A mask for patient ventilation comprises a frame portion, a retention portion, and a connector portion. A contact probe has an upper plunger having a contact stem portion, a lower plunger having an insertion hole with which the contact stem portion is capable of coming into contact, and a coil spring connected to the upper plunger and the lower plunger in such a way as to cover the contact stem portion. The parallax optic comprises rows and columns of parallax elements with the arrangement of pixels and parallax elements being such that each element co-operates with a respective pair of first and second pixels adjacent each other in the same row to form first and second viewing regions.