What do you mean by bottom-up and top-down processing in perception? How do you understand it?

It refers to the experience, expectation and motivation acquired by the perceiver, which guides the information selection, integration and representation construction of the perceiver in the process of perception, and is also called constructive perception theory.

According to cognitive psychology, perception is a process of determining the meaning of the stimuli people receive. Perception depends on two different forms of information, namely, information from the environment and information from the perceiver himself. The so-called information of the perceiver himself refers to the existing knowledge and concepts of the perceiver, and the top-down processing process is the process of processing the current information by using the existing knowledge and concepts when people are engaged in perceptual activities. For example, imagine that people want to perceive a graph similar to "13" if it appears in "12, 13, I4". If it appears in the series "A, 13, c", people will use their knowledge about English letters in their minds to perceive it as the English letter "B".