Chapter 4: Vision Flashcards
Visual acuity
The ability to see fine detail.
Visible light
Lightwaves visible to humans.
Portion of the electromagnetic field that humans can see.
Wavelenghts
The distance between successive peaks of a wave.
3 PHYSICAL DIMENSIONS OF LIGHT: Lenght determines:
Hue (what we perceive as colour).
3 PHYSICAL DIMENSIONS OF LIGHT: Amplitude determines:
Brightness
3 PHYSICAL DIMENSIONS OF LIGHT: Purity determines:
Saturation or richness of colour
Retina
- What is it?
- What does it do?
- A layer of light-sensitive tissue lining the back of the eyeball.
- Turns light waves into neural signals
Accomodation:
The process where the eye maintains a clear image on the retina.
The muscles in the eye change the shape of the lens.
Flatter lends for further objects.
Rounder lends for nearby objects.
Myopia (?)
Images are focused in the front the retina because the eyeball is too long or the lens is too rounded (?)
Hyperopia (?)
Images are focused behind the retina because the eyeball is too short and the lens is
Photoreceptors
Light-sensitive proteins that absorb light and transduce it into electrical signals.
Cones
- What does it do?
- What are there concentrated?
- What are the 3 types and what are they sensitive to?
- Helps to focus on fine detail and to detect colour under normal daylight conditions.
- They are concentrated at the fovea.
- • L-cones: Sensitive to long wavelengths (ex. red).
• M-cones: Sensitive to medium wavelenghts (ex. green)
• S-cones: Sensitive to short wavelenghts (ex. blue, purple).
How do the 3 cones determine brightness?
It is signalled by the total amount of activity across all three cone types.
How do the cones interpret colour?
Colour is signalled by the relative levels of activity between pairs of cone types..
Rods
Sensitivity to faint light in the periphery.
Activates in under low-light conditions, for night vision.
Periphery
In the retina, it is the area outside the fovea.
Fovea
The area in the retina where the cones are concentrated, allowing humans to see colour and fine detail. Area with the greatest visual acuity.
No rods at all.
Bipolar cells
Collects electrical signals from the rods and cones and transmits them to the retinal ganglion cells (RGCs) in the outmost layer of the retina.
Retinal ganglion cells
Organizes the electrical signals from the rods and cones and sends them to the brain.
Optic nerve is formed by…
The optic nerve is formed by the bundle of the retinal ganglion cells’ axons.
Blind spot
A location in the visual field that produces no sensation on the retina because of the optic nerve.
Quite a big hole, but our perceptual system automatically “fills in” using knowledge of the colour or texture around the blind spot.
Action potentials containing information about visual information from the retina travel to the brain along the ____ ____ and goes to the _____ ____ ____ (LGN) located in the _______ of each hemisphere. Then, the visual information goes to the ____ __
optic nerve
lateral geniculate nucleus
area VI
Colour deficiency (colour blindness):
A genetic disorder where one of the cone types and rarely, two.
Colour afterimage
Sensory adaptation caused by staring too long at one colour that it fatigues the type of cone that corresponds to that colour.
Colour-opponent system
Pairs of cones types work in opposition.
Explains colour aftereffects. If one is tired, and the other cone dominates, and another colour is perceived until the other cone rejuvenates.
Visual receptive field
A single retinal is sensitive to a very small area of visual space.
Info on V1 needed?
Binding problem
The problem of how the brain links features together so that we see unified objects in our visual worlds rather than free-floating or miscombined features.
Parallel processing
The brain’s ability to perform many activities at the same time.
Illusory conjunction
A perceptual mistake whereby the brain incorrectly combines features from multiple objects.
Ex. When colour and shape is combined incorrectly.
Feature-integration theory
The idea that focused attention is not required to detect the individual features of a stimulus (e.g., the colour, shape, size, and location of letters), but it is required to bind those features together.
