Perception is not the passive receipt of these signals, but is shaped by learning, memory, expectation, and attention.
Perception involves these "top-down" effects as well as the "bottom-up" process of processing sensory input.[4] The "bottom-up" processing transforms low-level information to higher-level information (e.g., extracts shapes for object recognition). The "top-down" processing refers to a person's concept and expectations (knowledge), and selective mechanisms (attention) that influence perception