“Rods” are incredibly sensitive to light, and can be triggered by a single photon. These cells are the primary photoreceptor cells active at very low light. The activation of cone cells requires significantly larger amounts of photostimulation; therefore, they function primarily in interpreting visual information in bright light. Photosensitive retinal ganglion cells, a group of cells that make up a very small percentage of overall photoreceptor cells, are less sensitive to photons and have a slower response time than either rods or cones.

There are three types of photoreceptor cells in the retina: “rods,” “cones,” and “photosensitive retinal ganglion cells.” While rods and cones directly communicate information about sight (e.g. contrast, brightness, and color), photosensitive retinal ganglion cells do not directly communicate visual information to the brain. Rather, they are involved in the pupillary reflex.

Myopia is nearsightedness, meaning the focal length is too short. This can be caused by too much refraction at the eye's lens or if the eyeball is too long. Myopia can be corrected using a concave (i.e. diverging) lens, which will increase the focal length as shown in the figure. 

Weber's law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. Because the original stimulus changes in each condition (i.e. low, medium, high), the ratio for the just-noticeable difference also changes; therefore, the magnitude necessary to detect a change will vary by condition. 

The eyes contain approximately seventy percent of the total sensory receptors of the body. Most of these are located in the retina, which has up to 200,000 photoreceptor cells per square millimeter in its densest location (i.e. the fovea centralis).

The “cocktail party effect” accounts for the fact that we are able to hear personally important information even if we are not involved with it. In this example, George was in a conversation amongst his friends, and not involved with the conversation of the group nearby. The cocktail party effect explains that even though he was not directly paying attention to the nearby conversation, he did not completely filter the information out. Instead, it is was if he "turned the volume down" and paid attention once the information became personally relevant, such as the mentioning of his brother's name.

“Divided attention” is when an individual focuses on multiple tasks at once. While it could be argued that George is attending to two conversations at once, the cocktail party effect best describes the reason he is able to hear his brother's name without any attempt to listen to two conversations at once. The “primacy effect” concerns our tendency to have better memory for things at the beginning of a list (e.g. if you are given a list of words to remember, you will be more likely to remember the ones at the beginning rather than ones in the middle of the list). “Heuristics” are short cuts used for problem solving. Last, “schemas” are mental frameworks we use for understanding new experiences.

A confounding variable is an extraneous variable that is inadvertently associated with the independent or dependent variables. The just-noticeable difference of a stimulus can change substantially over the course of a person's lifespan. In this case, age is associated with differences in hearing abilities. Normative hearing loss and certain medical conditions that contribute to hearing loss are more common as age increases. The other options (marital status, IQ, and depressive symptoms) are not associated with changes in hearing. 

The primary auditory cortex, the area of the brain responsible for processing auditory information, is located bilaterally in the temporal lobes in Brodmann areas 41 and 42. 

When we are infants, our movements are almost exclusively reflexive—healthy babies demonstrate the same general response to a specific type of stimuli. While most of these movements are technically functional (i.e. the rooting reflex serves the function of aiding in child in being able to eat), not all serve a specific purpose.

On the other hand, "autonomic" does not apply to movement, but rather to unconscious actions that keep our bodies in homeostasis, like our breathing. Very young infants have not yet developed the nervous system capabilities that allow for exploratory movements.

The just-noticeable difference is the amount that the stimulus needs to change in order for a human to perceive a difference half of the time or more. In this case, participants in the low amplitude condition were able to identify a difference half of the time when the amplitude was increased by ten decibels.