can you explain how this applies to perception
The schema you have for a situation will affect how you interpret the sensory inputs you receive. If your schema is that teachers are mean, you’ll be more likely to interpret a student crying when talking to a teacher as the teacher having chewed the student out. There might be other interpretations. That one will most likely occur to you first.
Schemas are how you organize concepts in your head. It can include a list of general characteristics about a concept. For example, we might hear a sound in the middle of the night. Since we are primed with horror movies, most of us have a schema that includes “night noises equals impending doom.”