The component of the healthy personality that is the first to develop is the sense of the trust. The crucial time for its emergence is the first year of life. As with other personality components, the sense of trust is not something that develops independent of other manifestations of growth. It is not that infants learn how to use their bodies for purposeful movement, learn to recognize people and objects around them, and also develop a sense of trust. Rather, the concept 'sense of trust' is a shortcut expression intended to convey the characteristic flavor of all the child's satisfying experiences at this early age. Or, to say it another way, this psychological formulation serves to condense, summarize, and synthesize the most important underlying changes, which give meaning to the infant's concrete and diversified experience. Trust can exist only in relation to something. Consequently, a sense of trust cannot develop until infants are old enough to be aware of objects and persons and to have some feeling that they are separate individuals. At about 3 months of age, babies are likely to smile, if somebody comes close and talks to them. This shows that they are aware of the approach of the other person, that pleasurable sensations are aroused. If, however, the person moves too quickly or speaks too sharply, these babies may look and cry. They will not 'trust' the unusual situation but will have a feeling of uneasiness, of mistrust, instead. Experience connected with feeding are a prime source for the development of trust. At around 4 months of age, a hungry baby will grow quiet and show signs of pleasure at the sound of an approaching footstep, anticipating (trusting) that he or she will be held and fed. This repeated experience of being hungry, seeing food, receiving food, and feeling relieved and comforted assures the baby that the world is a dependable place. Later experiences, starting at around 5 months of age, add another dimension to the sense of trust. Though endless repetitions of attempts to grasp for and hold objects, most babies are finally successful in controlling and adapting their movements in such a way as to reach their goal. Through these and other feats of muscular coordination, babies are gradually able to trust their own bodies to do their bidding. Studies of mentally-ill individuals and observations of infants who have been grossly deprived of affection suggest that trust is an early-formed and important element in the healthy personality. Psychiatrists find again and again that the most serious illnesses occur in patients who have been sorely neglected or abused or otherwise deprived of love in infancy. Similarly, it is a common finding of psychological and social investigators that individuals diagnosed as 'psychopathic personalities' were so unloved in infancy that they have no reason to trust the human race and therefore, no feeling of responsibility toward their fellow human beings. What dose 'this psychological formulation' (Paragraph 1) refer to?