Other facts add to your uncertainty. Thus, _the same stimulus_ acting on _different organs_ of sense will produce _different sensations_. A blow upon the eye will cause you to "see stars"; a similar _blow_ upon the ear will cause you to _hear_ an explosive sound. In other words, the vibratory effect of a _touch_ on eye or ear is the same as that of _light_ or _sound_ vibrations. [Sidenote: _Hearing the Lightning_] The notion you may form of any object in the outer world depends solely upon what part of your brain happens to be connected with that particular nerve-end that receives an impression from the object. You _see_ the sun without being able to _hear_ it because the only nerve-ends tuned to vibrate in harmony with the ether-waves set in action by the sun are nerve-ends that are connected with the brain center devoted to sight. "If," says Professor James, "we could splice the outer extremities of our optic nerves to our ears, and those of our auditory nerves to our eyes, we should hear the lightning and see the thunder, see the symphony and hear the conductor's movements." [Sidenote: _Importance of the Mental Make-Up_] In other words, the kind of impressions we receive from the world about us, the sort of mental pictures we form concerning it, in fact the character of the outer world, the nature of the environment in which our lives are cast--_all these things depend for each one of us simply upon how he happens to be put together, simply upon his individual mental make-up_. There is another way of examining into the intervening agencies that influence our mental conception of the material world about us. [Sidenote: _Unreality of "The Real"_] Look at the table or any other familiar object in the room in which you are sitting. Has it ever occurred to you that this object may have no existence apart from your mental impression of it? Have you ever realized that no object ever has been or ever could be known to exist unless there was an individual mind present to note its existence? If you have never given much thought to questions of this kind, you will be tempted to answer boldly that the table is obviously a reality, that you have a direct intuitive knowledge of it, and that you can at once assure yourself of its existence by looking at it or touching it. You will conceive your perception of the table as a sort of projection of your mind comfortably enfolding the table within itself. [Sidenote: _"Things" and their Mental Duplicates_] But perception is obviously only a state of mind. Can it, then, go outside of the mind to meet the table or even "hover in midair like a bridge between the two"? If you perceive the table, must not your perception of it exist wholly within your own mind? If, then, the table has any existence outside of and apart from your perception of it, then the table and your mental image of the table are two separate and distinct things.