Chp 5.3: Vision Flashcards
Cornea
a transparent protective structure at the front of the eye
Pupil
an adjustable opening that can dilate or constrict to control the amount of light that enters the eye.
Iris
Controls the size of the pupil by muscles (colour part of eye)
lens
- the transparent structure behind the pupil that changes its shape to focus images on the retina (thinner for far, thicker for near)
retina
the light-sensitive back surface of the eye that contains the visual receptors
Myopia (nearsightedness) (3)
- Difficulty seeing far away objects
- Eyeball is longer - back to front
- Lens focuses light in front of retina
Hyperopia (farsightedness) (3)
- Difficulty seeing close-up objects
- Eyeball is too short
- Lens focuses light behind retina
Rods (3)
•Function best in low illumination
•500 times more sensitive to light than cones
•Found mostly in periphery of retina –
though everywhere in retina except fovea
Cones (4)
- For colour and detail
- Function best in high illumination
- Concentrated in centre of retina
- Fovea (in centre of retina) contains only cones
fovea
a small area in the centre of the retina that contains only cones and in which visual acuity (clearness) is greatest
bipolar cells
the second layer of retinal cells with which the rods and cones synapse
ganglion cells
the third layer of retinal cells with which the bipolar cells synapse and whose axons form the optic nerve
optic nerve
a bundle of ganglion cell axons in the retina that transmits visual information to the brain
visual acuity
the ability to see fine detail
Visual transduction (3)
- Action of photopigments inside rods and cones
- Absorption of light changes rate of neurotransmitter release
- Greater rate of release = the stronger the signal passed on
photopigments
protein molecules within the rods and cones whose chemical reactions when absorbing light result in nerve impulses being generated
dark adaptation
the progressive increase in brightness sensitivity that occurs over time as photopigments regenerate themselves during exposure to low levels of illumination
Rods are insensitive to _____ light wavelengths
red
trichromatic theory (5)
(Young-Helmholtz)
•Three types of colour receptors in retina
•Cones most sensitive to blue, green, red wavelengths
•Visual system combines activity from these cells
•Colours are perceived by additive mixture of impulses
•If all are equally activated - white colour is produced
opponent-process theory
the theory proposed by Hering that the retina contains three sets of colour receptors that respond differentially to red-green, blue-yellow, and black-white; the opponent processes that result can produce a perception of any hue
dual-process theory (3)
- Combines trichromatic and opponent process theories
- 3 cone types sensitive to short (blue), medium (blue), and long (red) wavelengths stimulate opponent-process reactions
- Opponent processes occur in ganglion cells, neurons in relay stations, and visual cortex
Trichromats (2)
- Normal colour vision
* They are sensitive to all three systems: red-green, yellow-blue, and black-white
Dichromat (2)
-A person who is colour-blind in only one of the systems (red-green or yellow-blue).
•Deficiency is caused by an absence of hue-sensitive photopigment in certain cone types.
Monochromat
•Sensitive only to the black-white system and is totally colour-blind
Thalamus
the brain’s sensory switchboard
primary visual cortex
the area of the occipital lobe which receives impulses generated from the retina via the thalamus and analyzes visual input by using its feature detectors
feature detectors
sensory neurons that respond to particular features of a stimulus, such as its shape, angle, or colour
parallel processing
our ability to use our senses to take in a variety of information about an object and construct a unified image of its properties
visual association cortex (3)
- Attaching meaning to what we see
- Information goes to visual association cortex
- Interpreted in terms of our memories and knowledge
How does low/high levels of illumination change the pupil
- Low levels of illumination cause the pupil to dilate, letting more light into the eye to improve optical clarity
- Bright light triggers constriction of the pupil
