Listening involves a sender (a person, radio, television), a message, and a receiver (the listener). Listeners often must process messages as they come, even if they are still processing what they have just heard, without backtracking or looking ahead. In addition, listeners must cope with the sender's choice of vocabulary, structure, and rate of delivery. The complexity of the listening process is magnified in second language contexts, where the receiver also has incomplete control of the language.