Operating a switchable head-mounted display apparatus includes: providing a head-mounted display that includes a switchable viewing area that switches between a transparent state and an information display state; operating the head-mounted display in the information viewing state to display image-sequence information; analyzing the image-sequence information to produce a signal estimating the propensity of the image-sequence information to induce motion sickness or symptoms of motion sickness in the user; and modifying the image-sequence information or the state of at least a portion of the switchable viewing area in response to the signal to reduce the propensity of the image-sequence information to induce motion sickness or symptoms of motion sickness in the user.