Compare people field to current user?

On a Nintex form, I want to have a calculated value field that compares a user name in a people field to the current user.

I have tried:

equals(Current User,ctrlParticipant)

and

userEquals(Current User,ctrlParticipant)

and

Current User == ctrlParticipant

Each time the form shows as blank and if I turn on the debugger, I can see various errors being generated?

How do I compare a people field to the current user??