Vision Flashcards
Light
the stimulus
detected they eye, where the initial stages of processing are taken care of, then the result is sent to the brain for further processing
Variations in light waves
Amplitude
Wavelength
Purity
Amplitude
height of each wave
- variations affect brightness
- the bigger it is, the more light is being reflected or emitted
Wavelength
distance between peaks of successive waves
- variations affect perceptions of colour
- measured in nanometers
- larger = lower frequency; smaller = higher frequency
Visible Spectrum
the tiny position of the total range of wavelengths of the electromagnetic radiation that humans are sensitive to (360nm-750nm)
-some animals see other spectrums
Purity
affects perception of saturation
-light that is made up of a single wavelength is pure. We typically see a mixture of wavelengths and they are less intense than pure colour
Cornea
begins focusing process when light passes through
-transparent window out front of eye
Sclera
tougher membrane that covers rest of eye
Pupil
processes light after cornea
-round window (black dot)
Iris
controls size of pupil
- coloured part of the eye
- consists of a band of muscles controlled by the brain
- dilate pupil to allow more light
- constrict pupil to restrict light
Lens
processes light after pupil
- final focusing
- curvature causes images to land on the retina upside down and reversed left to right (the brain corrects this)
- flexible piece of tissue whose shape can be altered by surrounding muscles
Lens Accomodation
the lens can change shape to focus on object that vary in distance
- fatter/rounder for close objects
- flatter/elongated for far away objects
Vitreous Humor
light passes through after lens
-clear, jelly-like substance that comprises the main chamber inside the eyeball
Retina
light finally lands here
- natural tissue that lines back of eye
- made up of complex network that neural cells arranged in 3 layers
3 Layers of Retina
Ordered in an inside out fashion based on nutrition requirements of different cells
Photoreceptors
Bipolar Cells
Ganglion Cells
Photoreceptors
translate the physical stimulus of light into a neural signal that the brain can understand
-light must pass through other layers first
Retinal Pigment Epithelium (RPE)
provide nutrients for photoreceptors and located at back of eye (which is why the layers are arranged backwards)
Rods
125 Million
lower light intensities
night vision
no colour, poor visual acuity, concentrated surrounding fovea/periphery
Cones
6 Million
day vision
colour, good visual acuity, concentrated in fovea
Ganglion Cells
collect info from larger segment of retina
- axons of these cells converge at optic disk
- leave optic nerve which travels to brain
Blind Spot
area of the eye where the optic nerve leaves - there are no photoreceptors
Bipolar Cells
receive info from photoreceptors and send it to ganglion cells
Horizontal and Amacrine Cells
cells in the retina that allow areas in the retinal layer to communicate with each other
-allow info from adjacent photoreceptors to combine their info - cones and rods converge to travel along only one million
Receptive Field
collection of rods and cones in the retina that, when stimulated, affects the firing of a particular ganglion cell
-photoreceptors get divided into groups that get assimilated into one signal that affects a ganglion cell down the line
Visual Fields
right and left halves of our visual fields are processed by contralateral sides of the brain
- sends info to both eyes which are then received by both hemispheres
- right visual field = left hemisphere
- left visual field = right hemisphere
Optic Chiasm
the point at which the optic nerves form the inside half of each eye cross over to the opposite hemisphere
Main Pathway
when each visual field arrives in respective hemisphere after optic chiasm, optic nerves split and travel along 2 pathways
-most retinal/ganglion cells travel along main pathway and synapse in LGN
Lateral Geniculate Nucleus (LGN)
part of thalamus that receives visual information
Primary Visual Cortex
made up of areas in occipital lobe and processes visual info after LGN
- cells here are made up of receptive fields of LGN cells (made up of receptive fields of ganglion cells)
- area V1 on occipital lobe
- striate cortex
Extrastriate Cortex
occipital lobes V2-V5
-visual processing areas in occipital lobe outside of striate cortex
Topographical Organization in Visual Cortex
retinal coordinates are topographically mapped in visual cortex
-neighbouring locations in retina project to neighbouring location in visual cortex
Processing Streams of Extrastriate Cortex
processed visual info is sent out and separated into either the Dorsal or Ventral stream
-info is compressed as it travels along pathways
Dorsal Stream
“where” pathway
- depth and motion
- to parietal lobe
Ventral Stream
“what” pathway
- color and gorm
- to temporal lobe
Evolution of the Eye
new adaptations being layered upon old adaptations
- may have started out as a light sensitive patch
- may have mutated which caused a slight depression (allows light to be sensed)
Crude Lens
an early adaptation of the eye
- allows visual input at different distances
- allow better focusing and accommodation
Cumulative selection
evolutionary process whereby new adaptations are layered upon old adaptations
Cost Effectiveness of the Eye
benefits must outweigh the costs
- eyes are metabolically expensive
- has many evolutionary advantages
Evolutionary Advantages of the Eye
in most environments, vision makes it easier to find food, water, shelter, a mate, avoid predators/dangers
Factors that influence Variance among Species
do they live in an area with light or nah?
does the food come from above or below?
movement, shape and colour of prey
Compound Eyes
anthropods
- arrangement of individual tubular units called ommatidia that each point in a slightly different direction
- to gather light that lies directly in front
- form a single image by putting together many separate signals from each ommatidium
- good at detecting movement at close distances
Simple Eyes
vertebrates and molluscs
- eyeball, lens, retina
- vary according to environment (shape and orientation of pupil, size of eye, location of eye on head)
2 Functions of the Eye
Resolution (acuity)
Sensitivity (ability to get enough light)
Larger Eyes
better at both functions of the eye
-this benefit varies as some species need better resolution in the day and some need better sensitivity at night
Laterally Directed Eyes
on side of head = large total view, two separate fields of view
-poor depth perception (for avoiding predators)
Eyes Facing Front
narrow total view, single field of view = good depth perception (good for hunting)
Development in Visual Architecture
least developed at birth
formed at second prenatal month
reacts to light random firing of retinal cells at 6th prenatal month
At Newborn
weak lens muscles, single field of view, inconsistent pupil reactions, low cell density in retina (especially in fovea)
-dismal visual acuity
3 Months
adult-like focusing
11 years
Visual brain area development complete
