lab at Stanford I worked in, it was quite common to run studies using Mechanical Turk.