Tag: sensory

Posted in Psychology & Medicine

Synaesthesia

Posted on by Jinavie

What colour do you associate with the letter “E”? What sound do you hear when you feel the fluffiness of cotton? These sound strange to most people as we experience the senses in distinct ways. However, for 4% of the population, this is a completely normal experience.

Synaesthesia (“joined sensation”) is the neurological phenomenon where two or more senses are coupled together. This creates two kinds of synaesthesia: projection, where you physically sense something (such as seeing a purple circle when hearing piano music), and association, where you associate the sense with another sense (“that sounds quite orange”).

The most common form of synaesthesia that is reported is grapheme-colour synaesthesia, where certain people perceive letters and numbers as different colours. However, there are various kinds of synaesthesia, such as chromesthesia, where people associate sounds with colours (previously called “coloured hearing”). In fact, almost every combination of senses have been described, with some individuals experiencing multiple senses at the same time.

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The exact origin and mechanism of synaesthesia are yet to be fully explained. The most likely explanation is that in the brain of synaesthetes, the neural pathways for the various senses cross-over more than they should, causing the simultaneous activation. There are already some cross-overs between these pathways, as evidenced by various sensory illusions that the average person can enjoy. For example, a ventriloquist can fool the audience into thinking the puppet is talking as we hear speech and see the puppet’s mouth moving.

An alternative explanation is that there may be an element of ideasthesia – where concepts are paired with sensory experience. This would mean that synaesthetes are experiencing sensations due to the idea something represents, not because of the original sensory stimulus.

For example, when a synaesthete describes that the word “tree” tastes like brie cheese, it might not be the sound of the word, but rather the concept of a tree that triggers the sensation. We actually see examples of this in day to day life in the form of metaphors. We describe a wine having a round taste or a person being sweet.

There is much to learn about the phenomenon, but synaesthesia has already deepened our understanding of how we perceive the world, process it and commit it to memory through the use of associations and mnemonics.

Posted in Psychology & Medicine

A Sensational Experience

Posted on by Jinavie

We use our senses to interpret the world around us. Thanks to photography, video and sound recording, we are able to preserve what we see and hear in our lives. If you have the good fortune of seeing an incredible view such as a beautiful sunset, you can take a photo, look at it ten years later and remember what it was like watching it with your own eyes. If you miss the sound of your loved one’s voice, you can record the sound and play it again.

However, we are still unable to record senses such as taste, smell and touch. No matter how hard you try, you can never perfectly describe the taste of your mother’s cooking, the soft touch that you felt during your first kiss, or the scent of the person you love to another person using just words. This means that these sensations are only in your memories – and yours alone.

It is a shame that you cannot recall these experiences perfectly, as some of our best memories are associated with them. But perhaps you could think of it from a romantic point of view. You can share a photo or a sound clip with others to share your experience – even make it public so that everyone can know of it. However, with things like taste and smell, only you will know and remember that specific sensation. It is a truly unique experience that belongs only to you (and the few others who were lucky to have tasted your mother’s cooking).

Furthermore, as it is only in your memories, the moment you forget about it, the experience will disappear forever. Maybe that is why people cling to nostalgia of these senses – because it is a fragile yet precious thing that is worth treasuring and holding on to.

Posted in Psychology & Medicine

Rubber Hand Illusion

Posted on by Jinavie

The five senses are something we take for granted as we never even give a thought as to how complex the way we receive sensory information about the world we live in. As incredible the science behind all the senses may be, it is also interesting to see such intricate mechanisms being fooled by sensory illusions. An experiment that highlights how intricate the senses can be is that of the rubber hand illusion.

In this experiment, researchers made participants look at a dummy rubber hand, while obscuring their real hand from view. They then applied exactly the same stimulus to the real hand as the rubber hand, such as stroking it with a brush or feather. Within a short amount of time, the participants reported that they were convinced that the rubber hand was their real hand, confusing the visual sensation of seeing the rubber hand with the tactile sensation of their real hand being brushed.

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Because the brain is so good at piecing together things to come up with explanations, it links the two sensations and thus concludes that the rubber hand must be part of the body. The association is so strong that some participants would even feel pain when the rubber hand was attacked, pulling away their real arm.

One of the lesser known senses of the body is proprioception – the sensation of knowing where your body lies in three-dimensional space. This sensation is what lets you do things with your eyes closed, while also being responsible for the feeling of embarrassing yourself with a fall when someone pulls the chair out from under you. Proprioception is based on a delicate “body map” your brain draws out from various sensory information such as your joint position and touch sensation from your muscle and skin. It then adds more information such as vision and spatial orientation information from your inner ears to accurately predict how you will interact in your environment. In the case of the rubber hand illusion, the brain is fooled into remapping the body map to accommodate the rubber hand.

The application of this phenomenon, known as multisensory integration, extends from out-of-body experiences to phantom limb pain, where amputees feel pain and sensation from an amputated limb. There are also anecdotal evidence of men with penile prostheses being able to achieve orgasms, most likely thanks to the rubber hand illusion.

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Posted in Psychology & Medicine

Time Perception

Posted on by Jinavie

What exactly is the present? The present is the middle point between the past and future, the world that we experience and perceive on a real-time basis. But would you believe it if the world you perceive is not the true “present”? To experience the world, we use our five senses. The brain collates all these sensory information and processes it to construct “the present”. This process takes about 80 milliseconds. Ergo, the world we experience is actually the world as it was 80 milliseconds ago. For a similar phenomenon, consider the stars. The stars we observe are not what they look like now, but what the stars looked liked when they emitted the light that we see. Thus, the star you are looking at may not even exist anymore.

But 80 milliseconds is a very short time; surely it has no impact on our everyday life? To prove that this delay has a critical impact on our understanding of cause and effect, neuroscientists designed the following experiment. The researchers would ask the participant to press a button that caused a light to blink after a short delay. After about ten tries, the participants reported that the delay had disappeared and the light flashed immediately after they pressed the button. This was due to their brain editing out the time delay and directly connecting the cause (button) and the effect (flash). But a much more peculiar phenomenon was seen when the researches removed the delay between the button press and the flash. Participants reported that they saw the light flash before they even pressed the button. The participant’s brain had become so used to the editing process that it was confusing the order of the cause and the effect.

The brain’s time-editing ability can be seen in the following simple experiment. If you touch your nose and toe at the same time, logic dictates that as the toe is further from your brain, the signal will have to travel further and it will be felt later. But in reality, you feel both at the exact same time. This is because your brain uses a map of the body to edit the relative time the signal takes to reach the brain to better construct a “real-time present”.

Posted in Psychology & Medicine

Cranial Nerves

Posted on by Jinavie

Nerves can be divided broadly as spinal nerves and cranial nerves: the latter which is directly from the brain. There are 12 pairs of cranial nerves:

  1. CN I – Olfactory nerve (smell)
  2. CN II – Optic nerve (sight)
  3. CN III – Oculomotor nerve (eye movements, control of pupil and lens)
  4. CN IV – Trochlear nerve (eye movements)
  5. CN V – Trigeminal nerve (sensory information from face and mouth, chewing)
  6. CN VI – Abducens nerve (eye movements)
  7. CN VII – Facial nerve (taste, tear and salivary glands secretion, facial expressions)
  8. CN VIII – Vestibulocochlear nerve (hearing and sense of balance)
  9. CN IX – Glossopharyngeal nerve (taste, swallowing, parotid gland secretion, sensory information from oral cavity, information about blood)
  10. CN X – Vagus nerve (sensory and motor signals to and from many internal organs, glands and muscles)
  11. CN XI – Accessory nerve (movement of SCM and trapezius, which are neck/shoulder muscles)
  12. CN XII – Hypoglossal nerve (tongue movements)

As there are so many nerves and the names are all varied, there is a simple (yet very obscene) mnemonic to help medical students remember the names and order of nerves:

Oh, Oh, Oh, To Touch And Feel Virgin Girls’ Vaginas And Hymens
or
Oh, Oh, Oh, To Touch And Feel A Girl’s Very Soft Hands
(where vestibulocochlear -> auditory)

It is also worth noting the mnemonic for the types of nerves is:

Some Say Marry Money, But My Brother Says Big Boobs Matter More

Perhaps the only way to survive medical school is through humour.

Posted in Psychology & Medicine

Sensory Illusion

Posted on by Jinavie

The five senses we use to experience the world are simply wondrous. However, thanks to our not-so-perfect brain, these senses can easily be distorted. Illusions are a very good way to show how the brain processes sensory information and there are many fascinating examples.

Almost everyone has seen an optical illusion before, such as Penrose’s endless stairs or the Muller-Lyer illusion. There are countless more examples such as static pictures that appear to be moving and illusions in colour perception (A and B are the same colour). This is caused by the brain not recording images like a camera, but rather processing visual information and reconstructing an image. There are four main types of optical illusions: ambiguous (e.g. rabbit or duck), distortion (Café wall illusion), paradoxical (Penrose triangle) and fictional (only seen in hallucinations or by schizophrenics).

(Do you see the dolphins? Children cannot see the man and woman because they cannot comprehend it, whilst adults cannot overpower the sexual image)

Like vision, every other sense can be fooled in a similar fashion.
Auditory illusions that distort what we hear are fairly common, a good example being the infinitely ascending Shepard scale (which are just a series of the same ascending octave scale). Also, the McGurk effect shows how the brain uses a multimodal approach where it involves both hearing and vision when listening.

There are also tactile illusions. For example, if you pull your top lip to left and the bottom lip to the right, then prod the middle of the lips with a pencil, it feels like there are two. However, the more famous case is of the Phantom Limb, where an amputee’s brain still believes that the limb is there, causing it to “feel” the limb or even feel pain.

The other two senses aren’t as famous in terms of illusions, but definitely exist.
Smell is easy to fool through chemicals as it is the physiological method of detecting smell. It also exhibits olfactory fatigue where it becomes desensitised to a strong smell.
Taste illusions are more fascinating and easily seen. They are caused by two or more tastes forming a synergy to produce a completely different taste. For instance, mixing barley tea and milk produces a coffee milk taste, while cucumber and honey tastes like melons.
A more fascinating illusion involves Miracle Fruit Berries, which contain a substance called miraculin that distorts the taste of sourness to sweetness.

This shows how we can fool all five senses, and learn more about the mysterious organ that is the brain.