With your auto accident, you are more referring to recalling a
situation in more detail after it happens. During the accident, your
brain realizes this is an urgent/life threatening situation, so it
released chemicals into your blood stream and started taking in a lot
of input and rapidly storing it. Think of it like one of those high
speed cameras recording at thousands of frames per second. You don't
actually see/experience every 'frame' of the input. Later when you
recall the situation, your brain can go thru every frame of the high
speed recording in vivid detail.

This is very similar to what causes Post Traumatic Stress Syndrome.

Another related phenomenon is what some refer to as being 'in the
zone'. It isn't triggered by a sudden extreme situation as the
above is, but by intense mental concentration.

When the subject's mental concentration gets high enough, the brain
releases chemicals as well, not only to record more input in higher
detail at higher speeds, but to have sections of the brain repurpose
themselves to process and act on this new detail. The chemicals make
the brain run at a higher speed, like over clocking your CPU from
500MHz to 750MHz. The parts of the brain that normally did other parts
now working on processing the information is like adding another CPU or
two to your system. Suddenly the brain has several times more
processing power to review and react to all the new input than it does
normally.

Another way the brain can increase the focus is by essentially
discarding input that it believes isn't critical to surviving in the
situation. Most people will say that they suddenly couldn't hear
anything during an extreme situation. The other effect (and the most
dangerous one) is the narrowing of the visual sense. This is commonly
referred to as 'tunnel vision'. The brain discards visual input
from the far sides of the field of view and concentrates on center. If
things get really serious, the vision will drop unnecessary colours
going all the way to black and white, if needed.

The truth is, the subjects aren't going deaf, but the brain is trying
to use the audio processing centers of the brain for extra visual
analysis and also to stop what it thinks are extraneous sounds from
interrupting the brain concentrating on the visual processing and
reaction. The same is happening with vision in tunneling. The brain
doesn't want visual distractions off to the side disturbing it while
it focuses on what is right ahead. The parts of the brain that used to
monitor / process the vision on the side can help process all the extra
input / frames coming in from the center of view. If there is still too
much information to handle, colour information will be stripped away to
reduce the 'size' of each visual frame in order to speed up
processing.

If one can get the brain into the right mix of running at higher speed,
repurposing certain parts, but not going so far as to discard sound and
visual input, significantly higher than normal performance is possible.

If you ever do find yourself in a situation with 'time slowing
down', turn your head and verify you can see everything around you to
keep your situation awareness. Also try and confirm that you can still
hear and react to sounds or commands given via audio. While you may
feel like a superman, getting tunnel vision can be disastrous.

These conditions are common in law enforcement, especially in a long
high speed chase. Tunnel vision can cause the officer to not see an
innocent car or pedestrian off to the side who is entering the chase
path unaware of the speeding cars. The 'going deaf' symptom can be
life threatening during the chase by not hearing radio communications
and also after the chase when the officer is approaching the suspect.
The officer doesn't realize he can't hear, and other officers
behind him are unable to get his attention.


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