Book Excerpt: Sensation Versus Perception

Since I'm in the process of writing a book, I don't have much time to post. So here's a little excerpt from the book. It's about the distinction between sensation and perception.

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Although the terms sensation and perception are often used interchangeably in everyday life, psychologists distinguish between them. The distinction is very useful in understanding movement.

Sensation refers to the detection of some stimulus in the periphery and the transmission of a sensory signal towards the central nervous system. Perception is the process of taking that sensory information, filtering it, organizing it, and interpreting its meaning to create a subjective or conscious experience related to the sensation.

For example, through sensation the ears report information about sound waves to the brain, and through perception we hear music. In the context of movement, sensation reports proprioceptive information, and perception creates kinesthesia, or a felt sense of the movement. (By the way, the term "proprioception" sometimes causes confusion, because it is sometimes used to refer to a sensation, and others times a perception.)

It is useful to distinguish between the two because they are not identical. Many factors can modulate perception, including the way we focus our attention, our past experience, and our expectations. Thus, two people can receive the same sensory information, but perceive completely different things.

Look at the picture to the right. You can “see” it in two different ways – as one vase, or two faces looking at each other. The sensory data flowing to the eyes remains the same, but the perception of the picture completely changes as the brain alternates back and forth between competing interpretations of the meaning of sensory data. Notice that you can’t “see” both pictures at the same time!

As stated by prominent neuroscience researcher Paul Bach-Y-Rita: "We see with our brains, not with our eyes.”

The illusion reveals that there is a great degree of nearly instantaneous calculation and interpretation happening beneath our awareness, before we see anything. Our experience of vision is not a pure unmediated reflection of the real world – it is our brain’s construction of a picture that it thinks, based on available data, is a useful representation of what we need to know about the world.

Similarly, our kinesthetic sense of the body is not just a mirror of body position, but a construction that is created to serve functional goals. Just as you can see the same picture different ways, you can perceive the same movement in different ways, depending on how you interpret the sense data created by the movement.

Imagine performing a complex movement that you have never done before, such as a backflip, a new dance move, or a golf swing. Your perceptions about the relative positions of your joints during the movement will likely be confused and inaccurate. In other words, you literally won't know what you are doing, and you won't be able to predict the consequences of your movements.

This is not because of some defect in sensation, or the quality of proprioceptive information flowing to the brain. The problem is in perception - the brain’s ability to interpret the meaning of that information. In the case of a novel movement, the brain has no past experience organizing similar information, and therefore it does a poor job.

With practice, the brain gets feedback about the correspondence between a particular perception and actual reality. For example, if you perceive that your feet are in good position to land a flip, you will quickly realize your mistake when you land on your butt. As you get more feedback, perception about body position will improve, and eventually you will know where everything is and what it is doing during the movement.

Therefore, the difference between an elite athlete and an everyday Joe in terms of body sense is probably more about perception than sensation. Each are likely receiving similar sensory information about movement, but the athlete has far more skill in accurately and quickly interpreting the meaning of that information and creating functionally useful perceptions.

The distinction between sensation and perception is analogous to the distinction between nociception and pain. Nociception is just sensory information from the body, which does not result in a conscious perception until it is processed and interpreted. Further, like other perceptions, pain does not exist just to reflect the objective condition of the body, but to serve a functional purpose – protection against perceived threat.

In the next section we will look at the body maps, which will give us insight into how perceptions about the body are formed in the brain and how we can change them to move better and feel better - even without changing the underlying sensations.

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End of excerpt. What do you think?