How reliable is the knowledge provided by our senses?

How reliable is the knowledge provided by our senses?

There are many different theories about how our senses actually work. Initially, that may seem surprising: surely our senses just communicate what’s out there, be it an image, a sound, or a smell, to the brain? But of course, the process is far more complicated than that, and the variables that are involved means that there is room for debate over what exactly happens. Moreover, just a quick glance at the perceptive abilities of animals quickly reveals just how limited our senses are: in terms of our eyes, for example, our lenses are not capable of dealing with objects at long distance, the twin images they then project onto the retina are tiny and upside-down, and the retina itself is pretty much colour-blind. The optical abilities of human beings, then, are very poor. So how do we see with any certainty? Where there is uncertainty, there are theories…

Herman Grid Illusion

Herman Grid Illusion

Hermann von Helmholtz’s ideas

The first serious study into how the eye works was done by Hermann von Helmholtz (1821-1894). He was a German physician and physicist who investigated an unfeasibly large number of subjects, one of them being, the eye. Having decided that vision should be, physiologically speaking, all but impossible, Helmholtz ventured the theory that we construct images in our minds by inferring the whole based on past experience. In other words, we convert the shaky and rather inaccurate pictures generated by our eyes into something that makes sense based on our understanding of the world.

Verifying Helmholtz’s ideas

Scintillating Grid Illusion

Scintillating Grid Illusion

These two optical illusions are probably familiar. The images show two different grids on top of a black background. The first, known as the Hermann grid illusion after its nineteenth century ‘discoverer’, Ludimar Hermann, shows a series of white lines on top of the background. Except, that’s not what you see. You see white lines with black blobs at their intersecting points. The second one, which is even more arresting, is known as the scintillating grid illusion, and was created in 1994 by Lingelbach. This has intersecting grey lines on top of the background with white spots at the meeting points of the lines. Except when you are not focusing on these spots, they turn black.
The precise way in which these illusions work is very complex, and certainly not worth going into. For our purposes, it is enough to say that we have trouble perceiving the true image because of the frailties of our optical sense. Our minds try to put a picture together for us to comprehend, but is unable to do so because of conflicting models of comparison. This makes more sense when we consider the theory that advanced the ideas of Helmholtz.

Gestalt Theory

The German word ‘gestalt’ means “form”, “figure”, or “shape”, and is the label given to a group of psychologists based in Berlin who were working during the 1920s – 40s. They agreed with the idea that we make a ‘best fit’ of images created by our eyes, and added that we do so by perceiving the whole, rather than little bits of the object we are looking at individually. We do this unconsciously and very quickly. The phrase stating that, ‘the whole is greater than the sum of its parts’ is associated with Gestalt psychology.
The simplest example of this is how we perceive words: we do not base our understanding of words by individual letters, but by perceiving words, phrases and sentences. It is only when you come across a word that you have not encountered before do you have problems with individual word.

This sentence has

has something wrong

with it.


Do you see the dog?

Do you see the dog?

If you glance at the sentence above, you don’t initially notice the extra word, and you certainly don’t have any problem understanding what its meaning is.
A more complex example is the picture on the right. If you look at its individual parts, it is very hard to make sense of. However, if you allow your eyes to take in the whole of the image at once, you are able to determine what its subject is.
It is, of course, a Dalmatian dog sniffing around underneath a tree whose leaves have dropped onto the ground.

Latest theories

The weakness of the ideas of the Gestalt psychologists is that they generally describe, rather than explain, how our senses work. Modern theories are based on the ideas of computational neuroscience, which uses computers to build up models of how the senses work, and allows scientists much more scope to come up with explanations of how the brain functions.
However, what the ideas do provide us with is a way of understanding how we do not receive an objective picture of the world, and how our vision of the world – even at the basic level of sense perception – is often varied and subjective, and dependent on our powers of reason and emotion, which is where we are going next.

Beau Lotto on sense perception


Beau Lotto’s ‘Lotto Lab’ is dedicated to exploring how and why we perceive the world through our senses in the way we do. Lotto’s ideas are founded on the principle that we have evolved a way of seeing the world that suits us best, and that we are very selective in the way we view the world. He argues that context is everything: our minds often trick us into seeing things based on previous experience. At points during his TED talk, you will literally not be able to believe what you are seeing.


The implications of these illusions should not be underestimated, and the ‘fun’ side of them shouldn’t overshadow the what their significance is. As Lotto explains, our brains only see what they want to see – conditioned by evolutionary instincts of survival – no matter what our reason tries to impose on our minds. In other words, what we see may not match up to reality at all.
Here are some more extraordinary illusions which our brains simply cannot cope with.

Do the horizontal lines appear straight? They are.

Do the horizontal lines appear straight? They are.

Do the grains of rice appear to be moving? They're not

Do the grains of rice appear to be moving? They’re not

Does the image look as though it is expanding? It isn't

Does the image look as though it is expanding? It isn’t

Stare at the cross for 10 seconds. Do you see a green dot moving around the circle? It isn't there

Stare at the cross for 10 seconds. Do you see a green dot moving around the circle? It isn’t there


Explaining illusions


A fantastic short video on illusions, what they tell us about the way our minds work, and applications in the real world. Created by Michael Stevens of Vsauce.

Cite this page as: Dunn, Michael. How reliable is the knowledge provided by our senses? (10th May 2013). Last accessed: 23rd February 2017


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