In 2011, Griffiths and colleagues published the results of further studies designed to learn more about the optimum psilocybin doses needed for positive life-changing experiences, while minimizing the chance of negative reactions. In a 14-month followup, the researchers found that 94% of the volunteers rated their experiences with the drug as one of the top five most spiritually significant of their lives (44% said it was the single most significant). None of the 90 sessions that took place throughout the study were rated as decreasing well-being or life satisfaction. Moreover, 89% reported positive changes in their behaviors as a result of the experiences. The conditions of the experimental design included a single drug experience a month, on a couch, in a living-room-like setting, with eye shades and carefully chosen music (classical and world music). As an additional precaution to guide the experience, as with the 2006 study, the 2011 study included a "monitor" or "guide" whom the volunteers supposedly trusted. The monitors provided gentle reassurance when the volunteers experienced anxiety. The volunteers and monitors all remained blind to the exact dosages for the purpose of the experiment.