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PSYC 211 > L6 > Flashcards

L6 Flashcards

1
Q

what is the adaptive value of vision in evolution

A

• Vision enables the detection of prey, predators, and mates,
even at a distance.

• The success of vision depends on…
–localization of light reflected off distant objects in reference to the individual and the environment
– form of object identification based on size, shape, colour, past
experience
– movement detection
– compensation for changes in lighting conditions compensation for changes in lighting conditions

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2
Q

what is the pupil

A

• Pupil: The opening that allows light to enter the eye and reach the retina.

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3
Q

what is the iris

A

• Iris: A circular muscle that controls the size of the pupil.

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4
Q

what is the cornea

A

• Cornea: The transparent surface that covers the pupil and iris.

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5
Q

what is the sclera

A

• Sclera: The “white of the eye”; the sclera is continuous with the cornea.

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6
Q

what is the lense

A

• Lens: Helps focus rays of light on the retina.

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7
Q

what is the retina

A

• Retina: The internal lining of the rear two-thirds of the eye; the retina converts images into electrical
impulses, which are sent to the brain.

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8
Q

what is the maccular

A

• Macula: The central area of the retina that is specialized for central vision.

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9
Q

what is the fovea

A

• Fovea: The visual image received by the fovea is the least distorted; marks the centre of the retina
and the centre of the macula.

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10
Q

what is the optic nerve

A

• Optic Nerve: Made up of the axons of retinal ganglion cells; carries impulses for vision from the
retina toward the brain.

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11
Q

describe the muscles of the Eye

A

• Three pairs of extraocular muscles, which are inserted into the sclera, enable the eye to move within
its orbit.

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12
Q

what is light

A

• Light is electromagnetic energy that is emitted in the form of waves and is visible to our eyes.

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13
Q

what is visible light

A

• Only electromagnetic energy with wavelengths of 400-700 nm is visible to the naked human eye.

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14
Q

• Within this visible spectrum, different wavelengths appear as different colours.

why is this

A

because of the cones

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15
Q

where does the mammalian visual system begin

A

the eye. At the back of the eye is the retina, which

contains cells that convert light energy into neural activity.

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16
Q

describe the flow of visual information within the retina

A

Photoreceptors → Bipolar cells → Ganglion cells

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17
Q

describe photoreceptors

A

Absorb the light energy and turn it into electrical signal that the brain can understand

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17
Q

describe photoreceptors

A

Absorb the light energy and turn it into electrical signal that the brain can understand

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17
Q

describe photoreceptors

A

they are the receptors of vision

• The conversion of light energy into neural signals occurs in the millions of photoreceptors at the
back of the retina

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18
Q

what is the difference between the rods and the cones

A

Rods: specialized for low light levels

Cones: specialized for higher light levels and colour vision

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19
Q

describe the cones

A

Cones are conical-shaped structures. Under bright lighting, cones transmit most of the visual
information. The central retina has a higher concentration of cones.

there are 3 types of cones

a cone consists of a photopigment at the tip, a cell body and synaptic terminals

cortical vision = comes

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20
Q

describe the rods

A

Rods are rod-shaped structures that are 1000 times more sensitive to light than cones. Under dim
lighting, only rods contribute to vision. The peripheral retina has more rods than cones.

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21
Q

why can cones detect colour and rods cant

A

Photoreceptors have spectral sensitivity functions for rods and the three types of cones
• All rods contain the same photopigment.

• Variations in photopigments make the different cones sensitive to different wavelengths of light and enable colour vision. therefore the cone types have different sensitivity’s to light

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22
Q

• Light must pass through several cell layers before it reaches the photoreceptors at the back of the
retina.

what are some things that are in place so that light isn’t obstructed

A

The rods and the cones are transparent so they do not obstruct the light

At the area of the fovia the processes are pushed to the side to get rid of the minimal interference of the rods and the cones

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23
Q

• When the light-sensitive photopigments absorb light, a cascade of events is triggered within the
retina.

explain this

A

• Information about light flows from photoreceptors to bipolar cells to ganglion cells, which project axons out of the eye.
• The axons of retinal ganglion cells carry information from your eyes to your brain.
• The bipolar cells and ganglion cells are displaced laterally to allow light to strike the foveal
photoreceptors directly.

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24
Q

what causes the blind spot and how come we dont see it

A

• Where the axons of the retinal ganglion cells exit the retina, there are no photoreceptors. Therefore,
sensation of light cannot occur.
• Nonetheless, our perception of the visual world is seamless. We are not aware of any holes in our
field of vision because the brain “fills in” our perception of these areas.

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25
Q

describe The Visual Field for One Eye

A
  • The visual field is the total amount of space that can be viewed by the retina.
  • Note that images are inverted on the retina.

Right eye as it can see further towards the right then the left eye can

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26
Q

where do blood vessels in the retina originate from

A

• The blood vessels originate from the optic disk, which is also where the optic nerve fibres (i.e., the
axons of retinal ganglion cells) exit the retina and then form the optic nerve.

27
Q

where are why is there a lack of blood vessels in the eye

A

There is a lack of blood vessels at the region of the macula for better vission.

28
Q

what structures can the retina be separated into

A
  • The fovea marks the centre of the retina.
  • The half of the retina that is closer to the nose is called the nasal hemiretina. (hemi = 1/2)
  • The other half of the retina is called the temporal hemiretina.
29
Q

what part of the retina is the optic disc located in

the optic disk causes our blind spot, where is this located in our vision

A

located in your nasal hemiretina, therefore the blind spot affects your temporal hemifield.

• Your blind spot is about 15 degrees eccentric in your temporal hemifield

30
Q

what part of the visual field crosses over

A

• The axons of the ganglion cells
located in each nasal hemi-retina
cross the midline via the optic
chiasm.

• The axons of the ganglion cells
located in each temporal hemi-retina
do NOT cross the midline.

31
Q

some rental ganglion cells cross over at the optic chiasm and some don’t. what does this mean

A

ganglion cells in both
retinas that respond to visual stimuli
in the right hemifield project axons
into the left optic tract. (and vise versa)

32
Q

what would happen if the left optic nerve was cut

A

• If the left optic nerve is cut, vision in
the left eye will be lost completely,
resulting in a loss of left peripheral
vision.

33
Q

what would happen if the optic chiasm was cut

A

• If the optic chiasm is transected, peripheral vision will be lost bilaterally.

34
Q

optic nerve –> optic chiasm –> optic tract

A

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35
Q

what happens if the left optic tract is cut

A

• If the left optic tract is cut, vision of the right hemifield will be lost completely.

36
Q

where do the axons of the optic tract project to

A

– Superior Colliculus
– Thalamus (lateral geniculate nucleus)

thalamus is the main projection

minor projection to the pretectum which is related to pupillary reflex

37
Q

The superior colliculi are in the midbrain

A

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38
Q

there are 2 visual pathways what are they

A
  • Subcortical Vision: Retinotectal Pathway

* Cortical Vision: Retinogeniculostriate Pathway

39
Q

what structures are in the Subcortical Vision: Retinotectal Pathway

A

– Retina

– Superior Colliculus

40
Q

what structures are in the Cortical Vision: Retinogeniculostriate Pathway

A

– Retina
– Thalamus (LGN)
– Primary Visual Cortex

41
Q

what % of projections go to the Retinotectal Pathway

A

• About 10% of the ganglion cells in the retina project to a part of the midbrain called the superior
colliculus.

42
Q

what is the superior colliculus important for

A

movement and sensory vision

43
Q

in non-mammalian vertebrates, what is the superior colliculus called

A

the optic tectum.

tectum = colliculus

44
Q

the superior colliculus is retinotopically mapped. why is the map distorted

A
  • There is a retinotopic map of visual space in the superior colliculus.
  • The retinotopic map is distorted, with more neurons devoted to analysis of the central visual field.

this is because There is more neurons for the centre visual feild

45
Q

where is the LGN located

A

• The left and right LGN, located in the thalamus,

46
Q

what are the major targets of the two optic tracts

A

most retinal ganglion cells synapse on LGN neurons

47
Q

what information does the LGN receive

A

• The right LGN receives information about the left half of the visual field, and vice versa.

48
Q

• Like the superior colliculi, the LGN contain retinotopic maps.

A

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49
Q

where do most of the projections from the LGN go

A

• Most neurons in the LGN project their axon to primary visual cortex.

50
Q

what does the Primary Visual Cortex receive

A

• Receives visual inputs (relayed through the thalamus)

51
Q

what is the role of the PVC

A

• Primary visual cortex is the first region of cortex to process visual information via the
retinogeniculostriate pathway.

52
Q

Because the projections are orderly going into the PVC what does this allow for

A

PVC contains a complete neural map of the retina.

53
Q

where is the PVC located

A

• Located primarily in the medial part of the occipital lobe and buried within the calcarine fissure

54
Q

what are some other names for PVC

A

• Primary visual cortex = striate cortex = V1 = Brodmann’s area 17PVC

55
Q

how do we know that in primary visual cortex, the receptive fields of the cells define a retinotopic map.

A

• While viewing the stimulus on the left, the monkey was injected with a radioactive agent.
• Metabolically active cells in striate cortex absorbed the agent, revealing how the topography of the
retina is preserved across striate cortex (see image on right).

56
Q

Overview of ‘Cortical’ Vision
Flow of visual information:
– Retina (light energy is converted into a neural signal)
• Photoreceptors (rods and cones)
• Bipolar cells
• Ganglion cells
(optic nerve → optic chiasm → optic tract)

– Lateral geniculate nucleus of the thalamus

– Primary visual cortex in the occipital lobe

– Extrastriate cortex in the occipital, temporal, and parietal lobes

The thalamus is a subcortical cortical but it is called the cortical systen because its aim projection is the V1 which is a cortical structure

A

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57
Q

what is TMS

A

• TMS is a non-invasive method that causes a transient disruption of brain activity by emitting a brief
magnetic pulse. The disruption can be excitatory or inhibitory.

58
Q

what happens when TMS is placed over occipital cortex

A

• When placed over the occipital cortex, TMS can elicit light sensations (phosphenes) in the absence
of any visual stimuli.

59
Q

what are phosphenes

A

light flashes created by external ocipital lobe stimulation

60
Q

The minimum TMS intensity that evokes phosphenes is referred to as…..

A

the “phosphene threshold”.

61
Q

what does an increase and decrease in TMS intensity that evokes phosphenes represent

A

• A reduction in the minimum TMS intensity that evokes phosphenes reflects increased visual cortex excitability, whereas an increase in the phosphene threshold reflects reduced visual cortex
excitability.

62
Q

what were the results from an ecstasy and V1 excitability study

A

Participants in the ecstasy group had a significantly lower phosphene threshold than
participants in the control group.

Moreover, frequency of ecstasy use correlated negatively with phosphene threshold.

Within the ecstasy group, the phosphene threshold of participants who had hallucinations
was significantly lower than the phosphene threshold of participants who did not hallucinate.

63
Q

why is sensory integration know as unimodal and heteromodal

A

Although information about vision and audition is initially transmitted to unimodal (one mode) areas of cortex,
those primary sensory areas transmit the information to heteromodal regions of cortex so that
information from the different senses can be integrated and influence your perception.

64
Q

Integration of sensory information also occurs in some subcortical structures

what are some examples

A

• the inferior colliculus sends axons not only to the medial geniculate nucleus in the
thalamus but also to the superior colliculus, which is a target for visual information.

• Thus, visual and auditory information is integrated in the superior colliculus.

65
Q

the auditory and visual information are intergraded where

A

superior colliculis

66
Q

what is an example of how the auditory and visual systems are integrated

why does this occur

A

• The ventriloquist illusion provides an example of how visual and auditory information are
integrated.

• Ventriloquist Illusion – speech seems to be coming from the puppet’s mouth rather than the
puppeteer’s mouth.
• The ventriloquist illusion occurs due to the sound source being mislocalized towards a synchronous
but spatially discrepant visual event (in this case, the puppets mouth moving).

Your visual system is good at localisation but your auditory system is not therefore you get this illusion because the brain is trusting the visual information more than it is trusting the auditory system

67
Q

Summary of Sensory Systems
• Although sensory information is relayed from the external world to your brain via distinct pathways,
there are a number of overlapping characteristics across the different sensory systems.
• Examples of overlapping characteristics:
– Most sensory information is relayed through the thalamus en route to cortex.
– Spontaneous activity can lead to perceived sensation (e.g., hallucinations, tinnitus).

A

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PSYC 211 (26 decks)

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