W5 Changes in Vision

What are MWS and LWS cones?

Photoreceptor cells in the retina that enable colour vision

What age do infants have functional LWS and MWS cones?

As young as 2 weeks

What age do infants correctly and consistently name colour?

Around 4 years

How does visually evoked potential acuity measure in infants compared to visual acuity?

VEP measures of VA are higher than postnatal measures of visual acuity

Why does vision change so rapidly after birth?

Size, shape and density of cones

Development of lateral inhibition at 2 months of age

Post retinal factors

Which post-retinal factors affect how vision changes so quickly after birth?

Increase in cell size, change in synaptic density incomplete myelination of nerve fibres at birth

What is synaptogenesis?

The formation of synapses- they form long before birth it do not reach peak density until after birth

What is synapse elimination?

Follows synaptogenesis, eliminating interconnections between neurones that do not remain functional

How does synaptic density vary?

Increases during early post natal life, doubles from 2-4 months of age, declines after age 1 until 50-60% of the maximum are attained at 11-12 years

How do axon diameters and myelin sheaths vary?

They undergo conspicuous growth during the first 2 years it may not be fully mature until adolescence or even late adulthood

How is speed of neural transmission impacted?

Synapses between nerve cells, structural properties of axons

Which mechanisms enable normal visual development after birth?

Post natal changes, retinal development and post-retinal factors

Which mechanisms are involved in post natal changes?

Pupil diameter, amount of refraction, accommodation

How does the retina develop?

The cone length in a newborns fovea is less dense and shorter, limiting visual acuity. After birth, cones increase in size and elongate for better light absorption, visual acuity and effective transduction (conversion of light into electrical signals)

How do post retinal factors play a part in normal visual development?

Myelination of nerve fibres is incomplete in newborns- myelination increases during the postnatal stage o enhance speed and efficiency of neural signal transmission

Enlargement of neurones cell bodies and dendrites enables neurones in the visual cortex to form more extensive connections

What is synaptic pruning?

Excess connections between neurones are eliminated, easing to a more refined and efficient neural network