Types of perception
There are two interacting aspects of perception. They include bottom-up processing and top-down processing. Bottom-up processing is when a person receives an incoming stimuli from an environmental source. On the other hand top-down processing occurs when a person processes information based on the perceiver's previous knowledge. Top-down would be breaking something down from the largest component into smaller components to get better insight into the perceived situation. Whereas bottom-up processing would be taking all the smaller environmental stimulus and utilizing them to gain a better insight into the larger component. Both of these aspects occur every second of every day.
Speech and Perception
Speech can be changed and altered with the slightest production
difference, to the environment around the speaker. There are many speech
sounds that vary from the accent and dialect to the language of the
speaker. If you close your eyes and hear a sound it may differ from when
your eyes are open. Also, if someone is talking at the same time as
someone else, you might blend the sounds to hear something else.
Sometimes what you see s what you expect to hear, and this can stray
from the true sound production. The brain can perceive these sounds
differently than they are meant to come out.