The loudness of a continuous pure tone does not appear to change with time unless an interrupted tone is introduced at intervals during the course of the test; in consequence it is held that it is the interrupted tone which induces the loudness loss. This, however, cannot be called on to account for the marked change in quality or 'timbre' of a sustained pure tone which occurs over a period of time and which has the attributes of 'tonal adaptation', matching the time course of loudness adaptation revealed by dichotic loudness balance and other procedures. It is argued that the latter have to do with the measurement of sensation while judgement of the loudness of a continuous tone in isolation involves higher-order perceptual processes.