Light 1. Compare and contrast photopic and scotopic vision. 2. Why do we have both rods and cones?...
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Light Light 1. 1. Compare and contrast photopic and scotopic vision. Compare and contrast photopic and scotopic vision. 2. 2. Why do we have both rods and cones? (N) Why do we have both rods and cones? (N) 3. 3. Discuss the significance of convergence and divergence in the retinal processing of Discuss the significance of convergence and divergence in the retinal processing of rod and cone signals. (M) rod and cone signals. (M) 4. 4. Outline the visual processes that allow our vision to operate over a large Outline the visual processes that allow our vision to operate over a large luminance range. (N) luminance range. (N) 5. 5. How is the visual system able to function at widely varying levels of light intensity? How is the visual system able to function at widely varying levels of light intensity? (N,V) (N,V) 6. 6. In what ways can one quantify the performance of the eye? What factors limit its In what ways can one quantify the performance of the eye? What factors limit its performance? (M) performance? (M) 7. 7. What are believed to be the mechanisms of colour vision? How can defects in it be What are believed to be the mechanisms of colour vision? How can defects in it be explained? explained? 8. 8. How may visual acuity be tested? What factors influence it? (M) How may visual acuity be tested? What factors influence it? (M) 9. 9. Discuss factors affecting the quality of the optical image on the retina. To what Discuss factors affecting the quality of the optical image on the retina. To what extent does the quality limit visual acuity? extent does the quality limit visual acuity? 10. 10. How does the visual system cope with the conflicting demands of high absolute How does the visual system cope with the conflicting demands of high absolute sensitivity and high spatial acuity? (M) sensitivity and high spatial acuity? (M) 11. 11. What structural features of the retina help to explain visual acuity? (M) What structural features of the retina help to explain visual acuity? (M) 12. 12. What factors limit visual acuity at different light levels? What factors limit visual acuity at different light levels? 13. 13. What factors determine whether a visual stimulus will be seen? What factors determine whether a visual stimulus will be seen? 14. 14. Write a concise account of any two of the following: colour vision; visual acuity; Write a concise account of any two of the following: colour vision; visual acuity; dark adaptation; eye movements; pupillary reflexes. (V) dark adaptation; eye movements; pupillary reflexes. (V)
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Transcript of Light 1. Compare and contrast photopic and scotopic vision. 2. Why do we have both rods and cones?...
LightLight1.1. Compare and contrast photopic and scotopic vision.Compare and contrast photopic and scotopic vision.2.2. Why do we have both rods and cones? (N)Why do we have both rods and cones? (N)3.3. Discuss the significance of convergence and divergence in the retinal Discuss the significance of convergence and divergence in the retinal
processing of rod and cone signals. (M)processing of rod and cone signals. (M)4.4. Outline the visual processes that allow our vision to operate over a large Outline the visual processes that allow our vision to operate over a large
luminance range. (N)luminance range. (N)5.5. How is the visual system able to function at widely varying levels of light How is the visual system able to function at widely varying levels of light
intensity? (N,V)intensity? (N,V)6.6. In what ways can one quantify the performance of the eye? What In what ways can one quantify the performance of the eye? What
factors limit its performance? (M)factors limit its performance? (M)7.7. What are believed to be the mechanisms of colour vision? How can What are believed to be the mechanisms of colour vision? How can
defects in it be explained?defects in it be explained?8.8. How may visual acuity be tested? What factors influence it? (M)How may visual acuity be tested? What factors influence it? (M)9.9. Discuss factors affecting the quality of the optical image on the retina. Discuss factors affecting the quality of the optical image on the retina.
To what extent does the quality limit visual acuity?To what extent does the quality limit visual acuity?10.10. How does the visual system cope with the conflicting demands of high How does the visual system cope with the conflicting demands of high
absolute sensitivity and high spatial acuity? (M)absolute sensitivity and high spatial acuity? (M)11.11. What structural features of the retina help to explain visual acuity? (M)What structural features of the retina help to explain visual acuity? (M)12.12. What factors limit visual acuity at different light levels?What factors limit visual acuity at different light levels?13.13. What factors determine whether a visual stimulus will be seen?What factors determine whether a visual stimulus will be seen?14.14. Write a concise account of any two of the following: colour vision; visual Write a concise account of any two of the following: colour vision; visual
acuity; dark adaptation; eye movements; pupillary reflexes. (V)acuity; dark adaptation; eye movements; pupillary reflexes. (V)
Outline the visual Outline the visual processes that allow our processes that allow our vision to operate over a vision to operate over a large luminance rangelarge luminance range
Pupillary reflexPupillary reflex Rods vs. ConesRods vs. Cones
Pooling (spatial)Pooling (spatial) Temporal summationTemporal summation
Automatic gain control (mediated by fall in Automatic gain control (mediated by fall in Calcium)Calcium) Increases cGMP synthesis (GCAP)Increases cGMP synthesis (GCAP) Closes cGMP activated channel (Calmodulin)Closes cGMP activated channel (Calmodulin) Increases recoverin binding to Rh*Increases recoverin binding to Rh*
Horizontal cells (synaptic inhibition)Horizontal cells (synaptic inhibition) Bleaching (fewer receptors available)Bleaching (fewer receptors available)
Lamb model of Lamb model of photoreceptorphotoreceptor
Compare and contrast Compare and contrast photopic and scotopic photopic and scotopic
visionvision Rods - just rhodopsinRods - just rhodopsin B&WB&W More in peripheriesMore in peripheries Convergence 1000:1Convergence 1000:1
Rod bipolar, AII, gcRod bipolar, AII, gc Sensitivity 10Sensitivity 10-4-4 cd/m cd/m22
Acuity lowAcuity low Slower, temporal Slower, temporal
summationsummation
Cones - 3 kinds of Cones - 3 kinds of opsinsopsins
ColourColour Fovea (and rim)Fovea (and rim) Convergence smallConvergence small
On/off bipolar, gcOn/off bipolar, gc Mesopic and photopic Mesopic and photopic
onlyonly Acuity 2.5Acuity 2.5mm
Fast ‘on’ and ‘off’Fast ‘on’ and ‘off’
Contrast sensitivity Contrast sensitivity functionfunction
Decreasingcontrast
Frequency
