Size-weight interaction in judgements of compound stimuli

Recent work in the fields of multidimensional information transmission and perceptual accentuation due to value has led to theories concerning unidimensional judgements of compound stimuli. The present study attempts to explore these theories, adding the dimension of size to judged weight, following negative results with judgements of size when brightness is varied.

Three sets of stimulus objects were prepared. Variation of weight was the same in each set. However, the size of the objects was the same in one set, while in another set size increased with weight, and in a third set size and weight were negatively correlated. Three groups of 16 subjects were asked to make replicated absolute judgements of the weights in each set.

It appeared that judgements of weight are more affected by density when density varies than when changes of size produce constant density. As predicted, contrast between successive stimuli is greatest when size and weight are negatively correlated, and least with positive correlation. The extent of the judged scales, and the means of these scales, follow the same pattern. Differences in discriminability between the three series, whilst in the expected direction, are not significant. The hypothesis that these effects would be more apparent in the psychologically linked dimensions of size and weight, than in the relatively neutral case of size and brightness, was largely confirmed. These findings both amplify and modify the previous suggestions concerning compound stimuli.