Contrast and range effects for category, magnitude and labeled magnitude scales in judgements of sweetness intensity

The labeled magnitude scale (LMS) is a verbally anchored quasi-logarithmically spaced response scale with properties similar to magnitude estimation. Three experiments examined whether the LMS showed context effects similar to those found with magnitude estimation and category scales. Two versions of the LMS were used, one anchored at the high end to the strongest imaginable sweetness and the other to the strongest imaginable oral sensation. In a simple contrast experiment, subjects judged the sweetness of a 10% sucrose fruit beverage in the context of a less sweet (5%) beverage or a more sweet (20%) beverage. Consistent with previous literature, the sweetness was judged more intense in the low context and less intense in the high context, for all scaling methods. In a second experiment, this effect persisted (although was smaller) when the contextual item preceded the to-be-rated item, a so-called 'reversed-pair' design. Once again, the effect was highly significant for all scaling methods. In a third experiment, a range effect was examined using wide and narrow ranges of concentration. Psychophysical functions were flatter in a wide context and steeper in a narrow context, consistent with previous observations on range-mapping bias. This result was obtained for all scales. In three common contextual effects, the labeled magnitude scale behaved similarly to other scaling procedures. Its application to comparisons across individuals may be limited if those individuals have different experiential contexts within which they make their judgements.