Assertion (A): An unconditional match usually requires the same colourants.
Reason (R): Only identical colourants produce identical spectral reflectance curves.
Answer: C
Both are true and the reason gives the requirement, and different colourants give different curves. This is why substituting a colourant almost always produces a metameric match. Substitution changes the spectral curve.
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The Ishihara test screens for colour vision deficiency using
Answer: D
Correct answer: pseudoisochromatic plates of coloured dots
The Ishihara plates present a figure in dots that differ from the background in hue but not in lightness or size, so it can only be seen by using colour. Confusion colours are chosen so that a deficient observer sees a different figure or none. It is a fast screening test and identifies the type only broadly.
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Match each colour vision test with what it does.
List I
A. Ishihara plates
B. Farnsworth Munsell 100 hue
C. Anomaloscope
D. D-15 panel
List II
1. precise diagnosis and classification
2. rapid screening for red green deficiency
3. separating mild from severe deficiency
4. grading discrimination ability
Answer: A
Screening, grading and diagnosis are three separate purposes. Using a screening test to grade an observer is a common and misleading error. Each test answers a different question. Screening, grading and diagnosis are distinct tasks.
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Assertion (A): The Ishihara test does not grade the severity of a deficiency.
Reason (R): It is designed to separate normal from deficient rather than to measure degree.
Answer: B
Both are true and the reason gives the design intention, and an anomaloscope is needed for that. Screening and diagnosis are different tasks. An anomaloscope is needed for classification. Screening separates normal from deficient only.
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The Farnsworth Munsell 100 hue test measures
Answer: C
Correct answer: the ability to arrange coloured caps in correct hue order
The 100 hue test asks the observer to place caps of closely spaced hues in sequence, and the pattern of errors is plotted round a circle. Unlike a screening plate it grades discrimination rather than merely detecting a deficiency, and the axis of the error pattern indicates its type - which is why it is used for selecting colour matchers.
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Consider the following statements about the 100 hue test.
1. The error score grades discrimination ability.
2. The pattern of errors indicates the axis of confusion.
3. A perfect score is achieved by every normal observer.
Answer: D
The first two are correct and are why the test is used for selection. The third is not so, since normal observers vary considerably in their scores too. A perfect score is unusual even among normals. The score grades ability rather than presence.
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Anomalous trichromacy differs from dichromacy in that an anomalous trichromat
Answer: A
Discrimination is reduced rather than absent along the affected axis. A dichromat by contrast is missing one cone type entirely. Reduction differs from absence in degree. An anomalous trichromat retains three cone types.
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Match each colour vision condition with its description.
List I
A. Protanopia
B. Deuteranopia
C. Tritanopia
D. Anomalous trichromacy
List II
1. absence of the short wavelength cone
2. absence of the long wavelength cone
3. three cones with one sensitivity shifted
4. absence of the medium wavelength cone
Answer: B
The prefixes prot, deuter and trit refer to the first, second and third cone. The suffix anopia indicates absence and anomaly indicates a shift. The prefixes number the cone types in order. Anopia means absence and anomaly means a shift.
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Protanopia is distinguished from deuteranopia principally by
Answer: C
A protanope finds reds notably darker as well as confusing them with greens. A deuteranope confuses the same colours but without the loss of luminance. Protanopes find reds unusually dark. The missing cone carries much of the luminance.
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Assertion (A): A protanope perceives red objects as unusually dark.
Reason (R): The missing long wavelength cone contributes substantially to the luminance signal.
Answer: D
Both are true and the reason gives the cause, and a deuteranope shows no such darkening. The distinction is used clinically to separate the two conditions. Luminance loss distinguishes the two. Both confuse the same colours otherwise.
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