First-language acquisition of morphology refers to the process whereby native speakers gain full and automatic command of the inflectional and derivational machinery of their mother tongue. Despite language diversity, evidence shows that morphological acquisition follows a shared path in development in evolving from semantically and structurally simplex and non-productive to more complex and productive. The emergence and consolidation of the central morphological systems in a language typically take place between the ages of two and six years, while mature command of all systems and subsystems can take up to 10 more years, and is mediated by the consolidation of literacy skills. Morphological learning in both inflection and derivation is always interwoven with lexical growth, and derivational acquisition is highly dependent on the development of a large and coherent lexicon. Three critical factors platform the acquisition of morphology. One factor is the input patterns in the ambient language, including various types of frequency. Input provides the context for children to pay attention to morphological markers as meaningful cues to caregivers’ intentions in interactive sociopragmatic settings of joint attention. A second factor is language typology, given that languages differ in the amount of word-internal information they package in words. The “typological impact” in morphology directs children to the ways pertinent conceptual and structural information is encoded in morphological structures. It is thus responsible for great differences among languages in the timing and pace of learning morphological categories such as passive verbs. Finally, development itself is a central mechanism that drives morphological acquisition from emergence to productivity in three senses: as the filtering device that enables the break into the morphological system, in providing the span of time necessary for the consolidation of morphological systems in children, and in hosting the cognitive changes that usher in mature morphological systems in both speech and writing in adolescents and adults.
A fundamental question in epistemological philosophy is whether reason may be based on a priori knowledge—that is, knowledge that precedes and which is independent of experience. In modern science, the concept of innateness has been associated with particular behaviors and types of knowledge, which supposedly have been present in the organism since birth (in fact, since fertilization)—prior to any sensory experience with the environment. This line of investigation has been traditionally linked to two general types of qualities: the first consists of instinctive and inflexible reflexes, traits, and behaviors, which are apparent in survival, mating, and rearing activities. The other relates to language and cognition, with certain concepts, ideas, propositions, and particular ways of mental computation suggested to be part of one’s biological make-up. While both these types of innatism have a long history (e.g., debate by Plato and Descartes), some bias appears to exist in favor of claims for inherent behavioral traits, which are typically accepted when satisfactory empirical evidence is provided. One famous example is Lorenz’s demonstration of imprinting, a natural phenomenon that obeys a predetermined mechanism and schedule (incubator-hatched goslings imprinted on Lorenz’s boots, the first moving object they encountered). Likewise, there seems to be little controversy in regard to predetermined ways of organizing sensory information, as is the case with the detection and classification of shapes and colors by the mind. In contrast, the idea that certain types of abstract knowledge may be part of an organism’s biological endowment (i.e., not learned) is typically met with a greater sense of skepticism. The most influential and controversial claim for such innate knowledge in modern science is Chomsky’s nativist theory of Universal Grammar in language, which aims to define the extent to which human languages can vary; and the famous Argument from the Poverty of the Stimulus. The main Chomskyan hypothesis is that all human beings share a preprogrammed linguistic infrastructure consisting of a finite set of general principles, which can generate (through combination or transformation) an infinite number of (only) grammatical sentences. Thus, the innate grammatical system constrains and structures the acquisition and use of all natural languages.
Connectionism is an important theoretical framework for the study of human cognition and behavior. Also known as Parallel Distributed Processing (PDP) or Artificial Neural Networks (ANN), connectionism advocates that learning, representation, and processing of information in mind are parallel, distributed, and interactive in nature. It argues for the emergence of human cognition as the outcome of large networks of interactive processing units operating simultaneously. Inspired by findings from neural science and artificial intelligence, connectionism is a powerful computational tool, and it has had profound impact on many areas of research, including linguistics. Since the beginning of connectionism, many connectionist models have been developed to account for a wide range of important linguistic phenomena observed in monolingual research, such as speech perception, speech production, semantic representation, and early lexical development in children. Recently, the application of connectionism to bilingual research has also gathered momentum. Connectionist models are often precise in the specification of modeling parameters and flexible in the manipulation of relevant variables in the model to address relevant theoretical questions, therefore they can provide significant advantages in testing mechanisms underlying language processes.