Herding in humans

Herding is a form of convergent social behaviour that can be broadly defined as the alignment of the thoughts or behaviours of individuals in a group (herd) through local interaction and without centralized coordination. We suggest that herding has a broad application, from intellectual fashion to mob violence; and that understanding herding is particularly pertinent in an increasingly interconnected world. An integrated approach to herding is proposed, describing two key issues: mechanisms of transmission of thoughts or behaviour between agents, and patterns of connections between agents. We show how bringing together the diverse, often disconnected, theoretical and methodological approaches illuminates the applicability of herding to many domains of cognition and suggest that cognitive neuroscience offers a novel approach to its study.

Introduction

Cognitive psychology generally focuses on the individual as the fundamental unit of analysis [1]. Nevertheless, we are all embedded in a complex system of social structures, which ground and organize much of our behaviour [2], ranging from national identity to religious affiliation. Here, we consider one of the many bridges that link agents and the social structures in which they are embedded: a form of convergent social behaviour termed ‘herding’. Herding can be broadly defined as the alignment of thoughts or behaviours of individuals in a group (herd) through local interactions rather than centralized coordination. In other words, the apparent central coordination of the herd is an emergent property of local interactions.

Herding is an influential and well-documented feature of human behaviour in a number of domains, particularly economics and finance 3, 4, 5. Although the current economic turmoil has revealed the depth of herding among financial institutions and individual investors 6, 7 (and by implication the agents responsible for their decisions), this concept also has much broader relevance beyond the economic arena. Examples of phenomena that have been described as involving herd behaviour are diverse and varied, ranging from stock market bubbles and financial speculation to zealotry (e.g. the 2002 Gujarat mob violence [8]), political choice [9] and consumer preferences 10, 11. The concept is well known in ethology, where for example the biologist William Hamilton illustrated how herd behaviour can emerge from the uncoordinated behaviour of individuals engaged in predator avoidance [12]. The process has also been investigated in social psychology and terms such as Fad, Fashion, Mass Hysteria, Bandwagon Effect, Groupthink and Herd Instinct have entered common parlance.

Whereas the concepts behind herd mentality and herd behaviour have a rich history (Table 1), the methods, techniques and approaches currently used to elucidate them are relatively recent. In this article we review the extensive range of theoretical frameworks for describing herding. Similar ideas and explanations have emerged in many fields, albeit with different emphases, demonstrating the interdisciplinary nature of the concept. We propose a framework with which to organize these diverse approaches, which is based on a distinction between the mechanisms of transmission of a particular thought between individuals and the patterns of connections between individuals. We also distinguish between two main types of transmission: automatic contagion and rational deliberation. We suggest that cognitive neuroscience can reveal the mechanisms underlying the transmission of information, which can in turn help elucidate patterns of herd behaviour.