Visual Perception
, Key Readings:
Eysenck, M.W., & Keane, M.T. (2015) Cognitive psychology. A student’s handbook. 7th
Edition. Chapter 2: 37-62, 71-76; Chapter 3: 81-87, 101-108.
Ward, J (2010). The Student’s Guide to Cognitive Neuroscience (2nd edition). London:
Psychology Press (Chapter 6:103-126).
The Eye
A large area of our brains is devoted to visual processing. The visual cortex makes up about
20% of our brains, highlighting the importance of visual information processing in survival.
• When light reaches the retina there are three consequences:
o 1. Reception: Absorption of physical energy by the receptors in the eye.
o 2. Transduction: Physical energy is converted into an electrochemical signal
in the retina.
o 3. Coding: Direct one-to-one mapping between the physical stimulus (the
light) and the resultant pattern of neural activity.
• Light enters the eye through the lens which can be adjusted by a process called
accommodation to focus the light onto the retina.
• The retina consists of two types of receptor cells:
o 1. Cones: Colour vision and sharpness of vision
▪ There are about 6 Mio cones in the retina which are in the centre of
the retina, i.e. fovea.
o 2. Rods: Vision in dim light and movement
▪ There are about 125 Mio rods which are in the outer regions of the
retina, i.e. para-fovea.
• The vertebrate retina (i.e. all animals with spines) is quite odd because the optic
nerve approaches the receptor cells from the front, rather than behind (like in an
octopus, e.g. https://en.wikipedia.org/wiki/Blind_spot_(vision)). This means that the
optic nerve fibres need a way out of the eye, and so there is a small patch of retina
with no photoreceptors at all. This is your blind spot.
o To see yours: Close one eye and fixate a point in space. Hold out your hand
on the same side as the closed eye and stick out your thumb. Slowly move
your hand sideways. You should find one spot where your thumb disappears.
This is because there are no photoreceptors covering that part of your visual
field!
Colour Vision
• Why do we have colour vision?
o Colour helps us to segregate objects from their background and helps
perception.
o Colour helps us to recognise and categorize objects (e.g. is a fruit ripe or
over-ripe)
, Key Readings:
Eysenck, M.W., & Keane, M.T. (2015) Cognitive psychology. A student’s handbook. 7th
Edition. Chapter 2: 37-62, 71-76; Chapter 3: 81-87, 101-108.
Ward, J (2010). The Student’s Guide to Cognitive Neuroscience (2nd edition). London:
Psychology Press (Chapter 6:103-126).
The Eye
A large area of our brains is devoted to visual processing. The visual cortex makes up about
20% of our brains, highlighting the importance of visual information processing in survival.
• When light reaches the retina there are three consequences:
o 1. Reception: Absorption of physical energy by the receptors in the eye.
o 2. Transduction: Physical energy is converted into an electrochemical signal
in the retina.
o 3. Coding: Direct one-to-one mapping between the physical stimulus (the
light) and the resultant pattern of neural activity.
• Light enters the eye through the lens which can be adjusted by a process called
accommodation to focus the light onto the retina.
• The retina consists of two types of receptor cells:
o 1. Cones: Colour vision and sharpness of vision
▪ There are about 6 Mio cones in the retina which are in the centre of
the retina, i.e. fovea.
o 2. Rods: Vision in dim light and movement
▪ There are about 125 Mio rods which are in the outer regions of the
retina, i.e. para-fovea.
• The vertebrate retina (i.e. all animals with spines) is quite odd because the optic
nerve approaches the receptor cells from the front, rather than behind (like in an
octopus, e.g. https://en.wikipedia.org/wiki/Blind_spot_(vision)). This means that the
optic nerve fibres need a way out of the eye, and so there is a small patch of retina
with no photoreceptors at all. This is your blind spot.
o To see yours: Close one eye and fixate a point in space. Hold out your hand
on the same side as the closed eye and stick out your thumb. Slowly move
your hand sideways. You should find one spot where your thumb disappears.
This is because there are no photoreceptors covering that part of your visual
field!
Colour Vision
• Why do we have colour vision?
o Colour helps us to segregate objects from their background and helps
perception.
o Colour helps us to recognise and categorize objects (e.g. is a fruit ripe or
over-ripe)
