They're trying to achieve satisfaction through their mouth of a sort they didn't get in this very early stage of development.

他们想通过这种口腔运动,来获得本该在口腔期获得的满足感。

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So, for Piaget, the first stage is the sensorimotor stage or the sensorimotor period.

皮亚杰认为,第一个阶段,是感知运动阶段,或者说,感知运动期

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