Kap 6. Vision Flashcards
sensation
sensation involves the cells of the nervous system that are specialized to detect stimuli from the enviroment
perception
perception is the concious experience and interpretation of information from the senses that involves neurons in the central nervous system
tre dimensjoner som bestemmer persipert farge av lys
hue, saturation & brightness
sensory receptors
specialized neurons that detect a variety of physiological events
sensory transduction
stimuli that are detected by sensory receptors alter the membrane potentials of the cell
receptor potentials
change in membrane potential that cause electrical changes is called receptor potentials
the retina
inner lining of the eye. part of the brain (CNS)
layers of the retina
photoreceptive layer, bipolar layer and ganglion layer. light has to pass through the ganglion and bipolar before it hits the photoreceptive layer.
photoreceptor cells
cones and rods
Photoreceptors are active in the dark and become hyperpolarized when they absorb photons.
When photoreceptors are hyperpolarized they release less glutamate onto bipolar cells.
optic disk
located in the back of the eye, where the axons that convey visual information gather together and leave the eye through the optic nerve
horizontal and amacrine cells
both of which transmit information in a direction parallel to the surface of the retina and combine messages from adjacent photoreceptors
transduction
the process where stimuli is converted into a change in membrane potential
How long wavelength of electromagnetic radiation is visible to us?
a wavelength of between 380 and 760 nanometer
(nm = one-billionth of a meter)
Speed of light
ca. 300 000 km pr. sec
Hue
= Fargetone
Saturation
= Metning
the relative purtity of the light that is being perceived
Brigthness
“sclera”
feil
hold the eyes in place and move it
Its six extraocular muscles attached to the tough, white outer coat of the eye
Its also “opaque” and does not permit entry of light into the eye
cornea
outer layer at the front of the eye
transparent and
Fovea
central region of the retina
- our most acute vision
- contains only cones
cone
hues, sensitive to moderate to high levels of light. found in the central retina (fovea). gives excellent acuity
rods
sensitive to low levels of light, monochromatic, most prevalent in perepherial retina, gives poor acuity
The eye have two types of eye movement :
Vergence movement (Vergens): Øyebevegelser der øynene beveger seg mot hverandre (konvergens) eller fra hverandre (divergens) for å fokusere på objekter på ulike avstander.
saccadic movements: Raske, hoppende bevegelser øynene gjør for å skifte fokus fra ett punkt til et annet.
Pursuit movements (følgning): Glatte øyebevegelser som brukes for å følge et objekt som beveger seg.
Vergence movements
cooperative movements that keep both eyes fixed on the same target
saccadic movements
speed of eye movement
pursuit movements
“makes eye move slower”
Trichromatic theory (three color) -
suggested that the eye contained three receptors for different colors of light.
Opponent color theory
– suggested that light is represented as opponent colors, i.e. red versus green and yellow versus blue.
Visual agnosia
Damage to areas of extrastriate cortex in humans can result in a number of problems like …..
-Inability to identify common objects despite normal visual acuity.
-Some still have normal reading ability so reading in different brain area than object perception.
-Still able to recognise objects by touch.
- Normally damage to ventral visual stream.
Prosopagnosia
- Inability to recognize faces.
- Studies from people with brain damage and functional imaging suggest fusiform face area is essential.
- Some people have prosopagnosia with no obvious brain damage – may be due to difference in brain connectivity.
extrastriate body area (EBA).
region in ventral stream for body recognition
Monocular (one eye) information includes:
Perspective
Relative retinal size
Loss of detail through haze
Relative movement as we move our heads
Binocular information gives us …
stereoscopic vision, very important for fine movements of hands and fingers
Akinetopsia (disease)
- can be produced by bilateral damage to V5.
- Patients experience the world as a series of still frames.
