MENTAL ROTATION OF THREE-DIMENSIONAL OBJECTS

Shepard, R. N., & Metzler, J. (1971). Mental Rotation of Three-Dimensional Objects. Science, 171(3972), 701-703. http://www.cs.virginia.edu/~evans/cs1120-f09/ps/ps3/mental-rotation.pdf

Observable objects do not simply require only visual abilities from us to process their shapes and forms. Technically, three-dimensional objects are things that consist of length, width, and height. We can observe them roundly. A tricky part occurs when three-dimensional objects are replicated into twodimensional media. That is when mental rotation is essential to predict the unseen parts. Especially when it comes to comparison, people have to be able to imagine whole objects, in different angles if needed, out of partial presentations to get information as much as they can to make the determination. They progressively spent more time when objects had angular differences and did not spend significantly different amounts of time for rotations between a picture plane and depth, the report suggested.

Shepard and Metzler from the department of psychology, Stanford University, California, experimented on the time people were required to recognise if two three-dimensional objects portrayed in two-dimensional pictures are identical or not. The main objects they chose to project in pictures are made up of ten attached solid cubes with a structure of an arm that has three bent points. They conditioned the exercise into three sequences. Group A and B contained two identical objects in each group that were rotated in a picture plane and in depth, respectively. They categorised these two groups as “same” pairs. Group C contained two nonidentical three-dimensional objects. They categorised this latter group as “different” pair because the two objects cannot be matched by any rotating fashions. They also mirrored the objects in group C to avoid their distinctive features being exposed too easily. Mental rotation was compulsory for participants in every task.

For all 1,600 pairs of pictures, they were half divided into the “same” pairs, which consisted of “picture plane” and “depth” pairs, and the “different” pairs. In perspective projections, objects were turned around using a vertical axis for 20 degrees each time, from 0 to 180 degrees. The computer did the shuffle. Participants would receive a random set of presentations and be given 1 hour for a session. They were told to react as quickly as they could. After they heard a warning sound, the first pair of pictures and a timer appeared simultaneously. The moment participants reached a decision on whether the presented objects were identical or not, they would pull a lever on their right for matching objects and on their left for non-matching objects. This action subsequently removed the display and stopped the timer. Participants’ reaction times were recorded.

The inspection right after the experiment disclosed the way participants dealt with personal mental rotation inside their heads. They knew the objects were identical when they successfully fit one object’s end into another object’s end. Otherwise, they discovered two objects were non-identical.

For the result, in the aspect of accuracy, most participants got the answers right and kept their errors to a minimum. In the aspect of time, reaction for “picture plane” and “depth” pairs had similar timing. Although in the larger angular differences, it was slightly quicker for rotation in “depth” than in “picture plane”. Participants who were experienced with the method of this test still were consistent in reaction time as inexperienced participants, both in a “pure” set of presentations, where they were familiar with a vertical axis and were able to guess the rotating direction of coming pictures, and “mixed” set of presentations, when they had no idea on picture projecting patterns.

The consistency of reaction time recorded in this report could be useful as an implication of mental rotation of three-dimensional object process, in a typical circumstance. People gradually spent longer processing time as objects were portrayed in angular varieties. Pictures rotating in the picture plane did not produce an outstanding difference in the timing than the ones in depth. ■

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