The idea that there is an independent, insentient world out there, governed by scientific laws and impersonal processes is ultimately a human construct. A powerful and effective construct, but a human one nonetheless. Traditional Buddhist epistemology simply does not accept the Cartesian notion of an insurmountable gap between mind and matter. Most Buddhist philosophies hold that mind and object arise interdependently so there’s no easy way to seperate one’s understanding of the world from the world itself.
Another way of looking at this is from the point of neurobiology. In that field, its understood that any change in a subjective state must be associated with a change in a neuronal state. If I feel something, or dream it, a fine enough screening tool should detect a change in neuronal activity. Perception is governed by precepts. It is interesting to note that brain studies have shown identical activity in the visual cortex when a person is actually looking at a particular object or imagining it.
One participant in a study that involved remaining blindfolded for five days reported that after a few days she started seeing images: slow-moving fireworks, illuminated sperm sailing around and what not. Similar to what you see when you press on your closed eye for a while. Later in the study those ghostly trails would sometimes take a form. If a hand was waved over to the right of her head, and she knew it was happening, she would see a sort of badly-drawn hand doing what she knew was happening. She said it was as if her brain was saying “Hey! Hey! I can tell you all this is happening, so LOOK at it!” Without the actual visual input, her brain manifested what it knew she should see.
Similarly, in dreams our brains conjure up symbols and images of things that are happening in our psyches. We manifest the reality we perceive through other means than seeing, or, if you get right down to it, sensing in any way. It is certainly true that things we actually do hear, smell, feel or sense while sleeping can be incorporated into our dreams, and that is really the point. The input from actual senses, and the input that our brains expect have an equal footing in creating our experiences when we dream, whereas they don’t in waking life.
If activity in the non-visual parts of the brain can manifest as visual data, what does that say about imagination? I can visualize the Buddha while meditating – or, for that matter, I can visualize whirrled peas, world peace, or selling my house- and according to Buddhist philosophies, he is not in my imagination, but actually there. Mind and matter are as interchangeable in this philosophy as matter and energy are in physics (science philosophy?). That is to say, in conventional, day to day reality the two sides are interchangeable in theory only. Unless you count monks who can jump while sitting down.