Download Vision Lecture Notes

Vision
Visual Process…
light enters…the cornea  passes through the pupil (controlled by the iris)  reflects off of the lens
 to the retina
o once in the retina…
the light is detected by rods or cones → bipolar cell → ganglion cell (whose axons make up the optic
nerve) → thalamus → visual cortex
Rods vs. Cones (color)
CONES
Number
Location
Color sensitive?
Sensitivity in dim light?
Ability to detect detail?
Number of bipolar cells?
RODS
Vision
HEARING (Audition)
Physics of sound…
● Frequency (pitch): number of cycles completed by a wave in a given amount of time, usually a
second
● wavelength: the distance from the peak of one wave to the peak of the next.
● long wavelengths = low frequency/pitch
● short wavelengths = high frequency/pitch
● Amplitude/Intensity (Loudness): physical strength in a wave, usually determined by the height of
the wave (from peak to valley)
● decibel: measuring unit for sound strength/energy
Auditory process
●
outer ear (pinna) → auditory canal → tympanic membrane (eardrum) → ossicles (bones) of the
middle ear → oval window → cochlea → basilar membrane (hair cells) → auditory nerve →
auditory cortex
Perceiving Pitch
● 2 theories
● Frequency theory: the basilar membrane vibrates at the same rate as incoming sound waves,
triggering neural impulses at the same rate
● explains low-pitched sounds
● Place theory: different frequencies cause vibrations at different locations (hair cells) along the
basilar membrane, triggering the neurons at that place
● explains high-pitched sounds
Hearing Loss
● As we age, we lose the ability to detect the higher frequency/pitch sounds
● Why?
●
Conduction deafness: inability to hear resulting from damage to the structures of the middle ear
●
Sensorineural deafness (nerve deafness): inability to hear resulting from damage to the cochlea,
hair cells or auditory nerve
● Cochlear implant? Good or bad?
Vision
Blind spot? Place where your optic nerve exits retina…no receptors
Visual information processing
o feature detectors – neurons in the visual cortex that respond to specific features…edges, lines,
angles and movements
▪
from these, the brain (frontal, parietal and temporal lobes) assembles the image
● parallel processing – the brain processes several aspects of a problem simultaneously
Color vision
o Young-Helmholtz Trichromatic theory: sensation of color is due to 3 cones in the retina – red,
blue, green
▪
color deficiency (color blindness) because of lack of or weakened cone, usually red or green
cone
o Opponent-process theory: color is the product of opposing pairs of receptors – black/white,
yellow/blue and red/green
▪ color is produced when one receptor is stimulated and one is inhibited
● afterimages – occur when active color receptors become “tired”
Color constancy – the color of an object will remain roughly constant as the lighting and wavelengths
change/shift