Perception 2: Brightness and colour
22 October 2022 19:08
Learning objectives
Light: the stimulus for vision
• Visible light is a band of energy within the electromagnetic spectrum (400-700nm)
• Different wavelengths of light are associated with different colour perceptions
• Light can also be described as consisting of small packets of energy called photons
• The more photons of light, the more intense the light is
• Light intensity (luminance) is associated with perception of brightness
Wavelength and intensity are properties of the stimulus, whereas colour and brightness are
properties of our perception, and there is not a 1:1 relationship
Light interacts with objects and surfaces in the environment
• Absorption as photons collide with particles of matter
• Reflection as light strikes opaque surfaces
• Transmission as light passes through transparent matter
Different material properties are associated with different perceptions e.g. Bright objects reflect
more light than dark ones
The human eye
Two types of photoreceptor: rods and cones
Perception Page 1
, The visual pathways
(dont need to learn all of these parts)
Brightness perception
• Relationship between light intensity and brightness is not straightforward - perception is
influenced by both bottom-up and top-down processes
Bottom-up
• Retina doesnt simply record light intensities
• Responses are shaped by processes occurring within the retina
○ Light-dark adaptation and lateral inhibition
Top-down
• The brain uses knowledge about how light interacts with objects when determining perceived
brightness (e.g. Shadows)
Light/dark adaptation
Perception Page 2
22 October 2022 19:08
Learning objectives
Light: the stimulus for vision
• Visible light is a band of energy within the electromagnetic spectrum (400-700nm)
• Different wavelengths of light are associated with different colour perceptions
• Light can also be described as consisting of small packets of energy called photons
• The more photons of light, the more intense the light is
• Light intensity (luminance) is associated with perception of brightness
Wavelength and intensity are properties of the stimulus, whereas colour and brightness are
properties of our perception, and there is not a 1:1 relationship
Light interacts with objects and surfaces in the environment
• Absorption as photons collide with particles of matter
• Reflection as light strikes opaque surfaces
• Transmission as light passes through transparent matter
Different material properties are associated with different perceptions e.g. Bright objects reflect
more light than dark ones
The human eye
Two types of photoreceptor: rods and cones
Perception Page 1
, The visual pathways
(dont need to learn all of these parts)
Brightness perception
• Relationship between light intensity and brightness is not straightforward - perception is
influenced by both bottom-up and top-down processes
Bottom-up
• Retina doesnt simply record light intensities
• Responses are shaped by processes occurring within the retina
○ Light-dark adaptation and lateral inhibition
Top-down
• The brain uses knowledge about how light interacts with objects when determining perceived
brightness (e.g. Shadows)
Light/dark adaptation
Perception Page 2
