Can you recover from early blindness?

Question 1

Siki et al

Answer 1

(2013) - patient KP
- lost vision at 17, restored after 53 years
Results…
- Good object recognition
- Can determine depth using cues
- Failed to identify disintegrated pictures
- incorrectly classified gender of faces: strategy based on feature-by-feature analyis
- Unable to recognise objects outside of usual semantic context
THEREFORE
Failed to holistically perceive complex stimuli, relied on discrete features
Perhaps a faliure in higher-level integration processes, maybe from lack of experience

Question 2

Fine et al

Answer 2

(2003)- Patients MM - lost vision at 3.5 y/o, restored at 46 in one eye
Results…
Normal perception of colour and motion
-fMRI: normal cortical responses to visual-motion stimuli
Modest deficit in simple form
Severe deficits in complex form, object and face processing
- fMRI: lack of category-selective responses for faces and objects in ventral visual cortex
10 YEARS LATER? (Huber et al, 2015)
- no improvements
THEREFORE
Suggests high-level vision is based on visual architecture that is sensitive to deprivation at the age of 3.5 and has limited plasticity in adulthood

Question 3

Ostrovosky

Answer 3

(2006) - SRD - cataract at birth, restored at 12, tested when 30
Results…
High performance on form and face perception
however…
- changes in face illumination led to misidentification
- relied on head orientation (not eye position) for gaze direction
- longer RT in shape matching task
THEREFORE
- recovery is possible and visual cortex retains plasticity
BUT
Vision restored at 12 [still plastic] - earlier the better!
Tested long after restoration - may have become proficient at contextual cues, not just visual improvement

Question 4

Carlson et al

Answer 4

(1986) - Zambian PS, blind for 30 years. 18 years from restorative surgery and rehabilitation.
Results…
- Vision did not imrprove during year of rehab
WHY?
Low motivation - improvement of visual function directly related to amount of practice
Based on the authors previous successful case study, at least 1.5 years of rehab needed to imrpove vision to the point where it can be used in the world

Question 5

Gregory and Wallace

Answer 5

(1963) - Case SB - blind at 10m/o, restored at 52y/o
Results…
Could recognise colour and simple shapes
Good motion perception - could only recognise some objects when moving
Difficulty with complex shapes inc. erryday objects and faces
Poor depth perception
THEREFORE
Motion cues constituted information that SB could rely on confidently to use newly acquired vision
- fMRI in MM: normal size and activation of V5

Question 6

Why is motion maintained? (Dormal et al, 2012)

Answer 6

Based on MM and SB (normal motion perception and fMRI) it seems low levels abilities e.g. motion are spared and can be recovered, even following blindness.

Suggests that such abilities don’t require prolonged visual experience in order to crystallise, unlike more vental-related visual functions e.g. face perception

However, alternative account = such cases posses residual motion perception during blindness

• Majority of operable blind PS are near-blind, as in order to operate, retina and eye tissues must be at least partially functional
• SB had light perception in left eye, and right eye could perceive hand movements

BASICALLY
Even a brief period of vision after birth OR maintenance of crude visual abilities may be sufficient to tune motion system
Functions of dorsal-pathway set early in development and is resistent to later acquired experience

Question 7

Children born with dense bilateral cataracts who are treated during first year of life have reduced…

Answer 7

acuity and impairments in higher visual functions persisting later into life (e.g. deficits integrating local elements into a global form) (Lewis et al, 2002)
- Suggests even a brief period of early visual deprivation can disrupt the development of higher-level visual functions.

Question 8

Le grand

Answer 8

2001
Found that cataract-induced deprivation of patterned visual input from birth until 2-6 months = permanent deficits in configurable face processing
Even after 9 years of recovery, PS were severely impaired when differentiating faces that differed only in the spacing of their features
- normal in distinguishing those varying only in the shape of individual features
THEREFORE
Early visual experience is necessary for normal development of the neural architecture that will later specialise for the configural processing of faces, (a considerably higher-level function) but not all aspects of face processing.

Question 9

Children with bilateral cataracts still…

Answer 9

Develop normal sensitivity to high rates of flicker, are normal at discriminating between large shapes (inc. facial features) and are normal at detecting direction of eye gaze. (Ellemberg et al, 1999; Maurer et al, 1989; Geldart et al 1999)

• These skills exceed those present in birth in the visually normal child, therefore the neural circuits responsible for these skills have continued to develop in the absence of EVE and/or can recover completely after the deprivation
• This suggests normal EVE is not necessary for the development of these particular faculties.