What aspect of the speaker affects lipreading?

The factor that significantly influences lipreading is facial expression. When individuals attempt to understand speech through lipreading, they rely not only on the visual information of the lip movements but also on the emotional and contextual cues provided by facial expressions. Facial expressions can convey important information about the speaker's emotions, intent, and even slight nuances in the speech that might not be entirely apparent from lip movements alone.

For instance, a smile or frown can provide context that helps the lipreader better interpret what is being said. Additionally, the position of the mouth and the surrounding facial muscles during speech can change significantly with different emotions, which can either aid or hinder the lipreading process depending on the context of communication. Therefore, understanding a speaker's facial expressions is crucial for effective lipreading and enhances the ability to accurately interpret spoken language visually.