If a singer holds any of these factors constant and interferes with their progressive state of change, her laryngeal function tends to become static and eventually breaks occur, with obvious changes of tone quality. These breaks are often identified as register boundaries or as transition areas between registers. The distinct change or break between registers is called a passaggio or a ponticello. Vocal pedagogists teach that, with study, a singer can move effortlessly from one register to another with ease and consistent tone. Registers can even overlap while singing. Teachers who prefer the theory of "blending registers" usually help students through the "passage" from one register to another by hiding their "lift" (where the voice changes).