add a button that counts the clicks

I am currently designing a MediaLab-based study. The study is that participants are asked to write in an essay box while inhibit thinking of a white bear (whenever they fail to do so, they need to click a button).

To do so, I need to have a button that counts all the button clicks and an essay box. However, I don't know how to do this using custom items.

Could someone help me with this?

Thanks a lot!

you can do so with a little javascript inside your html-page

Yes, you could do this with some javascript within some HTML. I'm wondering though if you could get by with having them click a button on the keyboard instead of one on the screen. If so, there is way you could track that very easily while they write their essay using the "k" parameter (see user guide, or I can elaborate here). However, if it needs to be an [I]on screen[/I] button then we can discuss that more here.