Post natal pereception development
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Transcript of Post natal pereception development
Developmental aspectsBirth – not fully matured
Proper maturation- exposure to normal environment is required
Ocular dominanceMost binocular cortical neurons do not receive inputs from two eyes
Closure of an eye of an immature animal results in a lack of cortical cells driven by the deprived eye
Critical/ sensitive period
•Period in which visual system is influenced by environmental manipulation
•During critical period cortical cells of eye will compete
No binocular action- No stereopsis
Ocular Dominance
Nu
mb
er
of
cells
4 5 6 7321
Contralateral Ipsilateral
Six week through ten weeksR L
MONOCULAR DEPRIVATION DURING THE CRITICAL PERIOD CAN LEAD TO AN ASSYMETRICAL OCULAR DOMINANCE COLUMN
Synopsis of critical period- Hubel’s and weisel’s experiment
Synaptic connectivity in the in the cortex is strengthened by the neural activity and lack in the neural activity result in weakening of this connections
Amblyopia •Reduction in vision secondary to monocular deprivation during the critical period
•Amblyopia results from the abnormal cortical development, not an abnormality of eye
•It can occur secondary to• Anisometropia
• Strabismus
AMBLYOPIA
Occlusion amblyopia
-One eye occluded in critical period
-Monocular congenital cataract
-Lid ptosis
Anisometropic amblyopia
-Unequal refractive errors
Strabismic amblyopia
-Constant unilateral strabismus present
during critical period
-Diplopia
-Suppression
Meridional amblyopia
-Cortical neurons are orientation selective
-Meridional astigmatism
Age- months Average visual acuity
1 20/638
1.5 20/540
2.5 20/278
4 20/224
6 20/106
9 20/88
12 20/93
18 20/70
24 20/63
30 20/52
36 20/28
48 20/24
VISUAL ACUITY IN EARLY LIFE
Post natal vision
NEONATE
• 8 to 14 inches
• 20/200 - 20/600
• Mothers arm to her eyes
1-3 MONTH
• Start gazing at objects
• 2 months- eye’s coordination develop
• Hand-eye coordination
• Color perception
4-7 MONTH
• Enjoys more complex designs
• Till 1 meter
• Fine movement of objects
8-12 MONTH
• Focuses on a toy, crawl pull it and picks it
• Grasp and throw objects
• Can perceive depth
1 YEAR
• Depth perception continues
Stereopsis•Infant- Preferential looking test
•Rapid onset between 3 and 6 months
•6 months- 1 min of arc
Spatial visionVernier acuity
•Preferential looking
•Develops more slowly in late years
•Depends on cortical processing
•Adult levels at slightly older ages (6–8 years of age)
Grating acuity
•Preferential looking
•Forced choice
•1 month- 20/600
•1 year- 20/100
•Adult levels at 3- 5years – 20/20
Temporal Vision: Critical Flicker Fusion Frequency•40 Hz at 1 month
•55 Hz by 3 months- adult level
The retinal and cortical immaturities that slow the
development of grating and Vernier acuity apparently have
little effect on the maturation of temporal resolution
Scotopic Sensitivity•Adult-like at 1 month of age
•Shape of the function- Characteristics of rhodopsin
•Does not depend on postreceptoral processing
•Scotopic sensitivity- 507 nm
•Reaches adult levels by approximately 6 months
Colour Vision•Red–green discrimination arises during the second month of life
•Blue–yellow discrimination
•Adult like on the 1 year of life
•Photopic spectral sensitivity function is adult-like in young infants