Performance of a group solving a cognitive task: How does it scale? Some intellectual, cognitive and perceptual tasks can be solved collaboratively. It is common knowledge that group performance is better than that of each single individual due to exchange of information (and without going into issues of motivation).
One widely known phenomenon is Wisdom of Crowds - when a group decision is much more accurate due to the averaging of individual biases. However, it is not the only possibility. Sometimes, a task can be divided into parts (and each participant works efficiently on his/ her own). Sometimes there are tasks too difficult to solve but easy to demonstrate that an answer is correct (and it suffices to have only one person in the group who answers correctly to make the group decision correct).
What I am interested in is, how the group performance scales with the group size?
(The measure of performance can be error rate, time needed to complete a certain task or the deviation from the right answer.)
The question is motivated by one of my recent works, arXiv:1109.2044.
EDIT (clarification):
I am the most interested in low-level cognitive tasks (e.g. perceptual or linguistic), especially two-choice decisions (but also multiple choice, counting of blobs, solving a puzzle...). However, other quantifiable measures for cognitive task (including, say, time to complete a certain programming project vs number of programmers) are of my interest as well.
When it comes to the relation to my paper, I am curious if I miss an important reference or if my theoretical results can be supported (or undermined) by any existing experimental results (or even related in other context).
It's a big topic. The relationship between group size and performance on a cognitive task is going to vary by several factors.

Here are a few thoughts:


The form of interdependence adopted by the group on the task will matter. When everyone can just work independently (e.g., taking calls in a call centre), then it makes sense that output would increase almost linearly with increasing group size, in the absence of motivation or learning issues.
In the context of project teams, software teams, and so forth, I imagine the issues would be a lot more complex and that in some situations increasing group size might even reduce performance of the team. There a few articles cited here that discuss this.
A classic study in the context, albeit from a motor task, of the relationship between group-size and group performance is that by Ringelmann (see the wikipedia article) that looked at rope pulling power as a function of group size. The basic finding was that average pulling power declined with group size. This has been interpreted as evidence of social loafing, but their are also coordination issues as well.
Some tasks are heavily influenced by the performance of the weakest or strongest member. For example, a musical group will often sound bad if only one member plays poorly. Or other tasks it will be strongest member, as you say if you have are playing at a trivia night, and you have one person with all the right answers on the table.