Mrs Khan presents with episodes of intense vertigo over the past month. She reports that when she wakes up and rolls over in bed it produces symptoms lasting approximately one minute. There is no history of chest pain, breathlessness or vomiting. She is well in between episodes. A diagnosis of Benign Paroxysmal Positional Vertigo (BPPV) is suspected.
Which one of the following tests can be used to help confirm diagnosis?