October 25, 2018
Ever wonder why your immediate reaction to a loud noise is shutting your eyes? You hear a loud noise and immediately flinch or squeeze your eyes shut tight. This automatic response happens at the first sign (or sound) of danger; this act of mechanically blinking your eyes is known as acoustic startle reflex.
It is a defense mechanism that occurs when the body senses an oncoming attack. The limbs tense, the body retreats into itself, and the eyes close. This is something the body innately knows to do and begins to present itself in infants at around six weeks of age. Scientists consider acoustic startle reflex an “auditory phenomenon”. Researchers have also determined that the response originates in the brainstem. The severity can depend on how calm a person is prior to encountering loud stimuli. For instance, people with post-traumatic stress disorder (PTSD) may have a hyper-sensitive acoustic startle reflex. Conversely, people under the influence of alcohol may have a delayed or non-existent acoustic startle reflex.
Since acoustic startle reflex is just that – a reflex – there is no way to prevent the body from reacting in that way when there is a loud noise. There is, perhaps, a way to reduce it.
As a rule, it is always good practice to be aware of your surroundings, as increased attention to what is going on around you may help to ward off potential hazards, as well as the initiation of the acoustic startle reflex. This awareness is also known as mindfulness, which can be cultivated through a mindfulness practice such as meditation. Meditation can not only reduce the facial expression and automatic eye blink associated with a loud, sudden noise, but it can also keep your heart from racing once adrenaline kicks in at the potential threat of danger.
A pre-pulse inhibition (PPI) is a feature that occurs right before the reflex itself. A reduced or non-existent PPI could be a sign of something more severe like PTSD, Tourette’s syndrome, ADHD, or Huntington’s disease. A non-existent or reduced PPI could also be an indication of a hearing problem, however, studies have shown that there is more to acoustic startle reflex than an ability to hear loud, sudden noises.
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