Judgment error in category vs magnitude scales.

The effects of a variety of experimental conditions on the judgments (length of lines) of 16 normal and 16 mentally retarded observers were examined using category and magnitude scaling techniques. Using error and variability of judgment as criteria for measuring response bias, for normal subjects knowledge about the stimulus range, whether learned or provided, had as much to do with resulting judgments as the type of scale used. Judgment error of the retarded group was significantly greater than the normal group and appeared to be related to their limited ability to assign categories or proportions to the simuli used.