The pupil is the hole at the center of the iris which allows light to enter the eye and reach the photosensitive retina. The iris is a circular structure on the surface of the eye which controls the size of the pupil. When we discuss eye color, we are referring to the pigment of the iris. The iris and pupil can both expand and constrict. In order to protect the eyes from excessively bright light, in conditions of bright lighting, the iris will expand in size, causing the pupil to constrict, thus allowing less light to pass into the eyes. The opposite is true in dim lighting: the iris will constrict, causing the pupil to expand in size, and allow more light in.

Neither the iris nor the pupil  help to focus vision. Focusing is performed by the lens within the eye. This is done by correctly aligning light from an object with the retina, not to control the intensity of light entering the eye.

The lens is a crystalline structure within the eye. Like the lens in corrective glasses or contact lenses, the lens of the eye focuses light. In this case, it focuses light onto the photosensitive retina at the rear of the eye. The lens has an important role in vision because objects at different distances will reflect light at different angles. If we were unable to focus this variable light by means of the lens, then perceived images outside of a certain distance would appear unfocused and blurry. 

You can test this through a simple experiment. First, try to focus your gaze on an object less than a foot away from your head, then stare at something several feet away, and finally stare at something far away (e.g. out of your window). If the direction of your gaze has remained relatively constant, then part of the physical sensation you are feeling in your eyes is the lenses changing to focus the different images onto the retina.

On the other hand, the lens is not responsible for locating an image; muscular movements of the head and eyes control where and what they look at. Furthermore, the lens cannot not accommodate for the blind spot. Instead, binocular vision helps in filling in for missing visual details. Last, the lens does not control how much light enters the eye—that is the job of the pupil and iris. The lens merely controls the focusing of that light onto the retina.

"Congenital blindness" refers to blindness experienced from the time of birth onwards. This type of blindness has a variety of causes. For example, it may be inherited genetically or it may be the result of an infection during pregnancy/fetal development.

The other choices are incorrect. "Cortical blindness" refers to blindness caused by structural damage, alterations, or defects in the brain. This form of blindness may also be present from birth; however, it is often experienced later in life as the result of accident or injury and may only lead to partial blindness. "Color blindness," though genetic and present from birth, is only an insensitivity to certain colors and not a total blindness. Last, an "astigmatism" is a visual impairment caused by an imperfection in the eye's curvature, and does not result in blindness.

Cortical blindness refers to "total or partial blindness brought about from damage to the brain's occipital lobe." The occipital cortex is found in the back of the skull, and is responsible for—among other functions—primary vision and the processing of information pertaining to colors, shapes, movement, contrast, and depth. When damage occurs within this region of the brain, the result may often be a loss of vision, despite perfectly healthy eyes.

The other choices are incorrect. Although the description of blindness from birth is accurate, the name for this is congenital blindness. Cortical blindness is not the result of conditioning, nor is it an inability to perceive images clearly, but rather a partial or total blindness. Last, cortical blindness is neither a psychological condition in which the subject believes themselves to be blind when healthy, or healthy when blind, which does exist and is known as Anton-Babinski syndrome.

Hearing aids function by amplifying sound that reaches the ear, or by replacing the cochlea of the inner ear. This will resolve any cases of conduction deafness, which is deafness as a result of an inability to properly channel sound waves within the structures of the ear and inner ear. It will not resolve nerve deafness, which is brought about by damage to auditory cortex, or to the nerves leading from the ears to it. Correcting this damage would require technologies not yet available to medical science. Neither 'auditory' nor 'tympanic deafness' is a correct label for any type of deafness.

"Subliminal" is defined as "beneath the threshold" and it refers to information which is processed without entering into consciousness. Such information has been demonstrated to impact decision making in laboratory conditions, but failed to provide a significant enough influence to justify its use in advertising or politics. This allayed the concerns over a possible "brainwashing" of the public by the media which arose when this phenomenon was discovered.

Though in Freudian terminology the subconsciousness is described as a component of mental life which is inaccessible to regular consciousness, "unconsciousness" does not match this or the correct answer to the question. Finally, subliminal information is not "paranormal," or outside of the natural laws of physics, in any regard, and neither is it "subtypical", which is in fact, not a word at all.

Peripheral vision is our ability to see beyond the center of our gaze. Although our vision is less accurate in the far sides, top, and bottom of our visual field, the information contained within it remains vital. In the context of evolutionary history, the ability to perceive along the periphery of our visual field might have meant the difference between survival and becoming lunch for a stalking predator lurking in the bushes to the side. In contemporary life, peripheral vision remains important for safety while driving, for athletes, or any instance where tracking motion along a broad field of vision is required.

The other choices are incorrect. The fact that near and far objects move at different apparent speeds relative to an observer is described by motion parallax. The ability to gauge depth is known as depth perception. The ability to differentiate between superimposed images is described by the law of good continuation.

Weber's law states that the just-noticeable difference between any two stimuli is proportional to the magnitude of those stimuli. As an example, this means that if you added weight to a five pound barbell and found that the least difference you could perceive was the addition of a half of a pound, then on a then pound barbell the least difference you should be able to perceive would be one pound. In this case, the stimuli and the just-noticeable difference have increased proportionally by a factor of two.

The "just-noticeable difference" is a measure of how small of a change in a stimuli is enough to register it as being different. Below this value any changes in the stimuli will not be noticed, and it will appear to be the same. In the case of this hypothetical experiment, the researcher is asking the test subject to rate the tones as either "same" or "different." As a result, they must be seeking information related to the just-noticeable difference: the minimum value of change by which the tones will still be registered as distinct.

The other choices are incorrect. The "absolute threshold" is defined as the lowest level of a stimulus that an organism can detect. "Minimum threshold" roughly restates this, but is not itself a term used in this context. A dog whistle being inaudible to the human ear is an example of a stimulus outside of the absolute threshold of human hearing. Last, "pitch" is experienced as the note of a sound, and is a function of sound-wave frequency, not amplitude (i.e. volume).

The cochlea is responsible for the transduction of physical energy in the form of sound waves into electrical energy in the nervous system. If this area of the inner ear were damaged, then one's sense of hearing would be compromised, perhaps resulting in total deafness if the injury were severe enough. As a profession based around sound and hearing, this would constitute a great loss to a musician's career.

The other choices are incorrect. "Damage to the pinna" (i.e. the outer portion of the ear), would somewhat compromise hearing, but would be more easily and inexpensively corrected, and would have far less drastic of an effect than damage to the cochlea. A loss of the sense of smell ("olfactory loss"), or a loss in the ability to balance ("vestibular loss") would not be as compromising to a musician's career as a loss of hearing.