He was one of the first researchers who used direct observation of children as an experimental method, studying both healthy and unhealthy subjects.
Spitz coined the term "anaclitic depression" to refer to partial emotional deprivation (the loss of a loved object).
He found that the developmental imbalance caused by the unfavorable environmental conditions during the children's first year produces irreparable psychosomatic damage to normal infants.
[5] Another study of Spitz's showed that under favorable circumstances and adequate organization, a positive child development can be achieved.
[4] However, he still maintained in a comparison between orphanages and nursing homes that even if the former provided good food, hygienic living space, and medical care, the children raised in the former were more susceptible to infections and had higher death rate than the latter due to social deprivation.
Spitz noted three organizing principles in the psychological development of the child: 1) the smiling response, which appears at around three months old in the presence of an unspecified person 2) anxiety in the presence of a stranger, around the eighth month 3) semantic communication, in which the child learns how to be obstinate, which the psychoanalysts connect to the obsessional neurosis.