1. Object relations, dependency, and attachment;Ainsworth;Child Develpm.,1969
2. The development of the smiling response in early infancy;Ambrose,1961
3. Beebe, A. B. A. (1973), Ontogeny of positive affect in the third and fourth months of the life of one infant. Doctoral Thesis. Teachers College, Columbia University.
4. Conflict, Arousal, and Curiosity;Berlyne,1960