First, I am not from the field of psychology, but I assume that the research rules are equally applied to all fields.
A general comment: any idea you think that it is new -in any research area-, it is more likely to collide with the fact that it has already been explored and patented -if you have a small experience in the field of course-.
Validating your idea does not necessitate a direct involvement in academia. However, it is important to know the academic process, that consists of:
- Reviewing the state-of-the-art sufficiently. This means, reading the recently published papers (mainly from reputed journals and proceedings) and books by using specific search engines (e.g. google scholar) and references/cited-by of the publications you know. Please be aware that key-words might be different across different communities.
- If you are not directly involved in research, you may contact researchers interested in your topic and idea. Btw. your assumption that they wouldn't even listen is wrong. Researchers and academics (regardless of their research area) are always open to new ideas. We (a CS research group) do this all the time, where we discuss with companies and individuals about new ideas and collaborations.
- If you don't prefer contacting research groups and labs or you don't get an answer for any reason (which I don't it would happen), you can write the paper by yourself following what you have learnt in reviewing similar works (you can also check tutorial how to write a good paper). You will need to follow the journal or conference instructions (e.g. number of pages, etc). You then submit the paper and wait a couple of months to get the first decision.
Now regarding your assumption:
Write a book. This is definitely a non-scientific approach ....
It is incorrect if you aim to publish a scientific book. Generally, good publishers won't easily publish the work of unknown authors unless they publish it in a series which requires the acceptation of its editor. Here also, the work has to be proved by the editor to has the chance to be published.