I blindfolded and gagged someone and they subsequently invoked the XXXXXX. Should it be possible to invoke something you can't see?

Invocations, from my basic understanding, are a character's ability to pull from the special qualities of something. Should an invocation REQUIRE speech, then a gag would stop it.

But if it DOESN'T require speech, then it doesn't.

Some objects are made so that, simply by having or wearing the object, a clear thought in the object-possessor's head is enough to cause the object to react.