4. vision

Question 1

fo ran object to be visiible it must…

Answer 1

emit or reflect light

Question 2

what is EMR

Answer 2

Electromagnetic radiation

light is simply one a part of this continuum

Question 3

How is EMR generated

Answer 3

when an atom emits a particle called a photon

energy from photon s determine their wavelength

Question 4

Human eye is only capable of detecting light within a narrow range of wavelengths

describe the continuum

Answer 4

> gamma rays (Shortest wavelength)

> X rays

> Ultraviolet light

> VISIBLE LIGHT 
>> Violet
>> Blue 
>> green 
>> yellow
>> red 

> Infrared light

> Radar

> Radio waves (long wavelengths)

Question 5

what are the two categories of photoreceptors in the retina

Answer 5

Cones and Rods

Question 6

properties of Cones

Answer 6

• 6 million
• in fovea and periphery
• Fast dark adaptation
• low dark sensitivity
• yellow sensitive
• high acuity

Question 7

properties of rods

Answer 7

120 million

periphery

slow dark adaptation

high dark sensitivity

Green sensitive

Low acuity

Question 8

what did schultze propose about rods and cones

Answer 8

they are from two separate visual systems

> photopic = bright light vision via cones

> scotopic = dim light vision via rods

Question 9

von kries observed that individuals without rods are …

Answer 9

night blind

Question 10

von ries observed that individuals without cones were

Answer 10

day blind

able to see at night

Question 11

retinal physiology

overview of connections between retina and visual cortex

Answer 11

> receptor cells (some connected by horizontal)
> bipolar cells (some connected by horizontal/Amacrine cells)
» ganglion cells (some connected by Amacrine cells

Question 12

on average how many receptors connect to 1 ganglion cell

Answer 12

126 receptors conect to 1 ganglion cell

Massive convergence as move deeper into retina

Question 13

what do connecting cells (horizontal or amacrine) allow

Answer 13

events at one location to influence events at another

Question 14

describe receptive fields

Answer 14

ganglion calls have both excitatory and inhibitory connections within their receptive field

in centre surround receptive fields illumunation of

> centre = excititory
suround = inhibitory

or vise versa

Question 15

what act as edge detectors?

Answer 15

retinal ganglion cells can act as edge detectors

integrate patterns of lightness over an area and

indicated whether that pattern of lightness within the area is different to that in an adjacent area (an edge)

Question 16

hat are the three types of ganglion cells?

Answer 16

x-cells - exhibit centre-surround antagonisms

Y-cells - exhibit centre-surround antagonisms

W calls - don’t exhibit CS antagonism, fire regardless of which area of their receptive field is illuminated

Question 17

X cells and y cells are associated with what

Answer 17

two different visual channels

Parvocellular (X cellls)
and
Magnocellular (Y cells)

Question 18

describe the parvocellular system receptive field properties

Answer 18

Receptive Field size > small
Receptive field type > X
RF distribution > foveal

Question 19

describe the  parvocellular system properties
> ganglion cell size
> response type
> movement
> nerve transition

Answer 19

ganglion cell size > small
Response > sustained Movement > poor
Speed of nerve transmission > slow

Question 20

describe the parvocellular system function

Answer 20

Detail, space and colour

Question 21

describe the  magnocellular system properties
> ganglion cell size 
> response type 
> Movement 
> nerve transition speed

Answer 21

ganglion cell size > large response type > transient
Movement > good
nerve transition speed > fast

Question 22

describe the magnocellular system receptive field properties

Answer 22

size > large
Type > Y
Distribution > Peripheral

Question 23

describe the magnocellular system function

Answer 23

motion depth and time

Question 24

what does LGN stand for

Answer 24

Lateral Geniculate nucleus

Question 25

what are the properties of LGN cells

Answer 25

similar to those of ganglion cells

> centre-surround fields on the retina

> parvo and magno properties

> response simply to the presence of light

> receive input from the visual cortex (back projections) allowing feedback based on previously processed information

Question 26

where does the tectopulvinar system received information from

Answer 26

> magno retinal ganglion cells
> receptive fields on retina of cells in the superior colliculi

> tectopulvinar system also received back projections from the cortex

Question 27

describe the functions of the Tectopulivinar system

Answer 27

“old” in evolutionary terms

> localisation of objects in space

> guidance of eye movement

> gross pattern recognition

Question 28

where are the structures of the tectopulvinar system located

Answer 28

in the thalamic region called the tectum

Question 29

Schneider’s hamster study

no LGN = ___

No Superior colliculi =____

Answer 29

no LGN = unable to recognise patterns

no superior colliculi = able to recognise patterns but to able to accurately approach them

Question 30

what are the two pathways of the tectopulvinar system

Answer 30

focal system for recognition

Ambient system for localisation

Question 31

what happens when someone has damage to the focal system

Answer 31

Blindsight -

can still react to visual stimuli (point at it ) although claim they cant see them

Question 32

describe the visual cortex

Answer 32

2mm thick

contains 100 mil. cell sin 6 main layers

LGN fibres enter at layer 4 where the neurons have centre surround receptive fields like those in LGN and Ganglion cells

outer layers have more complex behaviours

Question 33

feature detectors in the primary visual cortex

Answer 33

simple cortical cells - respond to bars of a particular orientation

Complex cortical cells - response best to a correcty orientated bar moving across the entire receptive field
sometimes directive sensitive

hypercomplex cortical cells -
fire only to moving lines of a particular length or moving corners or angles

OVERALL cortical cells act as feature detectors