Monday, July 16, 2012

How does physical experience affect mental movement?

We use lots of mental images to help us plan actions.  I remember times when I helped friends move from one apartment to another.  The trickiest part of these moves was getting the couch out of the living room and outside onto a truck.  Yet, we often managed to do it successfully by first imagining how to position the couch to get it through narrow hallways and out of awkwardly placed doors.

The importance of this kind of imagery for performing actions in the world leads to questions about whether the ease of acting in the world affects the ease of manipulating your mental images.  This question was addressed in a paper by Stephen Flusberg and Lera Boroditsky in the February, 2011 issue of Psychonomic Bulletin and Review. 

These authors did a clever study using a version of a mental rotation experiment first done in the 1970s.  In the original mental rotation studies, people saw three-dimensional figures like the ones in the Figure shown here.  Sometimes people saw two identical objects, while sometimes the objects were mirror images of each other.  They had to judge whether the objects were the same.

As shown in the figure, the objects could appear in different rotations relative to each other.  The classic finding of these studies is that the larger the degree of rotation between the objects, the longer it takes people to respond whether they are identical.  These results suggest that people are mentally rotating an image of the objects until they are aligned so that they can judge whether they are identical.

Flusberg and Boroditsky had people play with the objects before doing the mental rotation task.  They built wooden versions of the figures.  Some of them were painted red and others were painted blue.  The figures were attached to an axle that was set in a can.  They acted as a handle on the axles.  The cans were set up so that some of them had sand in them, so that they were hard to turn, while others were empty and were easy to turn.

At the start of the study, participants were asked to turn the handles.  For each of the participants, one color was hard to turn and the other was easy.  For example, the red handles might be difficult to turn, and the blue ones easy.

After this experience with the physical handles people did a mental rotation study.  Participants saw pairs of pictures and judged whether the objects were identical, just as in the classic study.  There were two big differences from the previous work.  First, half of the objects were blue and half were red.  Second, half the participants were told to imagine physically moving the objects until they were aligned, while the other half were told just to imagine the objects moving on their own.

The group that was told to imagine the objects moving on their own showed the classic mental rotation effect, but no effect of the color of the objects.  That is, it took longer to make the judgment as the objects were rotated further from each other.  But, people’s previous experience with the objects had no effect on this mental rotation.

The group that was told to imagine moving the objects showed both the classic mental rotation effect and an effect of the color of the objects.  That is, those objects that were the same color as the ones that were harder to move were mentally rotated more slowly than those that were the same color as the ones that were easier to move.

These results demonstrate the close linkage between action and imagery.  When an object is hard to move, it is also hard to imagine moving it. 

Why would our ability to move objects affect our images? 

In order to solve problems like moving a couch, we need to bring to bear both our knowledge of the geometry of the object as well as our knowledge of our own physical abilities.  It would not be useful to envision ways of moving an object that we could not carry out physically.  So, incorporating both visual aspects of objects and movement makes your ability to plan more efficient, because you do not consider many possibilities that would be physically impossible to perform.

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