the visual system: retinal processing (2.1)

Question 1

light (2 ways of thinking)

Answer 1

particles of energy (photons); waves of evergy

Question 2

visible light (in humans)

Answer 2

waves of electromagnetic energy between 380-760 nm

Question 3

wavelength vs intensity

Answer 3

wavelength: color; shorter = blue, longer = red
intensity: brightness; depends on perception

Question 4

convex lens

Answer 4

bends light towards a focal point; slows down light rays (perception is 180 degree rotation)

Question 5

iris

Answer 5

donut-shaped bands of contractile tissue that give the eye its color; a round muscle with a hole in the center of it (pupil is its absence); regulates the amount of light reaching the retinas

Question 6

changes the size of the pupil

Answer 6

illumination

Question 7

sensitivity vs acuity

Answer 7

sensitivity: the ability to detect the presence of dimly lit objects
acuity: the ability to see the details of objects

Question 8

lens

Answer 8

focuses light on the retina

Question 9

ciliary muscles

Answer 9

alter the shape of the lens as needed

Question 10

accommodation

Answer 10

the process of adjusting the lens; allows us to see near and far objects simultaneously (lens flattens with distant objects)

Question 11

convergence

Answer 11

eyes must turn slightly inward when viewing objects (where the light rays intersect, we are going to get an idea of how far away an object is)

Question 12

binocular disparity

Answer 12

the difference in the position of the same image on the two retinas (greater for close objects than for distant objects)

Question 13

retina (job, “inside-out”, layers (5))

Answer 13

retina: converts light to neural signals (after light passes through the pupil and lens); conducts the signals toward the CNS and participates in their processing
“inside-out”: light passes through several (4) cell layers before reaching its receptors
layers: receptors (capture light), horizontal cells (lateral communication), bipolar cells (pathway from rods and cones to ganglion cells), amacrine cells, retinal ganglion cells (have the axons,;take info in and send it to brain)

Question 14

fovea

Answer 14

high-acuity area at the center of the retina; best vision; dominated by cones

Question 15

blind spot

Answer 15

no receptors where the retinal ganglion cell axons exit the eye (optic nerve); cannot physically see any light; nasal part of retina; fixed by completion (filling in)

Question 16

duplex theory of vision

Answer 16

rods and cones mediate different kinds of vision

Question 17

rods (scotopic vision)

Answer 17

high sensitivity (nighttime vision) low-acuity (high convergence); black and white, no color

Question 18

cones (photopic vision)

Answer 18

low sensitivity (daytime vision); high-acuity (low convergence); one-to-one; color

Question 19

spectral sensitivity in rods vs cones

Answer 19

rods: sensitive to shorter wavelengths; most sensitive to blue light
cones: sensitive to longer wavelengths; most sensitive to yellowish light (i.e., the sun)

Question 20

types of cones (3)

Answer 20

red: most sensitive to long wavelengths (L)
green: sensitive to the mid-range of wavelengths (M)
blue: sensitive to short wavelengths (S)

Question 21

theories of color vision (2)

Answer 21

component (trichromatic) theory: color is encoded by the ratio of activity in the three kinds of receptors (cones)
opponent-process theory: color processed in an antagonistic manner (red/green, blue/yellow, white/black)

Question 22

saccades

Answer 22

involuntary and quick eye movements (type of fixational eye movement)

Question 23

temporal integration

Answer 23

bits of visual information are summated over time [to form a complete image]

Question 24

visual transduction

Answer 24

conversion of light to neural signals by visual receptors (physical stimulus to PSP); indirect transduction where photon of light hits receptor then wanders over to the G protein which closes Na+ channel (depolarized in the dark and hyperpolarized in the light)

Question 25

receptive field

Answer 25

area of the visual field within which it is possible for a visual stimulus to influence the firing of a neuron

Question 26

transmission

Answer 26

indirect transmission; ganglion cells have the axons that bring in the APs

Question 27

center-surround/push-pull

Answer 27

one response in one direction, other cell responds in the opposite direction (doubles signal)

Question 28

off-center bipolar cells vs on-center bipolar cells

Answer 28

off-center: ionotropic glutamate receptors that allow Na+ to enter (depolarization) when photoreceptors are in the dark (release glutamate)
on-center: metabotropic glutamate receptors that allow K+ to exit (hyperpolarization) when photoreceptors are in the dark

Question 29

lateral inhibition

Answer 29

the inhibition that neighboring neurons in brain pathways have on each other; greatly increases the visual system’s ability to respond to the edges of a surface because “edge” neurons receive less or more inhibition, respectively, from their neighbors (edge detection)