altered state? the thing with meditation is, you're suppose to clear your mind and focus on nothing. this is a way to rest your brain, while doing this your 'spirit' should take over and this will help you by showing you visions. while someone could [and i've done it before] think of something and create it perfectly in their mind, that's not really a vision since you're consciously telling yourself something. your subconscious should take over and show you 'altered states'.
it takes time, sit and meditate, clearing your mind, don't seek to see anything, the first time i saw visions was after years of on and off meditation, and i wasn't looking for anything, i got use to the nothingness of my mind. of course you could try meditating with a tarot card, a totem of your spirit guide, a crystal, a magic tool, and so on to see if you'll see anything different with them. keep a journal handy to write down anything you come across be it nothing, a red ball, or a full blown vision.