The listener receives messages. During reception, the listener employs auditory and visual sensory receptors. While the listening process can include hearing sounds, listening and hearing are not the synonymous functions that many individuals assume. The auditory reception of the message is itself a detailed process involving the intricate hearing mechanism. The sound must enter the middle ear, set into vibration the tympanic membrane, and be conducted through the inner ear to the brain. Problems with the hearing mechanism can compound the receptive process. Research at the National Institutes of Health suggests that as many as one out of every nine Americans has some type of hearing loss. Exposure to loud music, especially through headsets, has been identified as a major contributor to this situation. While many researchers and practitioners have focused their definitions and models of listening on listening to auditory-only stimuli, listening also involves the visual channel when the source of the stimuli is in the presence of the listener. The visual channel is an influential communication media, and the other senses (smell, taste, touch) impact the listener as well.