In a Speed-Accuracy-Tradeoff (SAT) paradigm we investigated how adjective type and polarity modulate the on-line semantic composition of noun phrases (NPs). 22 German speakers read sentences like “The tradesman — buys — areal diamond”. Enriched adjectives (“real/fake”) highlighted or adjusted the noun’s meaning, whereas non-enriched adjectives(“white/flawed”) simply specified a property. Adjectives had positive (“white/real”) or negative polarity (“flawed/fake”). Uponthe display of critical NPs, participants indicated by a series of key presses if the sentence was correct. For the SAT responsefunction we computed the (i) asymptote (response accuracy as d’), (ii) rate (response speed) and (iii) intercept (point when ac-curacy departs from chance). Accuracy was significantly lower for semantically enriched vs. non-enriched NPs, suggesting thathighlighting and adjusting certain properties during composition is costly. Polarity affected temporal dynamics with negativeNPs showing a slower rate than positive NPs, indicating that negative information is processed in more depth.