We all have them. They make up part of our ear autonomy. In some instances, we even use them for beautification purposes. But do we know how they aid in our hearing? The ‘folds’ in our ears make up a critical component of our ability to interpret sounds. Scientifically, the part of the ear described as the ‘folds’ is known as the auricle or pinna.
The folds themselves include the helix, which is the prominent outer rim, and the antihelix, which is the inner curved ridge parallel to the helix.
The auricle also includes the scapha, which is the groove between the helix and antihelix, and the concha, which is the deep bowl-shaped part leading into the ear canal. Other areas in the auricle are the tragus and antitragus, which are the small cartilaginous projections near the ear canal opening, and the lobule, which is the fleshy lower part, better known as the earlobe.
To get a proper understanding of the pinna’s functions, Kenyans.co.ke spoke to Dr. Beatrice Onchari Isanda, an ear specialist in the area of special needs, specializing in solving hearing impairment. Dr. Isanda doubles up as a lecturer in the Department of Special Needs Education at Kenyatta University and is also the Director, the Directorate of Accommodation.
Dr. Isanda noted that the folds of the pinna (auricle) play a very important role in hearing and are responsible for three crucial functions.
Firstly, and perhaps crucially, the folds in the pinna assist in determining the direction of sound (localization). This includes vertical localization (up vs. down), where the folds create minute differences in how sound waves are reflected or diffracted, providing cues to the brain about whether a sound is coming from above or below.
In the same breadth, they assist in front-back localization. This entails how one is able to tell whether sounds heard come from the front or the back.
“Because of the shape and folds, sounds coming from the front and back have different reflections and intensities, helping the brain distinguish front from behind,” the specialist stated.
For example, if someone is calling your name and you can not see them, the folds in the pinna would help you know whether the person is ahead of or behind you.
Another key use of the folds in determining the direction of sound is in horizontal localization (left vs right).
While differences in arrival time and loudness between the two ears primarily determine horizontal localization, the pinna contributes by modifying the spectral content of sounds entering from different horizontal angles. This explains why you can distinguish whether a sound is coming from the left or the right.
In terms of how the folds influence hearing and direction perception, the irregular folds filter and reflect sound waves in a way that alters their frequency spectrum depending on the source direction.
This modification is analysed by the brain to interpret sound elevation and front-back differences, an ability known as monaural spectral cue processing. Consequently, without these folds, for instance, in the absence of the pinna or when it is covered, sound localization is significantly impaired, especially for vertical or front-back discrimination.
Another role of the pinna is to collect sound waves. The primary role of the ear is to collect sound waves, and this is where the pinna crucially comes in.
“They act as a funnel, gathering sound vibrations from the environment into the external auditory canal (meatus) towards the tympanic membrane (eardrum),” noted Dr Isanda.
The pinna/auricle also aids in amplifying certain frequencies. It enhances frequencies between 2,000-5,000 Hz, which are crucial for speech understanding. The pinna is assisted in this by the concha and external auditory canal, which together provide resonance that boosts these frequencies.
However, due to its exposed position, it's susceptible to various forms of trauma and conditions. Some common cases of damage to the pinna include auricular hematoma (cauliflower ear), lacerations, cuts, abrasions, perichondritis and chondritis, burns, frostbite, keloids, and allergic reactions.
Even so, the pinna is still an important cog in hearing, playing a key role in funnelling sound, amplifying critical frequencies, and providing directional cues through filtering and reflection effects essential for sound localisation.
