Sensation weighting in comparison and discrimination of heaviness

Participants lifted pairs of successively presented weights and compared th em for heaviness, using the constant method with 2, 3, or 6 judgment catego ries. The standard weight (St) was 100, 200, or 300 g, either roving or fix ed within a block. For each St, there were 5 comparison (Co) weights. The l ifting orders were St-Co and, with 6 categories, Go-St. Time-order errors w ere negatively related to St magnitude, particularly with roving St. In ter ms of Hellstrom's sensation-weighting theory, this result was accounted for by a smaller weighting coefficient for the first-presented stimulus than f or the second. Time-order errors were negative on average, which was explai ned as the result of this weighting in conjunction with a low position of t he reference level because of light background heaviness. With roving St, t he dispersion of the subjective intrapair difference increased with St magn itude, providing evidence for Ekman's law (G. Ekman, 1956, 1959).