University investigated the role of set and setting on the effects of psilocybin. They administered the drug to 175 volunteers from various backgrounds in an environment intended to be similar to a comfortable living room. Ninety-eight of the subjects were given questionnaires to assess their experiences and the contribution of background and situational factors. Individuals who had experience with psilocybin prior to the study reported more pleasant experiences than those for whom the drug was novel. Group size, dosage, preparation, and expectancy were important determinants of the drug response. In general, those in groups of more than eight felt that the groups were less supportive, and their experiences less pleasant. Conversely, smaller groups (fewer than six) were seen as more supportive, and reported more positive reactions to the drug in those groups. Leary and colleagues proposed that psilocybin heightens suggestibility, making an individual more receptive to interpersonal interactions and environmental stimuli. These findings were affirmed in a later review by Jos ten Berge (1999), who concluded that dosage, set, and setting were fundamental factors in determining the outcome of experiments that tested the effects of psychedelic drugs on artists' creativity. After ingesting psilocybin, a wide range of subjective effects may be experienced: feelings of disorientation, lethargy, giddiness, euphoria, joy, and depression. In one study, 31% of volunteers given a high dose reported feelings of significant fear and 17% experienced transient paranoia. In studies at Johns Hopkins among those given a moderate dose (but still enough to "give a high probability of a profound and beneficial experience"), negative experiences were rare, whereas 1/3 of those given the high dose experienced anxiety or paranoia. Low doses can induce hallucinatory effects. Closed-eye hallucinations may occur, where the affected individual sees multicolored geometric shapes and vivid imaginative sequences. Some individuals report synesthesia, such as tactile sensations when viewing colors. At higher doses, psilocybin can lead to "intensification of affective responses, enhanced ability for introspection, regression to primitive and childlike thinking, and activation of vivid memory traces with pronounced emotional undertones". Open-eye visual hallucinations are common, and may be very detailed although rarely confused with reality. A 2011 prospective study by Roland R. Griffiths and colleagues suggests that a single high dosage of psilocybin can cause long-term changes in the personality of its users. About half of the study participants—described as healthy, "spiritually active", and many possessing postgraduate degrees—showed an increase in the personality dimension