Which bodily function was once thought to be beyond voluntary control but nowadays can be changed with biofeedback?

Question

Quizplus · Accepted Answer

Biofeedback is a technique that uses electronic monitoring devices to provide information to individuals about their physiological processes, such as heart rate, blood pressure, and sweating. With practice and guidance, individuals can learn to control and change these bodily functions, which were once thought to be beyond voluntary control. Therefore, all of the options (A, B, and C) can be changed with biofeedback.

Which Bodily Function Was Once Thought to Be Beyond Voluntary