At first I was going to compare abrupt versus sustained sources of sound that have the ability to cause damage to one’s auditory system, such as a gunshot versus loud music, but then I thought of a much more interesting phenomenon. I do not know what most kids like to do when they go swimming, but, for a long time, I liked to just sink to the bottom of the deep end and pretend like I was dodging bullets – as if I were in one of the Matrix films. After a number of trips to the bottom of the pool, pressure would build in my head/ears, and I would have to take a break or call it a day. One afternoon, a companion of mine told me that if I held my nose shut and blew through my nostrils my ears would pop, just as if traveling at a high altitude. Without thinking clearly about what I was doing, I plugged my nose and blew as hard as I could. I’m quite sure I punctured an eardrum(s) – but did I do so without hearing any sound(s)?
If mammals hear because of pressure changes in a medium – furthermore due to vibrations – it makes good sense that a certain amount of pressure built up in one’s head will cause damage to their auditory system. The issue with my example is that the pressure that led to my punctured eardrum was not due to an external source of sound, nor did the pressure build from the outside in. In other words, the sound/pressure did not enter through my ears, but through my nasal cavity. My understanding is that, when plugging my nose and blowing through my nostrils, I was essentially attempting to balance the pressure between canals in the inner ear sections of my auditory system, and the outside environment (water).
The pressure of the water surrounding me at a depth of twelve feet was greater than the amount of pressure in my cochlear canals (parts of the inner ear where liquid is stored) – blowing lightly should have reduced this contrast in pressure, as it would have increased the pressure in my cochlear canals just the right amount. Unfortunately, I believe I did the complete opposite. By blowing really hard with my nostrils plugged, I increased the pressure in my ears so far beyond the pressure of the outside environment (water) that I did more harm than good. What exactly happened, I am not sure. I am most confused as to how pressure coming from within my body, not from vibrations in a medium in my surrounding environment, caused damage to my auditory system. It is not as if pressure/vibrations exited my body and re-entered through my ear, from the outside. Did I make a sound from within? Regardless, how did the pressure I induced reach my ear? If it came from inside, I feel like it would go through a different process/along a different path, before being interpreted as sound, than if it came from an external source. Can this pressure be considered a sound?
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A Flash-Bang Phenomenon
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.