Is there such a thing as a biofeedback device that measures pupil size?

Question

Is it an indication of different brain states? How so? What have people done with this? Do you know of any other interesting biofeedback devices/practices?

Answer 1

Like a year ago or so, baisball player Albert Pujols was the subject of a similar research done by Washington University in Saint Louis. The information was published in the Saint Louis Post dispatch...you might want to check this and see if it is of any use to you.