Your perception of anything in this world is derived from your sensory data, and this is called the data-driven, or bottom-up, approach. You must view the world as it is, rather than as you expect it. However, in many situations, your knowledge or expectation may influence the way you perceive things. This is called the schema-driven, or top-down, approach, where schema means prior experienced, seen, or known pattern. Top-down theories involve a higher level of thought process. The recipient of the stimulus builds upon the stimulus using sensory as well as other sources of information, which is derived from the recipient’s prior knowledge or experience.
An important way in which knowledge contributes to perception is that you can identify objects even if the stimulus quality is degraded. For example, it is easy to identify a visual object even if part of the object is obstructed. An auditory example is a poor phone connection. As long as you know the topic of the conversation, you probably can figure out what the person on the other end of the phone is saying. You frequently encounter degraded stimuli, and your knowledge of the world helps you in your perception without the need to put in too much cognitive effort.
Real-time information from the sensory systems interacts with your knowledge of the world and enables you to perceive and interact with your environment.
Let’s now focus on vigilance and detection theory.
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Do I See What I See?
Have you ever thought about how you see and hear things? Has it occurred to you that what you perceive is actually what is in your environment? If it has, then you’re not alone.
This is a picture showing both an old woman and a young girl. If you were not aware of this fact about the picture (knowledge), would you have been able to guess it? After you read about the picture, were you able to see the two figures? We usually function so well in our world that perception seems flawless, seamless, and like a direct reflection of our environment. However, perception is influenced by many factors. Your knowledge and cognitive processes also affect perception. Ambiguous figures provide a good example of how knowledge affects perception. Once you know what to look for, you will be able to see it (which you could not see without prior knowledge).