We are conscious of the world round about us, because we have certain capacities and organs which enable us to perceive it. If we had other organs, this world would present an entirely different aspect. For example, if a man had no eyes enabling him to see the light, but an organ enabling him instead to perceive electricity, then he would not see this room flooded with light, but he would perceive electricity in every wire, flashing, streaming through it. — The world round about us, what we call our world, is therefore dependent upon our sense-organs.
The astral world, too, is nothing but a sum of phenomena, which the human being experiences in his environment , when he has severed himself from his physical body and from his etheric body, so that he can use forces enabling him to see what he cannot otherwise see. This is the case, when he has discarded his physical body and his etheric body. The perceptive organs for the astral world are the organs of the astral body, analogous to the sense-organs of the physical body.
Source: Rudolf Steiner – GA 100 – Theosophy and Rosicrucianism – IV – Kassel, 19th June, 1907