Chapter 9: Vision Flashcards
What is a topographic map?
a spatially organized neural representation of the external world
What do Muller cells do?
help transmit light through neurons to the photoreceptors
What range of vision can humans see?
380nm-760nm
What wavelengths/colours correspond with small, medium and large cones in most mammals? How do humans differ?
Blue: 419nm - Human: 426nm
Green: 531nm - Human: 530nm
Red: 559nm - Human: 552 or 557
What type of light is below 400nm and what kind of animal can see it?
Ultraviolet light: butterflies and honeybees
What type of light is above 700nm and what kind of animal can see it?
Infrared (night vision): snakes
What is Myopia? What can it be caused by?
nearsightedness; a longer eyeball or curvature of the cornea; could be from too much strain (reading etc) or not enough bright light as a child (too much time indoors)
What is Hyperopia? What is it caused by?
it is farsightedness; caused by a shorter eyeball or a lense that is too flat
What is Presbyopia and what is it caused by?
oldsightedness; caused by the hardening of the lense so it can’t contract to view closer objects
What are some properties of rods and what wavelength are they most sensitive to?
specialized for functioning at low light, more numerous, longer and cylindrical;for 496nm
What are some properties of cones and what is the least common type of cone? What wavelength are they maximally responsive to?
specialized for colour and high visual acuity, responsive to bright light and fine detail; blue cones; 560nm
What are the 6 types of cells in the retina?
1) Retinal ganglion cell
2) Amacrine cell
3) Bipolar cell
4) Horizontal cell
5) Cone
6) Rod
What is a horizontal cell’s function?
to link the photoreceptors with bipolar cells
What is an amacrine cell’s function?
to link bipolar cells with RGC
What is a retinal ganglion cell? What are two categories of these cells?
a cell with axons that give rise to the optic nerve the transmit information from the photoreceptors to the brain; M cells and P cells
What are characteristics of magnocellular cells? Where do they project to in the LGN and striate?
larger and receive information from rods; sensitive to moving stimulus; project to layers 1-2 in LGN and bottom part of striate
What are characteristics of parvocellular cells? Where do they project to in the LGN and striate?
smaller and receive information from cones; sensitive to forms and colour; layers 3-6 in LGN and top part of striate
Where does the Geniculostriate system pathway go? What type of axons are in this pathway?
retina –> lateral geniculate nucleus (in thalamus) –> layer IV of the visual cortex; all the P axons and some M axons; 90% of RGCs in here
Where does the Tectopulvinar system pathway go? What type of axons are in this pathway?
retina –> superior collicus (in tectum) –> pulvinar (thalamus) –> parietal and temporal visual areas; the remaining M axons
Where does the Retinohypothalamic tract go and what is it’s function? What cells form it?
it is formed by photo-retinal ganglion cells (pRGCs) which are RGC that absorb blue wavelength (460-480nm); it goes from the pRGCsto the suprachaismatic nucleus; it allows light to entrain the SCN’s rhythmic activity and contracts the pupil in response to light
Where is the Dorsal Stream? What is it’s main function? What area of the visual cortex is crucial to it?
from area V1 to the parietal lobe; guides movements relative to objects; area V5
Where is the Ventral Stream? What is it’s main function? What area of the visual cortex is crucial to it?
from area V1 to the temporal lobe; object identification and perceiving related movements; area V4
What does ipsilateral mean? What layers in the thalamus do these neurons go to?
same side eye; layers 2, 3 & 5
What does contralateral mean? What layers in the thalamus do these neurons go to?
opposite side eye; layers 1, 4 & 6
Where do M cells go in the thalamus and where do they go in the visual cortex?
layers 1-2; IVC(alpha) in layer IV of cortex
Where do P cells go in the thalamus and where do they go in the visual cortex?
layers 3-6; IVC(beta) in layer IV of cortex
What is a corticol column and what is it’s orientation and size?
it is anatomic organization that represents a functional unit; 6 corticol layers deep and 0.5mm(squared) in size; perpendicular to the surface
Where is information sent from the medial and lateral pulvinar, respectively?
Medial: parietal lobe
Lateral: temporal lobe
What is a “blob” in area V1 and what does it do?
it is a region in area V1 that is revealed by staining cytochrome oxidase that contains colour sensitive neurons
What are the 3 types of information Area V2 receives? How are they distinguished by staining?
1) Movement - thick stain
2) Colour - thin stain
3) Form - pale stain
Where does information go after area V2?
to the other layers and then to area G in the parietal lobe and area E in the temporal lobe
Where is the central vs periphery of the visual field located in the visual cortex? How do they differ in size?
Central: near the back and larger as a % of it’s size
Periphery: more anterior and smaller as a % of it’s size
What is on/off centre cell? What is a characteristic of them as a group?
a cell that has an excitatory or inhibitory centre and then the opposite surrounding it (circle shaped); they overlap a ton
What is luminance contrast and what does it allow humans to do?
the amount of light an object reflects relative to its surroundings; it is how RGCs tell the brain about shape because it allows them to detect edges of shapes
What is a simple cell? What does it do?
a cell with on/off rectangular receptive fields that detect orientation of specific bars of light in a particular direction
What is a complex cell? What does it do?
a cell that is maximally excited by bars of light in a particular direction
What is a hypercomplex cell and what does it do?
a cell that is maximally excited by moving bars and is usually strongly inhibitory at one end (helps to distinguish direction)
How does the temporal cortex process shape? How are the neurons clustered in this area and why?
it responds to specialized things (faces, hands etc.); neurons with similar responsiveness to features cluster in columns - this helps with stimulus equivalence; these neurons are plastic
What is subtractive mixing? What are the primary colours?
it is removing light from the mix (paint mixing); red, blue and yellow
What is additive mixing? What are the primary colours?
increasing light to make colour; red, blue and green
What is the Trichromatic theory of colour vison?
colour vision is based on the coding of 3 primary colours: red, green and blue from cones
What is Protanopia?
a lack of red cones
What is Deuteranopia?
a lack of green cones; dogs etc. can see through camo (army)
What is Tritanopia?
a lack of blue cones
What does area V1 respond to in regards to colour?
it responds to particular wavelengths or colours (red-green vs. blue-yellow)
What does area V4 respond to in regards to colour? What may this be important for?
it responds to different PERCEIVED colours; important for colour constancy as lighting/backgrounds change
What is Homonymous hemianopia and what does it result from?
blindness in left/right half of visual field; injury to the visual pathway leading to the cortex
What is Quadratonopia and what does it result from?
blindness in part or “quadrant” of visual field; partial lesion to visual pathway leading to cortex
What is Scotoma and what is it caused by?
a small blind spot caused by a migraine or small lesion
What is Nystagmus and what does it prevent from being detected?
constant motion of the eye; Scotoma
What does damage to the what (ventral) pathway lead to? What is an example of this happening?
it impairs distinguishing what things are, are like or are doing; D.F. in the shower with C.O. poisoning
What is visual form agnosia? What is it a result of?
the inability to recognize objects or drawings of objects; damage to the ventral (what) pathway in the temporal lobe
What does damage to the how (dorsal) pathway lead to? What is an example of this happening?
it leads to a deficit in guiding movements in relation to objects, like reaching to grab things; R.V. and his failure to pick up objects
What is optic ataxia? What is it a result of?
deficit in visual control of reaching and other movements related to vision; damage to the dorsal (how) pathway in the parietal lobe
What is rhodopsin and what process is it used in?
it is a pigment in rods that is extremely light sensitive and bleaches upon exposure to light; it takes 45min to regenerate (takes a while to see well in the dark)
What is the Purkinje effect?
brightness of colours shifts; from yellow and red to blue at dusk because of a switch to usage of rods by the eyes
What is the process by which rhodopsin bleaches and then allows for night vision?
light closes the Na+ channels which hyperpolarizes the cell and the rods transduce that there is light through inhibition; in the dark Na+ channels are opened and NT are released causing the rods to become extra sensitive to any light
What is the association visual cortex and what is it’s function?
it is outside the primary visual areas; usually it is more developed/complex and gives meaning to what is seen
What is Prosopagnosia? What is damaged if this is present?
facial agnosia; the inferior prestriate cortex and adjoining portions of the inferotemporal cortex
What is Akinetopsia? Where is damage typically for it? What types of activities does it cause difficulty for?
the inability to perceive fluid motion; V5 damage; pouring drinks and crossing the street
