Silence, and then a reply, "Blinking?" Another pause, "I think it just gets dim when you look directly at it."
"Oh."
Air Force One had just ended, and we were sitting in darkness while it rewound. My friends had some of those glow-in-the-dark stars on the ceiling, and I was currently being entertained by a certain star that seemed to blink off and on. After the reply that the star got dimmer when you looked at it, I decided to try it. I looked away just enough so that I could still see the star out of the corner of my eye--it was fairly bright. Then, I turned my eyes to look directly at it, and the star seemed to nearly disappear. How curious. Then the proverbial light bulb suddenly switched on. Of course, Behavioral Neuroscience!
To you, stars may not seem intimately related to a neuroscience class. Maybe physics and astronomy, but neuroscience? Well, yes. We had been learning about vision for a week of so, and something we had just learned explained the whole flashing star thing. (In fact, I later realized that there was a demonstration similar to my experience, but using actual stars, in the text chapter on vision.) There are two classes of photoreceptors in the eye which transduce the light signal we see into an electrical signal that the brain can interpret. One of these types, the cones, allow us to see color. There are a lot of these types of cells in the center of the retina (the layer of neurons and such at the back of the eye). The other type of photoreceptor is the rod. There are a lot of rods on the periphery of the retina. Rods have a lot more photopigment in them, which allows us to see at night. (In fact, the cones are pretty useless in the dark, which is why we can't distinguish colors at night. ) This is part of the reason (a large degree of convergence of info. from the rods is also important) why the star was "blinking." When I looked directly at it, the light from the star was hitting the center of my retina, where there are few cones to detect the light, and thus the star was dim or non-visible. But when I saw the star out of the corner of my eye, the light was hitting the periphery of my retina, where there are lots of rods to pick up and respond to the light. Thus, the star was suddenly bright. Think about that the next time you are stargazing, be it in the great expanse of the wild, or only the great expanse of a dorm room.