The human visual system Flashcards Preview

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Flashcards in The human visual system Deck (25):
1

The electromagnetic spectrum (visible spectrum)

380 nanometers to 760 nanometers

2

Three dimensions of the colour of light

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

3

Cornea

transparent outer layer of the eye

4

Lens

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

5

Retina

the light sensitive structure

6

Vitreous humour

the gelatinous fluid that fills the eyeball

7

rods and cones

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

8

optic disk

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

9

How many rods and cones does the retina have?

120 million rods and 6 million cones

10

cones

- 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

11

Rods

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

12

Three layers of the retina

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

13

Short- wavelength (S) cones

peak sensitivity at 440nm (blue light)

14

Medium- wavelength (M) cones

peak sensitivity at 530nm (green light)

15

Long- wavelength (L) cones

peak sensitivity at 560nm (red light)

16

colour blindness

- 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

17

Primary visual cortex

the first visual area or V1

18

Area V4

has neurons that are sensitive to the colour of visual inputs

19

Area MT

responsive to moving visual stimuli

20

Inferior temporal cortex

contains neurons that are selectively responsive to complex objects and faces

21

Hemianopia

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

22

Hemiachromatopsia

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

23

Motion blindness (akinetopsia) - loss of motion perception

occurs when MT is damaged in both hemispheres

24

Visual object agnosia

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

25

Prosopagnosia (face blindness)

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