... different (usually a mirror image). The analog theory introduced by Shepard (1975) argues that the internal process involved are an analog process, in that it is a mental process that corresponds in some way to a physical process of actual rotation of the object into congruence with other, and only when this procedure is completed can the subject state whether the objects differ or remain the same. However, although similarity in mental and physical processing is involved, Shepard argued that this in no way stipulates that the internal representation of the object has to, in a structural sense, resemble the external object, nor is it required that the internal representation of its rotation structurally resemble its physical rotation. The internal mental representation produced by the subject captures the external object's three-dimensional structure, not in its entirety but only as the object appears relative to a particular angle of regard. ...

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