Mental rotation

Mental rotation is the ability to rotate mental representations of two dimensional and three dimensional objects.

Introduction
Mental rotation usually takes place in the right cerebral hemisphere, in the areas where perception also occurs. It is associated with the rate of spatial processing and intelligence (Johnson 1990, Jones 1982, Hertzog 1991).

Mental rotation can be separated into the following cognitive stages (Johnson 1990):


 * Create a mental image of an object
 * Rotate the object mentally until a comparison can be made
 * Make the comparison
 * Decide if the objects are the same or not
 * Report the decision.

How Mental Rotation Ability is Assessed
In a mental rotation test, the subject is asked to compare two 3D objects (or letters) and state if they are the same image or if they are mirror images (enantiomorphs). Commonly, the test will have pairs of images each rotated a specific amount of degrees (eg. 15º or 45º). Some pairs will be the same image rotated, and others will be mirrored. The subject will be shown a set number of the pairs. The subject will be judged on how accurately and rapidly they can distinguish between the mirrored and non-mirrored pairs.

Notable Research
Roger Shepard and Metzler (1971) originally discovered this phenomenon. Their research showed that the reaction time for participants to decide if the pair of items 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 2 images are of the same object or enantiomorphs (Sternberg 247).

In further research, Shepard and Cooper (1982) have proposed the concept of a "Mental Imagery" facility, which is responsible for the ability to mentally rotate visual forms. Additionally, it has been found it does not matter on which axis an object is rotated, but rather the degree to which it is rotated that has the most significant effect on response time. So rotations within the depth plane (i.e., 2D rotations) and rotations in depth (3D rotations) behave similarly. Thus, the matching requires more time as the amount of depth rotation increases, just as for within the depth plane.

In subsequent research, it has been found that response times increase for degraded stimuli and can decrease when participants are allowed to practice mentally rotating imagery (Sternberg 247). This research has been instrumental in showing how people use mental representations to navigate their environments.

Recent breakthroughs in medical sciences have allowed psychologists to discover what parts of the brain correspond to the use of this mental imagery function. Using Functional Magnetic Resonance Imaging, psychologists have shown that when participants are performing mental rotation tasks, there is activation in Brodmann's areas 7A and 7B, the middle frontal gyrus, extra-striate cortex, the hand somastosensory cortex, and frontal cortex (Cohen et al.).