(Received for publication February 9,1981; accepted February 16, 1981.) Figure 1. Tbe proportion of judgments tbat tbe variable was brighter than tbe standard as a function of tbe percent-cbange in intensity of tbe variable relative to tbe standard. Ascending series are sbown by open circles, and descending series are sbown by filled circles. Data were read from Figure 1 of Yelen (1980). 32 24 -16 -8 0 8 16