Waking up in the morning, for many, involves turning on a light after turning off an alarm. Although some people learn to navigate their way to the shower in the dark, most of us have to deal with a dramatic change in luminance, opening our eyes and immediately being overwhelmed by light. Whether this occurs because your parents are trying to get you up and moving, or because you want to see what you are doing in the bathroom, similar biological processes seem to be at work. Throughout the night while we sleep, most of us with our eyelids sealed shut, we adapt to a world of darkness. When experiencing such a sudden and drastic change in luminance – as when someone shines a flashlight in your eyes, you begin to see blobs of undefined figures circling around in your receptive field. When this happens to me, I usually see what I would compare to a slightly transparent blue ameba – regardless my vision becomes impaired to the extent that it is much harder to make out what is directly in front of me. I do not know exactly why this happens, but I believe it is primarily due to the bleaching of photopigments.
Retinal ganglion cells respond to changes in light, not the overall amount of light covering their receptive field – the change from dark to light is what causes visual impairment in the prior situations, not how bright either light source is. Whenever someone shines a light in your eye, a lot of photopigments are used up because they are trying to adapt to the change in luminance. This leaves fewer pigments available to process whatever other information is in one’s environment. Furthermore, I believe the more of one’s visual field encompassed by a sudden spurt of light, the more neurons fire, because light is coming at them from many more orientations/angles than if such a change occurred farther away. The more cells that fire, the more information striate cortex neurons have to filter out. Perhaps when there is too much information to process efficiently, this filtering sequence is slowed and disrupts the feed forward process. If so, would one’s mind start to group objects/stimuli that it normally would not combine? In essence, the more depleted photopigments, the more acuity is impaired, and the less detail an individual can make out.
Although cone photoreceptors regenerate more quickly than rods, they are also exhausted at a faster rate. Since such an abundance of cones are used up when one perceives a drastic change in luminance, (I think) the whole visual processing system falls into a chain reaction of information overload. The parvocellular pathway, dealing with details of stationary objects, simply tries to pass on too much information. Because there are now less photopigments available to process the current environment, and the filtering process in the striate cortex is busy with information it has just received, middle vision processes start to receive jumbled information. My guess is that this leads us to perceive similarities and differences from stimuli in our environment when such relationships do not exist. Furthermore, the feed forward process allows our brain to draw conclusions about what it perceives without needing a later processing sequence to communicate with earlier processing events, which I believe can lead to uncontrollable perceptual errors. In other words, an error that causes us to see bright blue blobs where they don’t exist. Perhaps law enforcement personnel use flash-bang grenades for the same reason; they have found a practical use for our visual system’s sensitivity to abrupt changes in luminance.
