unit 2a Flashcards
visual field
the entire area or field of view that can be seen when an eye is fixed straight at a point on space
Vertical Meridian
Description of visual field: line dividing field of view into left/right halves
Horizontal meridian
Description of visual field: line dividing field of view into top + bottom halves
Hemifield
‘Half the visual field’ refers to left & right halves ONLY
Quarterfield
‘one qtr or quadrant of visual field’ defined by the quadrant created by vertical + horizontal. meridian lines
Cornea
the transparent dome-shaped anterior portion of the outer covering of the eye
Lens
Situated behind the iris of the eye, focuses light entering eye onto the retina
Sclera
White part of the eye that, w cornea, forms the protective outer covering of the eye
Iris
the colored portion of the eye, a muscular diaphragm the controls the size of the pupil, which in turns controls the amt of light that enters the eye
Pupil
the hole located in center of iris, that allows light to strike the retina. Appears black b/c light rays entering the pupil are either absorbed by the tissues inside the eye
Fovea
part of the retina where vision is most acute + color vision is the best. Cone photoreceptors are most prevalent here.
Retina
the back of the eyeball, considered part of the brain, were light hits the photoreceptive cells + visual info begins being processed
Blind spot
the place in the visual field that corresponds to the lack of light-detecting photoreceptor(PR) cells on the optic disc of the retina (where axons of the retinal ganglion cells exit the retina & form the optic nerve)
Bc there’s no PR cells to detect light on the optic disc, corresp. part of visual field is invisible. Some process in our brain “fills-in” the blind spot w/ estimates of expected visual information based in surrounding info f/ other eye- so we normally dont perceive the blind spot.
Photoreceptor (PR) cells
cells that line the back of the retina + have parts that change shape when they are hit w/ a photon, allowing them to detect light in certain part of the visual field. Overall func. of PR cell is to convert light energy of photon into form of energy communicable to nervous syst. & readily usable to the organism.
This CONVERSION = signal transduction: humans have 2 main types (rods & cones [there are 3 diff subtypes of cones])
Rods
PR cell, located outside fovea. Highly sensitive to light + responsible for low-light (Scotopic) vision. Also contrib. to visual motion detection, but have poor visual acuity. They do not differentiate b/t colors.
Cones
PR cells that are concentrated in fovea. More sparsely extend into the periphery. Responsible for high acuity vision, but take more photos of light to activate (good for daytime PHOTOPIC vision)
3 types (responsive to diff light wavelength)
1. Long (L)
2. Middle (M)
3. Short (S)
wavelength cones corresp. to maximal absorption of red, green, + blue light, respectively) The combo of inputs f/ diff cones types thru OPPONENT PROCESSING produces for color vision
PR Proteins
light sensitive protein molecules involved in the sensing + response to light in a variety of organisms by undergoing structural change when they absorb light. Structural change opens ions channels, which cause change in graded potential (ion flow) of the PR [causes PR cell to signal that light has been detected]
Opsins
a type of photosensitive pigment protein found in PR
Ex: RHODOPSIN- in rods & PHOTOPSIN in cones ( 3 types are in cones, making L,M,S cone types) & Melanopsin in the melanopsin-containing retinal ganglion cells (aka intrinsically phptsenstive retinal gang cells)
Retinal ganglion cells
cells in retina that receive input f/ modulatory neurons (which get input f/ PR cells) & transmit the info down the optic nerve to brain.
Primary types include: Midget cells (parvocellular pathway), Parasol cells (magnocellular pathway) & Small bi-stratified cells (koniocellular pathway) Additional light absorbing type = melanospin-containing retinal gang cells
Opponent-processing Color Vision Theory
color vision theory that color is processed in 3 diff oppenency channels created by specific wiring together go cone PR + retinal gang cells
Red (L cone) v. green (M cone)
blue (S cone) v. yellow (L+M cone)
dark v. bright (red/L+green/M+blue/S)=> comparison produces luminance
Optic nerve
composed of the axons of the retinal gang cells that leave the retina + head back towards the optic chasm in the brain, taking w/ them visual info. this nerve is the reason humans have a blind spot, b/c no PR cells exist where the optic nerve exits the eye
Parvocellular pathway
a visual processing stream that pools over fewer receptors. the cells involved (midget retinal gang cells) have sustained response + are involved in processing color, fine details, textures + depth
Magnocellular pathway
a visual processing stream that pools over many receptors, whose ret.gang cells (parasol retgang cells) fire in bursts + are useful for detecting motion
Koniocellular pathway
a visual processing stream that gets S-cone input only (from Small Bi-stratisfied cells, processing low acuity visual info & innerving V1 + extrastraite cortex
Optic Chiasm
Where optic nerve cross in the brain, allowing info f/ left visual field (f/ both eyes) & right visual field (both eyes) to be separated & directed to approp. contralateral hemisphere
Thalamus
a part of brain involved in relaying sensory info f/ sensory organs to processing areas of cerebral cortex
Lateral geniculate nucleus (LGN)
part of Thalamus, where visual processing streams pass thru on their way to optic radiations & primary visual cortex
Optic radiations
Nerve pathways along the visual processing stream from the LGN to primary visual cortex
Primary sensory cortex
the 1st location in cortex that receives input f/ the peripheral sensory receptors- in this case: the retina
Primary visual cortex (V1)
the 1st area in brain where visual info is processed @ low lvl. Visual info flows into here f/ retina + flows to higher lvls of visual processing (V2,V3, etc) that do incr. complex visual processing. V1- AKA striate cortex- due to visible stripe of inputs f/ retina to Layer 4 of V1
