BY ARIANNE COHEN

Remember that time companies spent hundreds of millions of dollars on open-office layouts, only to discover that face-to-face interactions decrease by 70% in open-office plans? More fallout today: Ethan Bernstein, the Harvard researcher behind that finding, has taken to the Harvard Business Review to analyze why.

He says that workers in open spaces quickly develop psychological fourth walls, the conceptual boundaries that protect their public solitude. For example, coworkers quickly learn that wearing headphones or appearing to work intently will stop interruptions. “Especially in open spaces, fourth-wall norms spread quickly,” writes Bernstein.

The solution, however, may not come from asking individual employees what it is they actually want. “Offices overly focused on supporting individual preferences are unlikely to do an optimal job of supporting the overall team,” Bernstein writes.

Instead, he suggests that leaders need to increase the kind of collaborations that produce focused work, which are different for every office. He suggests iterating one floor of office layouts with A/B testing: worker bees who need uninterrupted focus should get that; necessary cross-team interactions should be facilitated.