AUDITORY PERCEPTION
It is particularly true, for the auditory modality, that the signal, which carries the message, is transient. It lasts for only a brief moment in time and is gone. Hence, the speed and efficiency of the processes that decode the signal are critical.
Speech is probably the most difficult of the auditory signals to process. It contains a stream of multitudinous and rapidly modulated variations.
Some of these change the meaning a lot, some change it a little, and some have no effect on the meaning.
In addition, meanings are being transmitted simultaneously on several levels including: non linguistic, phonetic, morphologic syntactic, semantic and pragmatic. As difficult as it is, we (humans) make it look easy.