Vision Flashcards
sensation
registration of physical stimuli from the environment by the sensory organs
perception
the interpretations of sensations by the brain
law of specific nerve energies
activity by a particular nerve always conveys the same type of info to the brain.
what is light?
Range of electromagnetic energy that is visible to humans:
-about 400 nanometers (violet) to 700 nanometers (red)
-nanometer (nm): one-billionth of a meter
blind spot:
region of retina without photoreceptors (optic nerve, blood vessels)
fovea
specialized centre of retina specialized for high acuity
myopia
Inability to bring distant objects into clear focus
Focal point of light falls short of the retina
hyperopia
Inability to focus on near objects
Focal point of light falls beyond the retina
presbyopia
Common form of hyperopia seen in older adults.
rods
Sensitve to low levels of light (dim light)
Used mainly for night vision
One type of pigment only
cones
Highly responsive to bright light
Specialized for color and high visual acuity
Located in the fovea only
Three types of pigment (RED, GREEN, BLUE)
phototopic
“Bright lights vision”
High acuity
Low sensitivity with few receptors
Low convergence
Fovea
Cones (RGB)
scotopic
dark/dim vision
Low acuity
High sensitivity with many receptors
High convergence
Periphery
Rods (only one pigment)
colourblindness
Genetic: sex-linked (X-chromosome)
5-8% of males are colourblind
0.5% of females are colourblind
Red-green colour blindness is more common than blue-yellow colourblindness
Result of some kind of anomaly in cones (e.g., low number or a complete lack of a particular cone)
trichromacy
Explanation of colour vision based on the coding of three primary colours: red, green, blue
Color we see is determined by the relative responses of the different cone types.
Pro: can explain different types of colorblind
Con: cannot explain afterimages