What is the name of the group not given the independent variable?

Baroreceptors in the aortic arch and carotid bodies are mechanoreceptors that respond to the stretch that occurs in these arterial walls with changes in blood pressure. if pressure changes rapidly, the baroreceptors initiate a feedback mechanism that reduces blood pressure; however, if pressure changes slowly, as in developing hypertension, the receptors do not respond. given this information, the baroreceptors are most likely which type of receptor?