Sensory adaptation is the diminished sensitivity that occurs with constant, unchanging stimulation. After a short time the stimulus is no longer noticed.

A cold pool feels shocking at first and then merely cool. A persistent odor fades from awareness. The pressure of clothing against the skin disappears within moments. Receptor cells and the neural pathways that follow them reduce their firing rate when the input remains steady, freeing the system to detect change. Adaptation is rapid for smell and touch, slower for vision under most conditions, and almost absent for pain.

The process is adaptive. Continuous awareness of unchanging stimuli would be metabolically costly and informationally useless. By responding preferentially to change, the sensory systems remain efficient detectors of events that may require action. Complete adaptation can be prevented by small eye movements, variations in stimulation, or active exploration.

What does not change soon ceases to be felt. That is sensory adaptation.