Our five senses help us perceive the world around us. The sense of touch, for example, can bring loved ones closer but, on a darker note, can also frustrate amputees. What bothers them particularly about their prosthetic arms is missing feedback. Is what they are touching hot or cold, liquid or solid, a rose or its thorn; an aspect so universal for the able-bodied that it is not given a second thought.
Though it has not escaped Artificial Intelligence (AI) researchers who are trying to replicate these senses (Engineering and Technology, August 2023). They have been busy developing artificial hands with softer fingers and embedded sensors. How long will it be before the problem is solved?
Well, a US company Atom Limb is expecting to release a mind-controlled prosthetic limb in 2024. In it the movement sensors in the hand section of the prosthesis send electronic signals to the wearer’s stump, where the neurons once connected to the amputated hand are still in place and capable of transmission to the brain.
Notice how we know at once when there is something crawling on our skin. In May 2022, researchers at Stanford University’s Bao Research Group announced the invention of artificial skin that is durable, paper thin and stretchable. This has the future potential of being wired into the wearer’s nervous system to give a real touch capability — namely, sensing temperature, pressure, vibration and location. Thus when the finger moves from the handle to the cup itself, you sense the change in temperature and distance.
Another sense, that of hearing or rather lack thereof, is not infrequently a source of humor. Possibly because the sufferers are able to compensate through other means. Beethoven suffered from Paget’s disease. It caused skull bone enlargement which pressed on the eighth cranial nerve associated with auditory function. The loss was gradual from the age 28 to 44 when he was quite deaf. While he could still hear a little, he would strap an ear trumpet on his head so he could conduct the orchestra with his hands. He also carried a notebook and pencil to jot down musical brainstorms but also to converse with friends.
Hence the somewhat morbid joke of someone seeing Beethoven sitting on his grave furiously erasing some sheet of music. “Maestro! Maestro! What are you doing,” the person asks, to which he gets the reply, “I am decomposing.”
Hearing loss when it is congenital is no joke, however. It can inhibit language learning and speech. Thus the words ‘deaf and dumb’ are often placed together with ‘dumb’ of late being replaced by the kinder ‘mute’.
Here again technology comes to the rescue. Cochlear implants have been around for quite a while. Invented in 1957, the first implant procedure is credited to Stanford University. A single-channel electrode was used but was found to be of limited utility for detecting speech. It took a further 20 years to get to the modern multi-channel type.
Hearing aids now are small enough to be barely visible. They work for most people and only those with profound hearing loss consider the implant option.
Our sense of sight helps us navigate the world around us, and enjoy its beauty. For some it may be taken away gradually through macular degeneration (AMD). It is a form of retinal deterioration that affects the sight of some 200 million people in the world. As the photoreceptors in the central retina degenerate, it impairs the ability to read or even recognize people.
The good news is that a prosthetic replacement is now being developed to replace the lost photoreceptors with photovoltaic pixels. These convert light into electricity which stimulates the neurons in the retina. While the present version leaves the recipient somewhat shortsighted, a newer one currently being tested in rats will restore 20/20 vision.
For the future, there is Science Eye, a device employing optogenetics. It uses gene therapy to restore optic nerve cells while an ultra-dense micro-LED display panel is inserted directly over the retina.
There are others in the field including Cortigent which is making headway with a system that does not require genetically modifying retinal cells because it is a direct cortical (brian layer) stimulator. Cortigent is in the process of designing a study to get their stimulator implant approved. They have already spent five years studying the safety and reliability of their devices.
Then there are our senses of smell and taste, to some extent linked. There is a good reason food seems bland and tasteless when a person has a bad cold — the sense of smell is absent. Thus when chefs talk about flavor, they imply both taste and smell.
Taste receptors in the mouth sense sweet, sour, salt, bitter and savory — the latter also known as umami. But try sucking a lemon flavored candy while pinching your nose. You will taste the sweetness, but not the lemon flavor. The tongue is, of course, also sensitive to cold and heat.
A promising approach to treatment for loss of smell is to train the olfactory nerve through inhaling a set of odors (originally rose, lemon, clove and eucalyptus) twice daily for three months. It was found to help the nerve to regenerate.
Taste has been with humans forever. Long before scientists and their experiments, humans knew to avoid plants that tasted bitter — it signified something harmful. Yet there are people unfortunate enough to be without this sense.
Having all the senses is so commonplace that we rarely ponder their absence. So let the next gustatory and olfactory experience, or the music we hear, or the walk we take in a park where we can also smell the flowers, be all the more meaningful for valuing our senses. Harnessing them and adding that subconscious sense of perception to enhance our understanding of the world as it is, and we need only imagination to observe the world as it could be … to be ready to take the first step on the journey to a better one, a world at peace.