What if the patient has a symmetrical hearing loss but thus far has not worn two hearing instruments; which ear should be the focus ear?
The ear that has been amplified should be the focus ear.
How many people have the right ear as the dominant ear?
Most people will have the right ear designated as the Focus Ear in Natural Directionality due to the Right Ear Advantage phenomenon of the human auditory system. This is due to the locations of brain areas that specialize in speech comprehension. The speech comprehension areas of the brain known as Wernicke’s area and Brodmann’s area 22 are usually located in the left hemisphere. Since the area of the brain is usually opposite to the site of the organ controlled, most people will have dominance in the right ear. Exceptions will be persons with congenital or early-onset acquired severe/profound deafness for the right ear. These people may develop the mentioned areas in the right hemisphere instead, and therefore have left ear dominance.
What happens when the focus ear is opposite from the signal of interest (i.e., how much does head shadow come into play)?
While head shadow may cause a certain amount of signal attenuation, this is not critical. First, attenuation is dependent on a number of sound source variables, such as angle, distance, frequency, and room acoustics/number of reflections. Second, in normal speech interaction people tend to turn their heads to the direction of the signal of interest. Few scenarios exist where the listener would not naturally move head positions to attend to the signal of interest. Further, in other types of directional modes, the signal of interest may not even be detected due to the lack of environmental awareness. Therefore, Natural Directionality actually helps people know to turn their head to the signal of interest.
How is localization not hampered by Natural Directionality II?
Because of the Surround Sound Processor and the synchronized omni response for the monitor ear, interaural time differences in the low frequencies are preserved with Natural Directionality II. A patient wearing Alera™ with Natural Directionality II may not localize as effortlessly as a normal-hearing individual, but they will be better off than with hearing instruments that do not have the Surround Sound Processor. Given experience with the devices, patients will be better off than without the hearing aids simply due to audibility. Ease of listening is a proven benefit of the Natural Directionality fitting approach over bilateral full directionality and omnidirectionality, and part of ease of listening includes the ease of spatial localization.
What is the main difference between Natural Directionality II and Natural Directionality?
Natural Directionality II utilizes band-split, which assigns a synchronized omnidirectional response to the low frequencies in both the focus and monitor ears which helps to preserve low-frequency cues important for spatial localization.
Will Natural Directionality II improve localization over Natural Directionality?
Yes. The band-split between low and high frequencies allows for spatial awareness, and because the band-split blending point is personalized to the person’s hearing loss, spatial awareness and localization is maximized.