Vision II Flashcards
What are the receptive fields of the eye?
-area of retina where light changes neuron’s membrane potential
-it consists of all the cells that are connected or influence this particular cell
-photoreceptors synapse with bipolar and horizontal cells
-in turn bipolar cells synapse onto retinal ganglion cells
-the size of the receptive field changes depending on where you are in the retina (they are circular and larger when far from fovea)
What are the aspects of Retinal Ganglion Cells?
-receptive fields for retinal ganglion cells are concentric
-they have an antagonistic center-surround organization
-two main types: ON center (OFF surround) and OFF center (ON surround)
What are the aspects of Centre-Surround Receptive fields?
-photoreceptors always hyperpolarize to light and synapse onto bipolar cells
-not all bipolar cells respond the same way to a photoreceptor’s glutamate
-bipolar cells determine whether the RGC is excited or inhibited by light
-photoreceptors may provide a neural signal to more than one retinal ganglion cell
-they can be part of several different receptive fields
What are the 2 glutamate receptor types?
-OFF bipolar cells: light inhibits them (hyperpolarizes)/dark excites them; ionotropic receptors depolarized by glutamate
-ON bipolar cells: light excites them (depolarizes)/dark inhibits them; metabotropic receptors hyperpolarized by glutamate
What are the characteristics of ganglion cell center-surround receptive fields?
-ganglion cells fire APs whether or not they are exposed to light
-most ganglion cells are not responsive to changes that conclude both center and surround
-most respond to difference in illumination within their receptive fields
-the center surround organization of the receptive fields exaggerates the contrast at borders
When do center-surround receptive fields respond the best?
-retinal ganglion cell receptive fields respond maximally to dots of light/dark
-center stimulation is slightly stronger than that of the surround
-center-surround organization emphasizes the contrast at light-dark edges
How do receptive fields impact illusions?
-the nature of receptive fields explains many visual illusions such as the Hermann grid:
-surround inhibition is greater at the intersections, so the RGC fires less, suggesting a darker spot
What are the multiple ganglion cell types?
-ON-center and OFF-center ganglion cells can be further subdivided functionally
-M and P ganglion cells: appearance; connectivity; electrophysiological properties
-this marks the beginning of parallel processing in the visual system
What are the different pathways?
-M-cells (magnocellular) - 5%
-P-cells (parvocellular) - 90%
-NonM-nonP (K) cells - 5%
What are the characteristics of M-cells (magnocellular)?
-larger cells and less common
-insensitive to color (achromatic)
-sensitive to moving stimuli
-transient burst response to stimulation (not maintained)
-low acuity
-faster conduction (adapt)
What are the characteristics of P-cells (parvocellular)?
-smaller and more common
-sensitive to color (chromatic) and fine detail
-higher acuity
-conduct slower
What are color-opponent cells?
-P and nonM-nonP cells are sensitive to wavelength
-red vs green: R+G- or G+R-
-blue vs yellow: B+Y- or Y+B-
-explains color-afterimage effect
-M-cells are insensitive to color because a variety of cones input to both center and surround
What are the different aspects of parallel visual processing?
-light levels: scotopic (rods) vs photopic (cones)
-achromatic: light vs dark (M-cells)
-chromatic: red vs green; blue vs yellow
-detail vs motion: P-type vs M-type RGCs
-depth: information from both eyes
Which kind of colorblindness is more common?
color blindness is more common in males (M: 8%; F: 0.5%), particularly red-green (X chromosome-linked)
What are the 3 kinds of colorblindness?
-protonopia
-deuteranopia
-trianopia
