So last week I wrote mainly about our hearing and pardon the pun, but I also touched on sight. In fact our dominant sense is sight, whilst hearing is our most sensitive due to the range of loudness over which our hearing operates. I am confident that most if not all of you will have watched a few episodes of the tv series ‘QI’, where the panel are told about facts which are Quite Interesting. The presenters often refer to the band of ‘QI elves’, a team of people who find out these interesting facts and figures and a team of them have been on another tv quiz show which I like, that being ‘Only Connect’. On one of the QI episodes the question was asked “How many senses do humans have?” to which one of the team, Alan Davies, replied quite innocently “five’. At this of course the klaxon sounded! It is the number which we are of course first taught at school, these being sight, hearing, touch, smell and taste. Except there are many more than we perhaps realise, as we do not necessarily attribute them to being true senses. But even these five main senses are technically more than a single sense. Sight itself combines two senses, given the two distinct types of receptors we have, one for colour (cones) and one for brightness (rods). Another sensor, but which is related to a chemical reaction, is our sense of smell and this combines with taste to produce flavours. You could argue that taste should count for five senses by itself due to the differing types of taste receptors, these being sweet, salty, sour, bitter, and umami, the latter being Japanese which means “a pleasant savoury taste.” Its receptors detect the amino acid glutamate, which is a taste generally found in meat and some artificial flavouring. Then there is touch, which has been found to be distinct from pressure, temperature, pain, and even itch sensors which have a distinct system from other touch-related senses. Pressure is obvious, so I’ll say no more on that one. But there are more.
Thermoception is the ability to sense heat and cold. This is also thought of as more than one sense — not just because of the two hot/cold receptors, but also because there is a completely different type of receptor in terms of the mechanism for detection in the brain. The thermo-receptors there are used for monitoring internal body temperature. I have mentioned sound, detecting vibrations along some medium, such as air or water that is in contact with your ear drums but linked to this are senses which work to control both body awareness, which is proprioception, which deals with how your brain understands where your body is in space. It includes the sense of movement and position of our limbs and muscles. For example, proprioception enables a person to touch their finger to the tip of their nose, even with their eyes closed. It enables a person to safely go up and down steps without looking at each one. Folk with poor proprioception may be clumsy and uncoordinated, which can happen when we might have consumed alcohol or taken drugs. So it is one of the things police officers test when they stop a vehicle when they suspect that the person driving may be doing so whilst under the influence of drink or drugs. The “close your eyes and touch your nose” request is testing that sense. It is also used all the time in little ways, such as when you scratch an itch on your foot, but never once look at your foot to see where your hand is in relation to your foot. Additionally there is equilibrioception, which is the sense that allows you to keep your balance and sense your own body movement in terms of acceleration and directional changes. This sense also allows for perceiving gravity, though I do not believe we use that sense much nowadays, if at all. Then we have tension sensors which are found in our muscles and these allow the brain the ability to monitor muscle tension. There are more senses yet! One is nociception, which in one word is pain. At one time this was considered the result of overloading other senses, such as touch. But it is now viewed as its own unique sensory system. There are three distinct types of pain receptors, which are the cutaneous (skin), somatic (bones and joints), and visceral (body organs). We also have stretch receptors which are found in the lungs, bladder, stomach and the gastrointestinal tract. These sense the dilation of blood vessels and so are often involved in headaches. Chemoreceptors trigger an area of the medulla in the brain that is involved in detecting blood borne hormones and drugs. It is also involved in the vomiting reflex. Now, we may not consider these next two as ‘senses’, but they are fairly obvious. One is for hunger, allowing your body to detect when you need to eat something and the other is thirst, which more or less allows your body to monitor its hydration level, so your body knows when it should tell you to drink. One that I was not aware of is magnetoreception, or the ability to detect magnetic fields. This sense is principally useful in providing a sense of direction when detecting the Earth’s magnetic field. Unlike most birds, humans do not have a strong magnetoreception but researchers have found some specialised cells in birds’ eyes that may help them see magnetic fields. It is thought that birds can use both the beak magnetite and the eye sensors to travel over long distances in areas that do not have many landmarks, such as the ocean. Experiments have demonstrated that we do tend to have some sense of magnetic fields. The mechanism for this is not completely understood, it is theorised that this has something to do with deposits of ferric iron in our noses. It seems that people who are given magnetic implants have been shown to have a much stronger sense of this magnetoreception than humans without them. Perhaps that is why many folk like wearing magnetic bracelets. The last one on this long list is time, but this one is debated. No singular mechanism has been found that allows people to perceive time. However, experimental data has shown humans have a startling accurate sense of time, particularly when younger. The mechanism we use for this seems to be distributed through specific parts of the brain.
Students take their senses for granted and often do not realise how they work together in providing different types of information about their immediate environment. This information allows them to respond to changes in their environment. Since students rarely lose one of their senses, they do not appreciate that they all work together. In situations when students may experience the temporary loss or the masking of one sense, such as losing their sense of taste when they have a cold, losing their sense of sight when walking from a well-lit room into a dark room, or losing their general sense of hearing when using an MP3 player and personal earphones, they may become more aware of having to use other senses to provide information regarding their environment. Students rarely have first hand experience of how people with any type of sensory loss obtain much-needed information about the environment by using other senses. Our five main senses of sight, taste, touch, hearing and smell all collect information about our environment and these are interpreted by the brain. We then comprehend all of this information by the combination of the information from each of our senses and linking this with previous experience. It is then further developed by later learning. We respond almost automatically to most sensory information and this quick response is important for survival in our environment and this has been the case for the continuance of the human race. Whichever sense is dominant varies between different animals. I have said that in humans our dominant sense is sight, whilst hearing is our most sensitive, due to the range of loudness over which it operates. However, advancements in science have enhanced the quality of life for many people with sensory disabilities by providing such things as alternative methods of communication, increased mobility, additional educational tools, and technology designed for sensory enhancement, such as cochlear implants.
These days, when being taught about all this students are encouraged to explore the relationships between the operation and role of the senses in ways that I never was. In some places they use Concept Development Maps to learn about forces and motion, living things, the structure of matter, our Earth as well as the apparent structure and nature of Space. There is one area which focusses on cells and organs and at this level includes learning experiences which encourage all the students to find out more about themselves and other animals. This is really important, so they begin by explicitly identifying the five senses and the organ(s) associated with each sense. Then, with the intention of moving towards an understanding of ‘systems,’ teachers provide opportunities for students to experience the ways that each sense provides information which helps and supports the other senses and the organism as a whole. These learning experiences allow students to consider everyday difficulties that may be experienced by people whose sensory input is disrupted or unreliable. They encourage students to identify items or systems that have been developed to enhance sensory input., such as Braille, bells at railway crossings, audible, vibrating and tactile pedestrian signals, hearing aids, guide dogs, talking clocks, walking canes, etc. Teachers may even provide a variety of experiences which can be built upon to explore each sense in detail by using ‘feely bags’, secret packages, taped sounds and taste tests of bitter, sweet, salty and sour-tasting foods to create learning experiences which rely on one sense collecting information. In this way, students may explore each sense in detail, like whether different tastes have the same effect on different parts of the tongue. What I like is for students to not just explore how senses work together, such as determining the success of our ability to correctly identify samples of food when sensory input is limited. One way is to get food samples, like pieces of orange, carrot, celery, cantaloupe, potato, apple, pear and banana. Samples are then placed in a paper bag and with a class of students organised into three groups, two of the groups are blindfolded. One of these blindfolded groups must then try to identify the wrapped food samples using only their sense of smell. The other blindfolded group may use only touch; their sense of smell is blocked (they should pinch their nose or put cotton wool in their nostrils). The final group is not blindfolded and may make full use of touch, smell and appearance to identify the food samples. Students then record their observations using science journals and present their results using graphs and tables. In this way, students can make generalisations about our ability to gather all the information and make sense of the world around us when any of our sensory inputs are restricted as compared to when all our senses work together. This can then be expanded to encompass the world around us, by comparing and contrasting human senses with those of animals. If the students consider how animals sense the outside world and the anatomical structures that allow them to do so, they will appreciate that bees have taste receptors on their jaws, forelimbs and antennae, the eyes of the chameleon can move independently so that it can see in two different directions at the same time, crickets hear using their legs when sound waves vibrate a thin membrane on the cricket’s front legs, falcons can detect a ten-centimetre object from a distance of one and a half kilometres away whilst dolphins and whales communicate using various high pitched ‘whistles’ and ‘clicks’, with some beyond the range of human hearing. This is valuable to them, as sound travels faster in water than in air. The speed of sound in water is about 3,300 miles per hour (1,480 metres per second) whilst the speed of sound through air at ground level under typical conditions is about 760 miles per hour (340 metres per second). All this though, as well as having watched recent episodes of a Jane Austen series has made me wonder whether sensibility is a sense. Apparently as nouns, the difference between sense and sensibility is that sense is as I have already described above, any of the manners by which living beings perceive the physical world with our main ones being sight, smell, hearing, touch, taste. But sensibility is the ability to sense, feel or perceive, most especially being sensitive to the feelings of another which in stressful times can so easily be overlooked. I have left the best until last, as it really needs no explanation but which we all need – a good sense of humour!
This week, an appropriate fun one…
A Chinese doctor cannot find a job in a hospital in America, so he opens a clinic and puts a sign outside that reads:
”GET TREATMENT FOR $20 – IF NOT CURED, GET BACK $100.”
An American lawyer thinks this is a great opportunity to earn $100 and goes to the clinic.
Lawyer: “I have lost my sense of taste.”
Doctor: “Nurse, bring medicine from box 14 and put 3 drops in patient’s mouth.”
Lawyer: “Ugh, this is kerosene.”
Doctor: “Congratulations, your sense of taste restored. Give me $20.”
The annoyed lawyer goes back after a few days to try to recover his money.
Lawyer: “I have lost my memory. I can’t remember anything.”
Doctor: “Nurse, bring medicine from box 14 and put 3 drops in his mouth.”
Lawyer (annoyed): “This is kerosene. You gave this to me last time for restoring my taste.”
Doctor “Congratulations. You got your memory back. Give me $20.”
The fuming lawyer pays him, then comes back a week later determined to get back $100.
Lawyer: “My eyesight has become very weak and I cannot see at all.”
Doctor: “I don’t have any medicine for that, so take this $100.”
Lawyer (staring at the note): “But this is $20, not $100!”
Doctor: “Congratulations, your eyesight is restored. Give me $20”