Online Social Networks

Human Cognitive Constraints in Facebook and Twitter Personal Graphs

Valerio Arnaboldi, Andrea Passarella, Marco Conti, Robin I.M. Dunbar

• Publisher: Elsevier
• Year: 2015
• ISBN:
  9780128030424
• Topic: Computer Science
• Subtopic: Computer Science General
• Index: Computer Science

Online Social Networks: Human Cognitive Constraints in Facebook and Twitter provides new insights into the structural properties of personal online social networks and the mechanisms underpinning human online social behavior.

As the availability of digital communication data generated by social media is revolutionizing the field of social networks analysis, the text discusses the use of large- scale datasets to study the structural properties of online ego networks, to compare them with the properties of general human social networks, and to highlight additional properties.

Users will find the data collected and conclusions drawn useful during design or research service initiatives that involve online and mobile social network environments.

• Provides an analysis of the structural properties of ego networks in online social networks
• Presents quantitative evidence of the Dunbar's number in online environments
• Discusses original structural and dynamic properties of human social network through OSN analysis

Chapter 1

Introduction

Abstract

In this chapter, we introduce the concept of ‘social network’, and we provide an intuitive and sharp distinction between ‘offline’ and ‘online’ social networks. Then, we describe the main features of Facebook and Twitter, the two online social networks (OSNs) discussed in this book. We show how they are actively contributing to the cyber-physical world convergence, and we motivate the need of novel analyses on the structural properties of OSNs. These are important for understanding human social behaviour in general, and for the creation of novel online social networking platforms that are more centred on human social needs. In particular, the analysis of personal social networks of individuals (called ‘ego networks’) in OSNs can tell us the extent to which the use of social media is impacting on the capacity of humans to socialise. We introduce the main results found for offline social networks, which indicate that the structural properties of ego networks are determined by the constrained nature of the brain, according to the social brain hypothesis. Then, we present the aim and structure of the book, which is to provide an extensive discussion about the structural properties of ego networks in Facebook and Twitter, and to assess the effects of cognitive limits of the human brain on OSNs.

Keywords

Online and offline social networks

Facebook

Twitter

Cyber-physical world

Social brain hypothesis

1.1 Offline and Online Social Networks

In its classical definition, a ‘social network’ represents a social structure containing a set of actors and a set of dyadic ties identifying social relationships existing between these actors in the considered social context (e.g. a workplace, a country, the scientific community) [1]. Social network analysis is aimed at understanding social phenomena arising in the contexts in question (e.g. the circulation of new ideas in a workplace, the spread of diseases or the creation of collaborations among scientists) by looking at structural properties of these networks.

The recent advent of social media, like Facebook and Twitter, is creating new opportunities for the analysis of social networks. In fact, some social media are now so widely used that they can represent a large portion of an individual’s entire social world, and their analysis could therefore provide new insights into our social behaviour. In contrast to more traditional means of communication (such as face-to-face interaction or communication by phone), social media are gradually generating a completely new ‘online’ social environment, where social relationships do not necessarily map pre-existing relationships established face-to-face, but can also be created and maintained only in the virtual world. To highlight the differences between these social environments, we define ‘online’ social networks (hereinafter OSNs) as the social networks formed of users of specific social media and the social links existing between them, and ‘offline’ social networks as all the other social networks not mediated by the use of social media (e.g. networks formed through face-to-face interactions and phone calls). Our definition of OSNs emphasises the capacity that social media offer for projecting ourselves in the virtual world of online communications, something that other communication services are not able to do. This distinction between ‘online’ and ‘offline’ social networks will be extensively used in this book to analyse and discuss the differences between the social environments they embody.

Facebook and Twitter surely represent nowadays the most important and the largest OSNs in the world, and they will be the main subject of discussion in this book. For the readers who are less familiar with them, we give a brief description of their main features, introducing the terms that we shall encounter in the rest of the book.

Facebook is the most used online social networking service in the world, with more than 1.3 billion monthly active users as of the first quarter of 2015 [2]. It was founded in 2004 and is open to everyone over 13 years old. Facebook provides several features for social interaction. Users have a profile which reports their personal information, and can be customised. Connected to their profile, users have a special message board called wall, which reports all the status messages they create (status updates) as well as messages received from other users (posts). Posts can contain multimedia information such as pictures, URLs and videos. Users can comment on posts to create discussions with other users or to add information to them. To be able to communicate with another user (e.g. writing posts on her wall and commenting on her posts or photos), a user must obtain her friendship. A friendship is a bi-directional relation that requires the acceptance of the involved users. Users can visualise a summary of the activity of their friends through a special page called a news feed. This page presents real-time notifications describing the activities performed by friends, including posts and the comments they create, photos they add, etc. Direct communication between Facebook users is provided through posts, which can be written on the wall of other users. Posts can also contain references to multiple users. Private communications are provided by a chat called messenger. Facebook also provides other mechanisms to communicate online, such as voice and video calls. A widely used feature of Facebook is the like button, which allows people to express their favourable opinion about contents (e.g. posts, pictures).

Twitter is an online social networking and microblogging service founded in 2006, with roughly 300 million monthly active users as of the second quarter of 2014 [3]. In Twitter, users can post short messages (with at most 140 characters) called tweets. Users can automatically receive notifications of new tweets created by other users by ‘following’ them (i.e. creating a subscription to their notifications). People following a user are called her followers, whilst the set of people followed by the user are her friends.

Tweets can be enriched with multimedia content (i.e. URLs, videos and pictures) and by some special marks. Specifically, a tweet can reference one or more users with a special mark called a mention. Users mentioned in a tweet automatically receive a notification, even though they are not followers of the tweet’s author. Users can also reply to tweets. In this case, a tweet is generated with an implicit mention to the author of the replied tweet.

In Twitter, users can retweet tweets, or, in other words, forward tweets to all their followers. Each tweet can be assigned to a topic through the use of a special character called hashtag (i.e. ‘#’) placed before the text indicating the topic. Hashtags are used by Twitter to classify the tweets and to obtain trending topics, which can be visualised and searched for through a special page. A trending topic is a word, phrase or topic that begins to be mentioned at unusually high frequencies.

1.2 OSNs in the Cyber-Physical Convergence Scenario

Without any doubt, OSNs, like Facebook and Twitter, have deeply changed the way people interact with each other, from teenagers to older folks. Perhaps more surprisingly, the cultural change they have enacted is going far beyond a simple mutation in the way we express ourselves and communicate. Every action which involves a social interaction can now be done through OSNs, such as looking for a new job, advertising something, or organising events, just to mention a few examples. In addition, we have access to OSNs potentially from everywhere, and all the time, thanks to the smart mobile devices in our pockets.

The use of mobile and pervasive devices is affecting the development of our ecosystems, by constantly interlinking the cyber and the physical realities in which we are immersed. Information related to the physical world is captured through mobile devices, and then transferred to the cyber world, affecting the state of virtual applications and services, which, in turn, can modify or adapt the physical world around us through actuators. This is contributing to a gradual convergence toward a cyber-physical world (CPW) [4]. This convergence is paving the way for the creation of innovative applications, which, by exploiting the physical and the social contexts of their users, can improve services in the cyber world.

In a converged CPW, physical events and actions affecting the personal and social spheres of users influence the way information is handled in the cyber world. Humans are at the core of this process, as, through the use of smart devices, they capture aspects of physical events by creating content (e.g. pictures, videos, text) and transferring them to the cyber world. Social media provide a powerful way of performing these actions, supporting a user-centric communication paradigm whereby people actively contribute to the creation and diffusion of information, influenced by the social structures that exist in our society. This places OSNs at the core of the CPW scenario. The analysis of OSNs is important for two main reasons. On the one hand, it is useful for understanding human social behaviour in a new virtual environment, and the social phenomena arising in this environment. On the other hand, it can help to create new human-centric services and applications which exploit the knowledge acquired from the study of OSNs.

As an example of how the study of OSN structures can be useful for understanding online social phenomena, we can consider the impact that OSNs are already having on information diffusion. Studies conducted hitherto on the global structure of OSNs indicate that they show typical properties of ‘small-world networks’, with short average distance between users, and high clustering coefficient. Moreover, OSNs show long-tailed distributions of the number of social connections per user (i.e. most people regularly contact only a few individuals, but a small number of people have a very large number of contacts). In addition, almost every user is reachable from all the other parts of the network, thus forming a connected ‘giant component’. This results in a very favourable condition for the diffusion of information, and is placing OSNs amongst the preferred communication channels for advertising, rapidly replacing traditional means such as the television and the radio. Despite these results, designing human-centred services by exploiting OSN structural properties is still in its infancy, and many more areas can be foreseen where this approach will be exploited.

In addition, from the standpoint of OSN analysis, significant effort has been put to analyse global properties of OSNs (which we shall describe in more detail in the rest of the book). However, from the standpoint of individuals, we still do not have a clear view of the effects of the use of OSNs on the structure of our personal social networks, and on our capacity for handling social relationships. Undoubtedly, OSNs are powerful means in that they allow us to connect, for example, with old classmates, or friends from overseas – individuals whom it would be too expensive to contact using other more conventional communication means. What is more difficult to assess is whether OSNs are also improving our social capacity, perhaps by increasing the total number of relationships we can actively maintain. It could be that OSNs simply represent another tool for maintaining our social relationships, one that is certainly very useful but perhaps not able to deeply alter the structure of our social system, due to cognitive or other constraints on our behaviour. A natural starting point, then, for the investigation of this is the analysis of the structural properties of personal social networks of OSN users, called egocentric networks or simply ego networks.

1.3 Ego Networks Analysis and the Social Brain Hypothesis

Ego networks govern the relationships between a user (ego) and her social peers (alters) and are therefore one of the fundamental building blocks that determine social behaviour in any type of human social network. In offline environments (outside OSNs), it has been found that the structural properties of ego networks are highly constrained. Specifically, our social capacity is bounded by a combination of the size of the human brain and of the limited time that can be allocated for the management of social relationships. These findings constit...