Behavioural psychology is the scientific field focused on explaining and predicting behaviour. In particular, cognitive psychology and developmental psychology aim at explaining mental processes in humans and how they change over time.
For language both disciplines describe processing and acquisition in light of human interaction and observable stimuli as well as effects. Developmental psy-chology is particularly important, because it studies the socio-cultural principles shaping the language acquisition13. Central findings are the phases of language development all children undergo consistently14 and the impact the environment as well at the caregiver – or more precisely the language teacher – have. Cognitive psychology studies mental mechanisms and principles in perception and production.
Especially findings on the learners body-centric modelling as well as on statistical characteristics of feedback are of particular importance.
Children’s Development in Natural Language
For language acquisition the first year after birth is most crucial. In contrast to other mammals the human child15 is not born mobile and matured, but develops capabilities and competencies postnatal [145]. The development of linguistic com-petence occurs in parallel – and highly interwoven – with the cognitive development of other capabilities such as multi-modal perception, attention, motion control, and reasoning, while the brain matures and wires various regions [78, 145]. In this process of individual learning the child undergoes several phases of linguistic comprehension and production competence, ranging from simple phonetic discrimination up to complex narrative skills [106, 145]:
• Prenatal: auditory system gets tuned to the mother’s voice and its phonetics (vowels).
• 0 – 5 months: perception of sounds, rhythm and prosody; production of reactive sounds and imitation of vowels.
• 5 – 9 months: inter-modal perception; canonical babbling, imitation of inton-ation, and production of vowels.
• 9 – 12 months: perception organised toward a phonological structure (map in A1 [231]) and segmentation and comprehension of words; production of first words; also pointing and iconic gestures are used as a pre-lingual method to express desires before the correct vocalisation is acquired.
• 12 – 16 months: comprehension with a corpus around 100 to 150 words and simple holo-phrases; production of around 20 to 30 words to name or request objects or actions.
13Or as discussed above, more preciselyenable the acquisition in the first place.
14Individual variability and underlying factors can be determined reasonably fine-grained [55].
15As a convention we use “child” to refer to a language learner of any age ranging over new-born baby, infant, toddler, and preschooler.
• 16 – 20 months: establishment of the comprehension of word categories;
production of two word combinations and undergoes a vocabulary spurt.
• 20 – 24 months: comprehension of word relations and word order; reorganise phonological production.
• 24 – 36 months: comprehension of complex sentences and inference of gram-matical rules for own production.
• 35+ months: start comprehension of metalanguage; syntax and morphology tuned in production.
During this development the child is exposed to steady streams of perceptual-cognitive information from the environment and its interaction with it. This can include both the perception of physical entities in the environment as well as a stream of spoken natural language for describing it and leads to the association of a sequence of sounds with that entity – a preposition for reference.
Smith and Yu showed that infants can indeed deal with an infinite number of possible referents in learning the first words by means of rapidly evaluating the statistical co-occurrences of words and scenes [265]. They revealed in their study that 12 – 14 month old infants can solve the uncertainty16across several trials with many words and many referents (e.g. objects). The authors claim that the learners actual make use of the complexity of the natural environments in terms of tracking multiple word-referent co-occurrences and their underlying regularities.
Psycholinguistics found a number of further critical principles working in lan-guage acquisition, including segmentation, body-relationality17 and social cognition [41, 106].
Segmentation: From Sounds to Utterances
The principle of segmentation is found very early in children’s development, as the new-borns are believed to instantly learn to segment vocals within the melodies of the mother’s speech [145]. With more clear evidence Saffran et al. found that infants in fact are able to learn language statistically [243, 244]. In their studies they showed that 8-month infants can learn to segment words solely based on the frequency of co-occurring syllables within continuous streams of speech that contained no further information on word boundaries like pauses or other acoustic or prosodic cues. Tenenbaum and Xu suggested that the early word learning follows the Bayesian inference principle [279]. In their study they proposed that correct word-referent mappings can develop fast by formulating and evaluating of hypotheses. For example, a wrong hypothesis formed in a first learning step could be corrected in a second learning step (again in an ambiguous scene) thus providing dis-confirming evidence. As a result this means that children can learn to segment words mostly by the usage. In this way they also learn novel words by exploiting highly familiar adjoining words.
16Originally referred to asindeterminacy problem in deriving meaning.
17Smith and Gasser originally named it the embodiment principle [264], but the definition for embodiment as given above is much more specific and central to this thesis.
Body-rationality: The Egocentric View on the World
As discussed earlier, the human intelligence in general and language competence in particular is strongly driven by the rational integration of the body in the environment. Sixty years ago Piaget suggested that any representations, which children might form, should have developed through sensorimotor level environ-mental interactions accompanied by goal-directed actions [216]. According to Smith and Gasser the physical world indeed contains rich regularities that constrain the human brain in perceiving and acting [264]. In developmental studies18 they found that knowledge can be realised by the body in a way that relative links to entities in the environment are available. In turn the knowledge can be stored and obtained just by the relation of aspects of the body to the link. For example linking objects to locations (and thus by a specific perception for that relative location) and linking events to the location and thus the object is sufficient to bind objects and predicates.
In fact, Smith and Gasser claim that the embodiment is the necessary precondition for building up higher thoughts.
Social Cognition: Language Learning Through Interaction
As introduced in section 2.1.1 the development of language was only possible by interaction of a child with a developing brain and a teacher that provides digestible amounts of spoken language [280]. Tomasello calls this inter-subjectivity and claims that the human is not only building up thoughts by linking the body to the environment, but also developed an awareness for the body-rational view on the world of others. Humans developed a profound competence to respond to motives and interests behind motions of others including to support expressing them. Hayes and Ahrens found from large data collections of natural conversations between children and their mothers that the mother provides an age-dependent simplification of grammar and focuses on more common words [114]. The word choice is supposedly based on the context of the common conversations and meant to kept lexically undemanding. In particular, Grimm refers to the mother-child interaction as a didactic system accompanying the development phases [106]:
• 0 – 12 months, baby talk: exaggerated intonation, long pauses between phrases, and simple words to support prosody and phonology,
• 12 – 24 months, scaffolding: joint attention and introduction of specific words to support the vocabulary (e.g. by pointing and active labelling [112]),
• 24+ months, motherese: model-language and questionnaires to support gram-matical competence.
Overall this means that the postnatal development of the processes of thought together with an appropriate interaction of the teacher enables the acquisition of language.
18Studies included the Baldwin task, in which 24-month-old children name objects correctly, for which they learned the labels under the condition of visual occlusion, but specific location [264].