Your presumption is false. Eyesight is a boon to communication, not a barrier. Attention to eyesight might distract you from another sense, but the choice is there.
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How can staring at someone become a barrier to communication
TV transmission from one antenna to other antenna is a clear example of line of sight communication.
A2, As Dinglebot points out, gibberish is a common communication barrier. Misheard or misunderstood terms would be another.
choo choo
Useing your diaphragm to speak