Color Vision Flashcards
4 areas of Infant Vision development
- Absolute Thresholds
- Spatial Summation Areas
- Increment Threshold Functions
- Color Vision
Absolute Thresholds Procedure
- Forced-choice PL
- Dark-adapted infant
- Large stimuli < 1 s duration presented to left or right
- Observer reports the stimulus position based on
infant’s eye and head movements
Absolute Threshold Result
- Absolute threshold decreases rapidly with age
Compared to adult AT
* 1.4 log units higher in 4 week old infants
* 1 log unit higher in 10 wk- olds
* 0.6 log unit higher in 18 wk-old
* Adult levels by 6 months
Spatial Summation Infants vs Adults
infants: Absolute threshold is constant over a large range of stimulus areas
Adults: For small stimuli, threshold is inversely proportional to stimulus area (Ricco’s law holds)
The critical area (the area beyond which Ricco’s law does not hold) is larger in infants than adults
Results of Increment Threshold Functions
Infant rod mediated threshold vs intensity functions (TVI) similar in shape to adults
* Threshold delta L is highest in 4 wk-old infants and decreases with age at each background level
* delta L/L Weber fraction decreases at the same rate as absolute threshold (by 6 mos)
* Where Weber’s law holds; delta L/L is a constant
– Adult slope = 1
– Infant slope = 1 by 2-4 mos
* Shallow slope of increment threshold v. background intensity function due to Immaturity or absence of rod-cone interactions
Infant Vision development in Absolute Threshold, Spatial Summation Areas, and Increment Threshold Functions
Absolute Thresholds
* Reach adult levels about 6 months after birth
Spatial Summation Areas
* Larger in 4 to 11 weeks old infants than adults
Increment Threshold Functions
* Similar to those of adults
* Obey Weber’s law by 2-4 months of age
What is Color Vision?
Capacity to discriminate among lights of different wavelength composition
How do you test color vision in infants?
Need to ensure that infant is responding to differences in wavelength rather than differences in luminance of the stimuli
How to test FPL studies for color vision development
Difficult to eliminate luminance clues
– Measure color discrimination in the presence of several luminance differences
–Present each color test stimulus at different luminances
» Infant with color vision fixates the colored target
when the luminance is equal to the white background
» Infant without color vision performs at chance level
* Infants make red-white discrimination on the basis of wavelength differences
FPL color vision
when do infants show dichromatic color vision?
Test other chromatic discriminations
Infants show dichromatic (tritanopic) color vision by 8 -10 weeks
–Fail in zones centered in the yellow-greens and mid-purples
Color Vision development: VEP measures ____
VEP measures
* Infants as young as 2 weeks of age have functional MWS and LWS cones and the post receptor circuits that are needed to relay color information to the visual cortex
* Infants as young as 5 weeks have functional SWS cones
achromatic CV by VEP
– Responses to achromatic reversing patterns at low spatial frequencies appeared early and changed rapidly
– Latencies of the achromatic reversal response decreased to mature values within the first 12-15 weeks of life
chromatic CV by VEP responses and waveforms
– Responses to chromatic pattern onsets appeared later (L-M: 4 weeks; S: 6-8 weeks) and changed continuously throughout the first year of life.
– The waveforms did not appear adult-like until about 12-14 years of age.
Infant Color Vision development for PL
- Rods and at least one cone type are functional by 1 month
- Infants show dichromatic (tritanopic) color vision by 8 -10 weeks
- Trichromatic vision is present by 3 months
Infant vision color development for VEP in
- chromatic waveforms develop later and are more complex than the achromatic reversal waveforms
- The latencies of the major fast components of the achromatic responses are mature by 3 months whereas the chromatic waveforms are still changing substantially at 12 months
- neural pathways that process chromatic information are not mature until around puberty. Noisier, less precise visual system
- Psychophysical studies show improvement in color sensitivity until late childhood. Subtle anatomical changes in primary visual cortex.
CV Test
HRR
CV Test made Easy
Portnoy Plates
F2 plates
* Testability for Pease-Allen plates n = 208
- High failure rate for red/green test plates in children <16 months
- Testability for CVTME test n = 5960
- 17% <37 months
- 57% 37-48 mo
- 89% 49-60 mo
- 98% 61-72 mo
- Prevalence varies by ethnicity
Congenital Color Vision Defects and prevalence
- X linked red/green
– 8% males
– 0.5% females - Autosomal dominant tritan
– 0.0015 to 0.007% - Achromatopsia
– 0.003%
Genetic Testing as a New Standard for Clinical Diagnosis of Color Vision Deficiencies.
- Causative mutations change the copy number or sequence of the L, M, S wavelength sensitive cone opsin genes.
- Direct sequencing of opsin genes and a novel genetic assay that characterizes single nucleotide polymorphisms (SNPs) using the MassArray system.
- The MassArray assay (opsin gene analysis) - useful in the dx of inherited color vision deficiency including presence vs absence, type, and severity, and provides info to pts about the underlying pathobiology of disease
Practical problems for children with color vision defects
Children report difficulty:
* seeing traffic lights; brake lights when cycling
* with board games
* choosing clothes which match
* certain foods look bad
– spinach-black
– cheese- very dark
* with pie charts, computer spreadsheets, laser pointer
* seeing colors in educational materials or on communication devices
