Sensation is the process of detecting an environmental stimulus and converting that stimulus into neural activity. The steps of sensation are similar for each of the five major senses, sight, hearing, touch, taste, and smell. First, sense organs receive a specific type of sensory stimulation, for example, light entering the eye.
Then specialized sensory receptor cells, in this case rods and cones in the retina, convert that environmental stimulus into a neural signal, a process called transduction. These signals then pass through the thalamus, a brain structure below the cortex that acts as a relay station for sensory systems. It's then routed to areas of the brain specialized to process that information. For example, the occipital lobe processes visual signals. Other senses follow a similar path.
Signals in response to sound are sent to the temporal lobe. The parietal lobe processes touch and temperature. And the gustatory cortex processes taste. The only stimulus that this doesn't apply to is smell.
Neural signals for smell don't pass through the thalamus. Instead, they pass through the amygdala, which is associated with emotion, and the hippocampus, which is associated with memory. The process doesn't end there.
Because after sensation comes perception, the identification and interpretation of a stimulus. Perception is what's done with sensory information that we take in. It's how we make sense of the world. Whether a stimulus is perceived depends on a number of characteristics.
The absolute threshold of sensation is the minimum amount of stimulus intensity needed for a receptor to react. For example, The absolute threshold for sound would be the lowest volume of a tone that can be perceived by individuals. The just noticeable difference is the minimum change in stimulus intensity that can be detected.
For example, it would be difficult to tell the difference between a 50-pound weight and a 51-pound weight, but relatively easy to tell the difference between a 1-pound weight and a 2-pound weight. Sensory adaptation occurs when a sensory receptor cells response start to decrease after continuous or repeated stimulation. which reduces the perceived intensity of a stimulus.
For example, you might easily detect a foul order when you walk into a room, but over time you perceive it less and less. Sensory adaptation can occur in any of the five major senses. An interesting aspect of perception is perceptual constancy, the tendency to see familiar objects as unchanging, even when there are slight changes to the stimulus. This allows us to recognize objects as having a constant shape, size, and color, regardless of viewing angle, lighting condition, or distance from the object.
Perceptual set is the human tendency to perceive some stimuli but not others, and to base expectations on past experiences. It can influence how people interpret ambiguous information and sometimes lead to processing errors. Perceptual constancy and perceptual set are both top-down processes that use what a person already knows to influence the interpretation of incoming sensory information. It's what allows us to read a sign even if it's missing several letters.
But we can also use bottom-up processing when the brain uses raw sensory data to create a perception.