an experimenter presents a subject with a standard weight of 100 grams followed by a comparison weight of 20 grams; the subject is asked if the two weights are the same or different. the standard is repeated followed by a comparison weight of 30 grams; the subject is again asked if the two are the same or different. this procedure continues with a comparison weight 10 grams heavier on each presentation until the subject says that both weights are the same. these steps are repeated starting with a comparison weight of 190 grams and decreasing it by 10 grams on each trial until the subject says the two weights are the same. what is the experimenter trying to measure?