Language is the association of vocalized sounds and written symbols with meaningful concepts or actions. Language processing refers to the mental capacities required to see or hear language, and then associate the appropriate person, thing, place, concept, question or action being communicated. In short, through language processing, humans understand when and how to respond to written or spoken communication. Since so much of the brain and its functions remain a mystery to modern science, the exact chemical and physical processes involved in processing language are unknown.
Doctors and researchers theorize that language processing is entirely a brain function, meaning that the brain handles all aspects of processing language. While the actual processing may indeed be conducted entirely within the confines of the human brain, other systems provide crucial input necessary to enable processing and understanding language. With this in mind, an argument could be made that language processing is contingent on channeling the flow of information from auditory and visual input systems to the brain. Actual processing of language may happen in the brain, but without systems to gather and channel information, no language processing would be necessary.
Due to the symbiotic nature of auditory systems and the brain's ability to process language, language and auditory processing are commonly referenced at the same time, and in some cases, thought to be interchangeable. Processing spoken language and gaining the appropriate understanding of sounds and syllables requires auditory processing capabilities. Any delay or deficit in auditory processing abilities results in delayed or ineffective language processing. In other words, if a person cannot properly hear and process auditory input, then obviously language processing for spoken words would be difficult as well. The two processes are heavily dependent on one another, but in fact, remain separate concepts and systems.
Written language, as with spoken language, also requires the same mental processing capabilities, in terms of neurological function. Naturally, no auditory processing is needed for written language. Instead, properly functioning visual abilities are needed. In language processing for written communications, the brain must interpret visual symbols, then immediately associate those symbols with an appropriate meaning and when warranted, an appropriate response. Any gaps, delays, or deficits in the visual system can contribute to language processing difficulties.
Research regarding how auditory and visual input systems send information to the brain for processing is still inconclusive. Scientists understand that the visual cortex of the brain receives visual input and that the auditory cortex receives sound input. What remains unknown is if the visual and auditory cortex use the same or different pathways to send information for language processing.