The human visual system

Question 1

The electromagnetic spectrum (visible spectrum)

Answer 1

380 nanometers to 760 nanometers

Question 2

Three dimensions of the colour of light

Answer 2

Hue: the wavelength of electromagnetic radiation
Brightness: the intensity of electromagnetic radiation
Saturation: the purity of electromagnetic radiation

Question 3

Cornea

Answer 3

transparent outer layer of the eye

Question 4

Lens

Answer 4

immediately behind the cornea, the lens is made up of a number of transparent layers. The shape of the lens can be altered to help focus the image onto the retina

Question 5

Retina

Answer 5

the light sensitive structure

Question 6

Vitreous humour

Answer 6

the gelatinous fluid that fills the eyeball

Question 7

rods and cones

Answer 7

light sensitive cells in the retina
cones- day light
rods- low levels of light

Question 8

optic disk

Answer 8

the point at which the axons of rods and cones are sent out. This causes a blindspot. The axons that are bundled together at the optic disk are known as the optic nerve

Question 9

How many rods and cones does the retina have?

Answer 9

120 million rods and 6 million cones

Question 10

cones

Answer 10

• important for seeing fine detail
• most active in the daylight
• concentrated in a region known as the fovea, responsible for the central few degrees of the visual field
• responsible for our ability to see colour

Question 11

Rods

Answer 11

• do not discriminate between different wavelengths
• cannot discriminate fine visual detail
• much more sensitive to light than cones
• most active in darkness

Question 12

Three layers of the retina

Answer 12

1. photoreceptor layer
2. bipolar cell layer
3. ganglion cell layer

Question 13

Short- wavelength (S) cones

Answer 13

peak sensitivity at 440nm (blue light)

Question 14

Medium- wavelength (M) cones

Answer 14

peak sensitivity at 530nm (green light)

Question 15

Long- wavelength (L) cones

Answer 15

peak sensitivity at 560nm (red light)

Question 16

colour blindness

Answer 16

• a genetic condition arising from anomalies in the pigments of one or more cone types in the retina
• more common in males than in females
• located in the X chromosome

Question 17

Primary visual cortex

Answer 17

the first visual area or V1

Question 18

Area V4

Answer 18

has neurons that are sensitive to the colour of visual inputs

Question 19

Area MT

Answer 19

responsive to moving visual stimuli

Question 20

Inferior temporal cortex

Answer 20

contains neurons that are selectively responsive to complex objects and faces

Question 21

Hemianopia

Answer 21

if V1 is damaged the patient will become blind to all visual stimuli arising to the contralateral side of their present fixation point. e.g. damage to V1 in the right hemisphere will cause blindness in the left visual field

Question 22

Hemiachromatopsia

Answer 22

Patients with damage that involves an area of the visual cortex called V4 are no longer able to perceive colour in the contralateral visual field. However these patients continue to see forms of movement

• This suggests that V4 is specialised for processing the wavelength of visual stimuli

Question 23

Motion blindness (akinetopsia) - loss of motion perception

Answer 23

occurs when MT is damaged in both hemispheres

Question 24

Visual object agnosia

Answer 24

typically occurs after unilateral or bilateral damage of the inferior part of the temporal cortex. It is the selective loss of the ability to recognise familiar objects through the modality of vision.
- other senses need to be used to make sense of an object

Question 25

Prosopagnosia (face blindness)

Answer 25

fusiform gyrus is particularly important in face recognition
bilateral damage of the fusiform gyrus or damage just in the right hemisphere may cause problems with face recognition