It is important to note that these changes are not merely emotional but cognitive and conceptual as well. Just as it is possible for us to have insights in fields like mathematics or biology, it is possible for us to have insights about the very nature of our own subjectivity. A variety of techniques, ranging from the practice of meditation to the use of psychedelic drugs, attest to the scope and plasticity of human experience. For millennia, contemplatives have known that ordinary people can divest themselves of the feeling that they call "I" and thereby relinquish the sense that they are separate from the rest of the universe.