9- Development of Vision Flashcards
What are the 2 main methods for studying infant vision?
Eye movement responses
and
Electrophysiological responses (from receptors and neurons that respond to visual input)
Forced-choice preferential looking and
Optokinetic nystagmus are both part of which method for studying infant vision?
Eye movement responses
Visual evoked potential (VEP) and Electroretinogram (ERG) are both part of which method for studying infant vision?
Electrophysiological responses
What is this?
a spatial frequency grating, it has a sinusoidal module in luminance. As you move from left to right, the spatial period of the grating changes (increases)
What is this?
Letter charts which make the spatial visual information of letters smaller to measure individuals recognition failing point.
The log of the minimum angle of resolution (gap in the middle of numbers are 1/5th of overall letter size)
Methods for studying infant vision
Which eye movement response task is this?
Infant looks at a reference and test stimuli randomly positioned on left or right
Observer decides whether infants is looking at left or right stimulus (based on eye movement of baby)
Significant result if infant looks at one stimulus more often than the other (more than 75% of the time)
Depends on infant preferentially looking at an “interesting” stimulus
(unusual stimuli are more likely to be stared at)
The spatial frequency of the gradient (that the baby is looking at) increases throughout trials until baby cannot identify it anymore.
Forced-choice preferential looking
Which eye movement response task depends on infant preferentially looking at an “interesting” stimulus
(unusual stimuli are more likely to be stared at)?
Forced-choice preferential looking
Methods for studying infant vision:
Which eye movement response task is this?
Oscillation of the eyes back and forth when looking at a slowly moving stimulus (looking outside the window on a train your eyes will focus on one object, follow it, then flick back).
Reliant on infants seeing the grating to be able to engage in this reflexive eye movement
Spin the striped pattern (change spatial frequency) to determine the thinnest stripes that elicits optokinetic nystagmus
Depends on primarily subcortical neural mechanisms and needs large stimulus
Optokinetic nystagmus
Which eye movement response task depends on primarily subcortical neural mechanisms and needs large stimulus?
Optokinetic nystagmus
Methods for studying infant vision:
Which Electrophysiological response task is this?
Electrical potential induced by visual stimulus and recorded from scalp over visual cortex (enian bone).
Measures performance of visual pathways from retina to visual cortex, producing a biphasic response
But depends on infant fixating on the stimulus on screen (be able to have ocular control over the eye) harder for younger babies which don’t have control over eye movements
Visual Evoked Potential
Which Electrophysiological response relies on infant fixating on the stimulus on screen (be able to have ocular control over the eye) and is harder for younger babies which don’t have control over eye movements?
Visual Evoked Potential
Methods for studying infant vision:
Which Electrophysiological response task is this?
Electrical potential recorded between front of the eye and the skin near the eye
Measures the combined activity of photoreceptors and RGC’s cells in the retina
Depends only on properties of the retina, not later stages of visual processing
Electroretinogram (ERG’s)
Which Electrophysiological response task depends only on properties of the retina, not later stages of visual processing?
Electroretinogram (ERG’s)
Brain activity before birth:
Before birth there is neural activity in the visual pathways
Spontaneous waves of action potentials are present in the retina weeks before any vision is present in the womb
These waves consist of domains of activity that form a mosaic pattern over the entire ganglion cell layer in the retina (part of the brain).
What are these used for?
used for path finding, setting up maps in LGN
- if we blocked these pathways using a sodium blocker, these paths fail to develop properly
-image: these are only retinal ganglion cells (rods and cones have not formed at this stage yet)
Several processes take place after young neurons have reached their final target location (pathfinding) these fall under the term?
Synaptogenesis
Which term do these processes describe?
- Cell loss through the death of some cells – genetic control
- Pruning of axon terminals and/or growth of new ones
- Differentiation of dendrites – ramification and retraction of spines
- Formation/loss of synapses
Synaptogenesis
- Each process above occurs during the development of the visual system.
- Number of synapses peaks at time when visual system is most susceptible to changes in sensory input.
Which processes are dependent on sensory input and occur after eye opening (post-natal)?
- Cell loss through the death of some cells – genetic control
- Pruning of axon terminals and/or growth of new ones
- Differentiation of dendrites – ramification and retraction of spines
- Formation/loss of synapses
2, 3, 4
Which processes can explain why early blind patients often have a thicker cortical sheet?
- Cell loss through the death of some cells – genetic control
- Pruning of axon terminals and/or growth of new ones
- Differentiation of dendrites – ramification and retraction of spines
- Formation/loss of synapses
due to a failure of axonal pruning and retraction of processes 2, 3.
Because you don’t eliminate the circuits of neurons, you end up with a thicker cortex.
Which process of synaptogenesis is this describing?
Pre-programmed cell death under genetic control (does not require visual input).
Apoptosis
Which process of synaptogenesis is this describing?
Growth of new axons
Pruning of axon terminals
Which process of synaptogenesis is this describing?
Dendrites receive synaptic input from other neurons. Allows neurons to receive more inputs and integrate more info.
Differentiation of dendrites
Which process of synaptogenesis is this describing?
Synapses can shrink or be removed during synaptic pruning to form a complex new network of connections.
Formation/ loss of synapses
Which ability/ process will fade if you do not use it early on in life (such as discriminating faces of different species due to it not being important to usage in everyday life anymore)?
Synaptic pruning
Infants can see at birth and have some limited control of eye movements with the capability of focusing objects at any distance.
They can:
See large objects (visual acuity 6 times worse than adults)
Distinguish shades of grey (contrast sensitivity 25 times worse than adults)
Distinguish large differences in colours (e.g. red and green) but not subtle colour differences (reddish-orange)
Distinguish large differences in the tilt, direction and speed of an object
Move their eyes and track large objects but eyes are not well coordinated
What can infants not see?
They cannot:
See in depth (no stereo acuity in 3D)
Distinguish mother’s face from other faces (poor face recognition)
See subtle colour differences (reddish-orange)
