Kao, Albert B. and Iain D. Couzin

Many animal groups exhibit signatures of persistent internal modular struc- ture, whereby individuals consistently interact with certain groupmates more than others. In such groups, information relevant to a collective decision may spread unevenly through the group, but how this impacts the quality of the resulting decision is not well understood. Here, we expli- citly model modularity within animal groups and examine how it affects the amount of information represented in collective decisions, as well as the accuracy of those decisions. We find that modular structure necessarily causes a loss of information, effectively silencing the input from a fraction of the group. However, the effect of this information loss on collective accu- racy depends on the informational environment in which the decision is made. In simple environments, the information loss is detrimental to collec- tive accuracy. By contrast, in complex environments, modularity tends to improve accuracy. This is because small group sizes typically maximize col- lective accuracy in such environments, and modular structure allows a large group to behave like a smaller group (in terms of its decision-making). These results suggest that in naturalistic environments containing correlated infor- mation, large animal groups may be able to exploit modular structure to improve decision accuracy while retaining other benefits of large group size.This article is part of the theme issue ‘Liquid brains, solid brains: How distributed cognitive architectures process information’.