At night, faint objects are best seen when not looked at directly. What is the basis of this phenomenon?

Question

A.  Rhodopsin is transported away from the fovea at night.
B.  Cis-retinal builds up in the fovea at night, and is degraded during the day.
C.  Cone photoreceptors are most sensitive in dim light, and few cones are present in the fovea.
D.  Rod photoreceptors are most sensitive in dim light, and few rods are present in the fovea.

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

Gather Content
What do you already know about vision? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 


Answer 1

D.  Rod photoreceptors are most sensitive in dim light, and few rods are present in the fovea.


Clarify Question
What is the key concept addressed by the question?
        · Why are faint objects hard to see directly?
What type of thinking is required?
            o This is an analyze question because you have to make a link between the characteristics of the retina and the function of looking directly or indirectly at an object.

Gather Content
What do you already know about vision? What other information is related to the question?
        · You already know that the retina of the eye is composed of photoreceptors. These photoreceptors come in two types- rods and cones. Rods are for black and white vision and are very sensitive in low light situations while cones are used for color vision and for high acuity in bright light situations. Cones are also concentration at the center of the retina, especially the fovea where focusing occurs, while rods are more prevalent in the peripheral regions of the retina.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · The statement that cone photoreceptors are most sensitive at night, and few cones are present in the fovea is opposite of the truth since this statement is defining rods, not cones. Also, rhodopsin and cis-retinal are not transported or build up in the fovea at night. Thus the correct answer is that rod photoreceptors are most sensitive in dim light, and few rods are present in the fovea.

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o Answering this question correctly depended not only on distinguishing between rods and cones, but understanding their distribution and function in the retina. If you got the answer wrong, did you get the characteristics of rods and cones reversed? Did you think that rhodopsin, which detects low level light, was transported from one part of the retina to another with a shift in light levels? That does not occur, but rhodopsin is found in rods, which are in the peripheral part of the retina. Thus a faint object can be seen best when not looking directly at it, which focuses on the fovea, and instead looking at it with your peripheral vision, which stimulates the rods of the retina.