Category rating is based on prototypes and not instances: evidence from feedback-dependent context effects

Context effects in category rating on a 7-point scale are shown to reverse direction depending on feedback. Context (skewed stimulus frequencies) was manipulated between and feedback within subjects in two experiments. The diverging predictions of prototype- and exemplar-based scaling theories were tested using two representative models: ANCHOR and INST. To gain coverage on one side of the continuum, a prototype-based category must lose on the opposite side. ANCHOR can exhibit both assimilative and compensatory context effects depending on feedback. INST always exhibits assimilative effects. The human data show a significant context-by-feedback interaction. The main context effect is assimilative in one data set and compensatory in the other. This pattern is consistent with ANCHOR but rules out INST, which fails to account for the compensatory effect and the interaction. This suggests that human category rating is based on unitary representations.