In a mental rotation test, the subject is asked to compare two patterns and state if they are the same image or if they are mirror images. The subject will be judged on how accurately and rapidly they can distinguish between the mirrored and non-mirrored pairs. Mental rotation is somewhat localized to the right cerebral hemisphere. It is thought to take place largely in the same areas as perception. It is associated with the rate of spatial processing and intelligence. Roger Shepard and Jacqueline Metzler (1971) originally discovered this phenomenon. Their research showed that the reaction time for participants to decide if the pair of patterns matched or not was linearly proportional to the angle of rotation from the original position. That is, the more an object has been rotated from the original, the longer it takes an individual to determine if the two patterns are of the same object or enantiomorphs.