Similarity judgments have traditionally been assumed to arise from an alignment process that seeks correspondences between the objects and relations for two entities. Several recent studies have shown that thematic relationships between items (e.g. bowl and spoon) can influence people's assessments of similarity above and beyond the effect of feature match and mismatch. We suggest that thematic similarity responses can be accounted for in terms of perceived processing fluency. We propose and

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... t a general framework for the role of fluency in similarity that is related to work by Jacoby and Whittlesea. In Study 1, participants assigned higher similarity ratings to word pairs previously encountered in a study list than to new pairs. In Study 2, participants assigned higher similarity ratings to word pairs that comprised familiar noun compounds (e.g. "garbage truck") than to corresponding reverse-ordered pairs ("truck garbage"). In Study 3, lower similarity ratings were observed for word pairs under low-contrast rather than normal viewing condition.