Some more unusual research results...this time about why people have trouble simultaneously drawing a circle with one hand and a square with the other hand. Yes, someone has done research on this!
David Rosenbaum, Director of Penn State's Laboratory for Cognition and Action, is responsible for this research about a "fundamental question: Why is it difficult to carry out two different movements at the same time?" His vague conclusion: "It is a fundamental limitation that the nervous system seems to impose on the hands for reasons that are not fully understood."
So what's the limitation...is it something related to the geometric shapes themselves...having to construct both straight and curved sides simultaneously? As part of his research, Rosenbaum first constructed an apparatus that produced different movement patterns and then asked volunteers to use their sense of touch to track those patterns....which they could do with no problem.
Rosenbaum's final conclusion: The limitation is not due to muscle difficulties nor to nervous system difficulties. Rather, Rosenbaum claims "the source of the limitation is conceptual, it's not in the execution." When faced with the task of drawing a square and circle simultaneously, "you need to keep those two forms in mind, and that's hard for us to do."
The next step...to investigate any connection/implications of this research to the teaching or learning of mathematics.