Helen learned to hear by feeling the vibrations people made when they spoke. What were these vibrations were felt through?

According to the passage, the vibrations that Helen Keller felt when people spoke were felt through their throats. Anne Sullivan, Helen's teacher, taught her to hear by putting her hands on people's throats, allowing her to feel the vibrations produced when they spoke. By feeling these vibrations, Helen learned to understand and interpret what people were saying, which was a significant breakthrough in her ability to communicate.