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Lecture 2: Perceptual process

In this step, we will discuss the important ‘principle’ of perceptual processing and two mechanisms to explain how perception is shaped.
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The first important ‘principle’ about perceptual processing is that perception is subjective. It is not a ‘copy’ of the objective form of things in the world. For example, what we see is not like taking a video. What we see is the end-product of the process of integrating information. Now in the case of ‘Necker cue’, please try to ‘see’ it carefully, and then you would find that you can ‘perceive’ two different 3-dimensional configurations of the same cube. From the sensory level, this ‘cube’ consists of the same lines and angles. But subjectively, we can integrate or ‘reconstruct’ different experiences from it.
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Now you may feel it confusing: if everything is subjective, is possible that our perception changes all the time? This is definitely not what we experience in our daily life. For example, the following pictures show some combination of a black and a grey quadrilateral. But if I tell you they all represent the same door and doorway – closed, half-closed, and fully opened, you should feel no difficulty in perceiving this. We know these are the ‘same door’. That means our perception consists of our interpretation of the world. Even though the lines and angles of the three pictures are different, we can perceive the same thing constantly – what we see is the same door.
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Traditionally, psychologists have two mechanisms to explain how perception is shaped. Here let’s take visual perception as a sample. The first mechanism we call is ‘bottom-up processing’. Here ‘bottom’ means the information from the environment, and ‘up’ means our mind. In bottom-up processing, our perception is shaped by detecting the features of an object. For example, we know something is a ring because it looks a circular shape. However, not all the circular stuff is a ring. Some psychologists proposed that there is a ‘prototype’ of a ring or the standard form of a ring. And therefore when we try to find a ring from pieces of jewellery, we match what we see to such a ‘prototypic ring’.
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Perhaps these ‘prototypes’ are composed of more fundamental elements, which can be simplified as simple geometric components. For example, when we try to distinguish between a sedan and an SUV, we notice that the SUV lacks the trunk, i.e., more or less a cuboid region, compared to a sedan. But both cars have tires, which represents a disc-shaped component. All the theories highlight the importance of detecting spatial features in our visual perception.
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Another crucial mechanism of perceptual processing is top-down processing, which means the ‘top’ part, i.e., our brain, play a key role. Here perception may be shaped by many mental functions, such as our knowledge, our belief and expectation. Expectation can be considered as an assembly of our knowledge and belief about the world. When we expect to see something, that means we are ready to receive the information. Now in an English class, we will immediately recognize the letters ABC. And in a math class, you will see 12, 13 and 14. However, the spatial features of this one are identical in both classes. If bottom-up processing dominates our perception, they should be perceived as the same symbol because they compose of the same features.
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The reason why we ‘see’ different symbols are that we have a different expectation – the symbol in between A and C should be another letter, in an English classroom. Sometimes we can be fooled by our expectations. For example, some websites would ask you to identify a combination of letters and numbers to judge if the user is a robot. Now if you know the keyword must be letters or numbers, you would expect it to be ABC or 12 13 14, respectively. But what if the combination includes letters and numbers? Now it becomes confusing.
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For example, here we got A 13 C or 12 B 14, we feel it more difficult to identify because what we perceive is guided by our knowledge and expectation in this situation.
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This is crucial to patient-dentist communication:
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you need to put a message right in patients’ expectations, and it’s very important. Because if we did not put the message into their expectations, otherwise, misunderstanding may just happen.
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Okay, here is a quick summary. Both bottom-up processing and top-down processing are critical to the shaping of perception. Bottom-up processing is more relevant to how sensory information is transformed and how the basic components of an object are detected. In visual perception, these components are mainly spatial features of an object. Top-down processing is more relevant to how the human mind interprets information. Here ‘human mind’ consists of multiple processes, such as our knowledge and memory, expectation and belief. In fact, professionalism is also a factor guiding top-down processing. A dentist can identify different instruments quickly, simply because they are trained for this.
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Now before ending this topic, I have to show you something really cool, if you have not seen this before. Please check the video by yourself from websites, a very good video that Ramachandran, a famous neuroscientist, explains the secret behind the Ames room. You might think the Ames room is just a kind of visual illusion for tricking children. However, the illusion is so strong that it provides a good example of how human expectation and general belief will influence the way we see the world.
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We can also study perception from an analytic or a holistic view. The analytic processing focuses on individual components and the holistic processing focuses on the ‘big picture’. For example, here the left panel shows 9 individual dots. But we also know they are aligned as a triangle. In the Chinese language, we call it the difference between seeing the trees and seeing the wood. The tendency to view things in an analytic or holistic way may be associated with cultural experience. Just like the Ames room, this is another good example to show that our perception is shaped by many factors. What we perceive is the end-product of information integration.
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These processes of perception happen all the time in our daily life and, of course, during our work. For example, during treatment dentists can easily pick up the dental instrument they need at the same time when they are paying full attention to patients. If you are a dentist or dental assistant, you won’t feel difficult to pick up the right instrument, such as the mouth mirror. This is because you can identify the feature of a mouth mirror easily. And most importantly, you expect that during the treatment, such as dental check, a mouth mirror will be used.
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In fact, such an expectation reflects your professionalism – you know very well the procedure of dental check and your brain is ready to pick up something with a stick and a shiny disc!

Perception is subjective

What does it mean?

In this step, we will learn that perception is subjective. It is not a ‘copy’ of the objective form of things in the world. Traditionally, psychologists have two mechanisms to explain how perception is shaped, including ‘bottom-up processing’ and ‘top-down processing’.

Both bottom-up processing and top-down processing are critical to the shaping of perception.

  • Bottom-up processing is more relevant to how sensory information is transformed and how the basic components of an object are detected.
  • Top-down processing is more relevant to how the human mind interprets information.

Before you move to the next step, we recommend you to check this video:

Ramachandran – Ramachandran – Ames room illusion explained

Ramachandran, a famous neuroscientist, explains the secret behind the Ames room.

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Brain, Behaviour, and Dentistry

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