A substantial portion of the professional and popular literature on the psychological problems of children and adolescents is devoted to family influences and to ways in which families can help their sons and daughters in distress. The famous nature-versus-nurture debate usually entails pitting family causation against genetics. However, “nurture” is not provided exclusively by parents. This chapter begins with a discussion of the relatively small professional literature in which family and peer influences are compared. The subsequent section is devoted to the basic characteristics and inherent features of relationships with peers and peer influence. A section on the distinction between close friendships and less intimate relationships with peer-group members follows. The dynamics of peer influence, an often-maligned phenomenon, are discussed next: Are peer-relations problems just a sign of general malfunctioning, a cause (or the cause) of the problem, or a mechanism through which problems can improve or worsen? Interventions designed to improve the peer relations of children and adolescents at risk for psychopathology are considered next. The chapter continues with a section on the much understudied role of the peers who typically live at home: one’s siblings. A brief plea that interpersonal relationships be given greater weight in the basic understanding of psychopathology than in most contemporary thinking appears at the end of the chapter.

Peer and family influences – separately and in combination

The idea of an anti-social peer group negating the benefits of a warm, supportive family upbringing is undoubtedly the most familiar connotation of the concept of peer influence. However, as noted in the previous chapter, it is probably much more common for the families and peers of an individual to match each other in terms of supportiveness, warmth and enjoyable interaction. Peers are also more likely to affirm the authority of parents than to undermine it (Clasen and Brown, 1985). Satisfying bonds with parents are likely to co-occur with satisfying relationships with friends and peers. One obvious reason for this is that attachment theory, also discussed in the previous chapter, is in fact reflected in research results: Children and adolescents who experienced warm, trusting and secure bonds with their caregivers tend to end up with the ability to relate intimately to peers, especially close friends (Schneider et al., 2001). As well, the interests, characteristics and social skills that emerge from effective, authoritative parenting may be applied by children to their own interchanges with peers (Brown and Mounts, 2007).

Eating disorders are among the most heart-rending of the psychological disorders of young people. As will be explained in this chapter, eating disorders have been attributed to the evils of modern Western society although, as with most other disorders, genetics, family upbringing and peer pressure are important correlates if not causes. What many see as an epidemic affecting adolescent females has been blamed on the pervasive emphasis on thinness, the breakdown of traditional, orderly thinking patterns as well as changes in the traditional roles of women (e.g., Nasser, Katzman and Gordon, 2001). Eating disorders are complex and often misunderstood. They tend to provoke emotional reactions ranging from bewilderment to fear to mistrust because many people cannot understand why a young person would not comply with the fundamental human need to eat or would assign so much importance to personal appearance that it ruins his or her life (Stein, Latzer and Merick, 2009).

In Western countries, mass media portray thinness as an ideal to impressionable young women (see meta-analysis by Groesz, Levine and Murnen, 2002). Young men are bombarded with media images emphasizing a muscular appearance (Agliata and Tantleff-Dunn, 2004). In parallel, “fast food” enterprises are increasingly “supersizing” the food they serve, contributing to a parallel epidemic of obesity among young people male and female. Although the pressures of modern society are often implicated in the probable increase in eating disorders in recent years, case studies indicate that these disorders were of concern even in ancient times. Parry-Jones and Parry-Jones (1991), in a historical account of the emergence of the phenomenon now known as bulimia nervosa, cite the case of Matthew Dakin, which was reported in medical journals in 1745. Matthew was a previously healthy 10-year-old from Black Barnsley, Yorkshire, England who, after an illness of unknown origin, began to display alternations of voracious eating and vomiting. He died, emaciated, shortly after.

At what point does substance use become substance abuse and at what point does substance abuse become substance use disorder (the term chosen by the DSM-5 Commission to replace the DSM-IV category of substance abuse disorder)? Almost every disorder could be conceptualized as the extreme of a continuum of problematic behavior rather than a discrete entity, as discussed in Chapter 3. This applies very clearly to substance use disorder, which in the DSM and ICD systems represents substance abuse that exceeds a certain degree of experimentation with dangerous substances. This brief chapter begins with information about the diagnostic criteria for substance abuse disorder, followed by data on its prevalence. The section that follows is devoted to the very substantial literature on the factors that make children and youth susceptible to substance abuse problems and the processes involved. Causes and correlates are discussed next, followed by a section on prevention and treatment.

Diagnostic criteria

There have been repeated arguments that the DSM-IV criteria for substance abuse disorder were developed with adults in mind and are not really applicable to children (Martin et al., 1995; Chung and Martin, 2005). Box 21.1 illustrates how this issue has been tackled by the DSM-5 Commission. As shown, the diagnostic criteria in DSM-IV and DSM-5 are based on the same concepts. However, there has been considerable fine tuning of the specific diagnostic criteria. Hopefully, research results will confirm over the next few years the predictive validity of the new DSM-5 criteria.

Scholars of several disciplines use different terms to refer to children’s psychological problems. The quest for a global descriptor that is accurate and that avoids stigma has so far been unsuccessful. In fact, there is probably not even a euphemism that enables its users to avoid debatable analogies and connotations that they would probably prefer not to evoke. This chapter is devoted to definitional issues, starting with the definitions of pathology and disease. Problems with all of the terms in common use to describe children’s and adolescents’ psychological problems are highlighted. Many of the issues raised in this chapter recur in subsequent chapters on the classification of mental illness and the physiological basis of child and adolescent psychopathology. Estimates of the total prevalence of psychopathology appear near the end of the chapter, followed by remarks about the notion of recovery in the context of mental illness.

Pathology; disease

Although the concepts of mental illness and disease have existed since ancient times, it is only in the past 200 years that coherent attempts have been made to differentiate transitory problems associated with the stressful experiences suffered by most people from full-blown conditions that merit more enduring concern and professional care. The German psychiatrist, Karl Kahlbaum, renowned in his own time but almost unknown since, is credited with introducing, in 1863, the idea that the concept of mental illness should include the course of the illness, its effect on the individual’s psychological well-being, the developmental stage at which it occurred and any accompanying conditions to which it might be secondary. Kahlbaum also applied these ideas to the study of children’s mental disorders, especially early forms of psychosis (Kahlbaum and Berrios, 2007; Millon, Grossman and Meagher, 2004). His delineation of mental illness and health, with considerable refinement, has become an integral part of mainstream thinking about child psychopathology.

Of the major psychological disorders that affect children and adolescents, autism is probably the one that remains the most shrouded in mystery. Is there any meaning to the stereotyped movements and idiosyncratic verbalizations of children with autism? Is their avoidance of social contact caused by any aspect of their environment? Is there a reason why the prevalence of autism seems to be increasing? And, most importantly, can children with autism be helped, and, if they can, how?

This chapter begins with a capsule historical sketch in which the emergence of the contemporary concept of autism is traced. Diagnostic criteria are presented next, including a discussion of the recent elimination of the category of Asperger’s syndrome in DSM-5. The apparent increase in the prevalence of autism in recent years is discussed next, together with controversial recent data about the stability of the disorder. The likely causes and features of the disorder are the focus in the following section, which includes both causal factors that are endorsed by contemporary research and some of those that are interesting museum pieces. Early signs of autism spectrum disorder are also presented in the section on causes and correlates. The chapter closes with the increasingly optimistic (or, better said, increasingly less pessimistic) story of the treatments that have been developed and evaluated.

This textbook provides an introduction to the conceptual underpinnings of communication technologies. Most of us directly experience such technologies daily: browsing (and audio/video streaming from) the Internet, sending/receiving emails, watching television, or carrying out a phone conversation. Many of these experiences occur on mobile devices that we carry around with us, so that we are always connected to the cyberworld of modern communication systems. In addition, there is a huge amount of machine-to-machine communication that we do not directly experience, but which is indispensable for the operation of modern society. This includes, for example, signaling between routers on the Internet, or between processors and memories on any computing device.

We define communication as the process of information transfer across space or time. Communication across space is something we have an intuitive understanding of: for example, radio waves carry our phone conversation between our cell phone and the nearest base station, and coaxial cables (or optical fiber, or radio waves from a satellite) deliver television from a remote location to our home. However, a moment's thought shows that that communication across time, or storage of information, is also an everyday experience, given our use of storage media such as compact discs (CDs), digital video discs (DVDs), hard drives, and memory sticks.

A communication link involves several stages of signal manipulation: the transmitter transforms the message into a signal that can be sent over a communication channel; the channel distorts the signal and adds noise to it; and the receiver processes the noisy received signal to extract the message. Thus, communication systems design must be based on a sound understanding of signals, and the systems that shape them. In this chapter, we discuss concepts and terminology from signals and systems, with a focus on how we plan to apply them in our discussion of communication systems. Much of this chapter is a review of concepts with which the reader might already be familiar from prior exposure to signals and systems. However, special attention should be paid to the discussion of baseband and passband signals and systems (Sections 2.7 and 2.8). This material, which is crucial for our purpose, is typically not emphasized in a first course on signals and systems. Additional material on the geometric relationship between signals is covered in later chapters, when we discuss digital communication.

Chapter plan

After a review of complex numbers and complex arithmetic in Section 2.1, we provide some examples of useful signals in Section 2.2. We then discuss LTI systems and convolution in Section 2.3. This is followed by Fourier series (Section 2.4) and the Fourier transform (Section 2.5).

Modulation is the process of encoding information into a signal that can be transmitted (or recorded) over a channel of interest. In analog modulation, a baseband message signal, such as speech, audio, or video, is directly transformed into a signal that can be transmitted over a designated channel, typically a passband radio-frequency (RF) channel. Digital modulation differs from this only in the following additional step: bits are encoded into baseband message signals, which are then transformed into passband signals to be transmitted. Thus, despite the relentless transition from digital to analog modulation, many of the techniques developed for analog communication systems remain important for the digital communication systems designer, and our goal in this chapter is to study an important subset of these techniques, using legacy analog communication systems as examples to reinforce concepts.

From Chapter 2, we know that a passband signal carries information in its complex envelope, and that the complex envelope can be represented either in terms of I and Q components or in terms of envelope and phase. We study two broad classes of techniques: amplitude modulation, in which the analog message signal appears directly in the I and/or Q components; and angle modulation, in which the analog message signal appears directly in the phase or in the instantaneous frequency (i.e., in the derivative of the phase) of the transmitted signal. Examples of analog communication in space include AM radio, FM radio, and broadcast television, as well as a variety of specialized radios.

Progress in telecommunications over the past two decades has been nothing short of revolutionary, with communications taken for granted in modern society to the same extent as electricity. There is therefore a persistent need for engineers who are well-versed in the principles of communication systems. These principles apply to communication between points in space, as well as communication between points in time (i.e., storage). Digital systems are fast replacing analog systems in both domains. This book has been written in response to the following core question: what is the basic material that an undergraduate student with an interest in communications should learn, in order to be well prepared for either industry or graduate school? For example, some institutions teach only digital communication, assuming that analog communication is dead or dying. Is that the right approach? From a purely pedagogical viewpoint, there are critical questions related to mathematical preparation: how much mathematics must a student learn to become well-versed in system design, what should be assumed as background, and at what point should the mathematics that is not in the background be introduced? Classically, students learn probability and random processes, and then tackle communication. This does not quite work today: students increasingly (and, I believe, rightly) question the applicability of the material they learn, and are less interested in abstraction for its own sake.

From the material in Chapters 4-6, we now have an understanding of commonly used modulation formats, noise models, and optimum demodulation for the AWGN channel model. Chapter 7 discusses channel coding strategies for these idealized models. In this final chapter, we discuss more sophisticated channel models, and the corresponding signal processing schemes required at the demodulator.

We first consider the following basic model for a dispersive channel: the transmitted signal passes through a linear time-invariant system, and is then corrupted by white Gaussian noise. The LTI model is broadly applicable to wireline channels, including copper wires, cable and fiber-optic communication (at least over shorter distances, over which fiber nonlinearities can be neglected), as well as to wireless channels with quasi-stationary transmitters and receivers. For wireless mobile channels, the LTI model is a good approximation over durations that are small compared with the time constants of mobility, but still fairly long on an electronic timescale (e.g., of the order of milliseconds). Methods for compensating for the effects of a dispersive channel are generically termed equalization. We introduce two common design approaches for this purpose.

The first approach is single-carrier modulation, which refers to the linear modulation schemes discussed in Chapter 4, where the symbol sequence modulates a transmit pulse occupying the entire available bandwidth. We discuss linear zero forcing (ZF) and minimum mean-squared error (MMSE) equalization techniques, which are suboptimal from the point of view of minimizing error probability, but are intuitively appealing and less computationally complex than optimum equalization.