Colour Vision and Observer Questions and Answers

Answer: C

The Bezold Brucke shift shows hue varying with luminance at constant wavelength. A few invariant points are the exception rather than the rule. Only a few invariant hues resist the shift. The rest move measurably with luminance.

Answer: D

Correct answer: the two eyes are presented with different colours

Presenting a different colour to each eye does not produce a stable blend: perception alternates between the two, or breaks into a patchwork. It shows that the combination of the eyes’ signals happens after wavelength has been encoded separately in each, and it is a laboratory phenomenon rather than a practical assessment problem.

Answer: A

Correct answer: adaptation combined with inference about the illuminant

A surface keeps roughly its apparent colour under daylight and tungsten even though the light reaching the eye changes greatly. Two things achieve this: receptor and neural adaptation rescale the responses, and the visual system uses cues from the whole scene to discount the illuminant. The physical spectrum reaching the eye is precisely what does not stay constant.

Answer: B

Both are true and the reason gives the additional mechanism, and adaptation alone is insufficient. Constancy fails in scenes offering few contextual cues. Inference requires something to infer from. Constancy fails in impoverished scenes.

Answer: C

Red, green, yellow and blue each stand alone in this respect. Orange by contrast can only be described as a mixture of red and yellow. Each unique hue stands alone in description. Orange requires two hue names to specify.

Answer: D

Correct answer: four

Red, green, yellow and blue are the unique hues - those described without reference to any other, a unique green containing no trace of yellow or blue. They sit at the ends of the two opponent axes, which is the perceptual evidence for opponent processing beyond the three cone types.

Answer: A

Unique green in particular varies widely between individuals. This variation is not explained by cone sensitivity differences alone. Unique green varies widely between individuals. Cone sensitivity differences do not explain it.

Answer: B

Both are true and the reason gives the level at which the variation arises. It is not accounted for by differences in the receptors themselves. The variation arises in the neural combination. Receptor differences alone are insufficient.

Answer: C

Correct answer: the spectral power distribution of the illuminant

Lens absorption, macular pigment density and the relative numbers of L and M cones all vary from person to person and cause genuinely different colour matches among people with normal vision. The illuminant is a property of the viewing condition, identical for everyone looking at the sample, so it produces no variation between observers at all.

Answer: D

Disputes between supplier and customer frequently rest on exactly this. Instrumental tolerances agreed in advance are the usual remedy. Disputes rest on exactly this variation. Agreed instrumental tolerances are the remedy.