Cones, rods, bipolar cells, and ganglion cells are receptor cells found in the outer layer of the retina. Energy is first transmitted to rods and cones, then to bipolar cells, and eventually to ganglion cells. Rods and cones differ in terms of their locations and purposes. Cones are found clustered around the fovea (area of central focus on the retina). Cones have a direct pathway to the brain. One cone will be connected to one bipolar cell. This ensures that each cone can have its individual message directed to the visual cortex. The specific connections allow for information to be preserved, also while providing a large input for the visual cortex from the fovea. As a result, cones are better capable of detecting detail. Rods, on the other hand, do not exhibit the same wiring as cones. Rods will share bipolar cells with other rods; therefore, their input reaches the visual cortex as shared information. 

As information is translated into neural impulses in the retina, the information is passed from the rods and cones to bipolar cells, which transfer the impulse to ganglion cells. Feature detectors are specialized neurons in the visual cortex that receive information from retinal ganglion. In order to receive the information, the impulses must pass through the optic chiasm. This is the "X" created by the two optic nerves crossing below the brain. The optic nerves will then meet at occipital lobe's visual cortex to deliver the information. Feature detectors are self-explanatory by their name. Their job is to detect a scene's features—edges, lines, angles, and movement. This information is then passed to cell clusters in other cortical areas that respond to more complex patterns. 

The Young-Helmholtz trichromatic (three color) theory states that the retina contains three color receptors. Thomas Young and Hermann von Helmholtz understood that any color could be created through combining the primary colors with varying wavelengths. They inferred that each receptor was especially sensitive to one of the primary colors. They deduced that one receptor was sensitive to red, one to green and one to blue. These receptors were later discovered to be cones. When different combinations of these cones are stimulated, then we are able to see different colors.

The ear is separated into three parts: the outer ear, the middle ear, and the inner ear. The outer ear is the visible part of the ear. It acts to funnel the vibrations into the middle ear. The middle ear only contains a piston made up of three tiny bones. These bones are the anvil, hammer, and stirrup. Their purpose is to amplify the vibrations so that they can continue into the inner ear and create the necessary ripples in the basilar membrane to bend hairs. The bending hairs will initiate neural impulses, sending messages to the brain. It is the inner ear that contains most of the structures required for sensing sounds (i.e. semicircular canals, cochlea, ear drum, and oval window).

Amplitude is the height of a wave. The greater the amplitude of a sound wave is, then the greater the activation of hair cells in the ear will be. Rather than acting singularly, the hair cells attuned for a specific frequency will react with its neighboring hair cells. Based on the amount of hair cells affected, the brain can interpret how loud the sound stimulus is; therefore, the greater the amplitude is, then the greater the volume of the sound will be. 

The cornea is the clear thin layer that covers the eye. Aside from the obvious task of protecting the eye from foreign invaders, it is responsible for a majority of the eye's ability to focus. Because it is the outermost layer of the eye, light will initially pass through this structure. As the cornea bends the light through the pupil, it will direct it to the lens. The lens then plays the role of refocusing the light and directing it to receptor cells. The iris is responsible for controlling the pupil's size; therefore, it would be an incorrect answer choice. The fovea—a structure residing at the back of the eye near the optic nerve—is part of the eye; however, it is not the initial point of central focus. 

The ear is separated into three parts: the outer ear, the middle ear, and the inner ear. The outer ear is the visible part of the ear. It acts to funnel the vibrations into the middle ear. The middle ear only contains a piston made up of three tiny bones. These bones are the anvil, hammer, and stirrup. Their purpose is to amplify the vibrations so that they can continue into the inner ear and create the necessary ripples in the basilar membrane to bend hairs. The bending hairs will initiate neural impulses, sending messages to the brain. It is the inner ear that contains most of the structures required for sensing sounds. 

Light will initially pass through the cornea and bend through the pupil to reach the lens. The lens is responsible for taking the refracted light and refocusing it. In doing so, the refocused rays will create an inverted image on the retina. This is accomplished through a process known as accommodation. The retina does not receive a complete image, but instead particles of light energy. Its receptor cells will take the light, translate it into neural impulses, and forward them to the brain where they will be reassembled right side up. 

The lens of the eye determines where the focus point will be in the rear chamber of the eye. When the lens is distorted, it can move the focus point slightly in front of or slightly behind the retina—back of the eye. When it is in front of the retina, it's called nearsightedness (e.g. a person can only see clearly when objects are near). When the focus point is behind the retina, it's called farsightedness (e.g. a person can only see clearly when objects are far away). Color blindness and macular degeneration do not have to do with where the focus point falls on the retina.

Rods allow us to see in black and white, and adapt much more than cones do when there is low light. In other words, they become even more sensitive in the dark. Cones are used for color vision and seeing in daylight. The fovea is a tiny spot in the center of the retina, but it contains only cones and allows for sharp visual acuity. The lens does not change depending on the lighting.