2 480 Responds to human voice, cooing, and vocalizes pleasure. 4 580 Vocal play. Eagerness and displeasure expressed vocally. 6 660 Imitates sounds. 9 770 First word. 11 850 Imitates syllables and words. Second word. 13 930 Vocabulary expands rapidly. 17 1,030 Names objects and pictures. 21 1,060 Combines words in speech. 23 1,070 Uses pronouns, understands prepositions, uses phrases and sentences. [7]Lilly, John C. _Man and Dolphin: A Developing Relationship_. London: Victor Gollancz, 1962. [8]Boston Children’s Hospital data from 1,198 records, in Coppoletta, J.M., and Wolbach, S.B., “Body Length and Organ Weights of Infants and Children,” _American Journal of Pathology_, IX (1933), 55-70. [9]Summarized from McCarthy, Dorothea, “Language Development in Children,” in Carmichael, Leonard, ed., _Manual of Child Psychology_. New York: John Wiley, 1946, pp. 476-581. Table 1 shows relations between age, brain weight, and speech performance, up to 23 months, 1070 grams, and the use of full sentences. By 17 years, the brain reaches and levels off at 1450 grams and the number of words, levels of abstraction, etc., are so large as to be difficult to assess. In these processes, what are the minimum necessary but not necessarily sufficient factors?[20] On the biological side, modern theory concentrates on two factors: total numbers of neurons and the number of interconnections between them. On the psychological side, modern theory concentrates on the numbers of occurrences of reinforced contingencies experienced, the number of repetitions, and the number of adequate presentations from the accepted set of the consensus known as “native language,” and the total numbers of sets in the stored memories at a given age. In addition, of course, is the adequate development of the transmitting and of the receiving equipment needed for speech and its ancillary behaviors.