In applying a behind-the-ear hearing-aid, the microphone (i.e. the instrument that picks up the sounds in the environment) is located outside the auricle (see figure). In this case the hearing-aid wearer also hears the sounds behind him amplified; not a particularly natural sensation. For this reason, certain hearing-aids incorporate directional microphones which are more sensitive to sounds coming frontally, in order to reproduce the natural function of the auricle.
Some particularly advanced appliances (programmable or digital) enable the directional function to be turned on or off, to further improve performance in extreme situations (e.g. driving a car and listening to passengers in the back seat).
With in-the-ear hearing-aids there is no problem since the position of the microphone inside the auditory canal enables the appliance to exploit the normal directionality provided by the auricle, thus giving an extremely natural feeling in the location of sounds.
