The answer is neural adaptation or sensory adaptation. It is an adjustment over time in the receptiveness of the sensory system to a continuous stimulus. It is typically encountered as a modification in the stimulus. For instance, if one lays one's hand on a desk, one instantaneously feels the table's surface on one's skin. In a few seconds, though, one stops to sense the table's surface. The sensory neurons moved by the table's surface react straightaway, but then answer less and less 'til they may not answer at all.
