It's not about individual productivity - it's about team and company productivity.

I doubt anyone questions whether individual effectiveness suffers from an open layout. However open layouts have several benefits that more than compensate: - Impromptu conversations are easy. The barrier to ask someone a question is lower - it's faster to get unblocked. - Shared context. With conversations happening in the open, others will often overhear, sometimes learn, and often will choose to participate. - Impromptu socialization leads to better morale. Someone drops by to chat socially, others join in, people build personal relationships. - Function-specific spaces. The space saved by having a denser desk layout is allocated to having everything from kitchens to massage chair rooms to ping-pong tables. At the same cost per employee, an open space layout has more 'perks'.

I've worked in both offices and open spaces and I far prefer open spaces with a good etiquette about when to interrupt someone.