A person has various senses. Stimulation of visual, hearing, tacticle, and smelling sense arouse sexual-feeling.

Generally these four senses are mainly although sense of taste also can be a factor for some people.

And human distinctive imaginative power and delusion are added in it, and that turns to a sexual-feeling.

We can get excited reading an erotic story or get a sexual-feeling with a sexual imagination.

And blindfold and bondage block a part of your five senses and sharpen your sexual-feeling to have an unknown ecstasy.

Eyesight is very sensitive to sexual stimulations.

Eyesight is the most necessary sense to get excited looking at AV or erotic magazines or your partner's body during the sexual time.

Tactical sense works when a man gets excited feeling a women's softness or temperature and a woman gets excited feeling a man's athletic body or erected penis
These senses are necessary for sex life.