Final answer:
Marianne is experiencing a Nonverbal barrier to communication due to the speaker's exaggerated gestures which are distracting and not complementing the verbal message.
Step-by-step explanation:
In the scenario where Marianne is distracted by a speaker's exaggerated gestures at a seminar, the form of communication barrier she is experiencing is a Nonverbal barrier. Nonverbal communication includes gestures, facial expressions, and other body language that can either complement or interfere with the verbal message being conveyed. In this case, the speaker's gestures are not complementing the message but are rather distracting, indicating a breakdown in communication due to nonverbal cues.