Sympathetic and Parasympathetic Control
The Pupil Reflex
Unconscious processes are controlled by the autonomic nervous system, which is divided into the sympathetic and parasympathetic systems. Sympathetic and parasympathetic often have the opposite effects. Heart rate and size of pupil are examples of autonomic processes. For instance, the constriction of the pupil due to exposure to bright light is a parasympathetic response. This limits the amount of light that passes through the eye and protects the eye from damage.