Download Introduction to Vision - School of Psychology and Human

Introduction to Vision
Implications for the developing
child
What is Vision?
• Our ability to see helps us to gather
information on:
• Form
• Colour
• Movement
• Depth
Vision: Key Questions
• How do we detect depth given that the
back of the eye is a two dimensional
sheet and that depth perception is not
directly preserved from the outset?
Vision: Key Questions
• How do we register shape in a way that
allows us to recognise familiar objects
under varying circumstances – including
when parts are missing or added?
Vision: Key Questions
• What is the relationship between vision
and mental imagery?
• What aspects of visual perception are
learned?
• What does it mean to ‘see’ something?
Sequence of visual learning
• First Awareness
• First Attention to
Light
• Then Attention
• Then Understanding
• Then People Then
Objects
• Then Tracking
• First Fixation
Sequence of visual learning
• First interest in
distant objects
• Then near objects
• Then Central Vision
• First Peripheral
Sequence of visual learning
• First preference for
familiar
• Then preference for
novel stimuli
• First viewing part of
an object
• Then viewing whole
of object
Sequence of visual learning
• First interest in
simple items and
designs
• Then interest in
complex items and
designs
• First interest in large
items
• Then interest in
small items
Beginnings
• The eyeballs develop during the 12th
week of gestation
• The eyes are part of the brain
• Seeing is a learnt and dynamic process
• Seeing is highly personal
Beginnings
• Vision is affects and is affected by, the
whole body and personality
The importance of vision
• Vision is only one of the five senses but
greater reliance is placed on it than all
the other senses put together.
Function
• Human eyes evolved to give good
eyesight in daylight
Eyes
• Eyeballs are spherical - diameter 23mm
• Eyeballs maintain their shape by means
of a fluid called aqueous at the front and
a jelly like substance called vitreous in
the main body
Functional Vision
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•
•
•
Relies on:
Spatial analysis
Temporal analysis
Cognitive analysis
Seeing Believing and Knowing
• Perception: The foundation of coming to
know about our world
• Memory: The ways we retain and build
on knowledge
• Mediation: The bridges between
aspects of perception
Parts of the Eye
• 1 The Front or “window” - cornea,
iris,lens
• 2 Middle - globe
• 3 Innermost coat - the retina which
contains rods and cones
Visual acuity
• The ability to discriminate high-contrast
fine detail at a distance
• The power of the eye to distinguish form
• The sharpness and clarity of vision
Assessment
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Distance
Near
Field of vision
Colour vision
Implications
• Near vision – N number (usually
smallest size child can read)
• Field – the area that can be seen from
all parts of the eye when looking ahead
• Colour – common red/green confusion
• Contrast sensitivity – need for clear
definition (central vision issues)
Visual Systems
• Two streams in development– where
and what
• Three streams of processing – where,
what and how
Ventral and Dorsal Streams
• One stream for perceptual processing
and one stream for controlling actions
• Ventral Pathways – contain specialised
areas for face perception (who)
• Dorsal Stream – controls eye
movements, reaching and grasping
(how)(action)
A Typical Visual Child: 3-5 years
• Can:
• See in detail with good contrast
sensitivity and accommodation
• See in colour
• See in depth
• Keep eyes straight
A Typical Visual Child: 3-5 years
• See all around whilst maintaining
interest on target centrally
• Move the eyes in controlled fashion –
Further refinement takes place 8-12
years
• The critical period: Up to 9-10 months
Intervention
• 1. Front of Eye – intervention +
• 2. Eye globe – intervention +• 3. Back of globe/neural path --?
Overall Impact of Visual
Impairment
• Range and variety of experience
• The ability to get about
• The control of the environment and self
in relation to it
Individual Differences Related
To
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•
•
•
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Degree of vision
Cause of visual impairment
Age and type of onset
Present condition
Personality
DEFINITIONS
• Snellen (1869) – acuity and field loss
• VI – visual acuity less than 6/18 but
better or equal to 6/60
• Severe VI – visual acuity of less than
6/60 but better or equal to 3/60
• Blind – visual acuity of less than 3/60
Degree of Vision
• Total blindness
• Partial Sight/Low Vision
Causation
• Ocular
• Cerebral
Age and Type of Onset
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Congenital
Acquired
Sudden
Gradual
Stable
Degenerative