Perception 2 Flashcards
Define visible light
Band of energy within the electromagnetic spectrum
What are different wavelengths of light associated with?
Different colour perceptions
What does light consist of?
Small packets of energy called photons
What is light intensity (luminance) associated with?
Perception of brightness
What is it called when photons collide with particles of matter?
Absorption
What is it called when light strikes opaque surfaces?
Reflection
What is it called when light passes through transparent matter?
Transmission
What does the eye use to project an image onto the retina?
Uses convex cornea and lens
What does directional sensitivity represent?
The spatial structure rather than sum total of light
What transducer light into an electrical potential?
Photoreceptors
What does the electrical potential in the eye reach when it flows through a network of neutrons?
Retinal ganglion cells
After the retinal ganglion cells, where does the electric potential go?
Back out the eye via the optic nerve
Where are rods located?
Peripheral retina
What are rods capable of?
Operating in low light levels
What is concentrated in the centre of the retina?
Cones
What requires higher light levels to respond?
Cones
What has 3 different photopigments, sensitive to short, medium and long wavelengths of light?
Cones
What is the main pathway of visual info from the retina to the brain?
Retina> optic nerve> optic chiasm> Lateral Geniculate Nucleus > primary visual cortex
What is light intensity related to?
Perceived brightness
Regarding bottom-up theories, what does the retina not record?
Light intensities
What does the bottom-up theory suggest?
Responses are shaped by processes occurring within the retina (light/ dark adaptation and lateral inhibition)
What does the top-down theory suggest?
The brain uses knowledge about how light interacts with objects when determining perceived brightness
What is perceiving a familiar object as having the same brightness under different conditions of illumination?
Brightness constancy
Is the sensitivity of the retina constantly adjusted to compensate for changes in mean luminance?
Yes
When is sensitivity reduced in the retina?
When the mean intensity of the image is high (visa versa)
What does the retina encode?
Contrast
Define lateral inhibition
Early form of info processing in retina- retinal ganglion cells receive both excitatory and inhibitory input from neighbouring photoreceptors
What is arranged in a centre-surround configuration across the retinal image?
the retinal ganglion cells in the retina
What does lateral inhibition do?
Makes the visual system sensitive to changes in luminance
What happens in your eyes when looking at the Herman grid illusion?
The intersections are surrounded by more high intensity (white). This results in more inhibition from the surround in on-center, off-surround receptive fields
Regarding top-down influences, how to we perceive the Checker-shadow illusion?
Our visual systems use knowledge of how light interacts with 3D objets when determining brightness
Why does the world appear in lacking of colour under low-light conditions?
Only rod photoreceptors are sensitive enough to operate, of which contain a single type of photopigment (rhodopsin). Light of different wavelengths can elicit identical responses, making it impossible to accurately signal different wavelengths
What are S-cones?
Cones that are preferentially sensitive to short wavelengths (blue cones)
What are M-cones?
Cones that are preferentially sensitive to middle wavelengths (green cones)
What are L-cones?
Cones that are preferentially sensitive to long wavelengths (red cones)
What does the relative outputs of the 3 cone types allow?
Unambiguous signalling of wavelength
What is Monochromacy?
When individuals have 0 or 1 functioning cones type, resulting in complete colour blindness (extremely rare)
What is Dichromacy?
When one has only 2 functioning cone types
What is Protanopia?
When one is missing L-cones
What is Deuteranopia?
When one is missing M-cones
What is Tritanopia?
When one is missing S-cones
What is Anomalous trichomacy?
Defect in one of the cone types- more common form of colour perception deficiency
What is Protanomaly?
L-cone deficit
What is Deuteranomoly?
M-cone deficit
What is Tritanonomaly?
S-cone deficit
How is Anomalous trichromacy commonly assessed?
Ishihara Colour test
What is Colour opponency?
When retinal ganglion cells receive excitatory and inhibitory input from different cone types- resulting in distinct Red/Green and Blue-Yellow pathways
How can colour opponent be demonstrated?
By using negative afterimages
Explain colour opponency in relation to red and green
Adaption to red causes a reduction in the sensitivity of long wavelength cones, creating an imbalance in the inputs to red/green opponent retinal ganglion cells
Define colour constancy
The tendency for the perceived colour of objects to remain the same, even if the lighting changes
How do we try to achieve colour constancy?
By accounting for the intensity and composition of light hitting different surfaces
