Sensation can be described as the process of how our nervous system and sensory receptors receive and translate stimuli from our environment. Perception is the process by which our brains organize and interpret sensory stimuli, which allows us to recognize significant events and objects. Sensation functions as a bottom-up process because it starts at a smaller level and works its way up (i.e. from sensory receptors to processing centers). Perception functions as a top-down process because it starts at a larger level and gets smaller as it continues (i.e. from the sensory input down to our expectations and experiences).

The signal detection theory predicts when we will detect weak signals (stimuli). This theory negates the idea of absolute thresholds because the purpose is to ascertain why individuals react to the same stimulus differently. Additionally, it seeks to understand why one individual may perceive a stimulus differently based on circumstances. For instance, an exhausted parent may jump at the slightest whimper of a sleeping baby but fail to recognize a louder noise (i.e. the dryer buzzer indicating dry clothes). The absolute threshold is defined as the minimum stimulus required for detection 50 percent of the time; therefore, it is an incorrect choice. Conversely, a stimulus may be considered subliminal when it is below one's conscious awareness: not detected 50 percent of the time. This is also incorrect. Transduction would be incorrect because it is the process by which stimuli are translated from sensation to perception. Last, priming is also incorrect because it is defined as the process of predisposing one's memory, perception, or response by making unconscious associations. This is usually exercised in experiments using flashing images and masking stimuli.

The difference threshold is the noticeable difference a person can detect between any two stimuli 50 percent of the time. The concept of difference threshold is often associated with Weber's law. This law states that in order for an individual to perceive a difference between to stimuli then the stimuli must be a certain percent different and not a given amount. This becomes an issue of proportion versus static amount. 

Ewald Hering created the opponent-process theory. While he saw truth in the Young-Helmholtz trichromatic theory, he felt that it left many questions of color vision unanswered. For example, how is it that people that cannot see red or green see yellow? Hering came to an understanding using “afterimages.” For instance, if you stare at a green square for long enough and then stare at a white sheet of paper, you will see a red square. Red in this case is green's opponent color. The same works for yellow and blue and black and white. You may be familiar with figures in text books having an image of a flag that's normally red, blue, and white be colored in green, yellow and black. with a blank white space next to it. This is an example of the afterimage effect, staring at the discolored flag for an ample period of time and then immediately staring at a blank white space will yield the creation of an image of the flag in its normal colors. A century later, researchers supported Hering’s theory. There are three sets of opponent retinal receptors: green-red, blue-yellow, and black-white. This theory complements the Young-Helmholtz theory. 

The periphery of the retina contains many more rods than cones. Rods allow people to easily detect changes in light, and cones allow us to see in color and are located in the center—fovea—of the retina where visual acuity is best. Rods might not help us with seeing things super accurately, but they do help us with detecting motion because of the changes in light. The blind spot is where the bundle of nerves at the rear of the eye chamber block incoming light to hit the retina; thus, creating a "hole" in our vision. Nearsightedness has to do with visual acuity based on distance from the object, not peripheral vision.

Sensory adaptation is a gradual decline in sensitivity to prolonged stimulation. Senses—in this case taste—will automatically adapt to decline their sensitivity to stimulation over time. Habituation is a closely related concept that involves less sensitivity over time; however, habituation has to do more with physiological, cognitive, and perceptual processes rather than basic sensory processes. Taste bud cell death does not occur after prolonged stimulation. 

Action potentials are caused when different ions cross the neuron's membrane. The inside of the neuron becomes more positive due to the rush of sodium into the cell during depolarization. This raises the membrane potential from resting (roughly ) to the threshold level of about , which triggers the action potential and raises the membrane potential to roughly .

Following the action potential, potassium exits the neuron to reduce the membrane potential before the sodium-potassium pump restores the resting potential.

Over time, a constant stimulus in the environment evokes less and less of a response from one's sensory system. Sensory neurons respond at first to these stimuli, but over time they stop responding in order to focus attention on other stimuli in the environment. 

The human retina has two types of cells that respond to light: cones and rods. Rods are more numerous, but can only detect light and dark shades. Cones respond to different wavelenghts of light, and can thus transmit color information. They are highly concentrated in the fovea of the retina.

Every visual field has a blind spot, where there are no rods and cones (known as photoreceptors) to detect external images. Our brain uses context clues from the environment to help fill in this blind spot to make a complete picture. The blind spot is located on the optic disk, which is the location where the optic nerve exits the back of the eye. Due to the nerve tissue in this spot, there are no photoreceptors to detect input.

In contrast, the fovea centralis is the region of the retina with the highest concentration of cones.