The eye and seeing Flashcards
Sensory receptors
- Vision
- Hearing
- Smell
- Taste
- Tocuh
The neuron
A signal is received by dendrites
Information is set along the axon via an action potential until it reaches the terminal buttons
Neuronal communication (3 activities from any signal cell)
- Spontaneous firing: when the cell is not receiving any signal, still random potential
- Excitatory activity: increase in frequency of action potential (increases chances of action potential)
- Inhibitory activity: fewer action potential compared to spontaneous (decreases chances of action potential)
Synapse
small gap between the terminal buttons and (typically) dendrites
Y-shape neural processing
excitatory connection
Straight-line neural processing
Inhibitory connection
Neural processing
The modulation of the neural signal at the synapse allows communication between different neurons/interactions between different stimuli
Spare coding
smaller of neurons that respond to a stimulus; stimulus is still coding by located at the distribution
Population coding
more neurons show activity; determined by the activity across the cells
Behaviour of light (2 sources of light)
- Point source: light coming from one point (ex. the sun, light bulb)
- Diffuse illumination: light comes from everywhere (ex. light on a cloudy day, the light is coming from every direction because the clouds are covering certain sections)
Radiance
how much light coming off a source
Light can do 3 things when it comes in contact with a surface
- Transmission (ex. light goes through the object)
- Absoprtion
- Reflection (ex. mirror)
Illuminance
how much light is hitting the surface
Reflectance
the proportion of luminance compared to illuminantion
Luminance
how much light is being reflecting from a surface
Brightness
psychological judgement of radiance and/or luminance
Refers to the absolute amount of light from an object
Think of when you walk into a bright room
Lightness
psychological judgement of reflectance
Refers to the percentage of light reflected from an object
Think of the shade (light = more white)
Pupil
like camera aperture to control the amount of light entering the light
Pinhole camera
a. the image is smaller and inverted
b. the image is very faint
c. the results in a blurry image
d. add a lens, so each point is now focused and the image is harp; the image is still inverted and small, but it is clearer
Lens
can accommodate focusing on object at different distances
Retina
where image is projected
Anterior chamber
the front part of the eye between the cornea and the iris
Cornea
hard structure outside of eye, to protect the eye; important for bending light
Iris
gives eye colour, ring of muscles to help pupil change sides
Posterior chamber
fluid, maintains pressure of eye
Scieria
our of circle of the eye
Optic disc
neurons leave the eye toward the brain; blood vessels in and out (blind spot is located) (no photoreceptors)
The lens: accommodation
lens changing shape to focus on different objects
Goal is for light to come to a point on the retina
Accommodation (thin lens)
Lens gets thinner to focus on far objects
Point that lens can no longer bring far objects into focus is called the far point
Accommodation (thick lens)
Lens is thick to focus on near objects
Point that lens can no longer bring near objects into focus is called the near point
Problem with accommodation (Myopia)
Myopia (nearsightedness)
The eyeball is too long or the lens is too thick
Negative lens diverges light allowing it to focus again on the retina
Problem with accommodation (Hyperipia)
Hyperopia (farsightedness)
The eyeball is too short or the lens is not able to accommodate sufficiently
Positive lens converges the light allowing it to focus on the retina
Problem with accommodation (Presbyopia)
Presbyopia (old vision)
The lens loses its ability to accommodate with age
Positive lens converges the light allowing it to focus on the retina
Cones (cones = colours)
Photopigment: photopsins I, II, III (opsins + retinal)
Important for colour vision)
Makes up our photopic system
Used for vision in bright light
Important for visual acuity
Mostly located in fovea
Rods
Not sensitive to colours
Makes up our scotopic system
Used for vision in dim light
Important for sensitivity to light
Mostly located in retinal periphery (none in fovea)
Photoreceptors
connected to each other via horizontal cells
Horizontal cells are important for modifying the strength of neighbouring photoreceptors (essential for lateral inhibition)
Bipolar cells can be categorized based on their size
- Diffuse bipolar cells are connected to many photoreceptors (usually connected to rods)
- Midget bipolar cells are only connected to one photoreceptor (usually connected to cones)
Bipolar cells can be categorized based on their response to light
ON bipolar cells respond to a light signal (reduced activity from photoreceptors)
OFF bipolar cells respond to the absence of a light signal (increased activity from photoreceptors)
Two types of Ganglion cells
P cells
- connected to cones via midget bipolar cells
- little convergence
- small receptive fields (little conversions, small # of cones that converge to P ganglia size)
- colour sensitivity
M cells
- connected to rods via diffuse bipolar cells
- lots of convergence
- large receptive fields
- colour insensitive
Two systems for light and dark
- Rods –> diffuse bipolar cells –> M ganglion cells –> light sensitivity
- Cones –> midget bipolar cells –> P ganglion cells –> visual acuity and colour
What is the output of an OFF bipolar cell that detects depolarization from s rod?
Depolarization
Less sensitive
in bright light; more pigments bleached
More sensitive
Dim light; fewer pigments bleached
Cones are quick to what?
quick to adapt (regenerate), but never get very sensitive to light
Rods are slow to adapt?
slow to adapt (regenerate), but are very sensitive to light
Little patch of dark, light everywhere else
OFF ganglion cells
Little patch on light, dark everywhere else
ON ganglion cells
Antagonistic ganglion receptive fields
result of lateral inhibition from horizontal cells and writing with bipolar cells
Light in centre = excitatory
Light outside = inhibition
