In preliminary practices of yoga the symbol can be an external object. Eventually, however, as your perception becomes more subtle, you should visualize your symbol internally. You should create an image in chidakasha, the mind-screen in front of the closed eyes. This inner image is more subtle and will take you much deeper’.
Most people have trouble maintaining a clear image of their symbol. Either they cannot visualize it or the image tends to fade away. Do not become frustrated, this is merely an indication of the state of your mind. It is difficult to visualize inner images with a disturbed mind; you will be able to think about it but not see it. As your mind becomes calmer you will find it progressively easier to visualize your symbol. When your mind is silent, perhaps after doing antar mouna stage 5, then you will be able to maintain a fixed inner vision of your psychic symbol7. This leads directly to dharana and dhyana, but time is required. Do not expect this to arise overnight. Regular practise for many months and years is necessary.