Two party leaders have to cooperate in a coalition government, despite their political differences. A referee and a linesman have to make a decision that could spell success or failure in an international sporting tournament. Two heads have to direct the same groovy body towards saving the galaxy. From politics to sport to interstellar hitchhiking, there are many situations that require two people to work together.

Now, Bahador Bahrami from the Interacting Minds Project has found evidence that two proverbial heads can indeed be better than one… but only under certain circumstances. Through a simple experiment where volunteers cooperated to find a hidden image in a screen, Bahrami found that pairs trump individuals if they freely discuss their disagreements, not just about what they saw but how confident they were in their decision.

But the partnership falls apart if one person is incompetent but isn’t aware of it, either through personal ineptitude or because they have dodgy information. In this case, two heads became worse than one, and the team would have done better by just ignoring the inept member. These principles of good communication and self-awareness might seem like standard management maxims but they’ve rarely been tested in a rigorous experimental setting (and, as we often see, conventional wisdom doesn’t always match with reality).

Bahrami’s team asked volunteers to watch six patches of white and dark stripes against a grey background and pick the one that had a slightly higher contrast. The volunteers sat in pairs but initially decided on an answer alone. When they eventually compared answers, they could discuss their disagreement to arrive at a joint decision. The task was a simple visual one because it’s clear that people can weigh up and combine information from different senses; the team wanted to see if two people could do the same together.

When they matched volunteers with equally sharp vision, they found that two heads were definitely better than one – the joint decisions were more likely to be right than the decisions of the more accurate individual. This mutual success hinged on good communication – about what they saw, but also how confident they were in their decision. When they weren’t allowed to say anything to each other except for their choice, and one of them (chosen at random) make the final call, they didn’t do any better than the best solo player.

More surprisingly, it didn’t matter whether the duo ever found out if they were right or not. In most of these trials, they were eventually told what the right answer was, but if this info wasn’t forthcoming, they still did better together if they were allowed to talk.

But that changed when Bahrami secretly made one of the volunteers more incompetent. Without telling them, he randomly added more visual noise to the images they saw, making their task much more challenging. If both recruits were stunted in this way, they still did better as a duo. But if only one of them was hindered, the pair actually did worse than the better individual. If one partner was incompetent, two heads were worse than one.

Bahrami’s work says a lot about how pairs of people make decisions together (at least within the general nature of the experiment, leaving aside big factors like power or stereotypes). It’s certainly not true that pairs always rely on the more accurate member, or that they make the choice randomly. The results of the first experiment (where two heads won out) suggests that duos are entirely capable of ‘optimal’ decision-making, where they combine their information to give them the best possible chance of being right.

But the experiment where one partner was unknowingly incompetent suggests that this only works if both partners are equally matched. If one is better than the other, Bahrami writes that she or he would be “best advised to avoid collaboration and instead should rely entirely on the more sensitive individual.” For the simple visual task in this experiment, the data can even identify the exact point where the more competent person should go solo: if their partner’s sensitivity is just 40% or less of their own, they should make the decision unilaterally.

This study contradicts earlier research which said that groups rarely perform better than their best member. People have put forward all sorts of explanations for this. Maybe people put less effort in when others are around. Maybe competition distracts them from doing the task. Perhaps their skills are shot to pieces by groupthink – the desire to get to a consensus without disagreement, at the expense of critical analysis.

But based on his work, Bahrami has a different explanation: the failure of groups to outperform their individual members comes from situations where people don’t communicate the evidence for their decision and how reliable that evidence is. Just like the unwittingly incompetent recruits, people who don’t know about their own shortcomings limit the potential of the group. As Bahrami writes, “We know all too well about the catastrophic consequences of consulting “evidence” of unknown reliability on problems as diverse as the existence of weapons of mass destruction and the possibility of risk-free investments.”

He also notes that previous explanations like groupthink rely on people depending on one another when they make decisions. In this experiment, the team kept the decision-making process independent, only allowing the volunteers to make collective judgments when they disagreed. Bahrami thinks that this is important and plans to test it further. He says, “The intuition we get [is] that effective collaboration is a mixture of independent and interdependent processes and the right balance is critical for its success.”

Reference: Science http://dx.doi.org/10.1126/science.1185718

More on decision-making:

• Caring with cash, or How Radiohead could have made more money
• When multi-tasking, each half of the brain focuses on different goals
• Requests work better than orders, even when we’re asking or ordering ourselves
• Becoming better mind-readers – to work out how other people see you, use the right lens
• Undecided voters aren’t really undecided – the hidden side of decision-making

If the citation link isn’t working, read why here

August 26th, 2010 by Ed Yong in Cooperation, Decision-making, Neuroscience and psychology | 4 comments | RSS feed | Trackback >