Bogus concerns about the false prototype enhancement effect

Two experiments addressed the mechanism responsible for the false prototype effect, the phenomenon in which a prototype gradient can be obtained in the absence of learning. Previous demonstrations of this effect have occurred solely in a single-category paradigm in which transfer patterns are assigned or not to the learning category. We tested the hypothesis that any extraneous variable potentially responsible for this effect, such as compactness varying with pattern distortion (Zaki & Nosofsky, 2004), may be functional in the single-category paradigm but not when multiple categories are available at the time of transfer. In the present study, subjects received a bogus or a real category learning phase, followed by a transfer test that required assignment into 1 or 3 prototype categories. The results showed that a minimal prototype gradient was obtained in the bogus conditions, with performance approaching chance levels when classification into 3 categories was required. In contrast, a substantial prototype gradient effect was found following learning. We conclude that the prototype gradient typically obtained following multiple-category learning is primarily driven by real learning and that the false prototype effect is itself an artifact of the single-category paradigm.