Chapter 6: The Visual System

Question 1

when do the pupils constrict?

Answer 1

when the level of illumination is high and sensitivity is not important

Question 2

how is an image effected by pupil constriction?

Answer 2

the image is sharper and there is a greater depth of focus

Question 3

what is the purpose of the lens?

Answer 3

focuses incoming light onto the retina

Question 4

binocular disparity

Answer 4

the difference in the position of the same image on the two different retinas

Question 5

what are the five types of neurons located in the retina?

Answer 5

receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells

Question 6

how do retinal neurons communicate?

Answer 6

both chemically via synapses and electrically via gap junctions

Question 7

fovea

Answer 7

an indentation at the center of the retina that is specialized for high-acuity vision

Question 8

duplexity theory of vision

Answer 8

cones and rods mediate different kinds of vision

Question 9

photopic vision

Answer 9

cone mediated vision that predominates in good lighting and provides high-acuity coloured perceptions of the world

Question 10

scotopic vision

Answer 10

rod mediated vision is more sensitive but lacks detail and colour

Question 11

what are the three kinds of involuntary fixational eye movements?

Answer 11

tremors, drifts, and saccades

Question 12

visual transduction

Answer 12

the conversion of light into neural signals by the visual receptors

Question 13

what is rhodopsin?

Answer 13

a G-protein-coupled receptor that responds to light rather than to neurotransmitter molecules

Question 14

retina-geniculate-striate pathways

Answer 14

largest visual pathways, which conduct signals from each retina to the primary visual cortex via the lateral geniculate nuclei of the thalamus

Question 15

parvocellular layers

Answer 15

composed of neurons with small cell bodies and runs through the top four layers of the geniculate nucleus and are responsive to colour, fine pattern details, and stationary or slowly moving objects
majority of input comes from cones

Question 16

magnocellular layers

Answer 16

composed of neurons with large cell bodies and runs through the bottom two layers of the geniculate nucleus and are responsive to movement
majority of input comes from rods

Question 17

receptive field of a visual neuron

Answer 17

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

Question 18

on-center cells

Answer 18

respond to light shone in the central region of their receptive fields with “on” firing and to light shone in the periphery of their receptive fields with inhibition

Question 19

off-center cells

Answer 19

respond with inhibition and “off” firing in response to lights in the center of their receptive fields and with “on” firing to lights in the periphery of their receptive fields

Question 20

simple cells

Answer 20

have receptive fields that can be divided into antagonistic “on” and “off” regions that are thus unresponsive to diffuse light
they are all monocular and respond best to bars of light in a dark field, dark bars in a light field, or single straight edges between dark and light areas

Question 21

complex cells

Answer 21

more numerous than simple cells
have rectangular receptive fields, respond best to straight-line stimuli in a specific orientation, and are unresponsive to diffuse light

Question 22

how do complex cells differ from simple cells?

Answer 22

they have larger receptive fields that cannot be separated into static “on” and “off” regions.
most are binocular

Question 23

tectopulvinar pathway

Answer 23

a subset of visual signals travel to the superior colliculus in the midbrain

Question 24

retinohypothalamic pathway

Answer 24

a small portion of signals make connections with the subrachiasmatic nucleus (SCN) in the hypothalamus

Question 25

what did Hubel and Wiesel study?

Answer 25

receptive fields of neurons along the visual pathway

Question 26

how is the visual cortex organized?

Answer 26

into columns based on location within the visual field

Question 27

what is accomplished in the temporal lobe?

Answer 27

object/face recognition

Question 28

what does the dorsal stream allow for?

Answer 28

allows you to interact with objects (spatial action)

Question 29

what does the ventral stream allow for?

Answer 29

allows you to determine the visual properties of an object

Question 30

myopia

Answer 30

nearsightedness

Question 31

hyperopia

Answer 31

farsightedness

Question 32

presbyopia

Answer 32

a natural part of aging defined by a gradual loss of the eye’s ability to focus on nearby objects.

Question 33

retinal ganglion cells

Answer 33

are the bridging neurons that connect the retinal input to the visual processing centres within the central nervous

Question 34

amacrine cells

Answer 34

the first neurons in the visual system to fire action potentials, and also the first to generate transient responses.

Question 35

bipolar cells

Answer 35

one of the main retinal interneurons and provide the main pathways from photoreceptors to ganglion cells, i.e. the shortest and most direct pathways between the input and output of visual signals in the retina.

Question 36

horizontal cells

Answer 36

the laterally interconnecting neurons having cell bodies in the inner nuclear layer of the retina of vertebrate eyes. They help integrate and regulate the input from multiple photoreceptor cells.

Question 37

isomerization

Answer 37

Photochemical events in vision involve the protein opsin and the cis/trans isomers of retinal. The cis-retinal fits into a receptor site of opsin. Upon absorption of a photon of light in the visible range, cis-retinal can isomerize to all-trans-retinal.