Judgments of differences and ratios of subjective heaviness.

Experimental instructions to judge differences or ratios of subjective heaviness numerically are generally assumed to produce judgments linearly proportional to the respective heaviness differences or heaviness ratios. In this study, participants were instructed to numerically judge the difference or ratio of heaviness between two weights being lifted separately, either unimanually or bimanually. Weight values were combined factorially. Patterns of factorial curves revealed that unimanual lifting triggered linear judgments of heaviness differences, whereas bimanual lifting triggered nonlinear judgments of heaviness ratios. Lifting conditions produced these judgments independently of the instruction specifications to judge differences or ratios. These results suggest the interpretation that unimanual lifting triggers linear judgments of heaviness differences by default, whereas bimanual lifting triggers nonlinear judgments of heaviness ratios learned through experience. Implications for sensory measurement are noted.