Visual Development

Question 1

What are the methods for measuring infant vision?

Answer 1

Preferential looking (gratings, optotypes)
Thumb sucking
Visual evoked potentials (VEPs)

Question 2

Discuss preferential looking

Answer 2

Acuity card: a central peephole, a grating on one side, either a blank patch or a different grating on the other side

Experimenter looks through the peephole to see which stimulus the baby looks at

Detection: grating vs blank patch (baby prefers grating) and if there’s no preference, the baby most likely cannot detect the stimulus

Discrimination: 2 gratings, baby habituates when a stimulus is presented repeatedly (and when the novel stimuli is put next to the habituated stimuli, the baby should prefer to look at the novel stimuli)

Question 3

Gratings and optotypes in preferential looking experiment

Answer 3

Gratings lose their appeal for children at 12 months of age, introduce mroe interesting stimuli

Optotypes - pictures drawn with balanced black white black lines of a particular spatial frequency

Question 4

Non-nutritive sucking

Answer 4

Adapt pacifier with a pressure transducer to measure sucking
When bored, newborns suck their thumbs / pacifiers
They pause when they are distracted with a stimulus

Question 5

Visually evoked potentials

Answer 5

Visual patterns cause changes in electrical activity in the brain (i.e. if there is activity, then infant can see the image that caused it)

External electrodes measure brain activity through the scalp

Question 6

Describe the development of spatial vision

Answer 6

Neonates vision is quite blurry (inability to see fine detail / high Spatial Frequency)

Visual acuity increases approximately linearly over the first 3 years

Approximate adult levels of grating acuity are reached around 8 years old

Question 7

What’s the difference between acuity and vernier acuity?

Answer 7

Acuity = the highest spatial frequency (narrowest stripes) that can be seen
Vernier acuity = the smallest displacement of a line that can be detected
Vernier acuity grows much faster and overtakes acuity, despite babies starting off with a poorer vernier acuity.

Question 8

Motion perception

Answer 8

‘Odd one out’ paradigm
The columns all go in the same direction except for one.
Motion perception develops around 10-12 weeks compared to orientation at 8 weeks

Medium speeds are detected earliest

Question 9

Depth and stereopsis: the visual cliff experiment

Answer 9

Glass surface covers textures - ‘clifftop and void’
Baby is enticed by rattle to cross the void - if they are reluctant, it implies development of depth perception (but not necessarily stereopsis)

Question 10

Face perception

Answer 10

• unlike adults, babies can discriminate between monkey faces as easily as human faces (this ability is lost by 10 months)
• unlike adults, babies don’t suffer from the ‘other race effect’

Question 11

What are selective rearing experiments and what are some examples?

Answer 11

Selective rearing experiments = raising an animal in a particular environment where they are exposed only to a certain environment
Example = monocular deprivation (sewing a cats left eye shut at birth) - results = all the cells for vision driven by the right eye
i.e. the input that you get into the brain determines development to a large extent

Example 2: raising kittens so they only see vertical stripes - therefore the adult cat becomes effectively blind to horizontal contours –> becomes a visual cortex cell bias towards vertical orientations

Question 12

What is the critical / sensitive period?

Answer 12

Deprivation is most effective when its during an early period where development is taking place.
If deprivation ends before the end of this period, normal development resumes.
For humans this can be up to 6 years.

Question 13

What is strabismic amblyopia

Answer 13

Failure of the eyes to align
2 retinas therefore received different inputs
sufferers usually favour one eye for fixation (otherwise they get diplopia)

this results in abnormal development of monocular and binocular cells for the non-favoured eye, and poor visual function

early eye alignment operation can help, but after the critical period its too late

Question 14

antisometropric amblyopia

Answer 14

unequal focussing in the two eyes
two retinas receive different inputs

low acuity for poorly focussed eye, few binocular cells

Question 15

How to prevent amblyopia

Answer 15

• remedy in critical period - patch good eye to force use of other eye
• up to 2 hr/day up to 6 years to work

Question 16

Active / passive vision?

Answer 16

Is proper visual input to both eyes in the critical period enough?
Kitten carousal - same visual input, one active one passive

Inversion goggles - findings that people who were active (not in a wheelchair) were much quicker in re-calibrating

Question 17

Vision in old age:

Answer 17

1. Presbyopia: lens loses flexibility - complete loss by 55 (corrective lenses required)
2. Yellowing of the lens (more blue light absorbed, therefore harder to detect blue from black)
3. Posterior Vitreous detachment (shrinkage of vitreous humour, creating floaters - does not lead to loss of acuity but may lead to detached retina)
4. Age Related Macular Degeneration (UV light absorbed by macula which can damage the retina)