For some, when in a heated conversation, emotions are not the only thing on the rise; so is the volume of the voice. When this occurs the individual is attempting to get their point across or be heard. The idea of increased volume = increased understanding is an irrational thought; meaning it is not based on factual evidence.
If you are a yeller you need to understand the following:
Abstract cognitive processes occur in the frontal part of our brains. This type of thinking is needed for successful communication. When you choose to yell at someone, you are forcing them into "Fight or Flight"; the survival mode of the brain. "Fight or Flight" occurs in the lower part of the brain far away from where purposeful thought occurs.
So what does this mean?
This means that when you yell at someone you are decreasing the likelihood of being heard or understood. So the next time your are in a heated conversation and you find yourself yelling and frustrated that you cannot get your point across....Now you know why; yelling defeats the purpose : )