Chapter 6 Flashcards
What is the function of the cornea?
- Clear outer coating in front of eye
- Starts to focus the image (initial focusing - majority of focusing occurs in lens)
- Protective function as well
What is the function of the pupil?
- Controls amount of light that enters the eye
(dilates in dim light, constricts in bright conditions) - Pupil reflexes are unconscious reflexes, controlled by signals in brainstem
What is the function of the iris?
- Contain muscles that help allow the pupil to dilate and constrict
- Coloured part of the eye
What is the function of the lens?
- Focuses a sharp image onto the back of the eye
- Muscles connected to the lens allow it to bend (change shape for objects closer and further away)
- gets more rigid as ppl age
What is the function of the retina?
- Where the image is focused on the back of the eye
- Retina is like a curved projection screen
- Thin layer of cells - major type are rods and cones along retina
What is the role of rods and cones?
Receptors that respond to light and convert it to neural signal - transduction of neural signal is carried out by the receptors
What is the blind spot?
A gap at the back of the eye where the visual signals leave the eye and travel towards the back of the brain so we can perceive what we are seeing
- part of the retina where axons of the ganglion cells are leaving the eye along the optic nerve (no rods or cones present)
What is the fovea?
- Part of the retina where the image is projected
- Directly behind the center of your field of view
- Central part of visual field
- Image projected on the fovea is an inverted image - (it is only later in visual pathway that these images are turned right-side up again)
What are the 2 problems of focus of the lens?
myopia - near-sightedness
hyperopia - far-sightedness
What is transduction and where does it occur in the eye?
Transduction = conversion of light energy into a neural signal
occurs in rods and cones of retina
Rods and cones pass on the transduced neural signal to what cells?
to bipolar cells, which pass to ganglion cells
Where do neural signals go after the ganglion cells?
the neural signals are transmitted to the optic nerve and towards the back of the brain
Do we have more rods or cones?
many more rods present than there are cones
What cells are found in the fovea?
only cones (rods are located in the periphery with cones as well)
What are the roles of rods and cones?
rods: sensitive to motion, allow us to detect motion in visual field (particularly in periphery)
- NOT present in fovea
cones: provide high visual activity, making images very sharp, allow for process of colour
- on found in fovea
Where do part of the signals from each eye cross over?
at the optic chiasm
Where do signals go after passing the optic chiasm?
travel to the thalamus, then to visual cortex located in occipital lobe
What is the wavelength of visible light?
400-700nm
What can see UV rays?
What can see infrared radiation?
insects - UV rays
snakes - infrared radiation
Does physical energy in the environment have perceptual qualities?
No
- light waves are not coloured, but wavelength determines the perception of colour
- our nervous system constructs these colours
What is colour reflectance?
Colour we perceive depends on the quality of the surface or object that the light is being reflected off of.
The colour we see is being reflected, all other wavelengths of light are being absorbed.
What is likely the most impressive animal when it comes to changing the colour of its skin?
Cuttle-fish
Explain how colour is an effective way to communicate information fast and effectively.
ex. stop signs - use of colour red
animals also use colours to warn of danger such as poisons and toxins
What is trichromatic vision?
- Refers to us having 3 different types of cones in our retina; each type of cone responds to a different range of wavelength
Long wavelength cones - respond to wavelengths in upper range (orange, red)
Medium wavelength cones - respond optimally to wavelengths in middle of visual spectrum (greenish)
Short wavelength cones - respond optimally to wavelengths in the low end of visual spectrum (blue)
What is dichromatism?
2 types of cones, instead of 3
Often: red-green colour deficiency; person lacks the long-wavelength cones, (contains only medium and short wavelength cones)
- wouldn’t see red or orange, and perception of green is not the same (more dull)
What is seen with colour afterimages?
colour of afterimages (showing white squares after coloured squares) –> colours are the opposite colours of those that were shown
What is opponent process?
How does it explain colour afterimages?
- Involves processing of the colour signals further down in the visual pathway, within the visual cortex.
- There are opposing channels (red vs. green, blue vs. yellow, achromatic - black vs. white)
○ Opposing colour channels are processed by special neurons located in the visual cortex
With colour afterimages, when you stare at that image, you are exhausting one end of that channel.
○ When original image is removed and there is just a white screen, then the opposite side of the channel is able to be freely expressed, because the other side of the channel being red is exhausted
How we see colour involves what 2 systems?
Are both needed for fully-functioning colour vision?
- trichromatic system
- opponent process
both are needed for fully-functioning colour vision
How do opponent process neurons work?
by processing the ration of cones responding within the retina
depending on the pattern of the responses, it can reveal the exact wavelength of light that produced it
What system allows us to make fine discriminations between colours that are close together within a wavelength spectrum?
Opponent process system