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
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
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.
Do you see the dog?
This sentence has
has something wrong
with it.
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.
Lotto’s inspiring TED talk can be seen
here. Watch it, and you will literally not be able to believe what you are seeing.
Implications
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 grains of rice appear to be moving? They’re not
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
Cite this page as: Dunn, Michael. How reliable is the knowledge provided by our senses? (10th May 2013). theoryofknowledge.net.
Columnist: Marc Berry
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