Armed with a list of bio-sensing possibilities around the body and some class readings I wanted to use this week to test a whole bunch of different sensors.
I started off testing eye tracking using the PS3 Eye and this code for processing with great results. Even without adding an IR LED to blacken the pupil the bounding boxes still seemed to track the pupil very accurately.
I then read about the Caloric Reflex Test as a way to test the automatic eye movement that stabilizes vision during head movement. When the head moves to the left, the eyes automatically compensate by moving to the right, and vice versa. I find it hard to actually test this yourself when the eyes are open as it seems you can override the reflex by choosing to settle vision in the same direction that the head is moving. But the compensation reflex is not actually dependent on visual input and works in complete darkness or when the eyes are closed. The reflex is driven by a mixture of two sensors in the inner ear; the semi circular canal that has tiny hairs that are sensitive to the movement of a fluid, and the otolith with is more of a solid structure that is sensitive to the bending and flexing caused by gravity. So the brain is able to pick up on both vertical movement (like in an elevator), horizontal movement (like acceleration) and the various movements on the head from side to side and up and down.
The whole pathway from the sensory input to the movement of the eyes needs to be quick for clear vision. One way to test it is to try to read something while rapidly moving the head from side to side. Another way of testing the response is to trick the sensors in the ear that the head is moving and induce the compensatory eye movement. This is done by creating a temperature difference between the body and the inner ear which creates a convection current in the fluid of the semi circular canal. This is picked up by the sensitive hairs in the canal as rapid head movement and the eyes will involuntarily dart from side to side. Hot water did not work for me but ice cold water almost immediately induced a sense of spinning and something like this:
I wanted to use the eye tracking apparatus to test the speed with which the reflex kicks in as a way to the test brainstem reflexes. However the test also induced pretty severe nausea for about half an hour and so I was reluctant to try it again.
I settled for a few more tests, using a DIY Galvanic Skin Response circuit and a simple graph in Processing and this pulse sensor.