Lecture 11 Flashcards
(36 cards)
Fovea
המרכז שבו האור מתקבץ ונותן התמונה הכי חדה, סיבים מקובצים יחד בדחיסות גדולה
The fovea is fixed and is found only in the nasal hemiretina.
There are only cones in the fovea (low sensitivity, high acuity)
Blind spot
בנקודה זאת אין תאי עצב שמפרשים את הפוטונים של האור, ולכן דברים שנופלים עליה אנחנו לא רואים. אנחנו לא מרגישים אותה בגלל שכל עין מפצה על נקודת העיוורון של העין האחרת.
Binocular Disparity
The brain can gauge the difference in the image’s position on the retina:
* Greater disparity = closer
* Lesser disparity = farther
מה הן חמשת סוגי תאי העצב במערכת הראייה?
1) photoreceptors
2) horizontal cells
3) bipolar cells
4) amacrine cells: inhibition
5) retinal ganglion cells: משם לסיב האופטי ואל נקודת העיוורון.
Rods - night or day light?
night
Cones - night or day light?
day
What do the rods and cones do?
מפרשים את האור ומתרגמים אותו לפעילות חשמלית.
What are the three types of cones?
1) Blue = short wavelength = Tritan
2) Green = medium wavelength = Deutan
3) Red = long wavelength = Protan
Photopic vision
occurs when there is plenty of light (=cones)
Low sensitivity & high acuity
Maximum sensitivity is around 650 nm.
Scotopic vision
occurs when light source is very dim (=rods)
High sensitivity & low acuity
Maximum sensitivity is around 500 nm.
Purkinje effect
Shift from bright (photopic vision) to dim light (scotopic vision) produces the Purkinje effect.
In bright light: yellow and red are the brightest.
In dim light: green and blue are the brightest.
Retina-geniculate -striate pathway
Optic chiasm - LGN in the thalamus - superior colliculus (visual reflexes, coordination, eye-head movement, fight or flight) - optic radiation - primary visual cortex
Magno-cellular layers
There are 2 of them in the LGN.
Respond to objects in motions & low spatial frequencies.
Parvo-cellular layers
There are 4 of them in the LGN.
Respond to fine details.
V1
Brodman’s area 17.
נמצא בגדות של ה- calcarine fissure.
פרשנות.
Retinotopic organization
Specific columns of neurons correspond to specific areas of the retina and thus the visual field.
Upper half of visual field represented below the calcarine. Lower half of visual field represented above the calcarine.
Disproportionally large representation of the fovea in posterior end (occipital pole).
Rceptive fields
שדה של תאי עצב הנמצא במוח המיועד עבור קידוד אינפורמציה ספציפית ומיוחדת במרחב.
Most V1 neurons are orientation selective, meaning that they respond strongly to lines, bars, or edges of a particular orientation (e.g., vertical) but not to the orthogonal orientation (e.g., horizontal).
Simple cells’ selectivity and location
Orientation, position
Brodman’s 17
Complex cells’ selectivity and location
Orientation, motion, direction
Brodman’s 17 & 18
Hypercomplex cells’ selectivity and location
Orientation, motion, direction, and length
Brodman’s 18 & 19
Ocular dominance columns
Stripes of neurons in the visual cortex that respond preferentially to input from one eye or the other.
Orientation columns
stimuli from similar spatial orientation.
Dorsal stream
Interprets spatial information (location/motion: Where)
Shape, movement and location – necessary for action on the stimulus.
Primary visual cortex – dorsal prestriate cortex –posterial parietal cortex.
Ventral stream
Interprets object characteristics (color/shape: What)
Shape, depth, color – necessary for recognition
Primary visual cortex – ventral prestriate cortex –inferotemporal cortex
