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Masahiro Ishii, Masaaki Todo, Kazuya Yamashita; Manual control is effective in disambiguating in kinetic depth effect. Journal of Vision 2007;7(9):70. doi: 10.1167/7.9.70.
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© ARVO (1962-2015); The Authors (2016-present)
A 3D object such as plural points distributed in 3D space appears flat when rear projected onto a translucent screen. Its 3D shape becomes apparent when it is rotated about an axis parallel to the screen. The effect is called kinetic depth effect (KDE). With parallel projection, depth information is given by the relative motion of the points but perspective information is not present. Without perspective, the relative depth of points can be perceived but not their depth order. It is impossible to tell which is the front and which is the back of the objects. The 3D object is ambiguous with respect to its reflection in the plane of the projection. As a result the object periodically appears to reverse in depth as well as direction of rotation. The sign of depth in a motion parallax display produced by parallel projection, however, is unambiguous when the motion of the display is coupled to side-to-side self-produced motion of the observer's head. Proprioceptive and vestibular information produced by self-motion is effective in disambiguating the depth structure. This study investigated if observers' manual control of the stimulus change removes ambiguity of KDE. In the experiment, the stimulus change could be controlled by the rotation of a computer trackball that the observer manually rotates rightward or leftward. As the result, manual control could remove the ambiguity in a part of our subjects: the perceived direction of rotation from KDE united the manual control. Prolonged viewing, however, made reverse the perceived direction of rotation. We measured duration from the beginning of stimulus change (i.e. rotation) until reverse. The mean duration in the case of manual control is almost equal to that of conventional KDE. Manual control had no effect in the rest of our subject. They always perceived unidirectional rotation from conventional KDE.
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