‘Eye’ Spy with my Little Eyes…

‘I spy with my little eyes someone who wants to learn about how we see!’ Our eyes are an important organ that gives us the sense of sight. The eyes allow us to see colours and shapes but also allow us to take in information for us to understand less direct information, like our friends’ emotions and what they want to do (based on eye movements and head direction). But how do our eyes help us to see what is going on around us?

This post will explain how our eyes give us the sense of sight in three different levels of complexity.

Level 1 (4-9 years old)- How do we look at things very close to us and very far from us? How do we see different colours? (Parents Corner is included at the bottom)

Why is it when I look at something very near me, everything around it is blur? Why is it when I look at something very far, everything near me is blur? How about colour? Why can I see so many colours? Let’s explore these questions in two parts: Focusing on objects near and far and Colour Vision. First, let’s talk about the parts of the eye to help us to answer these questions.

This is a drawing of how the eye looks like.

Focusing on Objects Near and Far

How we see involves how light enters our eyes. The cornea and lens help us to make sure that the light would hit a part of the eye, known as the retina. The retina would take this light and change it to information that is sent to the brain to help us to see the object. Let’s focus specifically on how the lens helps us to focus light on the retina to help us see objects that are near and far.

The lens can bend inwards or outwards to help focus light on the retina. The lens is able to bend because of the ciliary body and suspensory ligaments. This means that the ciliary body, suspensory ligaments and the lens help us to look at things close to us and things far from us.

When you are looking at something close, the ciliary body contracts (becomes shorter) and the suspensory ligaments relax (will be longer). This will cause the lens to become convex (more round) for the light to fall on the specific part of the retina.

When you are looking at something far, the opposite happens! The ciliary body relaxes (becomes longer) which pulls on the suspensory ligaments making it contract (becomes shorter). This will cause the lens to become concave (more flat) for the light to fall on that same part of the retina.

Colour Vision

On the retina, there are two types of photoreceptors (very small objects) which are rods and cones. These two photoreceptors have different roles. You can see their roles in the table here:

What it can help us seeVisionRodsHelp us to see in places that are very dark.Monochromatic (black and white) visionConesHelp us to see colours in bright lightTrichromatic (coloured) vision

Humans have trichromatic vision which means we have three different types of cones to sense different colours. Some animals have more than 3 different cone types which means that they can see more colours than we can!

Can you think about why it may be important for us to see colours?

Level 2 (10-14 years old)- Should we always trust what we see?

Our eyes are very important for us to see what is happening around us but should we always trust our eyes?

A visual illusion that suggests how cultures can influence our perception is the Müller-Lyer illusion that you can see below. Which line is longer?

What if I told you that the lines were the same length? Here is the same drawing but with lines to show that the lines are the same length:

So the question is why do we see line 1 as longer than line 2? Growing up in Singapore, you would see a lot of buildings (that tend to be right-angled). When we look at these buildings, we see the basic patterns of lines and arrows. Now, you may be wondering where do you see similar lines to those in the picture. Well, here is an example:

In this drawing of a building, you can see how line 1 looks longer than line 2 because it gives the impression of depth as line 1 seems closer to us and so the line appears longer even though line 1 and line 2 are actually of the same length. However, people of a different culture who may not have such environments may not fall for such illusions the same way we do. This is known as the ‘carpentered world hypothesis’ where the culture/environment influences our perception. However, people are still trying to find the best way to understand this visual illusion as the environment may only be one factor that affects our perception. Another example of how our eyes may play tricks on us is the McGurk effect.

When we are struggling to hear what our friends have said in a crowded room, we tend to focus more on their mouth movements to help us to understand what was said. However, there are times when the same sound is heard but the different mouth movements, that we observe, affect what we hear! This is known as the McGurk effect.

When the information from what we see and what we hear are not compatible, there is a change in what we think we hear based on what we see. Thus, it shows how connected our visual and auditory systems are in integrating information from what we see and what we hear seamlessly to make sense of the world around us. However, it also shows us that sometimes, our eyes can influence what we hear. To learn more about this effect, you can look at videos online to show how our eyes can really trick us into hearing different words with the same audio.

Level 3 (15 years old and above)- Do some people see sounds?

Can you imagine seeing sounds in different colours? How about when you look at a traffic light and you taste ketchup in your mouth? If you constantly experience such sensations, you may have synesthesia.

Synesthesia is a combination of two Greek words with ‘syn’ meaning together and ‘aisthesis’ that means sensation. Thus, synesthesia directly translated means joined sensations.

Synesthesia is a condition where one of the senses would also be simultaneously perceived by another sense. This can be in any two combinations of senses, like vision and hearing, vision and touch, hearing and touch and so on and so forth. The most common form of synesthesia is where colours are mapped onto different letters and numbers. People with this form of synesthesia are known to have grapheme-colour synesthesia but the colours that map onto these letters and numbers are specific to the individual and can differ across people with synesthesia. Now you may be wondering, how do you test these individuals with synesthesia?

Well, there is a test known as the Grapheme-Colour Synesthesia test where a screen pops up with a bunch of the same number/letter with one number/letter that differs and you have to find the odd one out on the screen. For an average person, like myself, I would take much longer to find the odd one out as I have to look at each number. However, for a person with grapheme-colour synesthesia, they would be able to identify the odd number or letter out easily because of the difference in colour. Therefore, they would perform a lot faster on the test with fewer (and even no) mistakes.

Another question you may be wondering is what are the explanations for synesthesia?

Cross-wiring hypothesis:

Some researchers have theorised that it may be that these connections across senses may actually be present at birth, that will eventually be lost and so, when we grow older, each sensory system is separated. Thus, these individuals with synesthesia do not have this pruning (reduction) of connections between the systems resulting in the senses still ‘crossing-over’.

Feedback is disinhibited:

Other researchers theorise that there are problems in the brain where the separated brain areas that typically process the different senses fail to inhibit (stop) the other brain areas that are involved in processing other senses, from activating which results in simultaneous perceptions or sensations.

In conclusion, synesthesia is still a relatively interesting area of research that helps researchers understand just how integrated all our senses are in helping us to perceive the world around us. What do you think can be some possible explanations of synesthesia and do you think synesthesia may benefit or be a hindrance to people?

Parents Corner (Level 1)

Here is an activity that can help your child to understand how the lens becomes more concave or convex using two masks.

Place the two masks together with the inner portions (where the nose and mouth goes) inside and the outer portions facing outwards.

Now hold the ends of the mask that loops around the ears with one side of the ‘loops’ in one hand. Your hands will act as the ciliary body and the ‘loop’ will represent the suspensory ligament.

Now, before you pull the ‘loops’ on each side (suspensory ligament), ask your child to predict whether they think that the masks will appear more flat or more curved.

You can say something like:

I am going to pull the sides of the mask very very tightly.

What do you think will happen to the mask? Will they become flat or curved?

And then pull on the ‘loops’.

Ask the child what they observe and whether they predicted it correctly or wrongly. You can say something like:

What did you observe? Is it the same as what you thought would happen?

Get the child to draw what they see.

Now, you are about to loosen the ‘loops’. Ask your child to predict what will happen by saying something like:

Now, I am going to relax the sides of the mask.

What do you think will happen to the mask? Will they become flat or curved?

You can loosen the ‘loops’ and ask your child what they observe and whether they correctly predicted what would happen.

You can ask the same questions and get your child to draw his/her observations:

What did you observe? Is it the same as what you thought would happen?

Have a short discussion with your child after about what he/she thought would happen and what they understand from the short activity. You can model this activity by using scaffolds like:

I thought… Now I understand…

By using such scaffolds, you are engaging your child in more deliberate and reflective thinking that is important for helping your child to better understand what was learnt in the activity.

References:

Muller-Lyer,F.C. (1889). Optische Urteilstiiuschungen. Dubois Reymonds Archive jar Anatomie und Physiologie (Suppl.), 263-270.

Neuroscience For Kids. (n.d.). Retrieved August 2, 2020, from https://faculty.washington.edu/chudler/retina.html

Neuroscience for kids - Synesthesia. (n.d.). UW Faculty Web Server. Retrieved August 2, 2020, from https://faculty.washington.edu/chudler/syne.html

Segall, M., Campbell, D. and Herskovits, M. J., (1966). The Influence of Culture on Visual Perception. New York: The Bobbs-Merrill Company.

Synesthesia: Opening the Doors of Perception. (n.d.). Retrieved August 02, 2020, from https://sites.dartmouth.edu/dujs/2010/05/30/synesthesia-opening-the-doors-of-perception/