2.15 Vision

Question 1

sensation

Answer 1

effect of a stimulus on sensory receptors w/n sensory organs

Question 2

Vision: stimulus, sensory organ, sensory receptors

Answer 2

lightwaves, eye, cones and rods (photoreceptors)

Question 3

Sensory Transduction

Answer 3

how stimulus is translated into neural signals that are transmitted to brain

Question 4

Perception

Answer 4

processing, organizing, and interpretation of neural signals, result in mental picture/understanding of stimulus

Question 5

Vision Process (light –> retina)

Answer 5

Light enters through cornea and pupil –> Iris controls how much light enters through pupil (dilation/constriction) –> lens focus/project light rays onto retina in the back of eyeball, where photoreceptors are located
-Image projected onto retina is inverted and reversed

Question 6

pupillary light reflex

Answer 6

Bright light → restrict amount of light entering eye, iris constricts pupils → allows less light into eye
Dim light → increase amount of light entering eye, iris muscles dilate pupils → more light let into eye

Question 7

visual gap

Answer 7

(blind spot) in optic disc b/c there are nerve bundles that lead to brain; no photoreceptors

Question 8

Visual Process (retina –> optic nerve)

Answer 8

1. Light projects to back of the retina, reaching rods and cones (densely packed)
2. When photoreceptors absorb light, they convert light waves into electrical signals and stimulate/inhibit (+ or -) bipolar cells (medium layer)
3. Bipolar cells, in turn, stimulate or inhibit retinal ganglion cells (neurons, top layer), that form bundles and ultimately generate action potentials through optic nerve to the brain

Question 9

Rods

Answer 9

Highly sensitive to light
Used at night/in low-light conditions
Low resolution (acuity)
Located in high density away from the fovea (center of visual field), concentrated in periphery (peripheral vision)
Highest sensitivity to blue-green light

Question 10

Cones

Answer 10

Less sensitive to light
Used during the dat/in bright light
High resolution (acuity)
Concentrated at fovea (focal vision)
S, M, L cones respond to short, medium, and long wavelengths of light (blue → red)

Question 11

Receptive Field

Answer 11

regions of sensory space in which a stimulus can lead to a neuronal response

Question 12

RF for neurons involved in vision

Answer 12

regions of space where when there is an appropriate visual stimulus (light wave) –> modifies neuron’s activity
-size and complexity of RF vary across layers in the retina and in different parts of the brain

Question 13

RF of photoreceptor

Answer 13

small circular points of light in the center or periphery of visual field

• photoreceptors in fovea have small receptive fields that correspond to center of visual field
• photoreceptors outside of fovea have larger receptive fields that correspond to the peripheral part of the visual field

Question 14

RF of retinal ganglion cells

Answer 14

larger and circular regions
-concentric circle (center-surround organization), where inner and outer part of circle oppose each other due to lateral inhibition of photoreceptors

Question 15

on-center off-surround cells

Answer 15

When light hits inner circle → depolarization, neuron will fire
When light hits outer circle → inhibition (hyperpolarization)

Question 16

Off-center on-surround cells

Answer 16

When light hits inner circle → inhibition (hyperpolarization)
When light hits outer circle → depolarization

Question 17

LGN

Answer 17

retinal ganglion cells project to the lateral geniculate nucleus (LGN) of the thalamus

Question 18

Lateral inhibition: center-surround organization

Answer 18

One ganglion cell receives inputs its own bipolar cells and photoreceptors as well as from surrounding ganglion cells and their corresponding bipolar cells and photoreceptors and transmits impulses (action potentials) to optic nerve

Question 19

Lateral inhibition: on-center off-surround cell

-if light hits inner circle

Answer 19

photoreceptors in the inner circle will transmit sensory input → bipolar cells → excite ganglion cell → relay action potential via optic nerve to brain

Question 20

Lateral inhibition: on-center off-surround cell

-if light hits outer circle

Answer 20

photoreceptors in the outer circle will relay sensory input → bipolar cells → ganglion cell layer
Ganglion cell layer will relay lateral inhibitory inputs to master ganglion cell → no action potential via optic nerve to brain

Question 21

importance of center surround organization

Answer 21

better detect changes in contrast (edges)

Question 22

Visual Process (optic nerve –> brain)

Answer 22

Retinal ganglion neurons exit eye, axons of which form optic nerve
Ganglion nerves synapse onto neurons in the thalamus (relay station) called the LGN (lateral geniculate nucleus - nucleus in thalamus that deals with vision)
Axons of LGN neurons project to the primary visual cortex (V1) when fired
-Neurons that relay info about right visual field map to the left V1
-Neurons that relay info about left visual field map to the right V1

Question 23

Receptive fields of neurons in primary visual cortex (V1)

Answer 23

rectangular

Question 24

simple cells

Answer 24

V1 neurons that respond to different orientations of rectangular bars of light of particular orientations
(e.g. diagonal bar of light –> more firing/action potentials, vertical bar of light –> fewer action potentials)

Question 25

retinotopic mapping

Answer 25

V1 neurons are mapped in similar ways that ganglion neurons are mapped in retina

Question 26

what is represented most heavily in V1 (primary visual cortex)

Answer 26

fovea

Question 27

when primary visual cortex is damaged

Answer 27

the photoreceptors in retina that correspond with the damaged portion of the V1 would be unable to absorb light → cortical blindness (blindspots in areas of visual space)

Question 28

blindsight

Answer 28

the ability to reflexively respond to visual information within the blindspot without being able to perceive the stimulus itself