<prompt> Third window effect is seen inPerforated tympanumDehiscent superior semicircular canalRound windowOval window  <response>: Ans. b. Dehiscent superior semicircular canal Dehiscence of bone overlying the superior semicircular canal can cause a constellation of vestibular and auditory symptoms and signs. These abnormalities can be understood in terms of the effect of the dehiscence in creating a third mobile window into the inner ear. 