Form Perception: Area and Jaggedness as Objective and Subjective Dimensions

Abstract

Ss performed magnitude estimation of the Area and Jaggedness of 6-, 8- and 10-sided polygons over 90 trials. Half of the Ss in each case received feedback after each estimation. In general, feedback resulted in reduced errors for the estimation of both features, but did not change the correlations between the objective measures of Area and Jaggedness and their corresponding subjective estimates. Either feedback or practice in estimation was judged sufficient to raise feature-estimation correlations to the level of .9 when Ss were tested with 30 additional polygons presented at two different tachistoscopic speeds. Speed of presentation did not affect estimation of either measure. In a final stage, Ss drew polygons with different specified values of both features: errors in drawing for Area were related to extremity with more extreme figures being drawn more accurately. Results are interpreted as supporting the validity of the particular physical measures used with respect to subjective dimensions utilized by Ss since extremely high correlations were present for both features even when no feedback was involved. Differences in absolute errors of estimation are interpreted as being due to a tendency in Ss to readjust the judgmental scales provided for them.