Because they cannot verbalize or fill out questionnaires, indirect techniques of naturalistic observation are used as the primary means of determining what infants can see, hear, feel, and so forth.

由于婴儿不能用语言表达或填写调查问卷，自然观察法的间接技巧被用来作为判断他们能看到、听到、感觉到什么等等的主要手段。