While the research information is relatively thin (as most work related research seems to be), it goes in line with my experience (and probably the commenter you've replied to).
If your productivity is measured by getting code out that works and is maintainable, or any other activity that requires focus for extended periods of time, then getting interrupted in an open layout office is going to bring it down. Having a quiet office that's insulated from drive-by management and other distractions can really help in that regards. If I remember correctly, Peopleware [1] devotes a longer explanation as to why.
If your work isn't that and requires more collaboration than concentration, open layout offices probably work better for those kinds of work.
I'm not saying one way or the other if it helps or hinders productivity. But productivity is such a nebulous idea. If you're getting at what I think you are, it's probably better to express it as an increased probability of becoming distracted. Dev team in our office each has headphones for that express reason :-)
I've never been able to work to music so I end up having to blast white noise over headphones to work in open office spaces. There is nothing like listening to white noise for 8 hours to make you hate open office spaces.
Headphones reduce (not eliminate) distractions from noise, they don't do anything for visual distractions. And they don't stop people from approaching and interrupting you (this of course still occurs in non-open layouts, but less frequently).
Of course, if you had an office with a door you could close when you needed uninterrupted focus time, that would pretty quickly stop the interruptions. This is the premise behind why C*O's supposedly need their own offices (to concentrate on all the important decisions), and there are some who advocate this approach for all programmers (look up Spolsky's offices for programmers).
