100% Brilliant

I recently had the pleasure of presenting a 45 minute seminar titled “The Psychology of Seeing” at a CET event in London (100% Optical) and had a wonderful time. I met old friends, new friends, optometrists, dispensing opticians, contact lens practitioners, journalists, designers… And the best part was that people actually thought my summary was interesting enough to spend their Saturday afternoons listening to me chat about Psychology/ Neuroscience! So to everyone who attended my talk and to the organisers who invited me to speak in the first place, I’d like to say: thank you so much! I hope you enjoyed it.

And I’m sure the education content next year will be phenomenal (as it always is, I even sat in on a few excellent talks this year without getting CET points!) so I highly recommend you keep the dates in your diary: 100% Optical, 27-29 Jan 2018.

Below I’ve drafted a tiny (brief) summary of my talk for those who might be interested:


The Psychology of Seeing

Retinal cells transduce light into neural signals which allow our brain to make sense of the visual world. You can’t have successful vision without this partnership!

In neurotypical individuals, nerve fibres from the retina then project to the brain in a very prescriptive fashion as outlined below:


This means that a scotoma identified using monocular fields tests can predict loci of damage along the pathway, e.g. damage to optic nerve affects one eye, whilst damage to one lateral geniculate nucleus (LGN) affects one hemifield. (Please see my Learning Materials for a little map of which scotoma might link to which part of the pathway).

However we are not all born with fully-functioning, ready-to-go visual brains. Instead neurons are created with the potential to learn how to process these signals and then our early experience determines how successful they become. A good real-life example of this is patching to prevent amblyopia in children – if the visual signal is not appropriately corrected before the ‘critical period’ ends then the neural processing capabilities will suffer.

This leads on to the idea that experience shapes our perception. Imagine we’re trying to identify this image here:
For this we can use a theory of perception from Gregory, 1997 to explain how we might achieve this goal:


At the bottom is the object we’re trying to identify (reality), which feeds into our idea of what it is (hypothesis generator). However, the input itself isn’t the only contribution to our perceptual decision – we also use experience from what we’ve seen before (objects explored/ conceptual and perceptual knowledge) and rules of what we know must be true. This allows us to perceive the 12 random lines as a cube when in fact it isn’t. (Technically it is a subset of well-placed lines on your monitor but to you, it’s a cube! Neat, right?).

We can also use visual illusions to measure this effect e.g. the Ponzo Illusion:


Which of the red lines is bigger? The one at the top, right?

(Wrong, they’re the same size… Sorry!!).

But they seem like different sizes because we’re assuming there’s an element of depth and distance to the oblique black lines. That means that for the red line to dissect the black lines at the top and not the bottom, the top line *must* be bigger and therefore we perceive it as bigger. What’s really great is that even though you know this to be true, you can’t un-see it because your brain is still trying to analyse the scene in the same way.

Clearly then, top-down processing plays a huge part in our perceptual understanding of the world and it may not necessarily be true to say that we are all perceiving the same image.

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