Social and socio-
Ontogeny and symbolism
The origins of language and thought in early childhood
The classical theories of the relation between language and thought in developmental psychology are those of Piaget and Vygotsky. Piaget's claim is that language depends on thought for its development, and is based on four sources of evidence: the period of infancy, in which fundamental principles of thought are exhibited well before language; the simultaneous emergence of language, deferred imitation, symbolic play, evocative memory, and mental imagery, suggesting language is but one outcome of more fundamental changes in cognitive abilities; the lack of effect of language upon reasoning abilities in middle childhood; and the nature of speech in early childhood, the claim being that the communicative function of speech results from cognitive developments. By contrast Vygotsky, while seeing thought and language as initially separate systems, considers the two merge at around two years of age, producing verbal thought. Mental operations are regarded as embodied in the structure of language, and hence cognitive development results from an internalization of language.
Current research on infancy has elucidated the perceptual and social sophistication of the neonate, and points to developments occurring from this base during the course of adult-infant social interchanges. Preverbal gestural communication is established between six and nine months, and by twelve months is under intentional control. The shift to referential communication is again mediated by social interaction, particularly the development of routines to bring about the joint attention of adult and infant upon the same object þ especially the production and mutual comprehension of manual pointing. In addition, underlying changes in the infant's abilities to relate 'parts' to 'wholes' and to construct relations between means and ends appear to inform the elaboration of the simultaneously emerging cognitive abilities noted by Piaget. This suggests that the entire symbolic function is a separate cognitive domain to which wider cognitive abilities may be applied.
For older children the influence of language on thought has proved difficult to investigate conclusively. Evidence for the Whorfian hypothesis is scarce, and is incomplete for the claim that language plays a major role in the developing self-regulation of the child's behaviour.
Previously, this material has been used somewhat uncritically
to inform phylogenetic speculation on the role of language in
the evolution of human cognitive abilities. Recapitulatory
theories of 'terminal addition' have overlooked the
possibility that behavioural development may not occur in
stages, and that such stages may not be additive; 'neotenous'
theories do not deal satisfactorily with how a rearrangement
of the timing of abilities can lead to 'qualitative' changes
in 'behavioural capacities'. Recent work explains parallels
in ontogeny and phylogeny by appeal to common constraints on
information-processing that reflect the demands of changing
levels of the structure of knowledge as it interacts with more
basic perceptual competencies [Eds].