Unidimensional scaling of multidimensional facial expressions.

It is often possible to construct unidimensional scales of multidimensional stimuli. Thurstonian scaling theory predicts that the standard deviations of differences in unidimensional paired-comparisons scaling of such stimuli should covary with the qualitative similarity between the stimuli being compared. In a test of this prediction, 78 5s judged 11 facial expressions from the Lightfoot series with respect to emotional intensity. Stimuli were selected so as to fall in 3 different clusters with large similarity within clusters and small similarity between clusters. Within-cluster comparisons gave smaller standard deviations than between-clusters comparisons for all 11 stimuli.