Communication model: speaker/source, message (actual thought expressed, made of auditory stimuli, visual and tactile cues, auditory feedback (provided to the speaker, gives opportunity for needed adjustment or corrections to occur, environment, receiver/listener (receives and decodes, provides additional feedback) **elimination of any one part may result in failure of the communication process. System is functional in utero by the second trimester. Begin to perceive auditory stimuli several weeks before birth. Newborn is able to discriminate between different sounds based on frequency, intensity, and temporal information, discrimination between speech sounds within first weeks after birth. Normal human ear is capable of perceiving frequencies of 20-20k hz. Maximum range of intensity we are capable of perceiving is 3k-4k hz and varies from 0 db. Speech detection and perception varies based on intensity, frequency, and duration. Normal speech: 65 db spl/45 db hl. Greatest amount of energy in speech is below 1k hz. Consonants are low frequency, however, are vital for intelligibility of speech.