Overall similarity in adults' classification: The child in all of us

Six experiments, with 108 undergraduates, tested the hypothesis that adults have direct, nonderived access to overall similarity in the classification of separable stimuli (size and brightness). In 2 experiments, high-speed classification by a similarity rule was either as equally accurate as or more accurate than classification by a dimensional rule, and similarity classification was consistently less affected by accelerating performance. Results suggest that adults' access to overall similarity relations of separable stimuli is not based on recombination of dimensional information. Four experiments tested the hypothesis that adults spontaneously use similarity relations when normal classification is disrupted. Spontaneous classifications under conditions of speed, with a concurrent task load, and with an instruction for impressionistic reponding, elicited overall similarity classifications. In a 2nd classification task, however, speed did not increase overall similarity responding. Results suggest an asymmetry of the integrality-separability distinction. Separable dimensions apparently offer 2 easily available classification modes, but integral dimensions offer only one. (61 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).