User Capabilities

I have a form on this page to allow members to be able to post items. The issue I am having is that I want to restrict what level of member can use (or see) the form. I found a nice little box under the “Visibility” tab. It said “Optional. Set the capability required for users to view this module.” So I entered Editor and then logged in as one of the Editor members on the site and POOF I could see the form. YES!! So I then added a comma and put Author, Contributor, Administrator. And it stopped working. I tried again without the commas and no luck. So I clicked on the Capability link but there was no information there that would help. So I am stuck. How to I create a form that only logged in members with specific levels, (author, contributor, editor) can see this form?

The page I need help with: [log in to see the link]