Feline night vision
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Feline night vision
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[post_date] => 2024-12-26 10:57:22
[post_date_gmt] => 2024-12-26 15:57:22
[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Cats are carnivorous mammals that have adapted to become more efficient and skillful hunters. Most domesticated cats have long, thick whiskers that enhance their sense of touch and perception of depth, increased numbers of olfactory receptors to detect distinct scents, and ear flaps that move toward the source of a sound. Their adaptations have also given them excellent vision and an uncanny ability to see at night. They are able to see well in the dark because of a specialized membrane known as the tapetum lucidum - which humans do not have. The tapetum lucidum is homologous to a specialized structure in the human eye, known as the choroid. In humans, the choroid is darkly pigmented, while cats lack this dark pigment; resulting in a shiny reflective coating in the back of the eyeball. This coating allows stray light rays which may have passed through the retina to be reabsorbed after being reflected off of the tapetum lucidum (why a cat’s eyes glow at night when you stare directly at them). In contrast, any stray light rays in the human eyeball would be absorbed by the pigmented choroid. The tapetum lucidum is evolutionarily advantageous to a cat -it enhances night vision due to the reflective properties of the membrane and allows the cat to hunt in the dark.
A researcher is interested in exploring the differences between feline and human ability to see at night. He recruits ten cat owners and their domesticated cats, and places a piece of fish in a complex, dark maze for them to find. Each owner and cat enters the maze alone, and the researcher times how long it takes for the owners and cats to find the fish. The average group times to find the food are outlined in Table 1.
Table 1.
[post_title] => Feline night vision
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[question] => Which of the following statements is correct? Cones are responsible for __ vision and are centered in the __; while rods are responsible for __ vision and are centered in the __. **
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[answer] => 2
[description] => Reason for the Correct Answer:
Colors appear dimmer at night, therefore the photoreceptor responsible for color vision is less active.
Highest visual acuity is achieved when staring directly at an object (such as words in a book). This is because by staring directly at an object, you are maximizing the amount of light that hits your fovea. The fovea is rich in photoreceptors responsible for color vision.
The fovea is extremely rich in cones, and is responsible for fine details in your visual field, as well as for color vision (due to the cones in the fovea). Rods are scattered throughout the eye, but mainly are found outside the foveal region in the periphery of the eye. Rods are extremely sensitive to light (and are thus very important for night vision), though do not differentially respond to light of different wavelengths, and thus are not able to detect color.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Cones are responsible for night vision and are centered in the periphery, while rods are responsible for color vision and are centered in the fovea.
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[1] => Array
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[each_answer] => B. Cones are responsible for color vision and are centered in the fovea, while rods are responsible for night vision and are centered in the periphery.
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[each_answer] => C. Cones are responsible for color vision and are centered in the periphery, while rods are responsible for night vision and are centered in the fovea.
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[each_answer] => D. Cones are responsible for night vision and are centered in the fovea, while rods are responsible for color vision and are centered in the periphery.
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => The visual field is broken down and results in light from the left visual field hitting the __ side of the left eye and the __ side of the right eye, and eventually being interpreted by the __ hemisphere in the brain.
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[answer] => 1
[description] => Reason for the Correct Answer:
The visual field is split into two halves, each interpreted by the contralateral side of the brain. Drawing a diagram may help.
The nasal side of the eye is the side closest to the nose, while the temporal side is the side closest to the ears.
Light from the left visual field enters the left eye and hits the nasal side of the left eye, and the temporal side of the right eye. Since the light is coming from the left visual field, it is interpreted by the opposite (contralateral) side of the brain (right hemisphere).
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[answers] => Array
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[each_answer] => A. Nasal; temporal; right
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[each_answer] => B. Temporal; nasal; left
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[2] => Array
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[each_answer] => C. Nasal; temporal; left
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[each_answer] => D. Temporal; nasal; right
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => The following graph depicts the relationship between photoreceptor density and displacement from the fovea. According to the graph, what is the ratio of cones to rods at the fovea?
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[answer] => 1
[description] => Reason for the Correct Answer:
The x-axis indicates the angle from the fovea, with 0 being the center of the fovea.
The fovea is very rich in cones, and has almost no rods.
In the graph, there is a spike in the number of cones at 0 degrees (this corresponds to the center of the fovea). The graph depicts about 150,000 cones at the center of the fovea, and depicts 0 rods in the same region. Therefore, the ratio of cones to rods would be 150,000 to 0.
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[each_answer] => A. 150,000 : 0
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[each_answer] => B. 50,000 : 10,000
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[each_answer] => C. 0 : 50,000
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[each_answer] => D. 10,000 : 150,000
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[quiz_unique_key] => 2261298308
[question] => In order, what structures would a ray of light pass through if it was reflected off of the tapetum lucidum?
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[answer] => 4
[description] => Reason for the Correct Answer:
Since the light is reflecting off of the back of the eye, trace the path of light through the various structures of the eye in reverse order.
The tapetum lucidum is directly behind the retina, which coats the back of the eyeball. A fluid filled structure is the next thing the light passes after it passes through the retina as the light ray exits the eye.
The structures a ray of light passes through as it enters the eye, in order, are the conjuctiva, cornea, aqeous humor, lens, vitreous humor, and retina. Since the light ray is reflecting off of the tapetum lucidum in the very back of the eye, the order of structures is reversed.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Retina, aqueous humor, lens, vitreous humor, cornea, conjuctiva
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[1] => Array
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[each_answer] => B. Vitreous humor, lens, aqueous humor, cornea, conjuctiva
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[2] => Array
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[each_answer] => C. Retina, choroid, vitreous humor, lens, aqueous humor, cornea, conjuctiva
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[each_answer] => D. Retina, vitreous humor, lens, aqueous humor, cornea, conjuctiva
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[quiz_unique_key] => 574431310
[question] => Based upon the study described in the passage, what limits the researchers ability to conclude that cats have better night vision than humans?
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[answer] => 3
[description] => Reason for the Correct Answer:
Consider what other senses cats can use to track food.
Although cats have better night vision than humans, other “heightened” senses may also be used to aid the cat in finding the food.
In the experiment, the difference in time could easily be attributable to other “heightened” senses, such as the cat’s sense of smell, rather than enhanced vision. Since the experiment didn’t control for confounding variables (such as blocking the sense of smell), other confounding variables could have contributed to the difference in time.
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[0] => Array
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[each_answer] => A. Only ten trials were conducted, decreasing the statistical significance of the difference in time.
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[1] => Array
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[each_answer] => B. The study was conducted in a maze instead of a large room.
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[each_answer] => C. Confounding variables may have contributed to the difference in time.
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[3] => Array
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[each_answer] => D. Time was recorded instead of distance travelled.
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[quiz_unique_key] => 2522974796
[question] => When looking at an image, it is necessary to extract features from the image that are later reconstructed in the brain to make sense of what is being looked at. What features are necessary to extract from all images and which pathway is responsible for each feature?
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[answer] => 1
[description] => Reason for the Correct Answer:
Form, motion and color are all features that must be extracted from any object in the visual field. The parvo pathway is responsible for spatial resolution, while the magno pathway is responsible for temporal resolution.
Spatial resolution includes fine details of an object, while temporal resolution includes rapidly changing aspects of an object.
The parvo pathway is responsible for detecting fine details, such as the form and color of an object, while the magno pathway detects rapidly changing components of an object, such as motion.
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[answers] => Array
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[0] => Array
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[each_answer] => A. The parvo pathway is responsible for encoding form & color, while the magno pathway is responsible for encoding motion.
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[1] => Array
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[each_answer] => B. The parvo pathway is responsible for encoding form, while the magno pathway is responsible for encoding motion & color.
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[2] => Array
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[each_answer] => C. The magno pathway is responsible for encoding form & color, while the parvo pathway is responsible for encoding motion.
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[each_answer] => D. The magno pathway is responsible for encoding form, while the parvo pathway is responsible for encoding motion & color.
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