In natural speech people use different levels of prominence to signal which parts of an utterance are especially important. Contrastive elements are often produced with stronger than usual prominence and their presence modifies the meaning of the utterance in subtle but important ways. We use a richly annotated corpus of conversational speech to study the acoustic characteristics of contrastive elements and the differences between them and words at other levels of prominence. We report our results for automatic detection of contrastive elements based on acoustic and textual features, finding that a baseline predicting nouns and adjectives as contrastive performs on par with the best combination of features. We achieve a much better performance in a modified task of detecting contrastive elements among words that are predicted to bear pitch accent.