What do you meant by perceptual norm and frame of reference?

The sensory experiences studied in psychophysics are stimulus-bound. They are based on discriminations of small intervals in a definite, controlled series of stimulus-presentations; and the capacities for the quantitative judgments required are considered as somewhat standard, that is, as pretty much the same for everybody, and as dependent upon fairly stable physiological conditions. From a phenomenological standpoint, however, dimensionalities in perception may occur that are not so closely bound to the immediate stimulus. No one can directly control or measure a percept. It has a right to be of any magnitude the individual experiences it to be; and the experience of its magnitude may at times vary considerably from what one might expect from measuring the magnitude of the stimulus. This does not mean that no measuring scale is being employed. It means only that the scale in use is, to a large extent, observer-involved. In such a situation perceived magnitude or intensity may depend to a large extent upon the subject's past, his immediate past chiefly, but also on his more remote past. It will depend also upon his range of experience with magnitudes or intensities in general.