This is second in the three-part series on the oddities of our sense organs.
Hearing (Audioception)
While chemicals trigger smell and taste, pressure stimulates hearing and touch. If you have ever been in a club, concert or any place where bass-heavy music is being played, you may have felt a very physical presence of sound. Sound, after all, is vibrations traveling through air (or any medium). The audible range for humans is between 20 Hz and 20,000 Hz which we all know. This range is actually mapped out in the ear!
High frequencies are picked up by those sensory cells at the beginning of the cochlea, moving backward as the frequency decreases. So, depending on the region of the cochlea that receives the signals, our brains help us perceive how high or low, the frequency of a certain sound is, like in a map. But, the effectiveness of this setup can be dented by physical features like ear wax or as it happens during old age, hardening of the tissues.
Hearing illusions called ‘endaural phenomena’ where such physical disturbances as discussed above may cause us to perceive sounds when there aren’t any. The brain can also cause havoc, leading to auditory hallucinations, wherein people hear ‘voices’, loud sounds or the related kind.
Touch (Tactioception)
First of all, touch isn’t a single sensory feature. Rather, it is made of several elements (that contribute to the overall sensitivity) like pressure, vibration, temperature, skin stretch and also the pain in some scenarios. Pain (Nociception) has its own dedicated system that is present all across the body (except the brain). Similar to the auditory sensors, the sensitivity of the skin is varied across the body, including a map of its own.
The sensory information from hands and lips send more information than the entire chest and back areas since we use the former parts for fine manipulation and sensations. This is also one the reasons behind developing the Braille (since the fingertips are sensitive to bumps). Interestingly, without visual cues, sometimes people misjudge the size and quantity of objects that they feel with their digits. This happens since the information from the touch and movement related sensors may confuse the brain, which in the absence of sight, can come up with wrong conclusions. This is called ‘Aristotle’s Illusion’.
Hearing and touch are also closer than was previously thought. A 2012 study by Henning Frenzel helped uncover the fact that those with sensitive hearing abilities also showed a finer touch sensitivity.
Vision (Opthalmoception)
If you have observed in the previous sections, the aspect of vision aiding other senses cannot be discounted. Well, given that the brain prioritizes vision over others, it does come equipped with an interesting line-up of features. We have all been there, or should I say ‘seen that’? On floor tiles, bread toasts, in the sky, fire, and even pizzas. Patterns, of all kind. Faces of famous people to obscure objects, we have seen them all. The wired part is that it’s all factual and not illusory. Once someone spots a pattern, everyone else does too, eventually.
Retina, one of the principal parts of the visual system is made up of the same tissues as the brain and is directly linked to it. As far as the receptors are concerned, there are two varieties. Rods, which are ultra-sensitive (useful during low light conditions) and cones which help us in the highly detailed colorful picture that we perceive during daylight. As far as the distribution of visual receptors is concerned, they are concentrated heavily at the center (in a region called fovea) while are scattered in the periphery. These receptors are grouped in so-called ‘receptive fields’, more in the middle (small and dense) and few (big and far apart) in the outer regions.
These receptive fields are activated as the constituent receptors are triggered by light falling on them. This explains a lot regarding what we see and observe. The fovea is where the finer details are perceived with the outer regions providing a rather blurry picture.
The brain behind the picture
When we squint to observe, we are basically reshaping our eyes to allow light to fall mostly on the middle region. Also, have you observed while you are reading this article, how you can focus on a single element (a word or a group of words) at a time? You are seeing the screen, but focusing only a few words at any given moment.
Luckily for us, you might have also realized that we move our eyes a lot. Due to this, the fovea scans and continuously sends the data back to the brain. These scans are stitched together in the brain, where they are overlapped with the blurry input from the periphery of the retina, and voila you have a clear picture of the world around you. The eyes also move not in a smooth manner but in a series short sweeps (called saccades). What about the time when you dilate or contract the pupil? Well, that’s controlled by a part of the brain called Pretectum. Quite fascinating!
The brain doesn’t stop just there. Remember how the eyes literally take a series of shots which are later stitched together? What else can it do? Read Part III to learn more about the wonder in our cranium.
Notes
Burnett, D. (2016).The Idiot Brain. 1st ed. London: Guardian Faber Publishing
Aristotle’s Illusion: A tactile illusion that is created when the eyes are closed, two fingers of one hand are crossed, and a small object such as an acorn is pressed (especially by another person) into the cleft between the tips of the crossed fingers. The sensation is that of touching two objects rather than one. The first written account of it was given by the Greek philosopher Aristotle (384–322bc) in the essay ‘On Dreams in the Parva Naturalia’. [Source: Oxford Reference]