This article from the WSJ (Chains That Set Us Free) discusses some of the experimental evidence.
And, this article on groupthink from The New Yorker is a nice summary of the history of the technique of brainstorming (thanks for John Ganter for bringing it to my attention), along with a refreshing discussion of why the lack of constraints in brainstorming seem to make it a relatively ineffective approach to innovation.
There seems to be a bit of a paradox here: many formal innovation activities that focus on the removal of boundaries to get folks "outside of their box" result only in shallow thinking.
This is consistent with my experience where such exercises usually result in bland lowest-common-denominator ideas with little new value. What seems to help is the creation of new "boxes" that help highlight and break existing (often unseen) boxes. Here's a few boundaries I've seen that helped unearth creative ideas:
- Identify key resource constraints in the domain under discourse and play with scenarios where they become either 10x more constrained or 10x less constrained. This highlights the constraint structure of the problem/solution landscape in a way that can help identify radically different solutions. IT-intensive domains are especially susceptible to this approach; even though we understand Moore's Law at a cognitive level, it's usually very unclear how that affects a solution space.
- Keep the group size to five or less. If you don't, the more assertive members will tend to define and structure a discourse landscape that's largely inside the boxes they know. If you keep the group small with diverse subject matter experts (see the next bullet), "ritual dissent" tends to emerge organically.
- Ensure that group members are subject matter experts in a different, but related, areas ... the goal is to force discussions about non-obvious, but key, underlying assumptions. The tendency toward lowest-common-denominator solutions means that each member should be at or above the level of innovation you're trying to achieve.
- Don't use a formal innovation process ... recipes generally produce minor variations of existing ideas instead of something new. Using Complicated approaches in a largely Complex domain is a common mistake.
- Incorporate multiple cycles of focused discussions, unfocused discussions, focused thinking alone, unfocused thinking alone. Ideally, scatter these over a period of weeks to months. Ideas need time to percolate.