David Oates discovered the phenomenon of reverse speech (RS). This is the theory that regular speech contains hidden messages that can only be heard when it is played backwards. It is believed that unconscious thoughts, memories, and experiences are embedded in our spoken language, and we can reveal these by recording speech and playing it in reverse. This is backmasking without a soundtrack.

If human speech is recorded and played backwards, mixed amongst the gibberish at regular intervals can be heard very clear statements. These statements usually appear in short sentence form and are nearly always related to the forward speech. It appears constantly throughout language, so much so in fact, that it is believed to be a natural part of our speech processes.

The pioneer and 32 year veteran of this field, Australian David John Oates, describes Reverse Speech as another form of human communication. He states that language is bi-level, forward and reverse. As the human brain constructs the sounds of speech, it forms those sounds in such a way that two messages are delivered simultaneously. One forwards, which is the conscious mind speaking, and the other in reverse, which is the unconscious mind speaking.