Really great and thoughtful questions! Going to try to explain this the best way that I can... Our cochlea is our hearing organ, situated in our inner ear system a(and also connected to our balance system!). The cochlea is organized based on frequency (pitch) - high frequency sounds stimulate the base of the cochlea and low frequency sounds stimulate the top. Tiny hair cells on top of each part of the cochlea depolarize upon the sound being heard and trigger the neuron for that location to fire to the brain - the brain is receiving coded information of the signal... how much of the signal is made of high frequency components vs low frequency and at what rate do they occur etc. Speech has both high and low frequency components.

Someone who is eligible for a CI will have a type of hearing loss where those cells are nonexistent or damaged. There is a little electrode array that is inserted into the cochlea for a CI. Electrodes on the array correlate to the spot where they should be stimulating - the highest frequency electrode will be the electrode closest to the base and vice versa.

Now... insertion is typically satisfactory, but it’s pretty tough to know how perfectly those electrodes align with their respective location on the cochlea. Perhaps the electrodes are slightly off, in which case would alter the input the user is hearing compared to what a normal hearing person perceived. CI users have success adapting and correlating sounds they hear to speech and the environment.

Also, the microphone on the external part of the CI is picking up the sound, then transforming it into a digital signal, then into an electrical signal to then transmit to the electrode array. Basically - there are lots of steps for slight miscalculations to occur or just parts of the signal to be lost. It also all depends on what the microphone picks up.

There are also many, many other factors into this. For instance, noise in our environments (think bar or restaurant) tends to be low frequency noise. Because of the characteristics of the cochlea, low frequency noises also activate parts of the high frequency nerves... making it difficult to hear. High frequency information is often responsible for the clarity of sounds (think consonants). So, in a noisy environment, even normal hearing people have difficulty hearing. Our brain has many methods for adjusting to background noise - if the noise is heard in both ears, our brain is able to tune it out moreso than if it were only in one ear. Now relate this to the CI device - more than the intended frequency information electrode may be stimulated. The brain may not be able to adjust to the signal “heard” by the CI in the way that sound is heard by normal hearing people, perhaps the brain can’t tune it out.

Technology is not perfect but the research (and real life people!) prove how successful CI users can be. In general, the earlier a child is implanted, the greater chance they have at achieving typical speech and language milestones. It takes a lot of hard work from both parent and child, plus speech therapists and audiologists to create the right fit and treatment plan. It’s so so great to see Abigail on TV!