A subsequent study at Brown University in 2004 also found that scents were not particularly effective at waking sleepers. Pepperment and pyridine scents were presented in different concentrations to sleepers at different stages of sleep. The odours scored mixed results, while audio tones played over a speaker were significantly more effective at rousing the sleepers, leading the researchers to conclude that "human olfaction is not reliably capable of alerting a sleeper".