No frequency effects when judging contrasts

In literature, experimental findings showed that absolute judgments are affected by contextual effects. In our experiment we tested if judgments of differences, in particular, judgments of brightness contrasts between two chips are affected by the skewing of frequency distributions of stimulus presentations. We asked participants to rate the degree of contrast by using two methods: the category rating method and the adjustment method. Experimental results show that frequency effects do not affect contrast judgments and that there is no difference between the subjective scales obtained with the two methods, except for the “regression effect”. Therefore, judgments of differences, contrarily to absolute judgments, are not affected by contextual effects.