It also studies how these units and rules develop in sophistication in children, and what difficulties in development or medical conditions handicap children and adults, and means for alleviating these difficulties. Speech and language pathology graduate programs train aides who work with children and adults suffering these difficulties. Perception of speech involves detecting the sounds and word units in a stream of sound that is often continuous, with pauses at select times, such as major phrase boundaries, and variation is stress to mark key terms or changes from one major unit to another. Good actors seek the proper places for stress in a line. Too little, and you sound like a Godfather, a Dalek or a Borg.
Phonemes are the sound elements of speech.
They are units of sound we vary to change meaning. If so, the sounds that follow the beginning phoneme can alter its percept. Take sounds on their own, versus in a conversational context. Ambiguity's resolution depends on context. We learn these intuitively as children, and can do so as adults to some extent.