Friday, June 15, 2012

Gestures help you imagine movements of objects

Language is our most powerful tool for thinking.  We talk to other people to solve problems, and we also use internal monologues to guide our thinking.  However, there are some things that language is not so good at.  One particular limitation of language is in describing and manipulating three-dimensional space.  For example, when you want to describe the size of an object, you often resort to comparing an object to something of known size (“That dog was the size of a small car!”) or using gestures to indicate sizes.
Movements of your hands and arms seem particularly well-suited to thinking about space.  We have to configure our hands to grasp objects, and so we must have ways to represent sizes in order to plan those movements.  In addition, the movements themselves provide a method for changing the location objects and their orientation.  In a store, the price of many objects is printed on the bottom, and so you just pick up the object and turn it over, effortlessly exposing the bottom. 
Does this ability to move objects around also help you to think about the movements of objects that aren’t physically present?  This question was addressed in a paper in the February, 2011 issue of the Journal of Experimental Psychology: General by Mingyuan Chu and Sotaro Kita. 
These researchers examined people’s performance in a mental rotation task.  In mental rotation, people see pictures of two objects.  The objects are either identical or one is the mirror image of the other.  In addition, the objects are rotated through some angle so that they are each in a different orientation.  Examples of the figures used in studies like this are in the figure.  The top row shows a pair of identical objects at a moderate degree of rotation.  The bottom row shows objects that are mirror images. 
Studies of mental rotation started with the work of Roger Shepard and his students in the 1970s.  Participants are asked to press a button as soon as they know whether the objects are identical or are mirror images.  The classic finding of this work is that as the difference in angle of rotation between the two objects increases, people take longer to respond and they make more errors.  This pattern of findings suggests that people may be mentally rotating the objects to place them in the same mental orientation in order to compare them.
In one study, Chu and Kita used this mental rotation task and told people they could take as much time as they needed to solve the problems.  They looked at whether people spontaneously made hand movements in which they rotated their hands as if they were rotating the objects.  In this study, people were far more likely to make rotating hand movements when there was a big difference in orientation between the objects than when there was a small difference in orientation.  That is, when the problems got difficult, people seemed to use hand movements to help them rotate an object that wasn’t actually there.
In a second study, participants were either explicitly encouraged to use gestures or they were forbidden to use gestures.  In the case where people were forbidden to use gestures, they had to sit on their hands.  In this case, people made many fewer errors in their judgments when they were allowed to gesture than when they were not.
Why do gestures help you imagine rotations?
Because you often use your arms and hands to change the position of objects in space, your visual system has a lot of experience witnessing these changes in position when you make particular kinds of movements.  You have picked up lots of objects and turned them over, and so there is a strong association between these movements and the changes in what you can see in the world.  This close connection between body movements and the state of the world may come to influence your mental images as well.  Turning your hands in a particular direction supports thinking about the object moving in that direction, because these turning movements often led to movements of objects in that direction in the past.
That means that when you are trying to solve a difficult spatial problem, it is a good idea to give yourself room to move around.  These movements may actually help you think about space and movements through space more easily.

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