The present work addresses the ability to acquire and make use of a language, an ability which is demonstrated by children throughout the world. The acquisition of language shows that children are endowed with a cognitive apparatus which is necessary for linguistic communication, and thereby for sustenance of the human species. Language is generally learned without noticeable efforts and without formal instruction. However, there are children who do not acquire language this easily and who are hampered with an impaired language years into adulthood. In Chaps. 2 and 8, I will discuss the diagnostic criteria, etiology and treatment of the language impairment of this group of children. In agreement with commonly used terminology, I shall exclude cases of recorded brain pathology, and instead refer to this disorder as developmental language impairment, in contrast to acquired language impairment or aphasia due to neural damage or brain disease.
The research literature recently published on developmental language impairments is considerable, and much of it will be reviewed in Chaps. 2 and 8. The other chapters will deal with aspects of language evolution which I think are relevant for a reevaluation of developmental language impairments. Many theories of the evolution of language do have implications for the way we deal with such impairments; however, these implications are rarely stated explicitly. At the same time, theories on developmental language impairment generally lack an evolutionary frame of reference.
The study of language evolutionāhow humans came to speak, use signs and writeāhas engaged researchers in a wide range of research fields, from cognitive neuroscience, linguistics and evolutionary anthropology to psychology and socio-linguistics. They all address, directly or indirectly, the problem of whether language emerged as a wholesale innovation, which made language unique in the natural world, or whether language evolved continuously as a reconfiguration of cognitive capacities that were present in the pre-human hominids. Also, cognitive capacities that evolved later in humans may have become integrated with evolutionary early capacities to form language in the modern era. The present work, which presents a new perspective on developmental language impairments, also addresses the different fields of expertise on language evolution and makes an attempt to integrate some influential research and discussion within these fields. In addition to the prehistory of language, speech and communication, I will also discuss language evolution in historical time since the invention of writing.
The literature reviews and discussions presented in this work were all selected and undertaken to provide a reevaluation of research on developmental language impairments, and in the long run to improve diagnostics and remedial treatment of such impairments. Let me therefore explain why a reconsideration of theories of evolution will also serve research on language impairments: If language did not evolve as a complete innovation (a position that lacks support from most researchers today), but rather as a continuous establishment of different linguistic capacities that are ultimately reconfigured to serve the use of language in contemporary societies, we will deal with evolutionary stages of linguistic competence, which are linked to different aspects of language and which may be selectively impaired in children. Some of these capacities evolved early, others belong to a later or recent epoch in the history of mankind. The selective impairments of capacities may correspond to different subgroups of language-impaired children, necessitating differentiated diagnostics and remedial treatment.
The prevalence of developmental language impairments in modern societies is considerable, yet disagreements exist about diagnoses as well as remedial treatment. I argue in this work that further progress of research on developmental language impairments can only be achieved by making use of new insights about the evolution of language, and therefore I aim to cover the combined field of evolution and development of language. I have therefore written this book hoping to improve and extend the theoretical basis for clinical work with language-impaired children.
In Chap. 2, I will explain why the major issues and controversies in the literature on language impairments may be, to a great extent, resolved when treated using the perspective of language evolution. The following chapters will deal with issues in theories of language evolution which have great relevance for an understanding of developmental language impairments. I will review and discuss a number of research works within a cognitive and neurobiological framework, and in Chap. 6 I will also discuss the growth of literacy since the invention of writing, which I think is also relevant for a renewed interpretation of developmental language impairment (see Sect. 1.5 below). Finally, in Chap. 8, I will summarize the implications of an evolutionary approach to the study of developmental language impairments, andāin agreement with the evolutionary perspectiveāI will survey important new methods of diagnostics and treatment.
Although the main aim of this book is an improved understanding of developmental language impairment, many of the following chapters will deal with general issues in studies of language evolution. The book does not aspire to be a comprehensive and up-to-date treatment of language evolution (for an expert introduction, see W. Tecumseh Fitch, The Evolution of Language, 2010); however, the following chapters need preparatory notes on (1) the concept of language and its subsystems, and (2) the conceptual framework of evolutionary biology.
1.1 Language and Its Subsystems
The Concept of Language
Many fields of research are involved in studies of language and language evolution. Thus it may be difficult to agree on a single definition of ālanguage.ā The multicomponent approach taken by Fitch indicates that language was considered to be a ācomplex system made up of several independent subsystems.ā Each of these subsystems has different functions, as demonstrated by the effects of brain lesions and the different maturation rates of language skills. However, no general agreement exists as to what, precisely, are the subsystems of language, and how are they organized in one complex system. Some subsystems are shared with other animals, others are not. Some are shared with other cognitive domains such as vision, procedural memory and music. To cast the net widely, Hauser, Chomsky, and Fitch (2002) introduced the term āFaculty of Language in a Broad senseā (FLB), which prevents any preconceptions as to whether or not some likely candidates of communicative mechanisms are actually part of language.
In linguistics and neurolinguistics, however, researchers have argued for more specific mechanisms that are both special to language and unique to humans. The definition of the āFaculty of Language in a Narrow senseā (FLN) presupposes an identification of such mechanisms or subsystems. Therefore, this type of definition is important, because, as indicated in the heading to this section, we shall shortly deal with the subcomponents of language. At the same time, it also raises a number of problems that will be explained below.
I consider the faculty of language to be an ability which evolved with humans, and this ability means that children are generally capable of learning and practicing the language of their caregivers. However, the ability is an abstraction from the specific expressions of language use. Therefore, language may also be considered as a learning potential that is present in the infant even when sensory and motor mechanisms are impaired. Thus, although we may consider the auditoryāvocal channel to be the default mode of linguistic communication, other channels of linguistic signaling and other equipotential means of articulation are generally available. In general, deaf and deaf/blind children have a potential for language that is realized on the premise of an adequate linguistic exposure in the environment (e.g., Helen Kellerās case). Therefore, the definition of the subsystems must not be modality-biased; rather, each of the subsystems will, in principle, apply across the sensory and motor modalities. (See Chap. 7 on language as a modality-independent capacity.)
Hockett (1960) suggested a list of ādesign features,ā also called ālanguage universals,ā wherein the features numbered 1ā5 referred to characteristics of speech, i.e., use of the auditoryāvocal channel. Later, contemporary researchers generally agreed that sign languages such as the American Sign Language (ASL), are well-structured languages on par with any spoken language; hence, the first five features in Hockettās list were no longer considered to be language universals. Feature 8 in Hockettās list says that meaning is arbitrarily related to the expressive form of signals (semanticity). An object may be labeled by signals of any modality, and therefore this feature may be said to invalidate the first features that involved speech only. In other words, a linguistic signal could be expressed in any modality, downplaying any role of iconicity. Bickerton (2014) described semanticity as displacement (the ability to talk about things which are not present here and now), rather than arbitrariness, thereby merging two different terms in Hockettās list. In this way, the concept of semanticity/ displacement also provided a link to mental time travels. Productivity/openness, the concept that an infinite number of sentences can be produced and understood, and duality of patterning, the concept that meaningless units can be combined to form meaningful utterances, were also emphasized as unique characteristics of human language. I shall have more to say about these features in other sections of the book.
The Subsystems of Language
I will make use of a general linguistic classification of the main subsystems of language, while emphasizing that each of them are aspects of a capacity abstracted from the modular expressions of particular linguistic responses. The classification presented here may be deemed a superficial one by linguistic researchers, and it may lack necessary descriptions of the interrelatedness of the described categories. However, it serves a preliminary and necessary reference for later discussions; hence, the following categories/subsystems will be addressed:
Signals
In contemporary linguistics, signals are generally considered parts of the phonological system, which means that at one level they are considered as meaningless segments that can be combined into larger meaningful strings (words), and these larger strings can also be combined into potentially meaningful utterances (see duality of patterning in Hockettās list of design features). This definition of signals, as parts of the phonological system, also means that they are treated as units in the perception of speech and can be further analyzed in terms of acoustic and phonetic subunits (phones). I find this link to phonology and phonetics unsatisfactory because other stimulus characteristics besides the vocal articulatory features may be included in the definition of signals in language (see Sect. 1.4.2 below).
Phonology
According to Fitch, phonology deals with āgenerative grammar level one,ā that is, the first level of description of the structure of language. The generative character of phonology is expressed in the principle of duality of patterning (see above). Thus, basic units such as the phoneme, are, by themselves, meaningless, but are defined by the way they signal distinctions of meaning. The phoneme may also be defined by a set of distinctive features such as voicing, nasality, manner and place of articulation. Jakobson and Halle (1971) defined a set of 12 articulatory defined features, most of which have survived in contemporary phonological theories. Meaningful units, such as morphemes and words, can be generated according to phonological rules, which are specific for each language. These rules also permit us to construct pseudo-words (nonwords), which may become words when systematically used to label new objects and actions. There are, however, phonotactic constraints for each language that define both the possible and impossible combinations of phonemes in each language.
Syntax
This is the next level at which we can describe the structure of a language. In general, syntax is said to deal with the combination of words into sentences; however, the lower level of syntactic structure are made up of morphemes, both bound and free-standing. The more general term āgrammarā includes both morphology and syntax. Thus, sometimes a distinction is mad...