Sensation and Perception
Take a moment to think about all of the sensory information surrounding you at this very moment. Focus on the colors of the room, the feel of your clothing, the sounds coming in from the street outside, and the scents wafting through the air. In a matter of seconds, you have gained information from four major senses: vision, touch, hearing, and smell. Your sensory system serves as an entrance for information about your environment, transmitting it to the brain so that you may then take action.
Sensation is the process by which the sensory receptors detect and then transduce, or “transform,” incoming stimulation from the external world — or from within the body — into neural impulses. These are then relayed to various areas of the central nervous system for further processing, which constitutes perception. Perception includes higher cognitive processes such as discriminating, recognizing, interpreting, and understanding the incoming information and it is closely integrated with other cognitive processes such as learning and memory. In other words, perception is how you “make sense” of the ongoing events in your world so you can function in it as well as acquire and accumulate knowledge about it.
Each of your senses responds to a different and specific kind of stimulation, but the senses do have some things in common. In addition to transduction, they have absolute thresholds — minimum levels of stimulation necessary to trigger them in a given situation. In order for something to be sensed, it must first be strong enough to be detected. For you to hear a sound, for example, it has to occur at some minimum intensity that will trigger the receptors in your ears. The senses also have difference thresholds, which refers to the amount of change in stimulation necessary for the change to be discernible. In order to notice alterations in a stimulus or changes in intensity, they must also occur at a minimum threshold that is different enough to detect — that is, there must be a noticeable difference.
Sensory adaptation is another process that is characteristic of all the senses. As receptors are continually exposed to the same stimuli, their thresholds increase and you become less aware of the stimulation — or perhaps entirely unaware of it. For example, as you sit in your chair and read this, you are unaware of the chair and the clothing in between pressing against your body — unless something calls your attention to it, such as this sentence. This characteristic of the senses is extremely important in allowing you to focus your attention. You couldn't function if you were constantly distracted by sensations such as the feel of shoes or a wristwatch, the drone of an air conditioner, sounds from outside, and so on.
It may occur to you that as you stare at something, your field of vision doesn't dim or go blank as sensory adaptation would predict. But vision is no exception. The receptors of the eyes never receive the same stimulation for long because of their automatic and rapid back-and-forth movements of which you are entirely unaware.
From a different perspective, what the senses also have in common is that how they work at the receptor level, where the information they transmit goes, and what perceptions they ultimately produce are relatively well understood. However, what goes on in the brain in between is not. Neuroscientists are in hot pursuit of how the specialized areas of the cortex process incoming stimulation from the senses, but they are only beginning to unravel these mysteries.
Of course, if sensory stimulation is too intense, relatively little adaptation takes place and you can't ignore it. The sound of a jackhammer on a sidewalk just outside your window is unlikely to “go away.” Similarly, the loud and steady thumping bass of someone's stereo in an apartment next door can be impossible to adapt to and ignore.