Creativity is essential to an organization's survival. In order to remain productive and adaptive, an organization's members must devise creative solutions - solutions that work, and that fall outside the set of known solutions. The cognitive network model (CNM) of creativity proposes a cognitive explanation of the mechanisms that cause creative solutions to occur in the human mind. This paper reports the results of an experimental test of CNM. Sixty-one four-person groups used either the FreeBrainstorming thinkLet or the DirectedBrainstorming thinkLet to generate solutions for one of two ill-structured tasks. In FreeBrainstorming, participants generate creative solutions without intervention from a moderator. In DirectedBrainstorming, a moderator presents a series of oral prompts at fixed intervals to stimulate new lines of thinking. To gain more insight into the mechanisms underlying creativity, we tested three levels of variety among the moderator's prompts. In both tasks, people using DirectedBrainstorming produced solutions with higher average creativity ratings, and higher concentrations of creative solutions than did people using FreeBrainstorming. Significant differences were also found among the three levels of variety used for DirectedBrainstorming.