This experiment is designed to test orientation cues with stereo 3D (S3D) displays. The subject is sat behind a curtain with a square cut out of it, and can't see that the television is in fact twisted through an angle, and therefore not perpendicular. However because of the display being S3D the subject cannot distinguish this change in orientation and assumes that the screen is frontoparallel (perpendicular). This means that when we show the stimulus (in this experiment a pair of rotating cubes) the stimulus look warped unless they are projected for the angle the subject is sat at (orthostereo), in contrast to when the curtain is removed and the television can be seen to be rotated, at which point the subjects brain corrects for not being perpendicular and sees the orthostereo cube (rendered for the angle) as warped, and the perpendicular cube as correctly projected.
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